47 files changed, 3439 insertions, 946 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 4cfa4c519..fdb62e6ea 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -82,12 +82,12 @@ checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
 
 [[package]]
 name = "backtrace"
-version = "0.3.51"
+version = "0.3.53"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ec1931848a574faa8f7c71a12ea00453ff5effbb5f51afe7f77d7a48cace6ac1"
+checksum = "707b586e0e2f247cbde68cdd2c3ce69ea7b7be43e1c5b426e37c9319c4b9838e"
 dependencies = [
  "addr2line",
- "cfg-if 0.1.10",
+ "cfg-if 1.0.0",
  "libc",
  "miniz_oxide",
  "object",
@@ -140,9 +140,9 @@ dependencies = [
 
 [[package]]
 name = "cc"
-version = "1.0.60"
+version = "1.0.61"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ef611cc68ff783f18535d77ddd080185275713d852c4f5cbb6122c462a7a825c"
+checksum = "ed67cbde08356238e75fc4656be4749481eeffb09e19f320a25237d5221c985d"
 
 [[package]]
 name = "cfg"
@@ -168,9 +168,9 @@ checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
 
 [[package]]
 name = "chalk-derive"
-version = "0.32.0"
+version = "0.33.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2d072b2ba723f0bada7c515d8b3725224bc4f5052d2a92dcbeb0b118ff37084a"
+checksum = "569014cab9084a6b826fe2507cc6d08f7897ba144fb1bc74e71b593dc8a0b952"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -180,9 +180,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-ir"
-version = "0.32.0"
+version = "0.33.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f60cdb0e18c5455cb6a85e8464aad3622b70476018edfa8845691df66f7e9a05"
+checksum = "8d9eab2a6590b696419f89c9ca3616fe8e8266ef676e6a6da8818c94963c9541"
 dependencies = [
  "chalk-derive",
  "lazy_static",
@@ -190,9 +190,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-recursive"
-version = "0.32.0"
+version = "0.33.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b14f40242102e7c0e2791a2cc86dbbc213a1d7b7acc0e22b7da329f4957d1722"
+checksum = "4a4671bcc70aa2d7e12ff4fe03f91d0c3c9ce387de915915e57fdf0c91dc5abd"
 dependencies = [
  "chalk-derive",
  "chalk-ir",
@@ -203,9 +203,9 @@ dependencies = [
 
 [[package]]
 name = "chalk-solve"
-version = "0.32.0"
+version = "0.33.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "981534d499a8476ecc0b520be4d3864757f96211826a75360fbf2cb6fae362ab"
+checksum = "45f75cc603f2fd302576c8b2976437f334e159e26d0afbb108a565b96c52184e"
 dependencies = [
  "chalk-derive",
  "chalk-ir",
@@ -737,9 +737,9 @@ checksum = "2448f6066e80e3bfc792e9c98bf705b4b0fc6e8ef5b43e5889aff0eaa9c58743"
 
 [[package]]
 name = "libloading"
-version = "0.6.3"
+version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2443d8f0478b16759158b2f66d525991a05491138bc05814ef52a250148ef4f9"
+checksum = "3557c9384f7f757f6d139cd3a4c62ef4e850696c16bf27924a5538c8a09717a1"
 dependencies = [
  "cfg-if 0.1.10",
  "winapi 0.3.9",
@@ -747,9 +747,9 @@ dependencies = [
 
 [[package]]
 name = "libmimalloc-sys"
-version = "0.1.17"
+version = "0.1.18"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2bd65748dfb74a807e8379fd49bf4d38964d92b8637b56f173f87e1d70433368"
+checksum = "82151ff13433c4d403cb15d0e6fbda14b24d65bd1a5b33f7d52ec983cc00752d"
 dependencies = [
  "cmake",
 ]
@@ -859,9 +859,9 @@ dependencies = [
 
 [[package]]
 name = "mimalloc"
-version = "0.1.21"
+version = "0.1.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "2e18b3d01186c4a7bec0b56cff9a4b9d5a1461aa162c7b8eaf2e5ee10b265b02"
+checksum = "4a5d2c9cb18f9cdc6d88f4aca6d3d8ea89c4c8202d6facfc7e56efdee97b80fa"
 dependencies = [
  "libmimalloc-sys",
 ]
@@ -981,9 +981,9 @@ dependencies = [
 
 [[package]]
 name = "object"
-version = "0.20.0"
+version = "0.21.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1ab52be62400ca80aa00285d25253d7f7c437b7375c4de678f5405d3afe82ca5"
+checksum = "37fd5004feb2ce328a52b0b3d01dbf4ffff72583493900ed15f22d4111c51693"
 
 [[package]]
 name = "once_cell"
@@ -1383,18 +1383,18 @@ checksum = "d29ab0c6d3fc0ee92fe66e2d99f700eab17a8d57d1c1d3b748380fb20baa78cd"
 
 [[package]]
 name = "scroll"
-version = "0.10.1"
+version = "0.10.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "abb2332cb595d33f7edd5700f4cbf94892e680c7f0ae56adab58a35190b66cb1"
+checksum = "fda28d4b4830b807a8b43f7b0e6b5df875311b3e7621d84577188c175b6ec1ec"
 dependencies = [
  "scroll_derive",
 ]
 
 [[package]]
 name = "scroll_derive"
-version = "0.10.2"
+version = "0.10.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e367622f934864ffa1c704ba2b82280aab856e3d8213c84c5720257eb34b15b9"
+checksum = "6dfde5d1531034db129e95c76ac857e2baecea3443579d493d02224950b0fb6d"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -1510,9 +1510,9 @@ version = "0.0.0"
 
 [[package]]
 name = "syn"
-version = "1.0.42"
+version = "1.0.44"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9c51d92969d209b54a98397e1b91c8ae82d8c87a7bb87df0b29aa2ad81454228"
+checksum = "e03e57e4fcbfe7749842d53e24ccb9aa12b7252dbe5e91d2acad31834c8b8fdd"
 dependencies = [
  "proc-macro2",
  "quote",
diff --git a/Cargo.toml b/Cargo.toml
index 218581d9d..87d33f06c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -19,18 +19,6 @@ miniz_oxide.opt-level = 3
 incremental = true
 debug = 0 # Set this to 1 or 2 to get more useful backtraces in debugger.
 
-# Ideally, we would use `build-override` here, but some crates are also
-# needed at run-time and we end up compiling them twice.
-[profile.release.package]
-chalk-derive.opt-level = 0
-proc-macro2.opt-level = 0
-quote.opt-level = 0
-salsa-macros.opt-level = 0
-serde_derive.opt-level = 0
-syn.opt-level = 0
-tracing-attributes.opt-level = 0
-xtask.opt-level = 0
-
 [patch.'crates-io']
 # rowan = { path = "../rowan" }
 
diff --git a/crates/assists/src/handlers/fix_visibility.rs b/crates/assists/src/handlers/fix_visibility.rs
index 7cd76ea06..d505e9444 100644
--- a/crates/assists/src/handlers/fix_visibility.rs
+++ b/crates/assists/src/handlers/fix_visibility.rs
@@ -324,14 +324,14 @@ pub struct Foo { pub bar: () }
 
     #[test]
     fn fix_visibility_of_enum_variant_field() {
-        check_assist(
+        // Enum variants, as well as their fields, always get the enum's visibility. In fact, rustc
+        // rejects any visibility specifiers on them, so this assist should never fire on them.
+        check_assist_not_applicable(
             fix_visibility,
             r"mod foo { pub enum Foo { Bar { bar: () } } }
               fn main() { foo::Foo::Bar { <|>bar: () }; } ",
-            r"mod foo { pub enum Foo { Bar { $0pub(crate) bar: () } } }
-              fn main() { foo::Foo::Bar { bar: () }; } ",
         );
-        check_assist(
+        check_assist_not_applicable(
             fix_visibility,
             r"
 //- /lib.rs
@@ -340,8 +340,6 @@ fn main() { foo::Foo::Bar { <|>bar: () }; }
 //- /foo.rs
 pub enum Foo { Bar { bar: () } }
 ",
-            r"pub enum Foo { Bar { $0pub(crate) bar: () } }
-",
         );
         check_assist_not_applicable(
             fix_visibility,
diff --git a/crates/base_db/src/input.rs b/crates/base_db/src/input.rs
index c330314d4..215ac4b41 100644
--- a/crates/base_db/src/input.rs
+++ b/crates/base_db/src/input.rs
@@ -221,6 +221,34 @@ impl CrateGraph {
         deps.into_iter()
     }
 
+    /// Returns all crates in the graph, sorted in topological order (ie. dependencies of a crate
+    /// come before the crate itself).
+    pub fn crates_in_topological_order(&self) -> Vec<CrateId> {
+        let mut res = Vec::new();
+        let mut visited = FxHashSet::default();
+
+        for krate in self.arena.keys().copied() {
+            go(self, &mut visited, &mut res, krate);
+        }
+
+        return res;
+
+        fn go(
+            graph: &CrateGraph,
+            visited: &mut FxHashSet<CrateId>,
+            res: &mut Vec<CrateId>,
+            source: CrateId,
+        ) {
+            if !visited.insert(source) {
+                return;
+            }
+            for dep in graph[source].dependencies.iter() {
+                go(graph, visited, res, dep.crate_id)
+            }
+            res.push(source)
+        }
+    }
+
     // FIXME: this only finds one crate with the given root; we could have multiple
     pub fn crate_id_for_crate_root(&self, file_id: FileId) -> Option<CrateId> {
         let (&crate_id, _) =
diff --git a/crates/hir/src/code_model.rs b/crates/hir/src/code_model.rs
index 031c91ccf..b65be4fe1 100644
--- a/crates/hir/src/code_model.rs
+++ b/crates/hir/src/code_model.rs
@@ -186,6 +186,16 @@ impl_from!(
     for ModuleDef
 );
 
+impl From<VariantDef> for ModuleDef {
+    fn from(var: VariantDef) -> Self {
+        match var {
+            VariantDef::Struct(t) => Adt::from(t).into(),
+            VariantDef::Union(t) => Adt::from(t).into(),
+            VariantDef::EnumVariant(t) => t.into(),
+        }
+    }
+}
+
 impl ModuleDef {
     pub fn module(self, db: &dyn HirDatabase) -> Option<Module> {
         match self {
@@ -245,6 +255,25 @@ impl ModuleDef {
             ModuleDef::BuiltinType(it) => Some(it.as_name()),
         }
     }
+
+    pub fn diagnostics(self, db: &dyn HirDatabase, sink: &mut DiagnosticSink) {
+        let id = match self {
+            ModuleDef::Adt(it) => match it {
+                Adt::Struct(it) => it.id.into(),
+                Adt::Enum(it) => it.id.into(),
+                Adt::Union(it) => it.id.into(),
+            },
+            ModuleDef::Trait(it) => it.id.into(),
+            ModuleDef::Function(it) => it.id.into(),
+            ModuleDef::TypeAlias(it) => it.id.into(),
+            ModuleDef::Module(it) => it.id.into(),
+            ModuleDef::Const(it) => it.id.into(),
+            ModuleDef::Static(it) => it.id.into(),
+            _ => return,
+        };
+
+        hir_ty::diagnostics::validate_module_item(db, id, sink)
+    }
 }
 
 pub use hir_def::{
@@ -348,6 +377,8 @@ impl Module {
         let crate_def_map = db.crate_def_map(self.id.krate);
         crate_def_map.add_diagnostics(db.upcast(), self.id.local_id, sink);
         for decl in self.declarations(db) {
+            decl.diagnostics(db, sink);
+
             match decl {
                 crate::ModuleDef::Function(f) => f.diagnostics(db, sink),
                 crate::ModuleDef::Module(m) => {
@@ -750,7 +781,15 @@ impl Function {
     }
 
     pub fn diagnostics(self, db: &dyn HirDatabase, sink: &mut DiagnosticSink) {
-        hir_ty::diagnostics::validate_body(db, self.id.into(), sink)
+        hir_ty::diagnostics::validate_module_item(db, self.id.into(), sink);
+        hir_ty::diagnostics::validate_body(db, self.id.into(), sink);
+    }
+
+    /// Whether this function declaration has a definition.
+    ///
+    /// This is false in the case of required (not provided) trait methods.
+    pub fn has_body(self, db: &dyn HirDatabase) -> bool {
+        db.function_data(self.id).has_body
     }
 }
 
@@ -1372,7 +1411,7 @@ impl Type {
         r#trait: Trait,
         args: &[Type],
         alias: TypeAlias,
-    ) -> Option<Ty> {
+    ) -> Option<Type> {
         let subst = Substs::build_for_def(db, r#trait.id)
             .push(self.ty.value.clone())
             .fill(args.iter().map(|t| t.ty.value.clone()))
@@ -1393,6 +1432,10 @@ impl Type {
             Solution::Unique(SolutionVariables(subst)) => subst.value.first().cloned(),
             Solution::Ambig(_) => None,
         }
+        .map(|ty| Type {
+            krate: self.krate,
+            ty: InEnvironment { value: ty, environment: Arc::clone(&self.ty.environment) },
+        })
     }
 
     pub fn is_copy(&self, db: &dyn HirDatabase) -> bool {
diff --git a/crates/hir/src/diagnostics.rs b/crates/hir/src/diagnostics.rs
index 363164b9b..da2b40849 100644
--- a/crates/hir/src/diagnostics.rs
+++ b/crates/hir/src/diagnostics.rs
@@ -2,5 +2,6 @@
 pub use hir_def::diagnostics::UnresolvedModule;
 pub use hir_expand::diagnostics::{Diagnostic, DiagnosticSink, DiagnosticSinkBuilder};
 pub use hir_ty::diagnostics::{
-    MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkInTailExpr, NoSuchField,
+    IncorrectCase, MismatchedArgCount, MissingFields, MissingMatchArms, MissingOkInTailExpr,
+    NoSuchField,
 };
diff --git a/crates/hir/src/semantics/source_to_def.rs b/crates/hir/src/semantics/source_to_def.rs
index 5918b9541..66fc11611 100644
--- a/crates/hir/src/semantics/source_to_def.rs
+++ b/crates/hir/src/semantics/source_to_def.rs
@@ -189,6 +189,10 @@ impl SourceToDefCtx<'_, '_> {
                         let def = self.type_alias_to_def(container.with_value(it))?;
                         def.into()
                     },
+                    ast::Variant(it) => {
+                        let def = self.enum_variant_to_def(container.with_value(it))?;
+                        VariantId::from(def).into()
+                    },
                     _ => continue,
                 }
             };
diff --git a/crates/hir_def/src/adt.rs b/crates/hir_def/src/adt.rs
index d69ff2fc7..6539959c3 100644
--- a/crates/hir_def/src/adt.rs
+++ b/crates/hir_def/src/adt.rs
@@ -14,7 +14,7 @@ use tt::{Delimiter, DelimiterKind, Leaf, Subtree, TokenTree};
 use crate::{
     body::{CfgExpander, LowerCtx},
     db::DefDatabase,
-    item_tree::{AttrOwner, Field, Fields, ItemTree, ModItem},
+    item_tree::{AttrOwner, Field, Fields, ItemTree, ModItem, RawVisibilityId},
     src::HasChildSource,
     src::HasSource,
     trace::Trace,
@@ -91,7 +91,7 @@ impl StructData {
         let cfg_options = db.crate_graph()[loc.container.module(db).krate].cfg_options.clone();
 
         let strukt = &item_tree[loc.id.value];
-        let variant_data = lower_fields(&item_tree, &cfg_options, &strukt.fields);
+        let variant_data = lower_fields(&item_tree, &cfg_options, &strukt.fields, None);
         Arc::new(StructData {
             name: strukt.name.clone(),
             variant_data: Arc::new(variant_data),
@@ -105,7 +105,7 @@ impl StructData {
         let cfg_options = db.crate_graph()[loc.container.module(db).krate].cfg_options.clone();
 
         let union = &item_tree[loc.id.value];
-        let variant_data = lower_fields(&item_tree, &cfg_options, &union.fields);
+        let variant_data = lower_fields(&item_tree, &cfg_options, &union.fields, None);
 
         Arc::new(StructData {
             name: union.name.clone(),
@@ -126,7 +126,8 @@ impl EnumData {
         for var_id in enum_.variants.clone() {
             if item_tree.attrs(var_id.into()).is_cfg_enabled(&cfg_options) {
                 let var = &item_tree[var_id];
-                let var_data = lower_fields(&item_tree, &cfg_options, &var.fields);
+                let var_data =
+                    lower_fields(&item_tree, &cfg_options, &var.fields, Some(enum_.visibility));
 
                 variants.alloc(EnumVariantData {
                     name: var.name.clone(),
@@ -296,13 +297,18 @@ fn lower_struct(
     }
 }
 
-fn lower_fields(item_tree: &ItemTree, cfg_options: &CfgOptions, fields: &Fields) -> VariantData {
+fn lower_fields(
+    item_tree: &ItemTree,
+    cfg_options: &CfgOptions,
+    fields: &Fields,
+    override_visibility: Option<RawVisibilityId>,
+) -> VariantData {
     match fields {
         Fields::Record(flds) => {
             let mut arena = Arena::new();
             for field_id in flds.clone() {
                 if item_tree.attrs(field_id.into()).is_cfg_enabled(cfg_options) {
-                    arena.alloc(lower_field(item_tree, &item_tree[field_id]));
+                    arena.alloc(lower_field(item_tree, &item_tree[field_id], override_visibility));
                 }
             }
             VariantData::Record(arena)
@@ -311,7 +317,7 @@ fn lower_fields(item_tree: &ItemTree, cfg_options: &CfgOptions, fields: &Fields)
             let mut arena = Arena::new();
             for field_id in flds.clone() {
                 if item_tree.attrs(field_id.into()).is_cfg_enabled(cfg_options) {
-                    arena.alloc(lower_field(item_tree, &item_tree[field_id]));
+                    arena.alloc(lower_field(item_tree, &item_tree[field_id], override_visibility));
                 }
             }
             VariantData::Tuple(arena)
@@ -320,10 +326,14 @@ fn lower_fields(item_tree: &ItemTree, cfg_options: &CfgOptions, fields: &Fields)
     }
 }
 
-fn lower_field(item_tree: &ItemTree, field: &Field) -> FieldData {
+fn lower_field(
+    item_tree: &ItemTree,
+    field: &Field,
+    override_visibility: Option<RawVisibilityId>,
+) -> FieldData {
     FieldData {
         name: field.name.clone(),
         type_ref: field.type_ref.clone(),
-        visibility: item_tree[field.visibility].clone(),
+        visibility: item_tree[override_visibility.unwrap_or(field.visibility)].clone(),
     }
 }
diff --git a/crates/hir_def/src/body/lower.rs b/crates/hir_def/src/body/lower.rs
index 2d91bb21f..01e72690a 100644
--- a/crates/hir_def/src/body/lower.rs
+++ b/crates/hir_def/src/body/lower.rs
@@ -107,7 +107,10 @@ impl ExprCollector<'_> {
                 let param_pat = self.alloc_pat(
                     Pat::Bind {
                         name: name![self],
-                        mode: BindingAnnotation::Unannotated,
+                        mode: BindingAnnotation::new(
+                            self_param.mut_token().is_some() && self_param.amp_token().is_none(),
+                            false,
+                        ),
                         subpat: None,
                     },
                     Either::Right(ptr),
diff --git a/crates/hir_def/src/data.rs b/crates/hir_def/src/data.rs
index 6190906da..ff1ef0df6 100644
--- a/crates/hir_def/src/data.rs
+++ b/crates/hir_def/src/data.rs
@@ -25,6 +25,7 @@ pub struct FunctionData {
     /// True if the first param is `self`. This is relevant to decide whether this
     /// can be called as a method.
     pub has_self_param: bool,
+    pub has_body: bool,
     pub is_unsafe: bool,
     pub is_varargs: bool,
     pub visibility: RawVisibility,
@@ -42,6 +43,7 @@ impl FunctionData {
             ret_type: func.ret_type.clone(),
             attrs: item_tree.attrs(ModItem::from(loc.id.value).into()).clone(),
             has_self_param: func.has_self_param,
+            has_body: func.has_body,
             is_unsafe: func.is_unsafe,
             is_varargs: func.is_varargs,
             visibility: item_tree[func.visibility].clone(),
diff --git a/crates/hir_def/src/item_scope.rs b/crates/hir_def/src/item_scope.rs
index 12c24e1ca..a8b3fe844 100644
--- a/crates/hir_def/src/item_scope.rs
+++ b/crates/hir_def/src/item_scope.rs
@@ -95,6 +95,12 @@ impl ItemScope {
         self.impls.iter().copied()
     }
 
+    pub fn values(
+        &self,
+    ) -> impl Iterator<Item = (ModuleDefId, Visibility)> + ExactSizeIterator + '_ {
+        self.values.values().copied()
+    }
+
     pub fn visibility_of(&self, def: ModuleDefId) -> Option<Visibility> {
         self.name_of(ItemInNs::Types(def))
             .or_else(|| self.name_of(ItemInNs::Values(def)))
diff --git a/crates/hir_def/src/item_tree.rs b/crates/hir_def/src/item_tree.rs
index 0fd91b9d0..8a1121bbd 100644
--- a/crates/hir_def/src/item_tree.rs
+++ b/crates/hir_def/src/item_tree.rs
@@ -505,6 +505,7 @@ pub struct Function {
     pub visibility: RawVisibilityId,
     pub generic_params: GenericParamsId,
     pub has_self_param: bool,
+    pub has_body: bool,
     pub is_unsafe: bool,
     pub params: Box<[TypeRef]>,
     pub is_varargs: bool,
diff --git a/crates/hir_def/src/item_tree/lower.rs b/crates/hir_def/src/item_tree/lower.rs
index 54814f141..3328639cf 100644
--- a/crates/hir_def/src/item_tree/lower.rs
+++ b/crates/hir_def/src/item_tree/lower.rs
@@ -330,12 +330,15 @@ impl Ctx {
             ret_type
         };
 
+        let has_body = func.body().is_some();
+
         let ast_id = self.source_ast_id_map.ast_id(func);
         let mut res = Function {
             name,
             visibility,
             generic_params: GenericParamsId::EMPTY,
             has_self_param,
+            has_body,
             is_unsafe: func.unsafe_token().is_some(),
             params: params.into_boxed_slice(),
             is_varargs,
diff --git a/crates/hir_def/src/item_tree/tests.rs b/crates/hir_def/src/item_tree/tests.rs
index 1a806cda5..4b354c4c1 100644
--- a/crates/hir_def/src/item_tree/tests.rs
+++ b/crates/hir_def/src/item_tree/tests.rs
@@ -240,9 +240,9 @@ fn smoke() {
             > #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("assoc_const"))] }, input: None }]) }]
             > Const { name: Some(Name(Text("CONST"))), visibility: RawVisibilityId("pub(self)"), type_ref: Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("u8"))] }, generic_args: [None] }), ast_id: FileAstId::<syntax::ast::generated::nodes::Const>(9) }
             > #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("assoc_method"))] }, input: None }]) }]
-            > Function { name: Name(Text("method")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: true, is_unsafe: false, params: [Reference(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("Self"))] }, generic_args: [None] }), Shared)], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(10) }
+            > Function { name: Name(Text("method")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: true, has_body: false, is_unsafe: false, params: [Reference(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("Self"))] }, generic_args: [None] }), Shared)], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(10) }
             > #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("assoc_dfl_method"))] }, input: None }]) }]
-            > Function { name: Name(Text("dfl_method")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: true, is_unsafe: false, params: [Reference(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("Self"))] }, generic_args: [None] }), Mut)], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(11) }
+            > Function { name: Name(Text("dfl_method")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: true, has_body: true, is_unsafe: false, params: [Reference(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("Self"))] }, generic_args: [None] }), Mut)], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(11) }
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("struct0"))] }, input: None }]) }]
             Struct { name: Name(Text("Struct0")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(1), fields: Unit, ast_id: FileAstId::<syntax::ast::generated::nodes::Struct>(3), kind: Unit }
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("struct1"))] }, input: None }]) }]
@@ -275,12 +275,12 @@ fn simple_inner_items() {
 
             top-level items:
             Impl { generic_params: GenericParamsId(0), target_trait: Some(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("D"))] }, generic_args: [None] })), target_type: Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("Response"))] }, generic_args: [Some(GenericArgs { args: [Type(Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("T"))] }, generic_args: [None] }))], has_self_type: false, bindings: [] })] }), is_negative: false, items: [Function(Idx::<Function>(1))], ast_id: FileAstId::<syntax::ast::generated::nodes::Impl>(0) }
-            > Function { name: Name(Text("foo")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
+            > Function { name: Name(Text("foo")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
 
             inner items:
 
             for AST FileAstId::<syntax::ast::generated::nodes::Item>(2):
-            Function { name: Name(Text("end")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(1), has_self_param: false, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(2) }
+            Function { name: Name(Text("end")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(1), has_self_param: false, has_body: true, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(2) }
 
         "#]],
     );
@@ -303,9 +303,9 @@ fn extern_attrs() {
 
             top-level items:
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr_a"))] }, input: None }, Attr { path: ModPath { kind: Plain, segments: [Name(Text("block_attr"))] }, input: None }]) }]
-            Function { name: Name(Text("a")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: true, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
+            Function { name: Name(Text("a")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: true, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr_b"))] }, input: None }, Attr { path: ModPath { kind: Plain, segments: [Name(Text("block_attr"))] }, input: None }]) }]
-            Function { name: Name(Text("b")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: true, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(2) }
+            Function { name: Name(Text("b")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: true, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(2) }
         "##]],
     );
 }
@@ -329,9 +329,9 @@ fn trait_attrs() {
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("trait_attr"))] }, input: None }]) }]
             Trait { name: Name(Text("Tr")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(0), auto: false, items: [Function(Idx::<Function>(0)), Function(Idx::<Function>(1))], ast_id: FileAstId::<syntax::ast::generated::nodes::Trait>(0) }
             > #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr_a"))] }, input: None }]) }]
-            > Function { name: Name(Text("a")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
+            > Function { name: Name(Text("a")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
             > #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr_b"))] }, input: None }]) }]
-            > Function { name: Name(Text("b")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(2) }
+            > Function { name: Name(Text("b")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(2) }
         "##]],
     );
 }
@@ -355,9 +355,9 @@ fn impl_attrs() {
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("impl_attr"))] }, input: None }]) }]
             Impl { generic_params: GenericParamsId(4294967295), target_trait: None, target_type: Path(Path { type_anchor: None, mod_path: ModPath { kind: Plain, segments: [Name(Text("Ty"))] }, generic_args: [None] }), is_negative: false, items: [Function(Idx::<Function>(0)), Function(Idx::<Function>(1))], ast_id: FileAstId::<syntax::ast::generated::nodes::Impl>(0) }
             > #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr_a"))] }, input: None }]) }]
-            > Function { name: Name(Text("a")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
+            > Function { name: Name(Text("a")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
             > #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("attr_b"))] }, input: None }]) }]
-            > Function { name: Name(Text("b")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(2) }
+            > Function { name: Name(Text("b")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(2) }
         "##]],
     );
 }
@@ -408,13 +408,13 @@ fn inner_item_attrs() {
             inner attrs: Attrs { entries: None }
 
             top-level items:
-            Function { name: Name(Text("foo")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(0) }
+            Function { name: Name(Text("foo")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(0) }
 
             inner items:
 
             for AST FileAstId::<syntax::ast::generated::nodes::Item>(1):
             #[Attrs { entries: Some([Attr { path: ModPath { kind: Plain, segments: [Name(Text("on_inner"))] }, input: None }]) }]
-            Function { name: Name(Text("inner")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
+            Function { name: Name(Text("inner")), visibility: RawVisibilityId("pub(self)"), generic_params: GenericParamsId(4294967295), has_self_param: false, has_body: true, is_unsafe: false, params: [], is_varargs: false, ret_type: Tuple([]), ast_id: FileAstId::<syntax::ast::generated::nodes::Fn>(1) }
 
         "##]],
     );
diff --git a/crates/hir_ty/Cargo.toml b/crates/hir_ty/Cargo.toml
index 0f3c85926..e9c62c6aa 100644
--- a/crates/hir_ty/Cargo.toml
+++ b/crates/hir_ty/Cargo.toml
@@ -17,9 +17,9 @@ ena = "0.14.0"
 log = "0.4.8"
 rustc-hash = "1.1.0"
 scoped-tls = "1"
-chalk-solve = "0.32"
-chalk-ir = "0.32"
-chalk-recursive = "0.32"
+chalk-solve = "0.33"
+chalk-ir = "0.33"
+chalk-recursive = "0.33"
 
 stdx = { path = "../stdx", version = "0.0.0" }
 hir_def = { path = "../hir_def", version = "0.0.0" }
diff --git a/crates/hir_ty/src/diagnostics.rs b/crates/hir_ty/src/diagnostics.rs
index 9ba005fab..dfe98571e 100644
--- a/crates/hir_ty/src/diagnostics.rs
+++ b/crates/hir_ty/src/diagnostics.rs
@@ -2,10 +2,11 @@
 mod expr;
 mod match_check;
 mod unsafe_check;
+mod decl_check;
 
-use std::any::Any;
+use std::{any::Any, fmt};
 
-use hir_def::DefWithBodyId;
+use hir_def::{DefWithBodyId, ModuleDefId};
 use hir_expand::diagnostics::{Diagnostic, DiagnosticCode, DiagnosticSink};
 use hir_expand::{name::Name, HirFileId, InFile};
 use stdx::format_to;
@@ -15,6 +16,16 @@ use crate::db::HirDatabase;
 
 pub use crate::diagnostics::expr::{record_literal_missing_fields, record_pattern_missing_fields};
 
+pub fn validate_module_item(
+    db: &dyn HirDatabase,
+    owner: ModuleDefId,
+    sink: &mut DiagnosticSink<'_>,
+) {
+    let _p = profile::span("validate_module_item");
+    let mut validator = decl_check::DeclValidator::new(owner, sink);
+    validator.validate_item(db);
+}
+
 pub fn validate_body(db: &dyn HirDatabase, owner: DefWithBodyId, sink: &mut DiagnosticSink<'_>) {
     let _p = profile::span("validate_body");
     let infer = db.infer(owner);
@@ -231,6 +242,66 @@ impl Diagnostic for MismatchedArgCount {
     }
 }
 
+#[derive(Debug)]
+pub enum CaseType {
+    // `some_var`
+    LowerSnakeCase,
+    // `SOME_CONST`
+    UpperSnakeCase,
+    // `SomeStruct`
+    UpperCamelCase,
+}
+
+impl fmt::Display for CaseType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let repr = match self {
+            CaseType::LowerSnakeCase => "snake_case",
+            CaseType::UpperSnakeCase => "UPPER_SNAKE_CASE",
+            CaseType::UpperCamelCase => "CamelCase",
+        };
+
+        write!(f, "{}", repr)
+    }
+}
+
+#[derive(Debug)]
+pub struct IncorrectCase {
+    pub file: HirFileId,
+    pub ident: AstPtr<ast::Name>,
+    pub expected_case: CaseType,
+    pub ident_type: String,
+    pub ident_text: String,
+    pub suggested_text: String,
+}
+
+impl Diagnostic for IncorrectCase {
+    fn code(&self) -> DiagnosticCode {
+        DiagnosticCode("incorrect-ident-case")
+    }
+
+    fn message(&self) -> String {
+        format!(
+            "{} `{}` should have {} name, e.g. `{}`",
+            self.ident_type,
+            self.ident_text,
+            self.expected_case.to_string(),
+            self.suggested_text
+        )
+    }
+
+    fn display_source(&self) -> InFile<SyntaxNodePtr> {
+        InFile::new(self.file, self.ident.clone().into())
+    }
+
+    fn as_any(&self) -> &(dyn Any + Send + 'static) {
+        self
+    }
+
+    fn is_experimental(&self) -> bool {
+        true
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use base_db::{fixture::WithFixture, FileId, SourceDatabase, SourceDatabaseExt};
@@ -242,7 +313,10 @@ mod tests {
     use rustc_hash::FxHashMap;
     use syntax::{TextRange, TextSize};
 
-    use crate::{diagnostics::validate_body, test_db::TestDB};
+    use crate::{
+        diagnostics::{validate_body, validate_module_item},
+        test_db::TestDB,
+    };
 
     impl TestDB {
         fn diagnostics<F: FnMut(&dyn Diagnostic)>(&self, mut cb: F) {
@@ -253,6 +327,9 @@ mod tests {
                 let mut fns = Vec::new();
                 for (module_id, _) in crate_def_map.modules.iter() {
                     for decl in crate_def_map[module_id].scope.declarations() {
+                        let mut sink = DiagnosticSinkBuilder::new().build(&mut cb);
+                        validate_module_item(self, decl, &mut sink);
+
                         if let ModuleDefId::FunctionId(f) = decl {
                             fns.push(f)
                         }
@@ -262,6 +339,8 @@ mod tests {
                         let impl_data = self.impl_data(impl_id);
                         for item in impl_data.items.iter() {
                             if let AssocItemId::FunctionId(f) = item {
+                                let mut sink = DiagnosticSinkBuilder::new().build(&mut cb);
+                                validate_module_item(self, ModuleDefId::FunctionId(*f), &mut sink);
                                 fns.push(*f)
                             }
                         }
diff --git a/crates/hir_ty/src/diagnostics/decl_check.rs b/crates/hir_ty/src/diagnostics/decl_check.rs
new file mode 100644
index 000000000..f987636fe
--- /dev/null
+++ b/crates/hir_ty/src/diagnostics/decl_check.rs
@@ -0,0 +1,833 @@
+//! Provides validators for the item declarations.
+//!
+//! This includes the following items:
+//!
+//! - variable bindings (e.g. `let x = foo();`)
+//! - struct fields (e.g. `struct Foo { field: u8 }`)
+//! - enum variants (e.g. `enum Foo { Variant { field: u8 } }`)
+//! - function/method arguments (e.g. `fn foo(arg: u8)`)
+//! - constants (e.g. `const FOO: u8 = 10;`)
+//! - static items (e.g. `static FOO: u8 = 10;`)
+//! - match arm bindings (e.g. `foo @ Some(_)`)
+
+mod case_conv;
+
+use hir_def::{
+    adt::VariantData,
+    expr::{Pat, PatId},
+    src::HasSource,
+    AdtId, ConstId, EnumId, FunctionId, Lookup, ModuleDefId, StaticId, StructId,
+};
+use hir_expand::{
+    diagnostics::DiagnosticSink,
+    name::{AsName, Name},
+};
+use syntax::{
+    ast::{self, NameOwner},
+    AstNode, AstPtr,
+};
+
+use crate::{
+    db::HirDatabase,
+    diagnostics::{decl_check::case_conv::*, CaseType, IncorrectCase},
+};
+
+pub(super) struct DeclValidator<'a, 'b: 'a> {
+    owner: ModuleDefId,
+    sink: &'a mut DiagnosticSink<'b>,
+}
+
+#[derive(Debug)]
+struct Replacement {
+    current_name: Name,
+    suggested_text: String,
+    expected_case: CaseType,
+}
+
+impl<'a, 'b> DeclValidator<'a, 'b> {
+    pub(super) fn new(
+        owner: ModuleDefId,
+        sink: &'a mut DiagnosticSink<'b>,
+    ) -> DeclValidator<'a, 'b> {
+        DeclValidator { owner, sink }
+    }
+
+    pub(super) fn validate_item(&mut self, db: &dyn HirDatabase) {
+        match self.owner {
+            ModuleDefId::FunctionId(func) => self.validate_func(db, func),
+            ModuleDefId::AdtId(adt) => self.validate_adt(db, adt),
+            ModuleDefId::ConstId(const_id) => self.validate_const(db, const_id),
+            ModuleDefId::StaticId(static_id) => self.validate_static(db, static_id),
+            _ => return,
+        }
+    }
+
+    fn validate_adt(&mut self, db: &dyn HirDatabase, adt: AdtId) {
+        match adt {
+            AdtId::StructId(struct_id) => self.validate_struct(db, struct_id),
+            AdtId::EnumId(enum_id) => self.validate_enum(db, enum_id),
+            AdtId::UnionId(_) => {
+                // Unions aren't yet supported by this validator.
+            }
+        }
+    }
+
+    fn validate_func(&mut self, db: &dyn HirDatabase, func: FunctionId) {
+        let data = db.function_data(func);
+        let body = db.body(func.into());
+
+        // 1. Check the function name.
+        let function_name = data.name.to_string();
+        let fn_name_replacement = if let Some(new_name) = to_lower_snake_case(&function_name) {
+            let replacement = Replacement {
+                current_name: data.name.clone(),
+                suggested_text: new_name,
+                expected_case: CaseType::LowerSnakeCase,
+            };
+            Some(replacement)
+        } else {
+            None
+        };
+
+        // 2. Check the param names.
+        let mut fn_param_replacements = Vec::new();
+
+        for pat_id in body.params.iter().cloned() {
+            let pat = &body[pat_id];
+
+            let param_name = match pat {
+                Pat::Bind { name, .. } => name,
+                _ => continue,
+            };
+
+            let name = param_name.to_string();
+            if let Some(new_name) = to_lower_snake_case(&name) {
+                let replacement = Replacement {
+                    current_name: param_name.clone(),
+                    suggested_text: new_name,
+                    expected_case: CaseType::LowerSnakeCase,
+                };
+                fn_param_replacements.push(replacement);
+            }
+        }
+
+        // 3. Check the patterns inside the function body.
+        let mut pats_replacements = Vec::new();
+
+        for (pat_idx, pat) in body.pats.iter() {
+            if body.params.contains(&pat_idx) {
+                // We aren't interested in function parameters, we've processed them above.
+                continue;
+            }
+
+            let bind_name = match pat {
+                Pat::Bind { name, .. } => name,
+                _ => continue,
+            };
+
+            let name = bind_name.to_string();
+            if let Some(new_name) = to_lower_snake_case(&name) {
+                let replacement = Replacement {
+                    current_name: bind_name.clone(),
+                    suggested_text: new_name,
+                    expected_case: CaseType::LowerSnakeCase,
+                };
+                pats_replacements.push((pat_idx, replacement));
+            }
+        }
+
+        // 4. If there is at least one element to spawn a warning on, go to the source map and generate a warning.
+        self.create_incorrect_case_diagnostic_for_func(
+            func,
+            db,
+            fn_name_replacement,
+            fn_param_replacements,
+        );
+        self.create_incorrect_case_diagnostic_for_variables(func, db, pats_replacements);
+
+        // 5. Recursively validate inner scope items, such as static variables and constants.
+        for (item_id, _) in body.item_scope.values() {
+            let mut validator = DeclValidator::new(item_id, self.sink);
+            validator.validate_item(db);
+        }
+    }
+
+    /// Given the information about incorrect names in the function declaration, looks up into the source code
+    /// for exact locations and adds diagnostics into the sink.
+    fn create_incorrect_case_diagnostic_for_func(
+        &mut self,
+        func: FunctionId,
+        db: &dyn HirDatabase,
+        fn_name_replacement: Option<Replacement>,
+        fn_param_replacements: Vec<Replacement>,
+    ) {
+        // XXX: only look at sources if we do have incorrect names
+        if fn_name_replacement.is_none() && fn_param_replacements.is_empty() {
+            return;
+        }
+
+        let fn_loc = func.lookup(db.upcast());
+        let fn_src = fn_loc.source(db.upcast());
+
+        // 1. Diagnostic for function name.
+        if let Some(replacement) = fn_name_replacement {
+            let ast_ptr = match fn_src.value.name() {
+                Some(name) => name,
+                None => {
+                    // We don't want rust-analyzer to panic over this, but it is definitely some kind of error in the logic.
+                    log::error!(
+                        "Replacement ({:?}) was generated for a function without a name: {:?}",
+                        replacement,
+                        fn_src
+                    );
+                    return;
+                }
+            };
+
+            let diagnostic = IncorrectCase {
+                file: fn_src.file_id,
+                ident_type: "Function".to_string(),
+                ident: AstPtr::new(&ast_ptr).into(),
+                expected_case: replacement.expected_case,
+                ident_text: replacement.current_name.to_string(),
+                suggested_text: replacement.suggested_text,
+            };
+
+            self.sink.push(diagnostic);
+        }
+
+        // 2. Diagnostics for function params.
+        let fn_params_list = match fn_src.value.param_list() {
+            Some(params) => params,
+            None => {
+                if !fn_param_replacements.is_empty() {
+                    log::error!(
+                        "Replacements ({:?}) were generated for a function parameters which had no parameters list: {:?}",
+                        fn_param_replacements, fn_src
+                    );
+                }
+                return;
+            }
+        };
+        let mut fn_params_iter = fn_params_list.params();
+        for param_to_rename in fn_param_replacements {
+            // We assume that parameters in replacement are in the same order as in the
+            // actual params list, but just some of them (ones that named correctly) are skipped.
+            let ast_ptr: ast::Name = loop {
+                match fn_params_iter.next() {
+                    Some(element)
+                        if pat_equals_to_name(element.pat(), &param_to_rename.current_name) =>
+                    {
+                        if let ast::Pat::IdentPat(pat) = element.pat().unwrap() {
+                            break pat.name().unwrap();
+                        } else {
+                            // This is critical. If we consider this parameter the expected one,
+                            // it **must** have a name.
+                            panic!(
+                                "Pattern {:?} equals to expected replacement {:?}, but has no name",
+                                element, param_to_rename
+                            );
+                        }
+                    }
+                    Some(_) => {}
+                    None => {
+                        log::error!(
+                            "Replacement ({:?}) was generated for a function parameter which was not found: {:?}",
+                            param_to_rename, fn_src
+                        );
+                        return;
+                    }
+                }
+            };
+
+            let diagnostic = IncorrectCase {
+                file: fn_src.file_id,
+                ident_type: "Argument".to_string(),
+                ident: AstPtr::new(&ast_ptr).into(),
+                expected_case: param_to_rename.expected_case,
+                ident_text: param_to_rename.current_name.to_string(),
+                suggested_text: param_to_rename.suggested_text,
+            };
+
+            self.sink.push(diagnostic);
+        }
+    }
+
+    /// Given the information about incorrect variable names, looks up into the source code
+    /// for exact locations and adds diagnostics into the sink.
+    fn create_incorrect_case_diagnostic_for_variables(
+        &mut self,
+        func: FunctionId,
+        db: &dyn HirDatabase,
+        pats_replacements: Vec<(PatId, Replacement)>,
+    ) {
+        // XXX: only look at source_map if we do have missing fields
+        if pats_replacements.is_empty() {
+            return;
+        }
+
+        let (_, source_map) = db.body_with_source_map(func.into());
+
+        for (id, replacement) in pats_replacements {
+            if let Ok(source_ptr) = source_map.pat_syntax(id) {
+                if let Some(expr) = source_ptr.value.as_ref().left() {
+                    let root = source_ptr.file_syntax(db.upcast());
+                    if let ast::Pat::IdentPat(ident_pat) = expr.to_node(&root) {
+                        let parent = match ident_pat.syntax().parent() {
+                            Some(parent) => parent,
+                            None => continue,
+                        };
+                        let name_ast = match ident_pat.name() {
+                            Some(name_ast) => name_ast,
+                            None => continue,
+                        };
+
+                        // We have to check that it's either `let var = ...` or `var @ Variant(_)` statement,
+                        // because e.g. match arms are patterns as well.
+                        // In other words, we check that it's a named variable binding.
+                        let is_binding = ast::LetStmt::cast(parent.clone()).is_some()
+                            || (ast::MatchArm::cast(parent).is_some()
+                                && ident_pat.at_token().is_some());
+                        if !is_binding {
+                            // This pattern is not an actual variable declaration, e.g. `Some(val) => {..}` match arm.
+                            continue;
+                        }
+
+                        let diagnostic = IncorrectCase {
+                            file: source_ptr.file_id,
+                            ident_type: "Variable".to_string(),
+                            ident: AstPtr::new(&name_ast).into(),
+                            expected_case: replacement.expected_case,
+                            ident_text: replacement.current_name.to_string(),
+                            suggested_text: replacement.suggested_text,
+                        };
+
+                        self.sink.push(diagnostic);
+                    }
+                }
+            }
+        }
+    }
+
+    fn validate_struct(&mut self, db: &dyn HirDatabase, struct_id: StructId) {
+        let data = db.struct_data(struct_id);
+
+        // 1. Check the structure name.
+        let struct_name = data.name.to_string();
+        let struct_name_replacement = if let Some(new_name) = to_camel_case(&struct_name) {
+            let replacement = Replacement {
+                current_name: data.name.clone(),
+                suggested_text: new_name,
+                expected_case: CaseType::UpperCamelCase,
+            };
+            Some(replacement)
+        } else {
+            None
+        };
+
+        // 2. Check the field names.
+        let mut struct_fields_replacements = Vec::new();
+
+        if let VariantData::Record(fields) = data.variant_data.as_ref() {
+            for (_, field) in fields.iter() {
+                let field_name = field.name.to_string();
+                if let Some(new_name) = to_lower_snake_case(&field_name) {
+                    let replacement = Replacement {
+                        current_name: field.name.clone(),
+                        suggested_text: new_name,
+                        expected_case: CaseType::LowerSnakeCase,
+                    };
+                    struct_fields_replacements.push(replacement);
+                }
+            }
+        }
+
+        // 3. If there is at least one element to spawn a warning on, go to the source map and generate a warning.
+        self.create_incorrect_case_diagnostic_for_struct(
+            struct_id,
+            db,
+            struct_name_replacement,
+            struct_fields_replacements,
+        );
+    }
+
+    /// Given the information about incorrect names in the struct declaration, looks up into the source code
+    /// for exact locations and adds diagnostics into the sink.
+    fn create_incorrect_case_diagnostic_for_struct(
+        &mut self,
+        struct_id: StructId,
+        db: &dyn HirDatabase,
+        struct_name_replacement: Option<Replacement>,
+        struct_fields_replacements: Vec<Replacement>,
+    ) {
+        // XXX: only look at sources if we do have incorrect names
+        if struct_name_replacement.is_none() && struct_fields_replacements.is_empty() {
+            return;
+        }
+
+        let struct_loc = struct_id.lookup(db.upcast());
+        let struct_src = struct_loc.source(db.upcast());
+
+        if let Some(replacement) = struct_name_replacement {
+            let ast_ptr = match struct_src.value.name() {
+                Some(name) => name,
+                None => {
+                    // We don't want rust-analyzer to panic over this, but it is definitely some kind of error in the logic.
+                    log::error!(
+                        "Replacement ({:?}) was generated for a structure without a name: {:?}",
+                        replacement,
+                        struct_src
+                    );
+                    return;
+                }
+            };
+
+            let diagnostic = IncorrectCase {
+                file: struct_src.file_id,
+                ident_type: "Structure".to_string(),
+                ident: AstPtr::new(&ast_ptr).into(),
+                expected_case: replacement.expected_case,
+                ident_text: replacement.current_name.to_string(),
+                suggested_text: replacement.suggested_text,
+            };
+
+            self.sink.push(diagnostic);
+        }
+
+        let struct_fields_list = match struct_src.value.field_list() {
+            Some(ast::FieldList::RecordFieldList(fields)) => fields,
+            _ => {
+                if !struct_fields_replacements.is_empty() {
+                    log::error!(
+                        "Replacements ({:?}) were generated for a structure fields which had no fields list: {:?}",
+                        struct_fields_replacements, struct_src
+                    );
+                }
+                return;
+            }
+        };
+        let mut struct_fields_iter = struct_fields_list.fields();
+        for field_to_rename in struct_fields_replacements {
+            // We assume that parameters in replacement are in the same order as in the
+            // actual params list, but just some of them (ones that named correctly) are skipped.
+            let ast_ptr = loop {
+                match struct_fields_iter.next() {
+                    Some(element) if names_equal(element.name(), &field_to_rename.current_name) => {
+                        break element.name().unwrap()
+                    }
+                    Some(_) => {}
+                    None => {
+                        log::error!(
+                            "Replacement ({:?}) was generated for a structure field which was not found: {:?}",
+                            field_to_rename, struct_src
+                        );
+                        return;
+                    }
+                }
+            };
+
+            let diagnostic = IncorrectCase {
+                file: struct_src.file_id,
+                ident_type: "Field".to_string(),
+                ident: AstPtr::new(&ast_ptr).into(),
+                expected_case: field_to_rename.expected_case,
+                ident_text: field_to_rename.current_name.to_string(),
+                suggested_text: field_to_rename.suggested_text,
+            };
+
+            self.sink.push(diagnostic);
+        }
+    }
+
+    fn validate_enum(&mut self, db: &dyn HirDatabase, enum_id: EnumId) {
+        let data = db.enum_data(enum_id);
+
+        // 1. Check the enum name.
+        let enum_name = data.name.to_string();
+        let enum_name_replacement = if let Some(new_name) = to_camel_case(&enum_name) {
+            let replacement = Replacement {
+                current_name: data.name.clone(),
+                suggested_text: new_name,
+                expected_case: CaseType::UpperCamelCase,
+            };
+            Some(replacement)
+        } else {
+            None
+        };
+
+        // 2. Check the field names.
+        let mut enum_fields_replacements = Vec::new();
+
+        for (_, variant) in data.variants.iter() {
+            let variant_name = variant.name.to_string();
+            if let Some(new_name) = to_camel_case(&variant_name) {
+                let replacement = Replacement {
+                    current_name: variant.name.clone(),
+                    suggested_text: new_name,
+                    expected_case: CaseType::UpperCamelCase,
+                };
+                enum_fields_replacements.push(replacement);
+            }
+        }
+
+        // 3. If there is at least one element to spawn a warning on, go to the source map and generate a warning.
+        self.create_incorrect_case_diagnostic_for_enum(
+            enum_id,
+            db,
+            enum_name_replacement,
+            enum_fields_replacements,
+        )
+    }
+
+    /// Given the information about incorrect names in the struct declaration, looks up into the source code
+    /// for exact locations and adds diagnostics into the sink.
+    fn create_incorrect_case_diagnostic_for_enum(
+        &mut self,
+        enum_id: EnumId,
+        db: &dyn HirDatabase,
+        enum_name_replacement: Option<Replacement>,
+        enum_variants_replacements: Vec<Replacement>,
+    ) {
+        // XXX: only look at sources if we do have incorrect names
+        if enum_name_replacement.is_none() && enum_variants_replacements.is_empty() {
+            return;
+        }
+
+        let enum_loc = enum_id.lookup(db.upcast());
+        let enum_src = enum_loc.source(db.upcast());
+
+        if let Some(replacement) = enum_name_replacement {
+            let ast_ptr = match enum_src.value.name() {
+                Some(name) => name,
+                None => {
+                    // We don't want rust-analyzer to panic over this, but it is definitely some kind of error in the logic.
+                    log::error!(
+                        "Replacement ({:?}) was generated for a enum without a name: {:?}",
+                        replacement,
+                        enum_src
+                    );
+                    return;
+                }
+            };
+
+            let diagnostic = IncorrectCase {
+                file: enum_src.file_id,
+                ident_type: "Enum".to_string(),
+                ident: AstPtr::new(&ast_ptr).into(),
+                expected_case: replacement.expected_case,
+                ident_text: replacement.current_name.to_string(),
+                suggested_text: replacement.suggested_text,
+            };
+
+            self.sink.push(diagnostic);
+        }
+
+        let enum_variants_list = match enum_src.value.variant_list() {
+            Some(variants) => variants,
+            _ => {
+                if !enum_variants_replacements.is_empty() {
+                    log::error!(
+                        "Replacements ({:?}) were generated for a enum variants which had no fields list: {:?}",
+                        enum_variants_replacements, enum_src
+                    );
+                }
+                return;
+            }
+        };
+        let mut enum_variants_iter = enum_variants_list.variants();
+        for variant_to_rename in enum_variants_replacements {
+            // We assume that parameters in replacement are in the same order as in the
+            // actual params list, but just some of them (ones that named correctly) are skipped.
+            let ast_ptr = loop {
+                match enum_variants_iter.next() {
+                    Some(variant)
+                        if names_equal(variant.name(), &variant_to_rename.current_name) =>
+                    {
+                        break variant.name().unwrap()
+                    }
+                    Some(_) => {}
+                    None => {
+                        log::error!(
+                            "Replacement ({:?}) was generated for a enum variant which was not found: {:?}",
+                            variant_to_rename, enum_src
+                        );
+                        return;
+                    }
+                }
+            };
+
+            let diagnostic = IncorrectCase {
+                file: enum_src.file_id,
+                ident_type: "Variant".to_string(),
+                ident: AstPtr::new(&ast_ptr).into(),
+                expected_case: variant_to_rename.expected_case,
+                ident_text: variant_to_rename.current_name.to_string(),
+                suggested_text: variant_to_rename.suggested_text,
+            };
+
+            self.sink.push(diagnostic);
+        }
+    }
+
+    fn validate_const(&mut self, db: &dyn HirDatabase, const_id: ConstId) {
+        let data = db.const_data(const_id);
+
+        let name = match &data.name {
+            Some(name) => name,
+            None => return,
+        };
+
+        let const_name = name.to_string();
+        let replacement = if let Some(new_name) = to_upper_snake_case(&const_name) {
+            Replacement {
+                current_name: name.clone(),
+                suggested_text: new_name,
+                expected_case: CaseType::UpperSnakeCase,
+            }
+        } else {
+            // Nothing to do here.
+            return;
+        };
+
+        let const_loc = const_id.lookup(db.upcast());
+        let const_src = const_loc.source(db.upcast());
+
+        let ast_ptr = match const_src.value.name() {
+            Some(name) => name,
+            None => return,
+        };
+
+        let diagnostic = IncorrectCase {
+            file: const_src.file_id,
+            ident_type: "Constant".to_string(),
+            ident: AstPtr::new(&ast_ptr).into(),
+            expected_case: replacement.expected_case,
+            ident_text: replacement.current_name.to_string(),
+            suggested_text: replacement.suggested_text,
+        };
+
+        self.sink.push(diagnostic);
+    }
+
+    fn validate_static(&mut self, db: &dyn HirDatabase, static_id: StaticId) {
+        let data = db.static_data(static_id);
+
+        let name = match &data.name {
+            Some(name) => name,
+            None => return,
+        };
+
+        let static_name = name.to_string();
+        let replacement = if let Some(new_name) = to_upper_snake_case(&static_name) {
+            Replacement {
+                current_name: name.clone(),
+                suggested_text: new_name,
+                expected_case: CaseType::UpperSnakeCase,
+            }
+        } else {
+            // Nothing to do here.
+            return;
+        };
+
+        let static_loc = static_id.lookup(db.upcast());
+        let static_src = static_loc.source(db.upcast());
+
+        let ast_ptr = match static_src.value.name() {
+            Some(name) => name,
+            None => return,
+        };
+
+        let diagnostic = IncorrectCase {
+            file: static_src.file_id,
+            ident_type: "Static variable".to_string(),
+            ident: AstPtr::new(&ast_ptr).into(),
+            expected_case: replacement.expected_case,
+            ident_text: replacement.current_name.to_string(),
+            suggested_text: replacement.suggested_text,
+        };
+
+        self.sink.push(diagnostic);
+    }
+}
+
+fn names_equal(left: Option<ast::Name>, right: &Name) -> bool {
+    if let Some(left) = left {
+        &left.as_name() == right
+    } else {
+        false
+    }
+}
+
+fn pat_equals_to_name(pat: Option<ast::Pat>, name: &Name) -> bool {
+    if let Some(ast::Pat::IdentPat(ident)) = pat {
+        ident.to_string() == name.to_string()
+    } else {
+        false
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::diagnostics::tests::check_diagnostics;
+
+    #[test]
+    fn incorrect_function_name() {
+        check_diagnostics(
+            r#"
+fn NonSnakeCaseName() {}
+// ^^^^^^^^^^^^^^^^ Function `NonSnakeCaseName` should have snake_case name, e.g. `non_snake_case_name`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_function_params() {
+        check_diagnostics(
+            r#"
+fn foo(SomeParam: u8) {}
+    // ^^^^^^^^^ Argument `SomeParam` should have snake_case name, e.g. `some_param`
+
+fn foo2(ok_param: &str, CAPS_PARAM: u8) {}
+                     // ^^^^^^^^^^ Argument `CAPS_PARAM` should have snake_case name, e.g. `caps_param`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_variable_names() {
+        check_diagnostics(
+            r#"
+fn foo() {
+    let SOME_VALUE = 10;
+     // ^^^^^^^^^^ Variable `SOME_VALUE` should have snake_case name, e.g. `some_value`
+    let AnotherValue = 20;
+     // ^^^^^^^^^^^^ Variable `AnotherValue` should have snake_case name, e.g. `another_value`
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_struct_name() {
+        check_diagnostics(
+            r#"
+struct non_camel_case_name {}
+    // ^^^^^^^^^^^^^^^^^^^ Structure `non_camel_case_name` should have CamelCase name, e.g. `NonCamelCaseName`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_struct_field() {
+        check_diagnostics(
+            r#"
+struct SomeStruct { SomeField: u8 }
+                 // ^^^^^^^^^ Field `SomeField` should have snake_case name, e.g. `some_field`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_enum_name() {
+        check_diagnostics(
+            r#"
+enum some_enum { Val(u8) }
+  // ^^^^^^^^^ Enum `some_enum` should have CamelCase name, e.g. `SomeEnum`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_enum_variant_name() {
+        check_diagnostics(
+            r#"
+enum SomeEnum { SOME_VARIANT(u8) }
+             // ^^^^^^^^^^^^ Variant `SOME_VARIANT` should have CamelCase name, e.g. `SomeVariant`
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_const_name() {
+        check_diagnostics(
+            r#"
+const some_weird_const: u8 = 10;
+   // ^^^^^^^^^^^^^^^^ Constant `some_weird_const` should have UPPER_SNAKE_CASE name, e.g. `SOME_WEIRD_CONST`
+
+fn func() {
+    const someConstInFunc: &str = "hi there";
+       // ^^^^^^^^^^^^^^^ Constant `someConstInFunc` should have UPPER_SNAKE_CASE name, e.g. `SOME_CONST_IN_FUNC`
+
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn incorrect_static_name() {
+        check_diagnostics(
+            r#"
+static some_weird_const: u8 = 10;
+    // ^^^^^^^^^^^^^^^^ Static variable `some_weird_const` should have UPPER_SNAKE_CASE name, e.g. `SOME_WEIRD_CONST`
+
+fn func() {
+    static someConstInFunc: &str = "hi there";
+        // ^^^^^^^^^^^^^^^ Static variable `someConstInFunc` should have UPPER_SNAKE_CASE name, e.g. `SOME_CONST_IN_FUNC`
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn fn_inside_impl_struct() {
+        check_diagnostics(
+            r#"
+struct someStruct;
+    // ^^^^^^^^^^ Structure `someStruct` should have CamelCase name, e.g. `SomeStruct`
+
+impl someStruct {
+    fn SomeFunc(&self) {
+    // ^^^^^^^^ Function `SomeFunc` should have snake_case name, e.g. `some_func`
+        static someConstInFunc: &str = "hi there";
+            // ^^^^^^^^^^^^^^^ Static variable `someConstInFunc` should have UPPER_SNAKE_CASE name, e.g. `SOME_CONST_IN_FUNC`
+        let WHY_VAR_IS_CAPS = 10;
+         // ^^^^^^^^^^^^^^^ Variable `WHY_VAR_IS_CAPS` should have snake_case name, e.g. `why_var_is_caps`
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn no_diagnostic_for_enum_varinats() {
+        check_diagnostics(
+            r#"
+enum Option { Some, None }
+
+fn main() {
+    match Option::None {
+        None => (),
+        Some => (),
+    }
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn non_let_bind() {
+        check_diagnostics(
+            r#"
+enum Option { Some, None }
+
+fn main() {
+    match Option::None {
+        SOME_VAR @ None => (),
+     // ^^^^^^^^ Variable `SOME_VAR` should have snake_case name, e.g. `some_var`
+        Some => (),
+    }
+}
+"#,
+        );
+    }
+}
diff --git a/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs b/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
new file mode 100644
index 000000000..3800f2a6b
--- /dev/null
+++ b/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
@@ -0,0 +1,194 @@
+//! Functions for string case manipulation, such as detecting the identifier case,
+//! and converting it into appropriate form.
+
+#[derive(Debug)]
+enum DetectedCase {
+    LowerCamelCase,
+    UpperCamelCase,
+    LowerSnakeCase,
+    UpperSnakeCase,
+    Unknown,
+}
+
+fn detect_case(ident: &str) -> DetectedCase {
+    let trimmed_ident = ident.trim_matches('_');
+    let first_lowercase = trimmed_ident.starts_with(|chr: char| chr.is_ascii_lowercase());
+    let mut has_lowercase = first_lowercase;
+    let mut has_uppercase = false;
+    let mut has_underscore = false;
+
+    for chr in trimmed_ident.chars() {
+        if chr == '_' {
+            has_underscore = true;
+        } else if chr.is_ascii_uppercase() {
+            has_uppercase = true;
+        } else if chr.is_ascii_lowercase() {
+            has_lowercase = true;
+        }
+    }
+
+    if has_uppercase {
+        if !has_lowercase {
+            DetectedCase::UpperSnakeCase
+        } else if !has_underscore {
+            if first_lowercase {
+                DetectedCase::LowerCamelCase
+            } else {
+                DetectedCase::UpperCamelCase
+            }
+        } else {
+            // It has uppercase, it has lowercase, it has underscore.
+            // No assumptions here
+            DetectedCase::Unknown
+        }
+    } else {
+        DetectedCase::LowerSnakeCase
+    }
+}
+
+/// Converts an identifier to an UpperCamelCase form.
+/// Returns `None` if the string is already is UpperCamelCase.
+pub fn to_camel_case(ident: &str) -> Option<String> {
+    let detected_case = detect_case(ident);
+
+    match detected_case {
+        DetectedCase::UpperCamelCase => return None,
+        DetectedCase::LowerCamelCase => {
+            let mut first_capitalized = false;
+            let output = ident
+                .chars()
+                .map(|chr| {
+                    if !first_capitalized && chr.is_ascii_lowercase() {
+                        first_capitalized = true;
+                        chr.to_ascii_uppercase()
+                    } else {
+                        chr
+                    }
+                })
+                .collect();
+            return Some(output);
+        }
+        _ => {}
+    }
+
+    let mut output = String::with_capacity(ident.len());
+
+    let mut capital_added = false;
+    for chr in ident.chars() {
+        if chr.is_alphabetic() {
+            if !capital_added {
+                output.push(chr.to_ascii_uppercase());
+                capital_added = true;
+            } else {
+                output.push(chr.to_ascii_lowercase());
+            }
+        } else if chr == '_' {
+            // Skip this character and make the next one capital.
+            capital_added = false;
+        } else {
+            // Put the characted as-is.
+            output.push(chr);
+        }
+    }
+
+    if output == ident {
+        // While we didn't detect the correct case at the beginning, there
+        // may be special cases: e.g. `A` is both valid CamelCase and UPPER_SNAKE_CASE.
+        None
+    } else {
+        Some(output)
+    }
+}
+
+/// Converts an identifier to a lower_snake_case form.
+/// Returns `None` if the string is already in lower_snake_case.
+pub fn to_lower_snake_case(ident: &str) -> Option<String> {
+    // First, assume that it's UPPER_SNAKE_CASE.
+    match detect_case(ident) {
+        DetectedCase::LowerSnakeCase => return None,
+        DetectedCase::UpperSnakeCase => {
+            return Some(ident.chars().map(|chr| chr.to_ascii_lowercase()).collect())
+        }
+        _ => {}
+    }
+
+    // Otherwise, assume that it's CamelCase.
+    let lower_snake_case = stdx::to_lower_snake_case(ident);
+
+    if lower_snake_case == ident {
+        // While we didn't detect the correct case at the beginning, there
+        // may be special cases: e.g. `a` is both valid camelCase and snake_case.
+        None
+    } else {
+        Some(lower_snake_case)
+    }
+}
+
+/// Converts an identifier to an UPPER_SNAKE_CASE form.
+/// Returns `None` if the string is already is UPPER_SNAKE_CASE.
+pub fn to_upper_snake_case(ident: &str) -> Option<String> {
+    match detect_case(ident) {
+        DetectedCase::UpperSnakeCase => return None,
+        DetectedCase::LowerSnakeCase => {
+            return Some(ident.chars().map(|chr| chr.to_ascii_uppercase()).collect())
+        }
+        _ => {}
+    }
+
+    // Normalize the string from whatever form it's in currently, and then just make it uppercase.
+    let upper_snake_case = stdx::to_upper_snake_case(ident);
+
+    if upper_snake_case == ident {
+        // While we didn't detect the correct case at the beginning, there
+        // may be special cases: e.g. `A` is both valid CamelCase and UPPER_SNAKE_CASE.
+        None
+    } else {
+        Some(upper_snake_case)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use expect_test::{expect, Expect};
+
+    fn check<F: Fn(&str) -> Option<String>>(fun: F, input: &str, expect: Expect) {
+        // `None` is translated to empty string, meaning that there is nothing to fix.
+        let output = fun(input).unwrap_or_default();
+
+        expect.assert_eq(&output);
+    }
+
+    #[test]
+    fn test_to_lower_snake_case() {
+        check(to_lower_snake_case, "lower_snake_case", expect![[""]]);
+        check(to_lower_snake_case, "UPPER_SNAKE_CASE", expect![["upper_snake_case"]]);
+        check(to_lower_snake_case, "Weird_Case", expect![["weird_case"]]);
+        check(to_lower_snake_case, "CamelCase", expect![["camel_case"]]);
+        check(to_lower_snake_case, "lowerCamelCase", expect![["lower_camel_case"]]);
+        check(to_lower_snake_case, "a", expect![[""]]);
+    }
+
+    #[test]
+    fn test_to_camel_case() {
+        check(to_camel_case, "CamelCase", expect![[""]]);
+        check(to_camel_case, "CamelCase_", expect![[""]]);
+        check(to_camel_case, "_CamelCase", expect![[""]]);
+        check(to_camel_case, "lowerCamelCase", expect![["LowerCamelCase"]]);
+        check(to_camel_case, "lower_snake_case", expect![["LowerSnakeCase"]]);
+        check(to_camel_case, "UPPER_SNAKE_CASE", expect![["UpperSnakeCase"]]);
+        check(to_camel_case, "Weird_Case", expect![["WeirdCase"]]);
+        check(to_camel_case, "name", expect![["Name"]]);
+        check(to_camel_case, "A", expect![[""]]);
+    }
+
+    #[test]
+    fn test_to_upper_snake_case() {
+        check(to_upper_snake_case, "UPPER_SNAKE_CASE", expect![[""]]);
+        check(to_upper_snake_case, "lower_snake_case", expect![["LOWER_SNAKE_CASE"]]);
+        check(to_upper_snake_case, "Weird_Case", expect![["WEIRD_CASE"]]);
+        check(to_upper_snake_case, "CamelCase", expect![["CAMEL_CASE"]]);
+        check(to_upper_snake_case, "lowerCamelCase", expect![["LOWER_CAMEL_CASE"]]);
+        check(to_upper_snake_case, "A", expect![[""]]);
+    }
+}
diff --git a/crates/hir_ty/src/diagnostics/unsafe_check.rs b/crates/hir_ty/src/diagnostics/unsafe_check.rs
index 61ffbf5d1..21a121aad 100644
--- a/crates/hir_ty/src/diagnostics/unsafe_check.rs
+++ b/crates/hir_ty/src/diagnostics/unsafe_check.rs
@@ -190,13 +190,13 @@ struct Ty {
     a: u8,
 }
 
-static mut static_mut: Ty = Ty { a: 0 };
+static mut STATIC_MUT: Ty = Ty { a: 0 };
 
 fn main() {
-    let x = static_mut.a;
+    let x = STATIC_MUT.a;
           //^^^^^^^^^^ This operation is unsafe and requires an unsafe function or block
     unsafe {
-        let x = static_mut.a;
+        let x = STATIC_MUT.a;
     }
 }
 "#,
diff --git a/crates/ide/src/completion/complete_postfix/format_like.rs b/crates/ide/src/completion/complete_postfix/format_like.rs
index 81c33bf3a..50d1e5c81 100644
--- a/crates/ide/src/completion/complete_postfix/format_like.rs
+++ b/crates/ide/src/completion/complete_postfix/format_like.rs
@@ -25,6 +25,7 @@ static KINDS: &[(&str, &str)] = &[
     ("fmt", "format!"),
     ("panic", "panic!"),
     ("println", "println!"),
+    ("eprintln", "eprintln!"),
     ("logd", "log::debug!"),
     ("logt", "log::trace!"),
     ("logi", "log::info!"),
@@ -259,6 +260,7 @@ mod tests {
     fn test_into_suggestion() {
         let test_vector = &[
             ("println!", "{}", r#"println!("{}", $1)"#),
+            ("eprintln!", "{}", r#"eprintln!("{}", $1)"#),
             (
                 "log::info!",
                 "{} {expr} {} {2 + 2}",
diff --git a/crates/ide/src/diagnostics.rs b/crates/ide/src/diagnostics.rs
index f5d627b6e..b30cdb6ed 100644
--- a/crates/ide/src/diagnostics.rs
+++ b/crates/ide/src/diagnostics.rs
@@ -96,6 +96,9 @@ pub(crate) fn diagnostics(
         .on::<hir::diagnostics::NoSuchField, _>(|d| {
             res.borrow_mut().push(diagnostic_with_fix(d, &sema));
         })
+        .on::<hir::diagnostics::IncorrectCase, _>(|d| {
+            res.borrow_mut().push(warning_with_fix(d, &sema));
+        })
         // Only collect experimental diagnostics when they're enabled.
         .filter(|diag| !(diag.is_experimental() && config.disable_experimental))
         .filter(|diag| !config.disabled.contains(diag.code().as_str()));
@@ -130,6 +133,15 @@ fn diagnostic_with_fix<D: DiagnosticWithFix>(d: &D, sema: &Semantics<RootDatabas
     }
 }
 
+fn warning_with_fix<D: DiagnosticWithFix>(d: &D, sema: &Semantics<RootDatabase>) -> Diagnostic {
+    Diagnostic {
+        range: sema.diagnostics_display_range(d).range,
+        message: d.message(),
+        severity: Severity::WeakWarning,
+        fix: d.fix(&sema),
+    }
+}
+
 fn check_unnecessary_braces_in_use_statement(
     acc: &mut Vec<Diagnostic>,
     file_id: FileId,
@@ -245,8 +257,37 @@ mod tests {
 
         assert_eq_text!(&after, &actual);
         assert!(
-            fix.fix_trigger_range.start() <= file_position.offset
-                && fix.fix_trigger_range.end() >= file_position.offset,
+            fix.fix_trigger_range.contains_inclusive(file_position.offset),
+            "diagnostic fix range {:?} does not touch cursor position {:?}",
+            fix.fix_trigger_range,
+            file_position.offset
+        );
+    }
+
+    /// Similar to `check_fix`, but applies all the available fixes.
+    fn check_fixes(ra_fixture_before: &str, ra_fixture_after: &str) {
+        let after = trim_indent(ra_fixture_after);
+
+        let (analysis, file_position) = fixture::position(ra_fixture_before);
+        let diagnostic = analysis
+            .diagnostics(&DiagnosticsConfig::default(), file_position.file_id)
+            .unwrap()
+            .pop()
+            .unwrap();
+        let fix = diagnostic.fix.unwrap();
+        let target_file_contents = analysis.file_text(file_position.file_id).unwrap();
+        let actual = {
+            let mut actual = target_file_contents.to_string();
+            // Go from the last one to the first one, so that ranges won't be affected by previous edits.
+            for edit in fix.source_change.source_file_edits.iter().rev() {
+                edit.edit.apply(&mut actual);
+            }
+            actual
+        };
+
+        assert_eq_text!(&after, &actual);
+        assert!(
+            fix.fix_trigger_range.contains_inclusive(file_position.offset),
             "diagnostic fix range {:?} does not touch cursor position {:?}",
             fix.fix_trigger_range,
             file_position.offset
@@ -790,4 +831,100 @@ struct Foo {
         let diagnostics = analysis.diagnostics(&DiagnosticsConfig::default(), file_id).unwrap();
         assert!(!diagnostics.is_empty());
     }
+
+    #[test]
+    fn test_rename_incorrect_case() {
+        check_fixes(
+            r#"
+pub struct test_struct<|> { one: i32 }
+
+pub fn some_fn(val: test_struct) -> test_struct {
+    test_struct { one: val.one + 1 }
+}
+"#,
+            r#"
+pub struct TestStruct { one: i32 }
+
+pub fn some_fn(val: TestStruct) -> TestStruct {
+    TestStruct { one: val.one + 1 }
+}
+"#,
+        );
+
+        check_fixes(
+            r#"
+pub fn some_fn(NonSnakeCase<|>: u8) -> u8 {
+    NonSnakeCase
+}
+"#,
+            r#"
+pub fn some_fn(non_snake_case: u8) -> u8 {
+    non_snake_case
+}
+"#,
+        );
+
+        check_fixes(
+            r#"
+pub fn SomeFn<|>(val: u8) -> u8 {
+    if val != 0 { SomeFn(val - 1) } else { val }
+}
+"#,
+            r#"
+pub fn some_fn(val: u8) -> u8 {
+    if val != 0 { some_fn(val - 1) } else { val }
+}
+"#,
+        );
+
+        check_fixes(
+            r#"
+fn some_fn() {
+    let whatAWeird_Formatting<|> = 10;
+    another_func(whatAWeird_Formatting);
+}
+"#,
+            r#"
+fn some_fn() {
+    let what_a_weird_formatting = 10;
+    another_func(what_a_weird_formatting);
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_uppercase_const_no_diagnostics() {
+        check_no_diagnostics(
+            r#"
+fn foo() {
+    const ANOTHER_ITEM<|>: &str = "some_item";
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn test_rename_incorrect_case_struct_method() {
+        check_fixes(
+            r#"
+pub struct TestStruct;
+
+impl TestStruct {
+    pub fn SomeFn<|>() -> TestStruct {
+        TestStruct
+    }
+}
+"#,
+            r#"
+pub struct TestStruct;
+
+impl TestStruct {
+    pub fn some_fn() -> TestStruct {
+        TestStruct
+    }
+}
+"#,
+        );
+    }
 }
diff --git a/crates/ide/src/diagnostics/fixes.rs b/crates/ide/src/diagnostics/fixes.rs
index 68ae1c239..0c75e50b0 100644
--- a/crates/ide/src/diagnostics/fixes.rs
+++ b/crates/ide/src/diagnostics/fixes.rs
@@ -3,7 +3,10 @@
 use base_db::FileId;
 use hir::{
     db::AstDatabase,
-    diagnostics::{Diagnostic, MissingFields, MissingOkInTailExpr, NoSuchField, UnresolvedModule},
+    diagnostics::{
+        Diagnostic, IncorrectCase, MissingFields, MissingOkInTailExpr, NoSuchField,
+        UnresolvedModule,
+    },
     HasSource, HirDisplay, Semantics, VariantDef,
 };
 use ide_db::{
@@ -17,7 +20,7 @@ use syntax::{
 };
 use text_edit::TextEdit;
 
-use crate::diagnostics::Fix;
+use crate::{diagnostics::Fix, references::rename::rename_with_semantics, FilePosition};
 
 /// A [Diagnostic] that potentially has a fix available.
 ///
@@ -99,6 +102,23 @@ impl DiagnosticWithFix for MissingOkInTailExpr {
     }
 }
 
+impl DiagnosticWithFix for IncorrectCase {
+    fn fix(&self, sema: &Semantics<RootDatabase>) -> Option<Fix> {
+        let root = sema.db.parse_or_expand(self.file)?;
+        let name_node = self.ident.to_node(&root);
+
+        let file_id = self.file.original_file(sema.db);
+        let offset = name_node.syntax().text_range().start();
+        let file_position = FilePosition { file_id, offset };
+
+        let rename_changes =
+            rename_with_semantics(sema, file_position, &self.suggested_text).ok()?;
+
+        let label = format!("Rename to {}", self.suggested_text);
+        Some(Fix::new(&label, rename_changes.info, rename_changes.range))
+    }
+}
+
 fn missing_record_expr_field_fix(
     sema: &Semantics<RootDatabase>,
     usage_file_id: FileId,
diff --git a/crates/ide/src/link_rewrite.rs b/crates/ide/src/doc_links.rs
index c317a2379..06af36b73 100644
--- a/crates/ide/src/link_rewrite.rs
+++ b/crates/ide/src/doc_links.rs
@@ -1,13 +1,27 @@
 //! Resolves and rewrites links in markdown documentation.
-//!
-//! Most of the implementation can be found in [`hir::doc_links`].
 
-use hir::{Adt, Crate, HasAttrs, ModuleDef};
-use ide_db::{defs::Definition, RootDatabase};
+use std::iter::once;
+
+use itertools::Itertools;
 use pulldown_cmark::{CowStr, Event, LinkType, Options, Parser, Tag};
 use pulldown_cmark_to_cmark::{cmark_with_options, Options as CmarkOptions};
 use url::Url;
 
+use hir::{
+    db::{DefDatabase, HirDatabase},
+    Adt, AsAssocItem, AsName, AssocItem, AssocItemContainer, Crate, Field, HasAttrs, ItemInNs,
+    ModuleDef,
+};
+use ide_db::{
+    defs::{classify_name, classify_name_ref, Definition},
+    RootDatabase,
+};
+use syntax::{ast, match_ast, AstNode, SyntaxKind::*, SyntaxToken, TokenAtOffset, T};
+
+use crate::{FilePosition, Semantics};
+
+pub type DocumentationLink = String;
+
 /// Rewrite documentation links in markdown to point to an online host (e.g. docs.rs)
 pub fn rewrite_links(db: &RootDatabase, markdown: &str, definition: &Definition) -> String {
     let doc = Parser::new_with_broken_link_callback(
@@ -80,6 +94,70 @@ pub fn remove_links(markdown: &str) -> String {
     out
 }
 
+// FIXME:
+// BUG: For Option::Some
+// Returns https://doc.rust-lang.org/nightly/core/prelude/v1/enum.Option.html#variant.Some
+// Instead of https://doc.rust-lang.org/nightly/core/option/enum.Option.html
+//
+// This should cease to be a problem if RFC2988 (Stable Rustdoc URLs) is implemented
+// https://github.com/rust-lang/rfcs/pull/2988
+fn get_doc_link(db: &RootDatabase, definition: Definition) -> Option<String> {
+    // Get the outermost definition for the moduledef. This is used to resolve the public path to the type,
+    // then we can join the method, field, etc onto it if required.
+    let target_def: ModuleDef = match definition {
+        Definition::ModuleDef(moddef) => match moddef {
+            ModuleDef::Function(f) => f
+                .as_assoc_item(db)
+                .and_then(|assoc| match assoc.container(db) {
+                    AssocItemContainer::Trait(t) => Some(t.into()),
+                    AssocItemContainer::ImplDef(impld) => {
+                        impld.target_ty(db).as_adt().map(|adt| adt.into())
+                    }
+                })
+                .unwrap_or_else(|| f.clone().into()),
+            moddef => moddef,
+        },
+        Definition::Field(f) => f.parent_def(db).into(),
+        // FIXME: Handle macros
+        _ => return None,
+    };
+
+    let ns = ItemInNs::from(target_def.clone());
+
+    let module = definition.module(db)?;
+    let krate = module.krate();
+    let import_map = db.import_map(krate.into());
+    let base = once(krate.declaration_name(db)?.to_string())
+        .chain(import_map.path_of(ns)?.segments.iter().map(|name| name.to_string()))
+        .join("/");
+
+    let filename = get_symbol_filename(db, &target_def);
+    let fragment = match definition {
+        Definition::ModuleDef(moddef) => match moddef {
+            ModuleDef::Function(f) => {
+                get_symbol_fragment(db, &FieldOrAssocItem::AssocItem(AssocItem::Function(f)))
+            }
+            ModuleDef::Const(c) => {
+                get_symbol_fragment(db, &FieldOrAssocItem::AssocItem(AssocItem::Const(c)))
+            }
+            ModuleDef::TypeAlias(ty) => {
+                get_symbol_fragment(db, &FieldOrAssocItem::AssocItem(AssocItem::TypeAlias(ty)))
+            }
+            _ => None,
+        },
+        Definition::Field(field) => get_symbol_fragment(db, &FieldOrAssocItem::Field(field)),
+        _ => None,
+    };
+
+    get_doc_url(db, &krate)
+        .and_then(|url| url.join(&base).ok())
+        .and_then(|url| filename.as_deref().and_then(|f| url.join(f).ok()))
+        .and_then(
+            |url| if let Some(fragment) = fragment { url.join(&fragment).ok() } else { Some(url) },
+        )
+        .map(|url| url.into_string())
+}
+
 fn rewrite_intra_doc_link(
     db: &RootDatabase,
     def: Definition,
@@ -138,7 +216,29 @@ fn rewrite_url_link(db: &RootDatabase, def: ModuleDef, target: &str) -> Option<S
         .map(|url| url.into_string())
 }
 
-// Rewrites a markdown document, resolving links using `callback` and additionally striping prefixes/suffixes on link titles.
+/// Retrieve a link to documentation for the given symbol.
+pub(crate) fn external_docs(
+    db: &RootDatabase,
+    position: &FilePosition,
+) -> Option<DocumentationLink> {
+    let sema = Semantics::new(db);
+    let file = sema.parse(position.file_id).syntax().clone();
+    let token = pick_best(file.token_at_offset(position.offset))?;
+    let token = sema.descend_into_macros(token);
+
+    let node = token.parent();
+    let definition = match_ast! {
+        match node {
+            ast::NameRef(name_ref) => classify_name_ref(&sema, &name_ref).map(|d| d.definition(sema.db)),
+            ast::Name(name) => classify_name(&sema, &name).map(|d| d.definition(sema.db)),
+            _ => None,
+        }
+    };
+
+    get_doc_link(db, definition?)
+}
+
+/// Rewrites a markdown document, applying 'callback' to each link.
 fn map_links<'e>(
     events: impl Iterator<Item = Event<'e>>,
     callback: impl Fn(&str, &str) -> (String, String),
@@ -239,6 +339,12 @@ fn ns_from_intra_spec(s: &str) -> Option<hir::Namespace> {
     .next()
 }
 
+/// Get the root URL for the documentation of a crate.
+///
+/// ```
+/// https://doc.rust-lang.org/std/iter/trait.Iterator.html#tymethod.next
+/// ^^^^^^^^^^^^^^^^^^^^^^^^^^
+/// ```
 fn get_doc_url(db: &RootDatabase, krate: &Crate) -> Option<Url> {
     krate
         .get_html_root_url(db)
@@ -255,8 +361,11 @@ fn get_doc_url(db: &RootDatabase, krate: &Crate) -> Option<Url> {
 
 /// Get the filename and extension generated for a symbol by rustdoc.
 ///
-/// Example: `struct.Shard.html`
-fn get_symbol_filename(db: &RootDatabase, definition: &ModuleDef) -> Option<String> {
+/// ```
+/// https://doc.rust-lang.org/std/iter/trait.Iterator.html#tymethod.next
+///                                    ^^^^^^^^^^^^^^^^^^^
+/// ```
+fn get_symbol_filename(db: &dyn HirDatabase, definition: &ModuleDef) -> Option<String> {
     Some(match definition {
         ModuleDef::Adt(adt) => match adt {
             Adt::Struct(s) => format!("struct.{}.html", s.name(db)),
@@ -266,7 +375,7 @@ fn get_symbol_filename(db: &RootDatabase, definition: &ModuleDef) -> Option<Stri
         ModuleDef::Module(_) => "index.html".to_string(),
         ModuleDef::Trait(t) => format!("trait.{}.html", t.name(db)),
         ModuleDef::TypeAlias(t) => format!("type.{}.html", t.name(db)),
-        ModuleDef::BuiltinType(t) => format!("primitive.{}.html", t),
+        ModuleDef::BuiltinType(t) => format!("primitive.{}.html", t.as_name()),
         ModuleDef::Function(f) => format!("fn.{}.html", f.name(db)),
         ModuleDef::EnumVariant(ev) => {
             format!("enum.{}.html#variant.{}", ev.parent_enum(db).name(db), ev.name(db))
@@ -275,3 +384,163 @@ fn get_symbol_filename(db: &RootDatabase, definition: &ModuleDef) -> Option<Stri
         ModuleDef::Static(s) => format!("static.{}.html", s.name(db)?),
     })
 }
+
+enum FieldOrAssocItem {
+    Field(Field),
+    AssocItem(AssocItem),
+}
+
+/// Get the fragment required to link to a specific field, method, associated type, or associated constant.
+///
+/// ```
+/// https://doc.rust-lang.org/std/iter/trait.Iterator.html#tymethod.next
+///                                                       ^^^^^^^^^^^^^^
+/// ```
+fn get_symbol_fragment(db: &dyn HirDatabase, field_or_assoc: &FieldOrAssocItem) -> Option<String> {
+    Some(match field_or_assoc {
+        FieldOrAssocItem::Field(field) => format!("#structfield.{}", field.name(db)),
+        FieldOrAssocItem::AssocItem(assoc) => match assoc {
+            AssocItem::Function(function) => {
+                let is_trait_method = matches!(
+                    function.as_assoc_item(db).map(|assoc| assoc.container(db)),
+                    Some(AssocItemContainer::Trait(..))
+                );
+                // This distinction may get more complicated when specialisation is available.
+                // Rustdoc makes this decision based on whether a method 'has defaultness'.
+                // Currently this is only the case for provided trait methods.
+                if is_trait_method && !function.has_body(db) {
+                    format!("#tymethod.{}", function.name(db))
+                } else {
+                    format!("#method.{}", function.name(db))
+                }
+            }
+            AssocItem::Const(constant) => format!("#associatedconstant.{}", constant.name(db)?),
+            AssocItem::TypeAlias(ty) => format!("#associatedtype.{}", ty.name(db)),
+        },
+    })
+}
+
+fn pick_best(tokens: TokenAtOffset<SyntaxToken>) -> Option<SyntaxToken> {
+    return tokens.max_by_key(priority);
+    fn priority(n: &SyntaxToken) -> usize {
+        match n.kind() {
+            IDENT | INT_NUMBER => 3,
+            T!['('] | T![')'] => 2,
+            kind if kind.is_trivia() => 0,
+            _ => 1,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use expect_test::{expect, Expect};
+
+    use crate::fixture;
+
+    fn check(ra_fixture: &str, expect: Expect) {
+        let (analysis, position) = fixture::position(ra_fixture);
+        let url = analysis.external_docs(position).unwrap().expect("could not find url for symbol");
+
+        expect.assert_eq(&url)
+    }
+
+    #[test]
+    fn test_doc_url_struct() {
+        check(
+            r#"
+pub struct Fo<|>o;
+"#,
+            expect![[r#"https://docs.rs/test/*/test/struct.Foo.html"#]],
+        );
+    }
+
+    #[test]
+    fn test_doc_url_fn() {
+        check(
+            r#"
+pub fn fo<|>o() {}
+"#,
+            expect![[r##"https://docs.rs/test/*/test/fn.foo.html#method.foo"##]],
+        );
+    }
+
+    #[test]
+    fn test_doc_url_inherent_method() {
+        check(
+            r#"
+pub struct Foo;
+
+impl Foo {
+    pub fn met<|>hod() {}
+}
+
+"#,
+            expect![[r##"https://docs.rs/test/*/test/struct.Foo.html#method.method"##]],
+        );
+    }
+
+    #[test]
+    fn test_doc_url_trait_provided_method() {
+        check(
+            r#"
+pub trait Bar {
+    fn met<|>hod() {}
+}
+
+"#,
+            expect![[r##"https://docs.rs/test/*/test/trait.Bar.html#method.method"##]],
+        );
+    }
+
+    #[test]
+    fn test_doc_url_trait_required_method() {
+        check(
+            r#"
+pub trait Foo {
+    fn met<|>hod();
+}
+
+"#,
+            expect![[r##"https://docs.rs/test/*/test/trait.Foo.html#tymethod.method"##]],
+        );
+    }
+
+    #[test]
+    fn test_doc_url_field() {
+        check(
+            r#"
+pub struct Foo {
+    pub fie<|>ld: ()
+}
+
+"#,
+            expect![[r##"https://docs.rs/test/*/test/struct.Foo.html#structfield.field"##]],
+        );
+    }
+
+    // FIXME: ImportMap will return re-export paths instead of public module
+    // paths. The correct path to documentation will never be a re-export.
+    // This problem stops us from resolving stdlib items included in the prelude
+    // such as `Option::Some` correctly.
+    #[ignore = "ImportMap may return re-exports"]
+    #[test]
+    fn test_reexport_order() {
+        check(
+            r#"
+pub mod wrapper {
+    pub use module::Item;
+
+    pub mod module {
+        pub struct Item;
+    }
+}
+
+fn foo() {
+    let bar: wrapper::It<|>em;
+}
+        "#,
+            expect![[r#"https://docs.rs/test/*/test/wrapper/module/struct.Item.html"#]],
+        )
+    }
+}
diff --git a/crates/ide/src/hover.rs b/crates/ide/src/hover.rs
index 53265488e..6290b35bd 100644
--- a/crates/ide/src/hover.rs
+++ b/crates/ide/src/hover.rs
@@ -14,7 +14,7 @@ use test_utils::mark;
 
 use crate::{
     display::{macro_label, ShortLabel, ToNav, TryToNav},
-    link_rewrite::{remove_links, rewrite_links},
+    doc_links::{remove_links, rewrite_links},
     markdown_remove::remove_markdown,
     markup::Markup,
     runnables::runnable,
diff --git a/crates/ide/src/inlay_hints.rs b/crates/ide/src/inlay_hints.rs
index 7d716577e..e2079bbcf 100644
--- a/crates/ide/src/inlay_hints.rs
+++ b/crates/ide/src/inlay_hints.rs
@@ -220,8 +220,8 @@ fn hint_iterator(
     }
     let iter_trait = FamousDefs(sema, krate).core_iter_Iterator()?;
     let iter_mod = FamousDefs(sema, krate).core_iter()?;
-    // assert this type comes from `core::iter`
-    iter_mod.visibility_of(db, &iter_trait.into()).filter(|&vis| vis == hir::Visibility::Public)?;
+    // assert this struct comes from `core::iter`
+    iter_mod.visibility_of(db, &strukt.into()).filter(|&vis| vis == hir::Visibility::Public)?;
     if ty.impls_trait(db, iter_trait, &[]) {
         let assoc_type_item = iter_trait.items(db).into_iter().find_map(|item| match item {
             hir::AssocItem::TypeAlias(alias) if alias.name(db) == known::Item => Some(alias),
@@ -231,12 +231,17 @@ fn hint_iterator(
             const LABEL_START: &str = "impl Iterator<Item = ";
             const LABEL_END: &str = ">";
 
-            let ty_display = ty.display_truncated(
-                db,
-                config
-                    .max_length
-                    .map(|len| len.saturating_sub(LABEL_START.len() + LABEL_END.len())),
-            );
+            let ty_display = hint_iterator(sema, config, &ty)
+                .map(|assoc_type_impl| assoc_type_impl.to_string())
+                .unwrap_or_else(|| {
+                    ty.display_truncated(
+                        db,
+                        config
+                            .max_length
+                            .map(|len| len.saturating_sub(LABEL_START.len() + LABEL_END.len())),
+                    )
+                    .to_string()
+                });
             return Some(format!("{}{}{}", LABEL_START, ty_display, LABEL_END).into());
         }
     }
@@ -1002,18 +1007,6 @@ fn main() {
 
     println!("Unit expr");
 }
-
-//- /alloc.rs crate:alloc deps:core
-mod collections {
-    struct Vec<T> {}
-    impl<T> Vec<T> {
-        fn new() -> Self { Vec {} }
-        fn push(&mut self, t: T) { }
-    }
-    impl<T> IntoIterator for Vec<T> {
-        type Item=T;
-    }
-}
 "#,
         );
     }
@@ -1043,17 +1036,6 @@ fn main() {
         //^ &str
     }
 }
-//- /alloc.rs crate:alloc deps:core
-mod collections {
-    struct Vec<T> {}
-    impl<T> Vec<T> {
-        fn new() -> Self { Vec {} }
-        fn push(&mut self, t: T) { }
-    }
-    impl<T> IntoIterator for Vec<T> {
-        type Item=T;
-    }
-}
 "#,
         );
     }
@@ -1183,4 +1165,41 @@ fn main() {
             "#]],
         );
     }
+
+    #[test]
+    fn shorten_iterators_in_associated_params() {
+        check_with_config(
+            InlayHintsConfig {
+                parameter_hints: false,
+                type_hints: true,
+                chaining_hints: false,
+                max_length: None,
+            },
+            r#"
+use core::iter;
+
+pub struct SomeIter<T> {}
+
+impl<T> SomeIter<T> {
+    pub fn new() -> Self { SomeIter {} }
+    pub fn push(&mut self, t: T) {}
+}
+
+impl<T> Iterator for SomeIter<T> {
+    type Item = T;
+    fn next(&mut self) -> Option<Self::Item> {
+        None
+    }
+}
+
+fn main() {
+    let mut some_iter = SomeIter::new();
+      //^^^^^^^^^^^^^ SomeIter<Take<Repeat<i32>>>
+      some_iter.push(iter::repeat(2).take(2));
+    let iter_of_iters = some_iter.take(2);
+      //^^^^^^^^^^^^^ impl Iterator<Item = impl Iterator<Item = i32>>
+}
+"#,
+        );
+    }
 }
diff --git a/crates/ide/src/lib.rs b/crates/ide/src/lib.rs
index 57f3581b6..aaf9b3b4b 100644
--- a/crates/ide/src/lib.rs
+++ b/crates/ide/src/lib.rs
@@ -45,8 +45,8 @@ mod status;
 mod syntax_highlighting;
 mod syntax_tree;
 mod typing;
-mod link_rewrite;
 mod markdown_remove;
+mod doc_links;
 
 use std::sync::Arc;
 
@@ -77,7 +77,10 @@ pub use crate::{
     hover::{HoverAction, HoverConfig, HoverGotoTypeData, HoverResult},
     inlay_hints::{InlayHint, InlayHintsConfig, InlayKind},
     markup::Markup,
-    references::{Declaration, Reference, ReferenceAccess, ReferenceKind, ReferenceSearchResult},
+    prime_caches::PrimeCachesProgress,
+    references::{
+        Declaration, Reference, ReferenceAccess, ReferenceKind, ReferenceSearchResult, RenameError,
+    },
     runnables::{Runnable, RunnableKind, TestId},
     syntax_highlighting::{
         Highlight, HighlightModifier, HighlightModifiers, HighlightTag, HighlightedRange,
@@ -221,8 +224,11 @@ impl Analysis {
         self.with_db(|db| status::status(&*db, file_id))
     }
 
-    pub fn prime_caches(&self, files: Vec<FileId>) -> Cancelable<()> {
-        self.with_db(|db| prime_caches::prime_caches(db, files))
+    pub fn prime_caches<F>(&self, cb: F) -> Cancelable<()>
+    where
+        F: Fn(PrimeCachesProgress) + Sync + std::panic::UnwindSafe,
+    {
+        self.with_db(move |db| prime_caches::prime_caches(db, &cb))
     }
 
     /// Gets the text of the source file.
@@ -382,6 +388,14 @@ impl Analysis {
         self.with_db(|db| hover::hover(db, position, links_in_hover, markdown))
     }
 
+    /// Return URL(s) for the documentation of the symbol under the cursor.
+    pub fn external_docs(
+        &self,
+        position: FilePosition,
+    ) -> Cancelable<Option<doc_links::DocumentationLink>> {
+        self.with_db(|db| doc_links::external_docs(db, &position))
+    }
+
     /// Computes parameter information for the given call expression.
     pub fn call_info(&self, position: FilePosition) -> Cancelable<Option<CallInfo>> {
         self.with_db(|db| call_info::call_info(db, position))
@@ -490,7 +504,7 @@ impl Analysis {
         &self,
         position: FilePosition,
         new_name: &str,
-    ) -> Cancelable<Option<RangeInfo<SourceChange>>> {
+    ) -> Cancelable<Result<RangeInfo<SourceChange>, RenameError>> {
         self.with_db(|db| references::rename(db, position, new_name))
     }
 
diff --git a/crates/ide/src/prime_caches.rs b/crates/ide/src/prime_caches.rs
index c5ab5a1d8..9687c2734 100644
--- a/crates/ide/src/prime_caches.rs
+++ b/crates/ide/src/prime_caches.rs
@@ -3,10 +3,45 @@
 //! request takes longer to compute. This modules implemented prepopulating of
 //! various caches, it's not really advanced at the moment.
 
-use crate::{FileId, RootDatabase};
+use base_db::SourceDatabase;
+use hir::db::DefDatabase;
 
-pub(crate) fn prime_caches(db: &RootDatabase, files: Vec<FileId>) {
-    for file in files {
-        let _ = crate::syntax_highlighting::highlight(db, file, None, false);
+use crate::RootDatabase;
+
+#[derive(Debug)]
+pub enum PrimeCachesProgress {
+    Started,
+    /// We started indexing a crate.
+    StartedOnCrate {
+        on_crate: String,
+        n_done: usize,
+        n_total: usize,
+    },
+    /// We finished indexing all crates.
+    Finished,
+}
+
+pub(crate) fn prime_caches(db: &RootDatabase, cb: &(dyn Fn(PrimeCachesProgress) + Sync)) {
+    let _p = profile::span("prime_caches");
+    let graph = db.crate_graph();
+    let topo = &graph.crates_in_topological_order();
+
+    cb(PrimeCachesProgress::Started);
+
+    // FIXME: This would be easy to parallelize, since it's in the ideal ordering for that.
+    // Unfortunately rayon prevents panics from propagation out of a `scope`, which breaks
+    // cancellation, so we cannot use rayon.
+    for (i, krate) in topo.iter().enumerate() {
+        let crate_name =
+            graph[*krate].declaration_name.as_ref().map(ToString::to_string).unwrap_or_default();
+
+        cb(PrimeCachesProgress::StartedOnCrate {
+            on_crate: crate_name,
+            n_done: i,
+            n_total: topo.len(),
+        });
+        db.crate_def_map(*krate);
     }
+
+    cb(PrimeCachesProgress::Finished);
 }
diff --git a/crates/ide/src/references.rs b/crates/ide/src/references.rs
index e0830eb4f..88e2f2db3 100644
--- a/crates/ide/src/references.rs
+++ b/crates/ide/src/references.rs
@@ -9,7 +9,7 @@
 //! at the index that the match starts at and its tree parent is
 //! resolved to the search element definition, we get a reference.
 
-mod rename;
+pub(crate) mod rename;
 
 use hir::Semantics;
 use ide_db::{
@@ -26,6 +26,7 @@ use syntax::{
 use crate::{display::TryToNav, FilePosition, FileRange, NavigationTarget, RangeInfo};
 
 pub(crate) use self::rename::rename;
+pub use self::rename::RenameError;
 
 pub use ide_db::search::{Reference, ReferenceAccess, ReferenceKind};
 
@@ -406,6 +407,23 @@ enum Foo {
     }
 
     #[test]
+    fn test_find_all_refs_enum_var_field() {
+        check(
+            r#"
+enum Foo {
+    A,
+    B { field<|>: u8 },
+    C,
+}
+"#,
+            expect![[r#"
+                field RECORD_FIELD FileId(0) 26..35 26..31 Other
+
+            "#]],
+        );
+    }
+
+    #[test]
     fn test_find_all_refs_two_modules() {
         check(
             r#"
@@ -669,6 +687,76 @@ fn g() { f(); }
         );
     }
 
+    #[test]
+    fn test_find_all_refs_struct_pat() {
+        check(
+            r#"
+struct S {
+    field<|>: u8,
+}
+
+fn f(s: S) {
+    match s {
+        S { field } => {}
+    }
+}
+"#,
+            expect![[r#"
+                field RECORD_FIELD FileId(0) 15..24 15..20 Other
+
+                FileId(0) 68..73 FieldShorthandForField Read
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_find_all_refs_enum_var_pat() {
+        check(
+            r#"
+enum En {
+    Variant {
+        field<|>: u8,
+    }
+}
+
+fn f(e: En) {
+    match e {
+        En::Variant { field } => {}
+    }
+}
+"#,
+            expect![[r#"
+                field RECORD_FIELD FileId(0) 32..41 32..37 Other
+
+                FileId(0) 102..107 FieldShorthandForField Read
+            "#]],
+        );
+    }
+
+    #[test]
+    fn test_find_all_refs_enum_var_privacy() {
+        check(
+            r#"
+mod m {
+    pub enum En {
+        Variant {
+            field<|>: u8,
+        }
+    }
+}
+
+fn f() -> m::En {
+    m::En::Variant { field: 0 }
+}
+"#,
+            expect![[r#"
+                field RECORD_FIELD FileId(0) 56..65 56..61 Other
+
+                FileId(0) 125..130 Other Read
+            "#]],
+        );
+    }
+
     fn check(ra_fixture: &str, expect: Expect) {
         check_with_scope(ra_fixture, None, expect)
     }
diff --git a/crates/ide/src/references/rename.rs b/crates/ide/src/references/rename.rs
index 8cbe1ae5a..f9a11e43d 100644
--- a/crates/ide/src/references/rename.rs
+++ b/crates/ide/src/references/rename.rs
@@ -6,11 +6,16 @@ use ide_db::{
     defs::{classify_name, classify_name_ref, Definition, NameClass, NameRefClass},
     RootDatabase,
 };
-use std::convert::TryInto;
+
+use std::{
+    convert::TryInto,
+    error::Error,
+    fmt::{self, Display},
+};
 use syntax::{
     algo::find_node_at_offset,
     ast::{self, NameOwner},
-    lex_single_valid_syntax_kind, match_ast, AstNode, SyntaxKind, SyntaxNode, SyntaxToken,
+    lex_single_syntax_kind, match_ast, AstNode, SyntaxKind, SyntaxNode, SyntaxToken,
 };
 use test_utils::mark;
 use text_edit::TextEdit;
@@ -20,17 +25,44 @@ use crate::{
     SourceChange, SourceFileEdit, TextRange, TextSize,
 };
 
+#[derive(Debug)]
+pub struct RenameError(pub(crate) String);
+
+impl fmt::Display for RenameError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        Display::fmt(&self.0, f)
+    }
+}
+
+impl Error for RenameError {}
+
 pub(crate) fn rename(
     db: &RootDatabase,
     position: FilePosition,
     new_name: &str,
-) -> Option<RangeInfo<SourceChange>> {
+) -> Result<RangeInfo<SourceChange>, RenameError> {
     let sema = Semantics::new(db);
+    rename_with_semantics(&sema, position, new_name)
+}
 
-    match lex_single_valid_syntax_kind(new_name)? {
-        SyntaxKind::IDENT | SyntaxKind::UNDERSCORE => (),
-        SyntaxKind::SELF_KW => return rename_to_self(&sema, position),
-        _ => return None,
+pub(crate) fn rename_with_semantics(
+    sema: &Semantics<RootDatabase>,
+    position: FilePosition,
+    new_name: &str,
+) -> Result<RangeInfo<SourceChange>, RenameError> {
+    match lex_single_syntax_kind(new_name) {
+        Some(res) => match res {
+            (SyntaxKind::IDENT, _) => (),
+            (SyntaxKind::UNDERSCORE, _) => (),
+            (SyntaxKind::SELF_KW, _) => return rename_to_self(&sema, position),
+            (_, Some(syntax_error)) => {
+                return Err(RenameError(format!("Invalid name `{}`: {}", new_name, syntax_error)))
+            }
+            (_, None) => {
+                return Err(RenameError(format!("Invalid name `{}`: not an identifier", new_name)))
+            }
+        },
+        None => return Err(RenameError(format!("Invalid name `{}`: not an identifier", new_name))),
     }
 
     let source_file = sema.parse(position.file_id);
@@ -103,7 +135,7 @@ fn rename_mod(
     position: FilePosition,
     module: Module,
     new_name: &str,
-) -> Option<RangeInfo<SourceChange>> {
+) -> Result<RangeInfo<SourceChange>, RenameError> {
     let mut source_file_edits = Vec::new();
     let mut file_system_edits = Vec::new();
 
@@ -125,7 +157,7 @@ fn rename_mod(
 
     if let Some(src) = module.declaration_source(sema.db) {
         let file_id = src.file_id.original_file(sema.db);
-        let name = src.value.name()?;
+        let name = src.value.name().unwrap();
         let edit = SourceFileEdit {
             file_id,
             edit: TextEdit::replace(name.syntax().text_range(), new_name.into()),
@@ -133,35 +165,40 @@ fn rename_mod(
         source_file_edits.push(edit);
     }
 
-    let RangeInfo { range, info: refs } = find_all_refs(sema, position, None)?;
+    let RangeInfo { range, info: refs } = find_all_refs(sema, position, None)
+        .ok_or_else(|| RenameError("No references found at position".to_string()))?;
     let ref_edits = refs
         .references
         .into_iter()
         .map(|reference| source_edit_from_reference(reference, new_name));
     source_file_edits.extend(ref_edits);
 
-    Some(RangeInfo::new(range, SourceChange::from_edits(source_file_edits, file_system_edits)))
+    Ok(RangeInfo::new(range, SourceChange::from_edits(source_file_edits, file_system_edits)))
 }
 
 fn rename_to_self(
     sema: &Semantics<RootDatabase>,
     position: FilePosition,
-) -> Option<RangeInfo<SourceChange>> {
+) -> Result<RangeInfo<SourceChange>, RenameError> {
     let source_file = sema.parse(position.file_id);
     let syn = source_file.syntax();
 
-    let fn_def = find_node_at_offset::<ast::Fn>(syn, position.offset)?;
-    let params = fn_def.param_list()?;
+    let fn_def = find_node_at_offset::<ast::Fn>(syn, position.offset)
+        .ok_or_else(|| RenameError("No surrounding method declaration found".to_string()))?;
+    let params =
+        fn_def.param_list().ok_or_else(|| RenameError("Method has no parameters".to_string()))?;
     if params.self_param().is_some() {
-        return None; // method already has self param
+        return Err(RenameError("Method already has a self parameter".to_string()));
     }
-    let first_param = params.params().next()?;
+    let first_param =
+        params.params().next().ok_or_else(|| RenameError("Method has no parameters".into()))?;
     let mutable = match first_param.ty() {
         Some(ast::Type::RefType(rt)) => rt.mut_token().is_some(),
-        _ => return None, // not renaming other types
+        _ => return Err(RenameError("Not renaming other types".to_string())),
     };
 
-    let RangeInfo { range, info: refs } = find_all_refs(sema, position, None)?;
+    let RangeInfo { range, info: refs } = find_all_refs(sema, position, None)
+        .ok_or_else(|| RenameError("No reference found at position".to_string()))?;
 
     let param_range = first_param.syntax().text_range();
     let (param_ref, usages): (Vec<Reference>, Vec<Reference>) = refs
@@ -169,7 +206,7 @@ fn rename_to_self(
         .partition(|reference| param_range.intersect(reference.file_range.range).is_some());
 
     if param_ref.is_empty() {
-        return None;
+        return Err(RenameError("Parameter to rename not found".to_string()));
     }
 
     let mut edits = usages
@@ -185,7 +222,7 @@ fn rename_to_self(
         ),
     });
 
-    Some(RangeInfo::new(range, SourceChange::from(edits)))
+    Ok(RangeInfo::new(range, SourceChange::from(edits)))
 }
 
 fn text_edit_from_self_param(
@@ -216,12 +253,13 @@ fn rename_self_to_param(
     position: FilePosition,
     self_token: SyntaxToken,
     new_name: &str,
-) -> Option<RangeInfo<SourceChange>> {
+) -> Result<RangeInfo<SourceChange>, RenameError> {
     let source_file = sema.parse(position.file_id);
     let syn = source_file.syntax();
 
     let text = sema.db.file_text(position.file_id);
-    let fn_def = find_node_at_offset::<ast::Fn>(syn, position.offset)?;
+    let fn_def = find_node_at_offset::<ast::Fn>(syn, position.offset)
+        .ok_or_else(|| RenameError("No surrounding method declaration found".to_string()))?;
     let search_range = fn_def.syntax().text_range();
 
     let mut edits: Vec<SourceFileEdit> = vec![];
@@ -235,7 +273,8 @@ fn rename_self_to_param(
             syn.token_at_offset(offset).find(|t| t.kind() == SyntaxKind::SELF_KW)
         {
             let edit = if let Some(ref self_param) = ast::SelfParam::cast(usage.parent()) {
-                text_edit_from_self_param(syn, self_param, new_name)?
+                text_edit_from_self_param(syn, self_param, new_name)
+                    .ok_or_else(|| RenameError("No target type found".to_string()))?
             } else {
                 TextEdit::replace(usage.text_range(), String::from(new_name))
             };
@@ -246,15 +285,18 @@ fn rename_self_to_param(
     let range = ast::SelfParam::cast(self_token.parent())
         .map_or(self_token.text_range(), |p| p.syntax().text_range());
 
-    Some(RangeInfo::new(range, SourceChange::from(edits)))
+    Ok(RangeInfo::new(range, SourceChange::from(edits)))
 }
 
 fn rename_reference(
     sema: &Semantics<RootDatabase>,
     position: FilePosition,
     new_name: &str,
-) -> Option<RangeInfo<SourceChange>> {
-    let RangeInfo { range, info: refs } = find_all_refs(sema, position, None)?;
+) -> Result<RangeInfo<SourceChange>, RenameError> {
+    let RangeInfo { range, info: refs } = match find_all_refs(sema, position, None) {
+        Some(range_info) => range_info,
+        None => return Err(RenameError("No references found at position".to_string())),
+    };
 
     let edit = refs
         .into_iter()
@@ -262,10 +304,10 @@ fn rename_reference(
         .collect::<Vec<_>>();
 
     if edit.is_empty() {
-        return None;
+        return Err(RenameError("No references found at position".to_string()));
     }
 
-    Some(RangeInfo::new(range, SourceChange::from(edit)))
+    Ok(RangeInfo::new(range, SourceChange::from(edit)))
 }
 
 #[cfg(test)]
@@ -280,25 +322,45 @@ mod tests {
     fn check(new_name: &str, ra_fixture_before: &str, ra_fixture_after: &str) {
         let ra_fixture_after = &trim_indent(ra_fixture_after);
         let (analysis, position) = fixture::position(ra_fixture_before);
-        let source_change = analysis.rename(position, new_name).unwrap();
-        let mut text_edit_builder = TextEdit::builder();
-        let mut file_id: Option<FileId> = None;
-        if let Some(change) = source_change {
-            for edit in change.info.source_file_edits {
-                file_id = Some(edit.file_id);
-                for indel in edit.edit.into_iter() {
-                    text_edit_builder.replace(indel.delete, indel.insert);
+        let rename_result = analysis
+            .rename(position, new_name)
+            .unwrap_or_else(|err| panic!("Rename to '{}' was cancelled: {}", new_name, err));
+        match rename_result {
+            Ok(source_change) => {
+                let mut text_edit_builder = TextEdit::builder();
+                let mut file_id: Option<FileId> = None;
+                for edit in source_change.info.source_file_edits {
+                    file_id = Some(edit.file_id);
+                    for indel in edit.edit.into_iter() {
+                        text_edit_builder.replace(indel.delete, indel.insert);
+                    }
                 }
+                let mut result = analysis.file_text(file_id.unwrap()).unwrap().to_string();
+                text_edit_builder.finish().apply(&mut result);
+                assert_eq_text!(ra_fixture_after, &*result);
             }
-        }
-        let mut result = analysis.file_text(file_id.unwrap()).unwrap().to_string();
-        text_edit_builder.finish().apply(&mut result);
-        assert_eq_text!(ra_fixture_after, &*result);
+            Err(err) => {
+                if ra_fixture_after.starts_with("error:") {
+                    let error_message = ra_fixture_after
+                        .chars()
+                        .into_iter()
+                        .skip("error:".len())
+                        .collect::<String>();
+                    assert_eq!(error_message.trim(), err.to_string());
+                    return;
+                } else {
+                    panic!("Rename to '{}' failed unexpectedly: {}", new_name, err)
+                }
+            }
+        };
     }
 
     fn check_expect(new_name: &str, ra_fixture: &str, expect: Expect) {
         let (analysis, position) = fixture::position(ra_fixture);
-        let source_change = analysis.rename(position, new_name).unwrap().unwrap();
+        let source_change = analysis
+            .rename(position, new_name)
+            .unwrap()
+            .expect("Expect returned RangeInfo to be Some, but was None");
         expect.assert_debug_eq(&source_change)
     }
 
@@ -313,11 +375,30 @@ mod tests {
     }
 
     #[test]
-    fn test_rename_to_invalid_identifier() {
-        let (analysis, position) = fixture::position(r#"fn main() { let i<|> = 1; }"#);
-        let new_name = "invalid!";
-        let source_change = analysis.rename(position, new_name).unwrap();
-        assert!(source_change.is_none());
+    fn test_rename_to_invalid_identifier1() {
+        check(
+            "invalid!",
+            r#"fn main() { let i<|> = 1; }"#,
+            "error: Invalid name `invalid!`: not an identifier",
+        );
+    }
+
+    #[test]
+    fn test_rename_to_invalid_identifier2() {
+        check(
+            "multiple tokens",
+            r#"fn main() { let i<|> = 1; }"#,
+            "error: Invalid name `multiple tokens`: not an identifier",
+        );
+    }
+
+    #[test]
+    fn test_rename_to_invalid_identifier3() {
+        check(
+            "let",
+            r#"fn main() { let i<|> = 1; }"#,
+            "error: Invalid name `let`: not an identifier",