29 files changed, 604 insertions, 134 deletions

diff --git a/crates/assists/src/ast_transform.rs b/crates/assists/src/ast_transform.rs
index bbcd2d488..835da3bb2 100644
--- a/crates/assists/src/ast_transform.rs
+++ b/crates/assists/src/ast_transform.rs
@@ -18,6 +18,34 @@ pub fn apply<'a, N: AstNode>(transformer: &dyn AstTransform<'a>, node: N) -> N {
     .rewrite_ast(&node)
 }
 
+/// `AstTransform` helps with applying bulk transformations to syntax nodes.
+///
+/// This is mostly useful for IDE code generation. If you paste some existing
+/// code into a new context (for example, to add method overrides to an `impl`
+/// block), you generally want to appropriately qualify the names, and sometimes
+/// you might want to substitute generic parameters as well:
+///
+/// ```
+/// mod x {
+///   pub struct A;
+///   pub trait T<U> { fn foo(&self, _: U) -> A; }
+/// }
+///
+/// mod y {
+///   use x::T;
+///
+///   impl T<()> for () {
+///      // If we invoke **Add Missing Members** here, we want to copy-paste `foo`.
+///      // But we want a slightly-modified version of it:
+///      fn foo(&self, _: ()) -> x::A {}
+///   }
+/// }
+/// ```
+///
+/// So, a single `AstTransform` describes such function from `SyntaxNode` to
+/// `SyntaxNode`. Note that the API here is a bit too high-order and high-brow.
+/// We'd want to somehow express this concept simpler, but so far nobody got to
+/// simplifying this!
 pub trait AstTransform<'a> {
     fn get_substitution(&self, node: &syntax::SyntaxNode) -> Option<syntax::SyntaxNode>;
 
diff --git a/crates/assists/src/handlers/add_missing_impl_members.rs b/crates/assists/src/handlers/add_missing_impl_members.rs
index 83a2ada9a..1ac5fefd6 100644
--- a/crates/assists/src/handlers/add_missing_impl_members.rs
+++ b/crates/assists/src/handlers/add_missing_impl_members.rs
@@ -111,8 +111,6 @@ fn add_missing_impl_members_inner(
 ) -> Option<()> {
     let _p = profile::span("add_missing_impl_members_inner");
     let impl_def = ctx.find_node_at_offset::<ast::Impl>()?;
-    let impl_item_list = impl_def.assoc_item_list()?;
-
     let trait_ = resolve_target_trait(&ctx.sema, &impl_def)?;
 
     let def_name = |item: &ast::AssocItem| -> Option<SmolStr> {
@@ -148,11 +146,14 @@ fn add_missing_impl_members_inner(
 
     let target = impl_def.syntax().text_range();
     acc.add(AssistId(assist_id, AssistKind::QuickFix), label, target, |builder| {
+        let impl_item_list = impl_def.assoc_item_list().unwrap_or(make::assoc_item_list());
+
         let n_existing_items = impl_item_list.assoc_items().count();
         let source_scope = ctx.sema.scope_for_def(trait_);
-        let target_scope = ctx.sema.scope(impl_item_list.syntax());
+        let target_scope = ctx.sema.scope(impl_def.syntax());
         let ast_transform = QualifyPaths::new(&target_scope, &source_scope)
-            .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_def));
+            .or(SubstituteTypeParams::for_trait_impl(&source_scope, trait_, impl_def.clone()));
+
         let items = missing_items
             .into_iter()
             .map(|it| ast_transform::apply(&*ast_transform, it))
@@ -162,12 +163,14 @@ fn add_missing_impl_members_inner(
                 _ => it,
             })
             .map(|it| edit::remove_attrs_and_docs(&it));
+
         let new_impl_item_list = impl_item_list.append_items(items);
-        let first_new_item = new_impl_item_list.assoc_items().nth(n_existing_items).unwrap();
+        let new_impl_def = impl_def.with_assoc_item_list(new_impl_item_list);
+        let first_new_item =
+            new_impl_def.assoc_item_list().unwrap().assoc_items().nth(n_existing_items).unwrap();
 
-        let original_range = impl_item_list.syntax().text_range();
         match ctx.config.snippet_cap {
-            None => builder.replace(original_range, new_impl_item_list.to_string()),
+            None => builder.replace(target, new_impl_def.to_string()),
             Some(cap) => {
                 let mut cursor = Cursor::Before(first_new_item.syntax());
                 let placeholder;
@@ -181,8 +184,8 @@ fn add_missing_impl_members_inner(
                 }
                 builder.replace_snippet(
                     cap,
-                    original_range,
-                    render_snippet(cap, new_impl_item_list.syntax(), cursor),
+                    target,
+                    render_snippet(cap, new_impl_def.syntax(), cursor),
                 )
             }
         };
@@ -311,6 +314,25 @@ impl Foo for S {
     }
 
     #[test]
+    fn test_impl_def_without_braces() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+trait Foo { fn foo(&self); }
+struct S;
+impl Foo for S<|>"#,
+            r#"
+trait Foo { fn foo(&self); }
+struct S;
+impl Foo for S {
+    fn foo(&self) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
     fn fill_in_type_params_1() {
         check_assist(
             add_missing_impl_members,
@@ -393,6 +415,41 @@ impl foo::Foo for S {
     }
 
     #[test]
+    fn test_qualify_path_2() {
+        check_assist(
+            add_missing_impl_members,
+            r#"
+mod foo {
+    pub mod bar {
+        pub struct Bar;
+        pub trait Foo { fn foo(&self, bar: Bar); }
+    }
+}
+
+use foo::bar;
+
+struct S;
+impl bar::Foo for S { <|> }"#,
+            r#"
+mod foo {
+    pub mod bar {
+        pub struct Bar;
+        pub trait Foo { fn foo(&self, bar: Bar); }
+    }
+}
+
+use foo::bar;
+
+struct S;
+impl bar::Foo for S {
+    fn foo(&self, bar: bar::Bar) {
+        ${0:todo!()}
+    }
+}"#,
+        );
+    }
+
+    #[test]
     fn test_qualify_path_generic() {
         check_assist(
             add_missing_impl_members,
diff --git a/crates/assists/src/handlers/auto_import.rs b/crates/assists/src/handlers/auto_import.rs
index b5eb2c722..ee7277c04 100644
--- a/crates/assists/src/handlers/auto_import.rs
+++ b/crates/assists/src/handlers/auto_import.rs
@@ -196,10 +196,10 @@ impl AutoImportAssets {
             })
             .filter_map(|candidate| match candidate {
                 Either::Left(module_def) => {
-                    self.module_with_name_to_import.find_use_path(db, module_def)
+                    self.module_with_name_to_import.find_use_path_prefixed(db, module_def)
                 }
                 Either::Right(macro_def) => {
-                    self.module_with_name_to_import.find_use_path(db, macro_def)
+                    self.module_with_name_to_import.find_use_path_prefixed(db, macro_def)
                 }
             })
             .filter(|use_path| !use_path.segments.is_empty())
@@ -291,6 +291,35 @@ mod tests {
     use crate::tests::{check_assist, check_assist_not_applicable, check_assist_target};
 
     #[test]
+    fn applicable_when_found_an_import_partial() {
+        check_assist(
+            auto_import,
+            r"
+            mod std {
+                pub mod fmt {
+                    pub struct Formatter;
+                }
+            }
+
+            use std::fmt;
+
+            <|>Formatter
+            ",
+            r"
+            mod std {
+                pub mod fmt {
+                    pub struct Formatter;
+                }
+            }
+
+            use std::fmt::{self, Formatter};
+
+            Formatter
+            ",
+        );
+    }
+
+    #[test]
     fn applicable_when_found_an_import() {
         check_assist(
             auto_import,
diff --git a/crates/assists/src/utils/insert_use.rs b/crates/assists/src/utils/insert_use.rs
index 09f4a2224..5719b06af 100644
--- a/crates/assists/src/utils/insert_use.rs
+++ b/crates/assists/src/utils/insert_use.rs
@@ -810,16 +810,6 @@ use std::io;",
     }
 
     #[test]
-    #[ignore] // FIXME: Support this
-    fn merge_partial_path() {
-        check_full(
-            "ast::Foo",
-            r"use syntax::{ast, algo};",
-            r"use syntax::{ast::{self, Foo}, algo};",
-        )
-    }
-
-    #[test]
     fn merge_glob_nested() {
         check_full(
             "foo::bar::quux::Fez",
diff --git a/crates/flycheck/src/lib.rs b/crates/flycheck/src/lib.rs
index 16078d104..d982c5f29 100644
--- a/crates/flycheck/src/lib.rs
+++ b/crates/flycheck/src/lib.rs
@@ -59,11 +59,12 @@ pub struct FlycheckHandle {
 
 impl FlycheckHandle {
     pub fn spawn(
+        id: usize,
         sender: Box<dyn Fn(Message) + Send>,
         config: FlycheckConfig,
         workspace_root: PathBuf,
     ) -> FlycheckHandle {
-        let actor = FlycheckActor::new(sender, config, workspace_root);
+        let actor = FlycheckActor::new(id, sender, config, workspace_root);
         let (sender, receiver) = unbounded::<Restart>();
         let thread = jod_thread::spawn(move || actor.run(receiver));
         FlycheckHandle { sender, thread }
@@ -81,7 +82,11 @@ pub enum Message {
     AddDiagnostic { workspace_root: PathBuf, diagnostic: Diagnostic },
 
     /// Request check progress notification to client
-    Progress(Progress),
+    Progress {
+        /// Flycheck instance ID
+        id: usize,
+        progress: Progress,
+    },
 }
 
 #[derive(Debug)]
@@ -95,6 +100,7 @@ pub enum Progress {
 struct Restart;
 
 struct FlycheckActor {
+    id: usize,
     sender: Box<dyn Fn(Message) + Send>,
     config: FlycheckConfig,
     workspace_root: PathBuf,
@@ -113,11 +119,15 @@ enum Event {
 
 impl FlycheckActor {
     fn new(
+        id: usize,
         sender: Box<dyn Fn(Message) + Send>,
         config: FlycheckConfig,
         workspace_root: PathBuf,
     ) -> FlycheckActor {
-        FlycheckActor { sender, config, workspace_root, cargo_handle: None }
+        FlycheckActor { id, sender, config, workspace_root, cargo_handle: None }
+    }
+    fn progress(&self, progress: Progress) {
+        self.send(Message::Progress { id: self.id, progress });
     }
     fn next_event(&self, inbox: &Receiver<Restart>) -> Option<Event> {
         let check_chan = self.cargo_handle.as_ref().map(|cargo| &cargo.receiver);
@@ -139,7 +149,7 @@ impl FlycheckActor {
                     command.stdout(Stdio::piped()).stderr(Stdio::null()).stdin(Stdio::null());
                     if let Ok(child) = command.spawn().map(JodChild) {
                         self.cargo_handle = Some(CargoHandle::spawn(child));
-                        self.send(Message::Progress(Progress::DidStart));
+                        self.progress(Progress::DidStart);
                     }
                 }
                 Event::CheckEvent(None) => {
@@ -153,11 +163,11 @@ impl FlycheckActor {
                             self.check_command()
                         )
                     }
-                    self.send(Message::Progress(Progress::DidFinish(res)));
+                    self.progress(Progress::DidFinish(res));
                 }
                 Event::CheckEvent(Some(message)) => match message {
                     cargo_metadata::Message::CompilerArtifact(msg) => {
-                        self.send(Message::Progress(Progress::DidCheckCrate(msg.target.name)));
+                        self.progress(Progress::DidCheckCrate(msg.target.name));
                     }
 
                     cargo_metadata::Message::CompilerMessage(msg) => {
@@ -179,7 +189,7 @@ impl FlycheckActor {
     }
     fn cancel_check_process(&mut self) {
         if self.cargo_handle.take().is_some() {
-            self.send(Message::Progress(Progress::DidCancel));
+            self.progress(Progress::DidCancel);
         }
     }
     fn check_command(&self) -> Command {
diff --git a/crates/hir/src/code_model.rs b/crates/hir/src/code_model.rs
index 849c8f6d0..567fd91af 100644
--- a/crates/hir/src/code_model.rs
+++ b/crates/hir/src/code_model.rs
@@ -383,6 +383,16 @@ impl Module {
     pub fn find_use_path(self, db: &dyn DefDatabase, item: impl Into<ItemInNs>) -> Option<ModPath> {
         hir_def::find_path::find_path(db, item.into(), self.into())
     }
+
+    /// Finds a path that can be used to refer to the given item from within
+    /// this module, if possible. This is used for returning import paths for use-statements.
+    pub fn find_use_path_prefixed(
+        self,
+        db: &dyn DefDatabase,
+        item: impl Into<ItemInNs>,
+    ) -> Option<ModPath> {
+        hir_def::find_path::find_path_prefixed(db, item.into(), self.into())
+    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -709,11 +719,23 @@ impl Function {
     }
 
     pub fn params(self, db: &dyn HirDatabase) -> Vec<Param> {
+        let resolver = self.id.resolver(db.upcast());
+        let ctx = hir_ty::TyLoweringContext::new(db, &resolver);
+        let environment = TraitEnvironment::lower(db, &resolver);
         db.function_data(self.id)
             .params
             .iter()
             .skip(if self.self_param(db).is_some() { 1 } else { 0 })
-            .map(|_| Param { _ty: () })
+            .map(|type_ref| {
+                let ty = Type {
+                    krate: self.id.lookup(db.upcast()).container.module(db.upcast()).krate,
+                    ty: InEnvironment {
+                        value: Ty::from_hir_ext(&ctx, type_ref).0,
+                        environment: environment.clone(),
+                    },
+                };
+                Param { ty }
+            })
             .collect()
     }
 
@@ -742,15 +764,21 @@ impl From<Mutability> for Access {
     }
 }
 
+pub struct Param {
+    ty: Type,
+}
+
+impl Param {
+    pub fn ty(&self) -> &Type {
+        &self.ty
+    }
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct SelfParam {
     func: FunctionId,
 }
 
-pub struct Param {
-    _ty: (),
-}
-
 impl SelfParam {
     pub fn access(self, db: &dyn HirDatabase) -> Access {
         let func_data = db.function_data(self.func);
@@ -1276,6 +1304,14 @@ impl Type {
         )
     }
 
+    pub fn remove_ref(&self) -> Option<Type> {
+        if let Ty::Apply(ApplicationTy { ctor: TypeCtor::Ref(_), .. }) = self.ty.value {
+            self.ty.value.substs().map(|substs| self.derived(substs[0].clone()))
+        } else {
+            None
+        }
+    }
+
     pub fn is_unknown(&self) -> bool {
         matches!(self.ty.value, Ty::Unknown)
     }
diff --git a/crates/hir/src/semantics.rs b/crates/hir/src/semantics.rs
index 0516a05b4..c61a430e1 100644
--- a/crates/hir/src/semantics.rs
+++ b/crates/hir/src/semantics.rs
@@ -697,6 +697,25 @@ fn find_root(node: &SyntaxNode) -> SyntaxNode {
     node.ancestors().last().unwrap()
 }
 
+/// `SemanticScope` encapsulates the notion of a scope (the set of visible
+/// names) at a particular program point.
+///
+/// It is a bit tricky, as scopes do not really exist inside the compiler.
+/// Rather, the compiler directly computes for each reference the definition it
+/// refers to. It might transiently compute the explicit scope map while doing
+/// so, but, generally, this is not something left after the analysis.
+///
+/// However, we do very much need explicit scopes for IDE purposes --
+/// completion, at its core, lists the contents of the current scope. The notion
+/// of scope is also useful to answer questions like "what would be the meaning
+/// of this piece of code if we inserted it into this position?".
+///
+/// So `SemanticsScope` is constructed from a specific program point (a syntax
+/// node or just a raw offset) and provides access to the set of visible names
+/// on a somewhat best-effort basis.
+///
+/// Note that if you are wondering "what does this specific existing name mean?",
+/// you'd better use the `resolve_` family of methods.
 #[derive(Debug)]
 pub struct SemanticsScope<'a> {
     pub db: &'a dyn HirDatabase,
diff --git a/crates/hir_def/src/diagnostics.rs b/crates/hir_def/src/diagnostics.rs
index 2ec0fd3fb..001b3c5db 100644
--- a/crates/hir_def/src/diagnostics.rs
+++ b/crates/hir_def/src/diagnostics.rs
@@ -69,4 +69,11 @@ impl Diagnostic for UnresolvedImport {
     fn as_any(&self) -> &(dyn Any + Send + 'static) {
         self
     }
+    fn is_experimental(&self) -> bool {
+        // This currently results in false positives in the following cases:
+        // - `cfg_if!`-generated code in libstd (we don't load the sysroot correctly)
+        // - `core::arch` (we don't handle `#[path = "../<path>"]` correctly)
+        // - proc macros and/or proc macro generated code
+        true
+    }
 }
diff --git a/crates/hir_def/src/find_path.rs b/crates/hir_def/src/find_path.rs
index ac2c54ac5..baf374144 100644
--- a/crates/hir_def/src/find_path.rs
+++ b/crates/hir_def/src/find_path.rs
@@ -4,6 +4,7 @@ use hir_expand::name::{known, AsName, Name};
 use rustc_hash::FxHashSet;
 use test_utils::mark;
 
+use crate::nameres::CrateDefMap;
 use crate::{
     db::DefDatabase,
     item_scope::ItemInNs,
@@ -18,7 +19,12 @@ use crate::{
 /// *from where* you're referring to the item, hence the `from` parameter.
 pub fn find_path(db: &dyn DefDatabase, item: ItemInNs, from: ModuleId) -> Option<ModPath> {
     let _p = profile::span("find_path");
-    find_path_inner(db, item, from, MAX_PATH_LEN)
+    find_path_inner(db, item, from, MAX_PATH_LEN, Prefixed::Not)
+}
+
+pub fn find_path_prefixed(db: &dyn DefDatabase, item: ItemInNs, from: ModuleId) -> Option<ModPath> {
+    let _p = profile::span("find_path_absolute");
+    find_path_inner(db, item, from, MAX_PATH_LEN, Prefixed::Plain)
 }
 
 const MAX_PATH_LEN: usize = 15;
@@ -36,11 +42,67 @@ impl ModPath {
     }
 }
 
+fn check_crate_self_super(
+    def_map: &CrateDefMap,
+    item: ItemInNs,
+    from: ModuleId,
+) -> Option<ModPath> {
+    // - if the item is the crate root, return `crate`
+    if item
+        == ItemInNs::Types(ModuleDefId::ModuleId(ModuleId {
+            krate: from.krate,
+            local_id: def_map.root,
+        }))
+    {
+        Some(ModPath::from_segments(PathKind::Crate, Vec::new()))
+    } else if item == ItemInNs::Types(from.into()) {
+        // - if the item is the module we're in, use `self`
+        Some(ModPath::from_segments(PathKind::Super(0), Vec::new()))
+    } else {
+        if let Some(parent_id) = def_map.modules[from.local_id].parent {
+            // - if the item is the parent module, use `super` (this is not used recursively, since `super::super` is ugly)
+            if item
+                == ItemInNs::Types(ModuleDefId::ModuleId(ModuleId {
+                    krate: from.krate,
+                    local_id: parent_id,
+                }))
+            {
+                return Some(ModPath::from_segments(PathKind::Super(1), Vec::new()));
+            }
+        }
+        None
+    }
+}
+
+#[derive(Copy, Clone, PartialEq, Eq)]
+pub enum Prefixed {
+    Not,
+    BySelf,
+    Plain,
+}
+
+impl Prefixed {
+    #[inline]
+    fn prefix(self) -> Option<PathKind> {
+        match self {
+            Prefixed::Not => None,
+            Prefixed::BySelf => Some(PathKind::Super(0)),
+            Prefixed::Plain => Some(PathKind::Plain),
+        }
+    }
+
+    #[inline]
+    fn prefixed(self) -> bool {
+        self != Prefixed::Not
+    }
+}
+
 fn find_path_inner(
     db: &dyn DefDatabase,
     item: ItemInNs,
     from: ModuleId,
     max_len: usize,
+    prefixed: Prefixed,
 ) -> Option<ModPath> {
     if max_len == 0 {
         return None;
@@ -51,41 +113,22 @@ fn find_path_inner(
     // - if the item is already in scope, return the name under which it is
     let def_map = db.crate_def_map(from.krate);
     let from_scope: &crate::item_scope::ItemScope = &def_map.modules[from.local_id].scope;
-    if let Some((name, _)) = from_scope.name_of(item) {
-        return Some(ModPath::from_segments(PathKind::Plain, vec![name.clone()]));
+    let scope_name =
+        if let Some((name, _)) = from_scope.name_of(item) { Some(name.clone()) } else { None };
+    if !prefixed.prefixed() && scope_name.is_some() {
+        return scope_name
+            .map(|scope_name| ModPath::from_segments(PathKind::Plain, vec![scope_name]));
     }
 
-    // - if the item is the crate root, return `crate`
-    if item
-        == ItemInNs::Types(ModuleDefId::ModuleId(ModuleId {
-            krate: from.krate,
-            local_id: def_map.root,
-        }))
-    {
-        return Some(ModPath::from_segments(PathKind::Crate, Vec::new()));
-    }
-
-    // - if the item is the module we're in, use `self`
-    if item == ItemInNs::Types(from.into()) {
-        return Some(ModPath::from_segments(PathKind::Super(0), Vec::new()));
-    }
-
-    // - if the item is the parent module, use `super` (this is not used recursively, since `super::super` is ugly)
-    if let Some(parent_id) = def_map.modules[from.local_id].parent {
-        if item
-            == ItemInNs::Types(ModuleDefId::ModuleId(ModuleId {
-                krate: from.krate,
-                local_id: parent_id,
-            }))
-        {
-            return Some(ModPath::from_segments(PathKind::Super(1), Vec::new()));
-        }
+    if let modpath @ Some(_) = check_crate_self_super(&def_map, item, from) {
+        return modpath;
     }
 
     // - if the item is the crate root of a dependency crate, return the name from the extern prelude
     for (name, def_id) in &def_map.extern_prelude {
         if item == ItemInNs::Types(*def_id) {
-            return Some(ModPath::from_segments(PathKind::Plain, vec![name.clone()]));
+            let name = scope_name.unwrap_or_else(|| name.clone());
+            return Some(ModPath::from_segments(PathKind::Plain, vec![name]));
         }
     }
 
@@ -138,6 +181,7 @@ fn find_path_inner(
                 ItemInNs::Types(ModuleDefId::ModuleId(module_id)),
                 from,
                 best_path_len - 1,
+                prefixed,
             ) {
                 path.segments.push(name);
 
@@ -165,6 +209,7 @@ fn find_path_inner(
                     ItemInNs::Types(ModuleDefId::ModuleId(info.container)),
                     from,
                     best_path_len - 1,
+                    prefixed,
                 )?;
                 path.segments.push(info.path.segments.last().unwrap().clone());
                 Some(path)
@@ -181,7 +226,13 @@ fn find_path_inner(
         }
     }
 
-    best_path
+    if let Some(prefix) = prefixed.prefix() {
+        best_path.or_else(|| {
+            scope_name.map(|scope_name| ModPath::from_segments(prefix, vec![scope_name]))
+        })
+    } else {
+        best_path
+    }
 }
 
 fn select_best_path(old_path: ModPath, new_path: ModPath, prefer_no_std: bool) -> ModPath {
@@ -304,7 +355,7 @@ mod tests {
     /// `code` needs to contain a cursor marker; checks that `find_path` for the
     /// item the `path` refers to returns that same path when called from the
     /// module the cursor is in.
-    fn check_found_path(ra_fixture: &str, path: &str) {
+    fn check_found_path_(ra_fixture: &str, path: &str, absolute: bool) {
         let (db, pos) = TestDB::with_position(ra_fixture);
         let module = db.module_for_file(pos.file_id);
         let parsed_path_file = syntax::SourceFile::parse(&format!("use {};", path));
@@ -324,9 +375,20 @@ mod tests {
             .take_types()
             .unwrap();
 
-        let found_path = find_path(&db, ItemInNs::Types(resolved), module);
+        let found_path = if absolute { find_path_prefixed } else { find_path }(
+            &db,
+            ItemInNs::Types(resolved),
+            module,
+        );
+        assert_eq!(found_path, Some(mod_path), "absolute {}", absolute);
+    }
+
+    fn check_found_path(ra_fixture: &str, path: &str) {
+        check_found_path_(ra_fixture, path, false);
+    }
 
-        assert_eq!(found_path, Some(mod_path));
+    fn check_found_path_abs(ra_fixture: &str, path: &str) {
+        check_found_path_(ra_fixture, path, true);
     }
 
     #[test]
@@ -337,6 +399,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "S");
+        check_found_path_abs(code, "S");
     }
 
     #[test]
@@ -347,6 +410,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "E::A");
+        check_found_path_abs(code, "E::A");
     }
 
     #[test]
@@ -359,6 +423,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "foo::S");
+        check_found_path_abs(code, "foo::S");
     }
 
     #[test]
@@ -373,6 +438,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "super::S");
+        check_found_path_abs(code, "super::S");
     }
 
     #[test]
@@ -384,6 +450,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "self");
+        check_found_path_abs(code, "self");
     }
 
     #[test]
@@ -395,6 +462,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "crate");
+        check_found_path_abs(code, "crate");
     }
 
     #[test]
@@ -407,6 +475,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "crate::S");
+        check_found_path_abs(code, "crate::S");
     }
 
     #[test]
@@ -418,6 +487,7 @@ mod tests {
             pub struct S;
         "#;
         check_found_path(code, "std::S");
+        check_found_path_abs(code, "std::S");
     }
 
     #[test]
@@ -430,14 +500,14 @@ mod tests {
             pub struct S;
         "#;
         check_found_path(code, "std_renamed::S");
+        check_found_path_abs(code, "std_renamed::S");
     }
 
     #[test]
     fn partially_imported() {
         // Tests that short paths are used even for external items, when parts of the path are
         // already in scope.
-        check_found_path(
-            r#"
+        let code = r#"
             //- /main.rs crate:main deps:syntax
 
             use syntax::ast;
@@ -449,12 +519,11 @@ mod tests {
                     A, B, C,
                 }
             }
-        "#,
-            "ast::ModuleItem",
-        );
+        "#;
+        check_found_path(code, "ast::ModuleItem");
+        check_found_path_abs(code, "syntax::ast::ModuleItem");
 
-        check_found_path(
-            r#"
+        let code = r#"
             //- /main.rs crate:main deps:syntax
 
             <|>
@@ -465,9 +534,9 @@ mod tests {
                     A, B, C,
                 }
             }
-        "#,
-            "syntax::ast::ModuleItem",
-        );
+        "#;
+        check_found_path(code, "syntax::ast::ModuleItem");
+        check_found_path_abs(code, "syntax::ast::ModuleItem");
     }
 
     #[test]
@@ -481,6 +550,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "bar::S");
+        check_found_path_abs(code, "bar::S");
     }
 
     #[test]
@@ -494,6 +564,7 @@ mod tests {
             <|>
         "#;
         check_found_path(code, "bar::U");
+        check_found_path_abs(code, "bar::U");
     }
 
     #[test]
@@ -507,6 +578,7 @@ mod tests {
             pub struct S;
         "#;
         check_found_path(code, "std::S");
+        check_found_path_abs(code, "std::S");
     }
 
     #[test]
@@ -520,6 +592,7 @@ mod tests {
             pub use prelude::*;
         "#;
         check_found_path(code, "S");
+        check_found_path_abs(code, "S");
     }
 
     #[test]
@@ -537,6 +610,8 @@ mod tests {
         "#;
         check_found_path(code, "None");
         check_found_path(code, "Some");
+        check_found_path_abs(code, "None");
+        check_found_path_abs(code, "Some");
     }
 
     #[test]
@@ -553,6 +628,7 @@ mod tests {
             pub use crate::foo::bar::S;
         "#;
         check_found_path(code, "baz::S");
+        check_found_path_abs(code, "baz::S");
     }
 
     #[test]
@@ -567,6 +643,7 @@ mod tests {
         "#;
         // crate::S would be shorter, but using private imports seems wrong
         check_found_path(code, "crate::bar::S");
+        check_found_path_abs(code, "crate::bar::S");
     }
 
     #[test]
@@ -585,6 +662,7 @@ mod tests {
             pub use super::foo;
         "#;
         check_found_path(code, "crate::foo::S");
+        check_found_path_abs(code, "crate::foo::S");
     }
 
     #[test]
@@ -605,6 +683,7 @@ mod tests {
         }
         "#;
         check_found_path(code, "std::sync::Arc");
+        check_found_path_abs(code, "std::sync::Arc");
     }
 
     #[test]
@@ -629,6 +708,7 @@ mod tests {
         }
         "#;
         check_found_path(code, "core::fmt::Error");
+        check_found_path_abs(code, "core::fmt::Error");
     }
 
     #[test]
@@ -652,6 +732,7 @@ mod tests {
         }
         "#;
         check_found_path(code, "alloc::sync::Arc");
+        check_found_path_abs(code, "alloc::sync::Arc");
     }
 
     #[test]
@@ -669,6 +750,7 @@ mod tests {
         pub struct Arc;
         "#;
         check_found_path(code, "megaalloc::Arc");
+        check_found_path_abs(code, "megaalloc::Arc");
     }
 
     #[test]
@@ -683,5 +765,7 @@ mod tests {
         "#;
         check_found_path(code, "u8");
         check_found_path(code, "u16");
+        check_found_path_abs(code, "u8");
+        check_found_path_abs(code, "u16");
     }
 }
diff --git a/crates/hir_expand/src/name.rs b/crates/hir_expand/src/name.rs
index 49841c7a1..a5750d829 100644
--- a/crates/hir_expand/src/name.rs
+++ b/crates/hir_expand/src/name.rs
@@ -43,8 +43,8 @@ impl Name {
     }
 
     /// Shortcut to create inline plain text name
-    const fn new_inline_ascii(text: &[u8]) -> Name {
-        Name::new_text(SmolStr::new_inline_from_ascii(text.len(), text))
+    const fn new_inline(text: &str) -> Name {
+        Name::new_text(SmolStr::new_inline(text))
     }
 
     /// Resolve a name from the text of token.
@@ -127,7 +127,7 @@ pub mod known {
             $(
                 #[allow(bad_style)]
                 pub const $ident: super::Name =
-                    super::Name::new_inline_ascii(stringify!($ident).as_bytes());
+                    super::Name::new_inline(stringify!($ident));
             )*
         };
     }
@@ -210,8 +210,8 @@ pub mod known {
     );
 
     // self/Self cannot be used as an identifier
-    pub const SELF_PARAM: super::Name = super::Name::new_inline_ascii(b"self");
-    pub const SELF_TYPE: super::Name = super::Name::new_inline_ascii(b"Self");
+    pub const SELF_PARAM: super::Name = super::Name::new_inline("self");
+    pub const SELF_TYPE: super::Name = super::Name::new_inline("Self");
 
     #[macro_export]
     macro_rules! name {
diff --git a/crates/hir_ty/Cargo.toml b/crates/hir_ty/Cargo.toml
index bc86df2b1..03215be44 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 = { version = "0.27.0" }
-chalk-ir = { version = "0.27.0" }
-chalk-recursive = { version = "0.27.0" }
+chalk-solve = { version = "0.28.0" }
+chalk-ir = { version = "0.28.0" }
+chalk-recursive = { version = "0.28.0" }
 
 stdx = { path = "../stdx", version = "0.0.0" }
 hir_def = { path = "../hir_def", version = "0.0.0" }
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 2b53b8297..9a7785c76 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -555,7 +555,7 @@ impl<'a> InferenceContext<'a> {
 
     fn resolve_lang_item(&self, name: &str) -> Option<LangItemTarget> {
         let krate = self.resolver.krate()?;
-        let name = SmolStr::new_inline_from_ascii(name.len(), name.as_bytes());
+        let name = SmolStr::new_inline(name);
         self.db.lang_item(krate, name)
     }
 
diff --git a/crates/hir_ty/src/traits/chalk.rs b/crates/hir_ty/src/traits/chalk.rs
index 27f0ed628..009b17a7f 100644
--- a/crates/hir_ty/src/traits/chalk.rs
+++ b/crates/hir_ty/src/traits/chalk.rs
@@ -129,8 +129,12 @@ impl<'a> chalk_solve::RustIrDatabase<Interner> for ChalkContext<'a> {
         debug!("impls_for_trait returned {} impls", result.len());
         result
     }
-    fn impl_provided_for(&self, auto_trait_id: TraitId, struct_id: AdtId) -> bool {
-        debug!("impl_provided_for {:?}, {:?}", auto_trait_id, struct_id);
+    fn impl_provided_for(
+        &self,
+        auto_trait_id: TraitId,
+        application_ty: &chalk_ir::ApplicationTy<Interner>,
+    ) -> bool {
+        debug!("impl_provided_for {:?}, {:?}", auto_trait_id, application_ty);
         false // FIXME
     }
     fn associated_ty_value(&self, id: AssociatedTyValueId) -> Arc<AssociatedTyValue> {
@@ -422,6 +426,7 @@ fn well_known_trait_from_lang_attr(name: &str) -> Option<WellKnownTrait> {
         "fn_mut" => WellKnownTrait::FnMut,
         "fn" => WellKnownTrait::Fn,
         "unsize" => WellKnownTrait::Unsize,
+        "coerce_unsized" => WellKnownTrait::CoerceUnsized,
         _ => return None,
     })
 }
@@ -437,6 +442,7 @@ fn lang_attr_from_well_known_trait(attr: WellKnownTrait) -> &'static str {
         WellKnownTrait::Fn => "fn",
         WellKnownTrait::Unsize => "unsize",
         WellKnownTrait::Unpin => "unpin",
+        WellKnownTrait::CoerceUnsized => "coerce_unsized",
     }
 }
 
diff --git a/crates/ide/src/completion/complete_postfix.rs b/crates/ide/src/completion/complete_postfix.rs
index 84c4e129d..26a5af5b9 100644
--- a/crates/ide/src/completion/complete_postfix.rs
+++ b/crates/ide/src/completion/complete_postfix.rs
@@ -175,6 +175,9 @@ pub(super) fn complete_postfix(acc: &mut Completions, ctx: &CompletionContext) {
     )
     .add_to(acc);
 
+    postfix_snippet(ctx, cap, &dot_receiver, "ok", "Ok(expr)", &format!("Ok({})", receiver_text))
+        .add_to(acc);
+
     postfix_snippet(
         ctx,
         cap,
@@ -189,6 +192,16 @@ pub(super) fn complete_postfix(acc: &mut Completions, ctx: &CompletionContext) {
         ctx,
         cap,
         &dot_receiver,
+        "dbgr",
+        "dbg!(&expr)",
+        &format!("dbg!(&{})", receiver_text),
+    )
+    .add_to(acc);
+
+    postfix_snippet(
+        ctx,
+        cap,
+        &dot_receiver,
         "call",
         "function(expr)",
         &format!("${{1}}({})", receiver_text),
@@ -263,9 +276,11 @@ fn main() {
                 sn box   Box::new(expr)
                 sn call  function(expr)
                 sn dbg   dbg!(expr)
+                sn dbgr  dbg!(&expr)
                 sn if    if expr {}
                 sn match match expr {}
                 sn not   !expr
+                sn ok    Ok(expr)
                 sn ref   &expr
                 sn refm  &mut expr
                 sn while while expr {}
@@ -286,7 +301,9 @@ fn main() {
                 sn box   Box::new(expr)
                 sn call  function(expr)
                 sn dbg   dbg!(expr)
+                sn dbgr  dbg!(&expr)
                 sn match match expr {}
+                sn ok    Ok(expr)
                 sn ref   &expr
                 sn refm  &mut expr
             "#]],
diff --git a/crates/ide/src/completion/completion_context.rs b/crates/ide/src/completion/completion_context.rs
index 161f59c1e..671b13328 100644
--- a/crates/ide/src/completion/completion_context.rs
+++ b/crates/ide/src/completion/completion_context.rs
@@ -1,7 +1,7 @@
 //! FIXME: write short doc here
 
 use base_db::SourceDatabase;
-use hir::{Semantics, SemanticsScope, Type};
+use hir::{Local, ScopeDef, Semantics, SemanticsScope, Type};
 use ide_db::RootDatabase;
 use syntax::{
     algo::{find_covering_element, find_node_at_offset},
@@ -91,6 +91,7 @@ pub(crate) struct CompletionContext<'a> {
     pub(super) impl_as_prev_sibling: bool,
     pub(super) is_match_arm: bool,
     pub(super) has_item_list_or_source_file_parent: bool,
+    pub(super) locals: Vec<(String, Local)>,
 }
 
 impl<'a> CompletionContext<'a> {
@@ -119,6 +120,12 @@ impl<'a> CompletionContext<'a> {
             original_file.syntax().token_at_offset(position.offset).left_biased()?;
         let token = sema.descend_into_macros(original_token.clone());
         let scope = sema.scope_at_offset(&token.parent(), position.offset);
+        let mut locals = vec![];
+        scope.process_all_names(&mut |name, scope| {
+            if let ScopeDef::Local(local) = scope {
+                locals.push((name.to_string(), local));
+            }
+        });
         let mut ctx = CompletionContext {
             sema,
             scope,
@@ -167,6 +174,7 @@ impl<'a> CompletionContext<'a> {
             if_is_prev: false,
             is_match_arm: false,
             has_item_list_or_source_file_parent: false,
+            locals,
         };
 
         let mut original_file = original_file.syntax().clone();
diff --git a/crates/ide/src/completion/presentation.rs b/crates/ide/src/completion/presentation.rs
index 24c507f9b..987cbfa7a 100644
--- a/crates/ide/src/completion/presentation.rs
+++ b/crates/ide/src/completion/presentation.rs
@@ -191,6 +191,17 @@ impl Completions {
         func: hir::Function,
         local_name: Option<String>,
     ) {
+        fn add_arg(arg: &str, ty: &Type, ctx: &CompletionContext) -> String {
+            if let Some(derefed_ty) = ty.remove_ref() {
+                for (name, local) in ctx.locals.iter() {
+                    if name == arg && local.ty(ctx.db) == derefed_ty {
+                        return (if ty.is_mutable_reference() { "&mut " } else { "&" }).to_string()
+                            + &arg.to_string();
+                    }
+                }
+            }
+            arg.to_string()
+        };
         let name = local_name.unwrap_or_else(|| func.name(ctx.db).to_string());
         let ast_node = func.source(ctx.db).value;
 
@@ -205,12 +216,20 @@ impl Completions {
                 .set_deprecated(is_deprecated(func, ctx.db))
                 .detail(function_declaration(&ast_node));
 
+        let params_ty = func.params(ctx.db);
         let params = ast_node
             .param_list()
             .into_iter()
             .flat_map(|it| it.params())
-            .flat_map(|it| it.pat())
-            .map(|pat| pat.to_string().trim_start_matches('_').into())
+            .zip(params_ty)
+            .flat_map(|(it, param_ty)| {
+                if let Some(pat) = it.pat() {
+                    let name = pat.to_string();
+                    let arg = name.trim_start_matches("mut ").trim_start_matches('_');
+                    return Some(add_arg(arg, param_ty.ty(), ctx));
+                }
+                None
+            })
             .collect();
 
         builder = builder.add_call_parens(ctx, name, Params::Named(params));
@@ -864,6 +883,106 @@ fn main() { foo(${1:foo}, ${2:bar}, ${3:ho_ge_})$0 }
     }
 
     #[test]
+    fn insert_ref_when_matching_local_in_scope() {
+        check_edit(
+            "ref_arg",
+            r#"
+struct Foo {}
+fn ref_arg(x: &Foo) {}
+fn main() {
+    let x = Foo {};
+    ref_ar<|>
+}
+"#,
+            r#"
+struct Foo {}
+fn ref_arg(x: &Foo) {}
+fn main() {
+    let x = Foo {};
+    ref_arg(${1:&x})$0
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn insert_mut_ref_when_matching_local_in_scope() {
+        check_edit(
+            "ref_arg",
+            r#"
+struct Foo {}
+fn ref_arg(x: &mut Foo) {}
+fn main() {
+    let x = Foo {};
+    ref_ar<|>
+}
+"#,
+            r#"
+struct Foo {}
+fn ref_arg(x: &mut Foo) {}
+fn main() {
+    let x = Foo {};
+    ref_arg(${1:&mut x})$0
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn insert_ref_when_matching_local_in_scope_for_method() {
+        check_edit(
+            "apply_foo",
+            r#"
+struct Foo {}
+struct Bar {}
+impl Bar {
+    fn apply_foo(&self, x: &Foo) {}
+}
+
+fn main() {
+    let x = Foo {};
+    let y = Bar {};
+    y.<|>
+}
+"#,
+            r#"
+struct Foo {}
+struct Bar {}
+impl Bar {
+    fn apply_foo(&self, x: &Foo) {}
+}
+
+fn main() {
+    let x = Foo {};
+    let y = Bar {};
+    y.apply_foo(${1:&x})$0
+}
+"#,
+        );
+    }
+
+    #[test]
+    fn trim_mut_keyword_in_func_completion() {
+        check_edit(
+            "take_mutably",
+            r#"
+fn take_mutably(mut x: &i32) {}
+
+fn main() {
+    take_m<|>
+}
+"#,
+            r#"
+fn take_mutably(mut x: &i32) {}
+
+fn main() {
+    take_mutably(${1:x})$0
+}
+"#,
+        );
+    }
+
+    #[test]
     fn inserts_parens_for_tuple_enums() {
         mark::check!(inserts_parens_for_tuple_enums);
         check_edit(
diff --git a/crates/ide/src/syntax_highlighting/test_data/highlighting.html b/crates/ide/src/syntax_highlighting/test_data/highlighting.html
index cde42024c..1d8a3c404 100644
--- a/crates/ide/src/syntax_highlighting/test_data/highlighting.html
+++ b/crates/ide/src/syntax_highlighting/test_data/highlighting.html
@@ -44,7 +44,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="keyword">pub</span> <span class="keyword">trait</span> <span class="trait declaration">Copy</span> <span class="punctuation">{</span><span class="punctuation">}</span>
 <span class="punctuation">}</span>
 
-<span class="attribute">#</span><span class="attribute">[</span><span class="function attribute">derive</span><span class="punctuation">(</span><span class="attribute">Clone</span><span class="punctuation">,</span><span class="attribute"> Debug</span><span class="punctuation">)</span><span class="attribute">]</span>
+
 <span class="keyword">struct</span> <span class="struct declaration">Foo</span> <span class="punctuation">{</span>
     <span class="keyword">pub</span> <span class="field declaration">x</span><span class="punctuation">:</span> <span class="builtin_type">i32</span><span class="punctuation">,</span>
     <span class="keyword">pub</span> <span class="field declaration">y</span><span class="punctuation">:</span> <span class="builtin_type">i32</span><span class="punctuation">,</span>
@@ -74,7 +74,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="punctuation">}</span>
 <span class="punctuation">}</span>
 
-<span class="attribute">#</span><span class="attribute">[</span><span class="function attribute">derive</span><span class="punctuation">(</span><span class="attribute">Copy</span><span class="punctuation">,</span><span class="attribute"> Clone</span><span class="punctuation">)</span><span class="attribute">]</span>
+<span class="attribute">#</span><span class="attribute">[</span><span class="function attribute">derive</span><span class="punctuation">(</span><span class="attribute">Copy</span><span class="punctuation">)</span><span class="attribute">]</span>
 <span class="keyword">struct</span> <span class="struct declaration">FooCopy</span> <span class="punctuation">{</span>
     <span class="field declaration">x</span><span class="punctuation">:</span> <span class="builtin_type">u32</span><span class="punctuation">,</span>
 <span class="punctuation">}</span>
@@ -144,7 +144,7 @@ pre                 { color: #DCDCCC; background: #3F3F3F; font-size: 22px; padd
     <span class="variable">y</span><span class="punctuation">;</span>
 
     <span class="keyword">let</span> <span class="keyword">mut</span> <span class="variable declaration mutable">foo</span> <span class="operator">=</span> <span class="struct">Foo</span> <span class="punctuation">{</span> <span class="field">x</span><span class="punctuation">,</span> <span class="field">y</span><span class="punctuation">:</span> <span class="variable mutable">x</span> <span class="punctuation">}</span><span class="punctuation">;</span>
-    <span class="keyword">let</span> <span class="variable declaration">foo2</span> <span class="operator">=</span> <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="unresolved_reference">clone</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
+    <span class="keyword">let</span> <span class="variable declaration">foo2</span> <span class="operator">=</span> <span class="struct">Foo</span> <span class="punctuation">{</span> <span class="field">x</span><span class="punctuation">,</span> <span class="field">y</span><span class="punctuation">:</span> <span class="variable mutable">x</span> <span class="punctuation">}</span><span class="punctuation">;</span>
     <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="function">quop</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
     <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="function mutable">qux</span><span class="punctuation">(</span><span class="punctuation">)</span><span class="punctuation">;</span>
     <span class="variable mutable">foo</span><span class="punctuation">.</span><span class="function consuming">baz</span><span class="punctuation">(</span><span class="variable consuming">foo2</span><span class="punctuation">)</span><span class="punctuation">;</span>
diff --git a/crates/ide/src/syntax_highlighting/tests.rs b/crates/ide/src/syntax_highlighting/tests.rs
index 57d4e1252..211e62ea1 100644
--- a/crates/ide/src/syntax_highlighting/tests.rs
+++ b/crates/ide/src/syntax_highlighting/tests.rs
@@ -18,7 +18,7 @@ pub mod marker {
     pub trait Copy {}
 }
 
-#[derive(Clone, Debug)]
+
 struct Foo {
     pub x: i32,
     pub y: i32,
@@ -48,7 +48,7 @@ impl Foo {
     }
 }
 
-#[derive(Copy, Clone)]
+#[derive(Copy)]
 struct FooCopy {
     x: u32,
 }
@@ -118,7 +118,7 @@ fn main() {
     y;
 
     let mut foo = Foo { x, y: x };
-    let foo2 = foo.clone();
+    let foo2 = Foo { x, y: x };
     foo.quop();
     foo.qux();
     foo.baz(foo2);
diff --git a/crates/mbe/src/syntax_bridge.rs b/crates/mbe/src/syntax_bridge.rs
index a8ad917fb..d987b2500 100644
--- a/crates/mbe/src/syntax_bridge.rs
+++ b/crates/mbe/src/syntax_bridge.rs
@@ -636,7 +636,10 @@ impl<'a> TreeSink for TtTreeSink<'a> {
                     let (text, id) = match leaf {
                         tt::Leaf::Ident(ident) => (ident.text.clone(), ident.id),
                         tt::Leaf::Punct(punct) => {
-                            (SmolStr::new_inline_from_ascii(1, &[punct.char as u8]), punct.id)
+                            assert!(punct.char.is_ascii());
+                            let char = &(punct.char as u8);
+                            let text = std::str::from_utf8(std::slice::from_ref(char)).unwrap();
+                            (SmolStr::new_inline(text), punct.id)
                         }
                         tt::Leaf::Literal(lit) => (lit.text.clone(), lit.id),
                     };
diff --git a/crates/project_model/src/lib.rs b/crates/project_model/src/lib.rs
index 288c39e49..258f60e28 100644
--- a/crates/project_model/src/lib.rs
+++ b/crates/project_model/src/lib.rs
@@ -308,7 +308,13 @@ impl ProjectWorkspace {
                     .crates()
                     .filter_map(|(crate_id, krate)| {
                         let file_path = &krate.root_module;
-                        let file_id = load(&file_path)?;
+                        let file_id = match load(&file_path) {
+                            Some(id) => id,
+                            None => {
+                                log::error!("failed to load crate root {}", file_path.display());
+                                return None;
+                            }
+                        };
 
                         let env = krate.env.clone().into_iter().collect();
                         let proc_macro = krate
diff --git a/crates/project_model/src/project_json.rs b/crates/project_model/src/project_json.rs
index 545f254aa..a6895ecdd 100644
--- a/crates/project_model/src/project_json.rs
+++ b/crates/project_model/src/project_json.rs
@@ -13,7 +13,7 @@ use crate::cfg_flag::CfgFlag;
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ProjectJson {
     pub(crate) sysroot_src: Option<AbsPathBuf>,
-    project_root: Option<AbsPathBuf>,
+    project_root: AbsPathBuf,
     crates: Vec<Crate>,
 }
 
@@ -34,10 +34,17 @@ pub struct Crate {
 }
 
 impl ProjectJson {
+    /// Create a new ProjectJson instance.
+    ///
+    /// # Arguments
+    ///
+    /// * `base` - The path to the workspace root (i.e. the folder containing `rust-project.json`)
+    /// * `data` - The parsed contents of `rust-project.json`, or project json that's passed via
+    ///            configuration.
     pub fn new(base: &AbsPath, data: ProjectJsonData) -> ProjectJson {
         ProjectJson {
             sysroot_src: data.sysroot_src.map(|it| base.join(it)),
-            project_root: base.parent().map(AbsPath::to_path_buf),
+            project_root: base.to_path_buf(),
             crates: data
                 .crates
                 .into_iter()
@@ -85,17 +92,17 @@ impl ProjectJson {
                 .collect::<Vec<_>>(),
         }
     }
+    /// Returns the number of crates in the project.
     pub fn n_crates(&self) -> usize {
         self.crates.len()
     }
+    /// Returns an iterator over the crates in the project.
     pub fn crates(&self) -> impl Iterator<Item = (CrateId, &Crate)> + '_ {
         self.crates.iter().enumerate().map(|(idx, krate)| (CrateId(idx as u32), krate))
     }
-    pub fn path(&self) -> Option<&AbsPath> {
-        match &self.project_root {
-            Some(p) => Some(p.as_path()),
-            None => None,
-        }
+    /// Returns the path to the project's root folder.
+    pub fn path(&self) -> &AbsPath {
+        &self.project_root
     }
 }
 
diff --git a/crates/rust-analyzer/Cargo.toml b/crates/rust-analyzer/Cargo.toml
index 8db0b0d72..631ffc4a7 100644
--- a/crates/rust-analyzer/Cargo.toml
+++ b/crates/rust-analyzer/Cargo.toml
@@ -21,7 +21,7 @@ env_logger = { version = "0.7.1", default-features = false }
 itertools = "0.9.0"
 jod-thread = "0.1.0"
 log = "0.4.8"
-lsp-types = { version = "0.80.0", features = ["proposed"] }
+lsp-types = { version = "0.82.0", features = ["proposed"] }
 parking_lot = "0.11.0"
 pico-args = "0.3.1"
 oorandom = "11.1.2"
diff --git a/crates/rust-analyzer/src/caps.rs b/crates/rust-analyzer/src/caps.rs
index de4bc2813..c589afeaf 100644
--- a/crates/rust-analyzer/src/caps.rs
+++ b/crates/rust-analyzer/src/caps.rs
@@ -5,7 +5,7 @@ use lsp_types::{
     CallHierarchyServerCapability, ClientCapabilities, CodeActionKind, CodeActionOptions,
     CodeActionProviderCapability, CodeLensOptions, CompletionOptions,
     DocumentOnTypeFormattingOptions, FoldingRangeProviderCapability, HoverProviderCapability,
-    ImplementationProviderCapability, RenameOptions, RenameProviderCapability, SaveOptions,
+    ImplementationProviderCapability, OneOf, RenameOptions, SaveOptions,
     SelectionRangeProviderCapability, SemanticTokensFullOptions, SemanticTokensLegend,
     SemanticTokensOptions, ServerCapabilities, SignatureHelpOptions, TextDocumentSyncCapability,
     TextDocumentSyncKind, TextDocumentSyncOptions, TypeDefinitionProviderCapability,
@@ -42,16 +42,16 @@ pub fn server_capabilities(client_caps: &ClientCapabilities) -> ServerCapabiliti
             work_done_progress_options: WorkDoneProgressOptions { work_done_progress: None },
         }),
         declaration_provider: None,
-        definition_provider: Some(true),
+        definition_provider: Some(OneOf::Left(true)),
         type_definition_provider: Some(TypeDefinitionProviderCapability::Simple(true)),
         implementation_provider: Some(ImplementationProviderCapability::Simple(true)),
-        references_provider: Some(true),
-        document_highlight_provider: Some(true),
-        document_symbol_provider: Some(true),
+        references_provider: Some(OneOf::Left(true)),
+        document_highlight_provider: Some(OneOf::Left(true)),
+        document_symbol_provider: Some(OneOf::Left(true)),
         workspace_symbol_provider: Some(true),
         code_action_provider: Some(code_action_provider),
         code_lens_provider: Some(CodeLensOptions { resolve_provider: Some(true) }),
-        document_formatting_provider: Some(true),
+        document_formatting_provider: Some(OneOf::Left(true)),
         document_range_formatting_provider: None,
         document_on_type_formatting_provider: Some(DocumentOnTypeFormattingOptions {
             first_trigger_character: "=".to_string(),
@@ -60,7 +60,7 @@ pub fn server_capabilities(client_caps: &ClientCapabilities) -> ServerCapabiliti
         selection_range_provider: Some(SelectionRangeProviderCapability::Simple(true)),
         semantic_highlighting: None,
         folding_range_provider: Some(FoldingRangeProviderCapability::Simple(true)),
-        rename_provider: Some(RenameProviderCapability::Options(RenameOptions {
+        rename_provider: Some(OneOf::Right(RenameOptions {
             prepare_provider: Some(true),
             work_done_progress_options: WorkDoneProgressOptions { work_done_progress: None },
         })),
diff --git a/crates/rust-analyzer/src/global_state.rs b/crates/rust-analyzer/src/global_state.rs
index 212f98a30..96313aaec 100644
--- a/crates/rust-analyzer/src/global_state.rs
+++ b/crates/rust-analyzer/src/global_state.rs
@@ -63,7 +63,7 @@ pub(crate) struct GlobalState {
     req_queue: ReqQueue,
     pub(crate) task_pool: Handle<TaskPool<Task>, Receiver<Task>>,
     pub(crate) loader: Handle<Box<dyn vfs::loader::Handle>, Receiver<vfs::loader::Message>>,
-    pub(crate) flycheck: Option<FlycheckHandle>,
+    pub(crate) flycheck: Vec<FlycheckHandle>,
     pub(crate) flycheck_sender: Sender<flycheck::Message>,
     pub(crate) flycheck_receiver: Receiver<flycheck::Message>,
     pub(crate) config: Config,
@@ -115,7 +115,7 @@ impl GlobalState {
             req_queue: ReqQueue::default(),
             task_pool,
             loader,
-            flycheck: None,
+            flycheck: Vec::new(),
             flycheck_sender,
             flycheck_receiver,
             config,
diff --git a/crates/rust-analyzer/src/main_loop.rs b/crates/rust-analyzer/src/main_loop.rs
index 8d3132581..06ab9d508 100644
--- a/crates/rust-analyzer/src/main_loop.rs
+++ b/crates/rust-analyzer/src/main_loop.rs
@@ -266,8 +266,8 @@ impl GlobalState {
                     }
                 }
 
-                flycheck::Message::Progress(status) => {
-                    let (state, message) = match status {
+                flycheck::Message::Progress { id, progress } => {
+                    let (state, message) = match progress {
                         flycheck::Progress::DidStart => {
                             self.diagnostics.clear_check();
                             (Progress::Begin, None)
@@ -284,14 +284,21 @@ impl GlobalState {
                         }
                     };
 
-                    self.report_progress("cargo check", state, message, None);
+                    // When we're running multiple flychecks, we have to include a disambiguator in
+                    // the title, or the editor complains. Note that this is a user-facing string.
+                    let title = if self.flycheck.len() == 1 {
+                        "cargo check".to_string()
+                    } else {
+                        format!("cargo check (#{})", id + 1)
+                    };
+                    self.report_progress(&title, state, message, None);
                 }
             },
         }
 
         let state_changed = self.process_changes();
         if prev_status == Status::Loading && self.status == Status::Ready {
-            if let Some(flycheck) = &self.flycheck {
+            for flycheck in &self.flycheck {
                 flycheck.update();
             }
         }
@@ -490,7 +497,7 @@ impl GlobalState {
                 Ok(())
             })?
             .on::<lsp_types::notification::DidSaveTextDocument>(|this, params| {
-                if let Some(flycheck) = &this.flycheck {
+                for flycheck in &this.flycheck {
                     flycheck.update();
                 }
                 if let Ok(abs_path) = from_proto::abs_path(&params.text_document.uri) {
diff --git a/crates/rust-analyzer/src/reload.rs b/crates/rust-analyzer/src/reload.rs
index b819618cb..de0dbcad4 100644
--- a/crates/rust-analyzer/src/reload.rs
+++ b/crates/rust-analyzer/src/reload.rs
@@ -201,11 +201,14 @@ impl GlobalState {
             let mut crate_graph = CrateGraph::default();
             let vfs = &mut self.vfs.write().0;
             let loader = &mut self.loader;
+            let mem_docs = &self.mem_docs;
             let mut load = |path: &AbsPath| {
-                let contents = loader.handle.load_sync(path);
-                let path = vfs::VfsPath::from(path.to_path_buf());
-                vfs.set_file_contents(path.clone(), contents);
-                vfs.file_id(&path)
+                let vfs_path = vfs::VfsPath::from(path.to_path_buf());
+                if !mem_docs.contains_key(&vfs_path) {
+                    let contents = loader.handle.load_sync(path);
+                    vfs.set_file_contents(vfs_path.clone(), contents);
+                }
+                vfs.file_id(&vfs_path)
             };
             for ws in workspaces.iter() {
                 crate_graph.extend(ws.to_crate_graph(
@@ -232,29 +235,37 @@ impl GlobalState {
         let config = match self.config.flycheck.clone() {
             Some(it) => it,
             None => {
-                self.flycheck = None;
+                self.flycheck = Vec::new();
                 return;
             }
         };
 
         let sender = self.flycheck_sender.clone();
-        let sender = Box::new(move |msg| sender.send(msg).unwrap());
         self.flycheck = self
             .workspaces
             .iter()
-            // FIXME: Figure out the multi-workspace situation
-            .find_map(|w| match w {
-                ProjectWorkspace::Cargo { cargo, sysroot: _ } => Some(cargo.workspace_root()),
+            .enumerate()
+            .filter_map(|(id, w)| match w {
+                ProjectWorkspace::Cargo { cargo, sysroot: _ } => Some((id, cargo.workspace_root())),
                 ProjectWorkspace::Json { project, .. } => {
                     // Enable flychecks for json projects if a custom flycheck command was supplied
                     // in the workspace configuration.
                     match config {
-                        FlycheckConfig::CustomCommand { .. } => project.path(),
+                        FlycheckConfig::CustomCommand { .. } => Some((id, project.path())),
                         _ => None,
                     }
                 }
             })
-            .map(move |root| FlycheckHandle::spawn(sender, config, root.to_path_buf().into()))
+            .map(|(id, root)| {
+                let sender = sender.clone();
+                FlycheckHandle::spawn(
+                    id,
+                    Box::new(move |msg| sender.send(msg).unwrap()),
+                    config.clone(),
+                    root.to_path_buf().into(),
+                )
+            })
+            .collect();
     }
 }
 
diff --git a/crates/rust-analyzer/src/to_proto.rs b/crates/rust-analyzer/src/to_proto.rs
index dcbf837d6..59e780b7d 100644
--- a/crates/rust-analyzer/src/to_proto.rs
+++ b/crates/rust-analyzer/src/to_proto.rs
@@ -285,12 +285,18 @@ pub(crate) fn signature_help(
         })
     };
 
-    let signature =
-        lsp_types::SignatureInformation { label, documentation, parameters: Some(parameters) };
+    let active_parameter = call_info.active_parameter.map(|it| it as i64);
+
+    let signature = lsp_types::SignatureInformation {
+        label,
+        documentation,
+        parameters: Some(parameters),
+        active_parameter,
+    };
     lsp_types::SignatureHelp {
         signatures: vec![signature],
         active_signature: None,
-        active_parameter: call_info.active_parameter.map(|it| it as i64),
+        active_parameter,
     }
 }
 
diff --git a/crates/syntax/src/ast/edit.rs b/crates/syntax/src/ast/edit.rs
index 45cf31f13..dda0a0319 100644
--- a/crates/syntax/src/ast/edit.rs
+++ b/crates/syntax/src/ast/edit.rs
@@ -93,6 +93,22 @@ where
     }
 }
 
+impl ast::Impl {
+    #[must_use]
+    pub fn with_assoc_item_list(&self, items: ast::AssocItemList) -> ast::Impl {
+        let mut to_insert: ArrayVec<[SyntaxElement; 2]> = ArrayVec::new();
+        if let Some(old_items) = self.assoc_item_list() {
+            let to_replace: SyntaxElement = old_items.syntax().clone().into();
+            to_insert.push(items.syntax().clone().into());
+            self.replace_children(single_node(to_replace), to_insert)
+        } else {
+            to_insert.push(make::tokens::single_space().into());
+            to_insert.push(items.syntax().clone().into());
+            self.insert_children(InsertPosition::Last, to_insert)
+        }
+    }
+}
+
 impl ast::AssocItemList {
     #[must_use]
     pub fn append_items(
diff --git a/crates/syntax/src/ast/make.rs b/crates/syntax/src/ast/make.rs
index 6868feed9..4a0ffcbb0 100644
--- a/crates/syntax/src/ast/make.rs
+++ b/crates/syntax/src/ast/make.rs
@@ -21,6 +21,10 @@ pub fn ty(text: &str) -> ast::Type {
     ast_from_text(&format!("impl {} for D {{}};", text))
 }
 
+pub fn assoc_item_list() -> ast::AssocItemList {
+    ast_from_text("impl C for D {};")
+}
+
 pub fn path_segment(name_ref: ast::NameRef) -> ast::PathSegment {
     ast_from_text(&format!("use {};", name_ref))
 }