5 files changed, 234 insertions, 228 deletions

diff --git a/crates/hir_ty/src/diagnostics/decl_check.rs b/crates/hir_ty/src/diagnostics/decl_check.rs
index eaeb6899f..6773ddea3 100644
--- a/crates/hir_ty/src/diagnostics/decl_check.rs
+++ b/crates/hir_ty/src/diagnostics/decl_check.rs
@@ -23,6 +23,7 @@ use hir_expand::{
     diagnostics::DiagnosticSink,
     name::{AsName, Name},
 };
+use stdx::{always, never};
 use syntax::{
     ast::{self, NameOwner},
     AstNode, AstPtr,
@@ -31,7 +32,7 @@ use test_utils::mark;
 
 use crate::{
     db::HirDatabase,
-    diagnostics::{decl_check::case_conv::*, CaseType, IncorrectCase},
+    diagnostics::{decl_check::case_conv::*, CaseType, IdentType, IncorrectCase},
 };
 
 mod allow {
@@ -40,7 +41,7 @@ mod allow {
     pub(super) const NON_CAMEL_CASE_TYPES: &str = "non_camel_case_types";
 }
 
-pub(super) struct DeclValidator<'a, 'b: 'a> {
+pub(super) struct DeclValidator<'a, 'b> {
     db: &'a dyn HirDatabase,
     krate: CrateId,
     sink: &'a mut DiagnosticSink<'b>,
@@ -77,7 +78,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
             AdtId::StructId(struct_id) => self.validate_struct(struct_id),
             AdtId::EnumId(enum_id) => self.validate_enum(enum_id),
             AdtId::UnionId(_) => {
-                // Unions aren't yet supported by this validator.
+                // FIXME: Unions aren't yet supported by this validator.
             }
         }
     }
@@ -111,63 +112,50 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
         // 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
-        };
+        let fn_name_replacement = to_lower_snake_case(&function_name).map(|new_name| Replacement {
+            current_name: data.name.clone(),
+            suggested_text: new_name,
+            expected_case: CaseType::LowerSnakeCase,
+        });
 
         // 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 {
+        let fn_param_replacements = body
+            .params
+            .iter()
+            .filter_map(|&id| match &body[id] {
+                Pat::Bind { name, .. } => Some(name),
+                _ => None,
+            })
+            .filter_map(|param_name| {
+                Some(Replacement {
                     current_name: param_name.clone(),
-                    suggested_text: new_name,
+                    suggested_text: to_lower_snake_case(&param_name.to_string())?,
                     expected_case: CaseType::LowerSnakeCase,
-                };
-                fn_param_replacements.push(replacement);
-            }
-        }
+                })
+            })
+            .collect();
 
         // 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));
-            }
-        }
+        let pats_replacements = body
+            .pats
+            .iter()
+            // We aren't interested in function parameters, we've processed them above.
+            .filter(|(pat_idx, _)| !body.params.contains(&pat_idx))
+            .filter_map(|(id, pat)| match pat {
+                Pat::Bind { name, .. } => Some((id, name)),
+                _ => None,
+            })
+            .filter_map(|(id, bind_name)| {
+                Some((
+                    id,
+                    Replacement {
+                        current_name: bind_name.clone(),
+                        suggested_text: to_lower_snake_case(&bind_name.to_string())?,
+                        expected_case: CaseType::LowerSnakeCase,
+                    },
+                ))
+            })
+            .collect();
 
         // 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(
@@ -199,8 +187,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
             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!(
+                    never!(
                         "Replacement ({:?}) was generated for a function without a name: {:?}",
                         replacement,
                         fn_src
@@ -211,7 +198,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
             let diagnostic = IncorrectCase {
                 file: fn_src.file_id,
-                ident_type: "Function".to_string(),
+                ident_type: IdentType::Function,
                 ident: AstPtr::new(&ast_ptr).into(),
                 expected_case: replacement.expected_case,
                 ident_text: replacement.current_name.to_string(),
@@ -225,12 +212,12 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
         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
-                    );
-                }
+                always!(
+                    fn_param_replacements.is_empty(),
+                    "Replacements ({:?}) were generated for a function parameters which had no parameters list: {:?}",
+                    fn_param_replacements,
+                    fn_src
+                );
                 return;
             }
         };
@@ -240,23 +227,25 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
             // 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(element) => {
+                        if let Some(ast::Pat::IdentPat(pat)) = element.pat() {
+                            if pat.to_string() == param_to_rename.current_name.to_string() {
+                                if let Some(name) = pat.name() {
+                                    break name;
+                                }
+                                // This is critical. If we consider this parameter the expected one,
+                                // it **must** have a name.
+                                never!(
+                                    "Pattern {:?} equals to expected replacement {:?}, but has no name",
+                                    element,
+                                    param_to_rename
+                                );
+                                return;
+                            }
                         }
                     }
-                    Some(_) => {}
                     None => {
-                        log::error!(
+                        never!(
                             "Replacement ({:?}) was generated for a function parameter which was not found: {:?}",
                             param_to_rename, fn_src
                         );
@@ -267,7 +256,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
             let diagnostic = IncorrectCase {
                 file: fn_src.file_id,
-                ident_type: "Argument".to_string(),
+                ident_type: IdentType::Argument,
                 ident: AstPtr::new(&ast_ptr).into(),
                 expected_case: param_to_rename.expected_case,
                 ident_text: param_to_rename.current_name.to_string(),
@@ -309,8 +298,8 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
                         // 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()
+                        let is_binding = ast::LetStmt::can_cast(parent.kind())
+                            || (ast::MatchArm::can_cast(parent.kind())
                                 && ident_pat.at_token().is_some());
                         if !is_binding {
                             // This pattern is not an actual variable declaration, e.g. `Some(val) => {..}` match arm.
@@ -319,7 +308,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
                         let diagnostic = IncorrectCase {
                             file: source_ptr.file_id,
-                            ident_type: "Variable".to_string(),
+                            ident_type: IdentType::Variable,
                             ident: AstPtr::new(&name_ast).into(),
                             expected_case: replacement.expected_case,
                             ident_text: replacement.current_name.to_string(),
@@ -341,17 +330,12 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
         // 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 {
+        let struct_name_replacement = if !non_camel_case_allowed {
+            to_camel_case(&struct_name).map(|new_name| Replacement {
                 current_name: data.name.clone(),
                 suggested_text: new_name,
                 expected_case: CaseType::UpperCamelCase,
-            };
-            if non_camel_case_allowed {
-                None
-            } else {
-                Some(replacement)
-            }
+            })
         } else {
             None
         };
@@ -403,8 +387,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
             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!(
+                    never!(
                         "Replacement ({:?}) was generated for a structure without a name: {:?}",
                         replacement,
                         struct_src
@@ -415,7 +398,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
             let diagnostic = IncorrectCase {
                 file: struct_src.file_id,
-                ident_type: "Structure".to_string(),
+                ident_type: IdentType::Structure,
                 ident: AstPtr::new(&ast_ptr).into(),
                 expected_case: replacement.expected_case,
                 ident_text: replacement.current_name.to_string(),
@@ -428,12 +411,12 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
         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
-                    );
-                }
+                always!(
+                    struct_fields_replacements.is_empty(),
+                    "Replacements ({:?}) were generated for a structure fields which had no fields list: {:?}",
+                    struct_fields_replacements,
+                    struct_src
+                );
                 return;
             }
         };
@@ -442,13 +425,14 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
             // 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()
+                match struct_fields_iter.next().and_then(|field| field.name()) {
+                    Some(field_name) => {
+                        if field_name.as_name() == field_to_rename.current_name {
+                            break field_name;
+                        }
                     }
-                    Some(_) => {}
                     None => {
-                        log::error!(
+                        never!(
                             "Replacement ({:?}) was generated for a structure field which was not found: {:?}",
                             field_to_rename, struct_src
                         );
@@ -459,7 +443,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
             let diagnostic = IncorrectCase {
                 file: struct_src.file_id,
-                ident_type: "Field".to_string(),
+                ident_type: IdentType::Field,
                 ident: AstPtr::new(&ast_ptr).into(),
                 expected_case: field_to_rename.expected_case,
                 ident_text: field_to_rename.current_name.to_string(),
@@ -480,31 +464,24 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
         // 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
-        };
+        let enum_name_replacement = to_camel_case(&enum_name).map(|new_name| Replacement {
+            current_name: data.name.clone(),
+            suggested_text: new_name,
+            expected_case: CaseType::UpperCamelCase,
+        });
 
         // 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 {
+        let enum_fields_replacements = data
+            .variants
+            .iter()
+            .filter_map(|(_, variant)| {
+                Some(Replacement {
                     current_name: variant.name.clone(),
-                    suggested_text: new_name,
+                    suggested_text: to_camel_case(&variant.name.to_string())?,
                     expected_case: CaseType::UpperCamelCase,
-                };
-                enum_fields_replacements.push(replacement);
-            }
-        }
+                })
+            })
+            .collect();
 
         // 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(
@@ -534,8 +511,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
             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!(
+                    never!(
                         "Replacement ({:?}) was generated for a enum without a name: {:?}",
                         replacement,
                         enum_src
@@ -546,7 +522,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
             let diagnostic = IncorrectCase {
                 file: enum_src.file_id,
-                ident_type: "Enum".to_string(),
+                ident_type: IdentType::Enum,
                 ident: AstPtr::new(&ast_ptr).into(),
                 expected_case: replacement.expected_case,
                 ident_text: replacement.current_name.to_string(),
@@ -559,12 +535,12 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
         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
-                    );
-                }
+                always!(
+                    enum_variants_replacements.is_empty(),
+                    "Replacements ({:?}) were generated for a enum variants which had no fields list: {:?}",
+                    enum_variants_replacements,
+                    enum_src
+                );
                 return;
             }
         };
@@ -573,15 +549,14 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
             // 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()
+                match enum_variants_iter.next().and_then(|v| v.name()) {
+                    Some(variant_name) => {
+                        if variant_name.as_name() == variant_to_rename.current_name {
+                            break variant_name;
+                        }
                     }
-                    Some(_) => {}
                     None => {
-                        log::error!(
+                        never!(
                             "Replacement ({:?}) was generated for a enum variant which was not found: {:?}",
                             variant_to_rename, enum_src
                         );
@@ -592,7 +567,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
             let diagnostic = IncorrectCase {
                 file: enum_src.file_id,
-                ident_type: "Variant".to_string(),
+                ident_type: IdentType::Variant,
                 ident: AstPtr::new(&ast_ptr).into(),
                 expected_case: variant_to_rename.expected_case,
                 ident_text: variant_to_rename.current_name.to_string(),
@@ -637,7 +612,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
         let diagnostic = IncorrectCase {
             file: const_src.file_id,
-            ident_type: "Constant".to_string(),
+            ident_type: IdentType::Constant,
             ident: AstPtr::new(&ast_ptr).into(),
             expected_case: replacement.expected_case,
             ident_text: replacement.current_name.to_string(),
@@ -685,7 +660,7 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
 
         let diagnostic = IncorrectCase {
             file: static_src.file_id,
-            ident_type: "Static variable".to_string(),
+            ident_type: IdentType::StaticVariable,
             ident: AstPtr::new(&ast_ptr).into(),
             expected_case: replacement.expected_case,
             ident_text: replacement.current_name.to_string(),
@@ -696,22 +671,6 @@ impl<'a, 'b> DeclValidator<'a, 'b> {
     }
 }
 
-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 test_utils::mark;
diff --git a/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs b/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
index 14e4d92f0..3ab36caf2 100644
--- a/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
+++ b/crates/hir_ty/src/diagnostics/decl_check/case_conv.rs
@@ -5,7 +5,7 @@
 // from file /compiler/rustc_lint/src/nonstandard_style.rs
 
 /// Converts an identifier to an UpperCamelCase form.
-/// Returns `None` if the string is already is UpperCamelCase.
+/// Returns `None` if the string is already in UpperCamelCase.
 pub(crate) fn to_camel_case(ident: &str) -> Option<String> {
     if is_camel_case(ident) {
         return None;
@@ -17,7 +17,7 @@ pub(crate) fn to_camel_case(ident: &str) -> Option<String> {
         .split('_')
         .filter(|component| !component.is_empty())
         .map(|component| {
-            let mut camel_cased_component = String::new();
+            let mut camel_cased_component = String::with_capacity(component.len());
 
             let mut new_word = true;
             let mut prev_is_lower_case = true;
@@ -30,9 +30,9 @@ pub(crate) fn to_camel_case(ident: &str) -> Option<String> {
                 }
 
                 if new_word {
-                    camel_cased_component.push_str(&c.to_uppercase().to_string());
+                    camel_cased_component.extend(c.to_uppercase());
                 } else {
-                    camel_cased_component.push_str(&c.to_lowercase().to_string());
+                    camel_cased_component.extend(c.to_lowercase());
                 }
 
                 prev_is_lower_case = c.is_lowercase();
@@ -41,16 +41,16 @@ pub(crate) fn to_camel_case(ident: &str) -> Option<String> {
 
             camel_cased_component
         })
-        .fold((String::new(), None), |(acc, prev): (String, Option<String>), next| {
+        .fold((String::new(), None), |(acc, prev): (_, Option<String>), next| {
             // separate two components with an underscore if their boundary cannot
             // be distinguished using a uppercase/lowercase case distinction
-            let join = if let Some(prev) = prev {
-                let l = prev.chars().last().unwrap();
-                let f = next.chars().next().unwrap();
-                !char_has_case(l) && !char_has_case(f)
-            } else {
-                false
-            };
+            let join = prev
+                .and_then(|prev| {
+                    let f = next.chars().next()?;
+                    let l = prev.chars().last()?;
+                    Some(!char_has_case(l) && !char_has_case(f))
+                })
+                .unwrap_or(false);
             (acc + if join { "_" } else { "" } + &next, Some(next))
         })
         .0;
@@ -92,14 +92,12 @@ fn is_camel_case(name: &str) -> bool {
     let mut fst = None;
     // start with a non-lowercase letter rather than non-uppercase
     // ones (some scripts don't have a concept of upper/lowercase)
-    !name.chars().next().unwrap().is_lowercase()
+    name.chars().next().map_or(true, |c| !c.is_lowercase())
         && !name.contains("__")
         && !name.chars().any(|snd| {
-            let ret = match (fst, snd) {
-                (None, _) => false,
-                (Some(fst), snd) => {
-                    char_has_case(fst) && snd == '_' || char_has_case(snd) && fst == '_'
-                }
+            let ret = match fst {
+                None => false,
+                Some(fst) => char_has_case(fst) && snd == '_' || char_has_case(snd) && fst == '_',
             };
             fst = Some(snd);
 
diff --git a/crates/hir_ty/src/diagnostics/expr.rs b/crates/hir_ty/src/diagnostics/expr.rs
index 107417c27..66a88e2b6 100644
--- a/crates/hir_ty/src/diagnostics/expr.rs
+++ b/crates/hir_ty/src/diagnostics/expr.rs
@@ -2,8 +2,10 @@
 
 use std::sync::Arc;
 
-use hir_def::{expr::Statement, path::path, resolver::HasResolver, AdtId, DefWithBodyId};
-use hir_expand::diagnostics::DiagnosticSink;
+use hir_def::{
+    expr::Statement, path::path, resolver::HasResolver, AdtId, AssocItemId, DefWithBodyId,
+};
+use hir_expand::{diagnostics::DiagnosticSink, name};
 use rustc_hash::FxHashSet;
 use syntax::{ast, AstPtr};
 
@@ -15,7 +17,7 @@ use crate::{
         MissingPatFields, RemoveThisSemicolon,
     },
     utils::variant_data,
-    ApplicationTy, InferenceResult, Ty, TypeCtor,
+    InferenceResult, Ty,
 };
 
 pub(crate) use hir_def::{
@@ -24,6 +26,8 @@ pub(crate) use hir_def::{
     LocalFieldId, VariantId,
 };
 
+use super::ReplaceFilterMapNextWithFindMap;
+
 pub(super) struct ExprValidator<'a, 'b: 'a> {
     owner: DefWithBodyId,
     infer: Arc<InferenceResult>,
@@ -40,6 +44,8 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
     }
 
     pub(super) fn validate_body(&mut self, db: &dyn HirDatabase) {
+        self.check_for_filter_map_next(db);
+
         let body = db.body(self.owner.into());
 
         for (id, expr) in body.exprs.iter() {
@@ -150,20 +156,76 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
         }
     }
 
-    fn validate_call(&mut self, db: &dyn HirDatabase, call_id: ExprId, expr: &Expr) -> Option<()> {
+    fn check_for_filter_map_next(&mut self, db: &dyn HirDatabase) {
+        // Find the FunctionIds for Iterator::filter_map and Iterator::next
+        let iterator_path = path![core::iter::Iterator];
+        let resolver = self.owner.resolver(db.upcast());
+        let iterator_trait_id = match resolver.resolve_known_trait(db.upcast(), &iterator_path) {
+            Some(id) => id,
+            None => return,
+        };
+        let iterator_trait_items = &db.trait_data(iterator_trait_id).items;
+        let filter_map_function_id =
+            match iterator_trait_items.iter().find(|item| item.0 == name![filter_map]) {
+                Some((_, AssocItemId::FunctionId(id))) => id,
+                _ => return,
+            };
+        let next_function_id = match iterator_trait_items.iter().find(|item| item.0 == name![next])
+        {
+            Some((_, AssocItemId::FunctionId(id))) => id,
+            _ => return,
+        };
+
+        // Search function body for instances of .filter_map(..).next()
+        let body = db.body(self.owner.into());
+        let mut prev = None;
+        for (id, expr) in body.exprs.iter() {
+            if let Expr::MethodCall { receiver, .. } = expr {
+                let function_id = match self.infer.method_resolution(id) {
+                    Some(id) => id,
+                    None => continue,
+                };
+
+                if function_id == *filter_map_function_id {
+                    prev = Some(id);
+                    continue;
+                }
+
+                if function_id == *next_function_id {
+                    if let Some(filter_map_id) = prev {
+                        if *receiver == filter_map_id {
+                            let (_, source_map) = db.body_with_source_map(self.owner.into());
+                            if let Ok(next_source_ptr) = source_map.expr_syntax(id) {
+                                self.sink.push(ReplaceFilterMapNextWithFindMap {
+                                    file: next_source_ptr.file_id,
+                                    next_expr: next_source_ptr.value,
+                                });
+                            }
+                        }
+                    }
+                }
+            }
+            prev = None;
+        }
+    }
+
+    fn validate_call(&mut self, db: &dyn HirDatabase, call_id: ExprId, expr: &Expr) {
         // Check that the number of arguments matches the number of parameters.
 
         // FIXME: Due to shortcomings in the current type system implementation, only emit this
         // diagnostic if there are no type mismatches in the containing function.
         if self.infer.type_mismatches.iter().next().is_some() {
-            return None;
+            return;
         }
 
         let is_method_call = matches!(expr, Expr::MethodCall { .. });
         let (sig, args) = match expr {
             Expr::Call { callee, args } => {
                 let callee = &self.infer.type_of_expr[*callee];
-                let sig = callee.callable_sig(db)?;
+                let sig = match callee.callable_sig(db) {
+                    Some(sig) => sig,
+                    None => return,
+                };
                 (sig, args.clone())
             }
             Expr::MethodCall { receiver, args, .. } => {
@@ -175,22 +237,25 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
                     // if the receiver is of unknown type, it's very likely we
                     // don't know enough to correctly resolve the method call.
                     // This is kind of a band-aid for #6975.
-                    return None;
+                    return;
                 }
 
                 // FIXME: note that we erase information about substs here. This
                 // is not right, but, luckily, doesn't matter as we care only
                 // about the number of params
-                let callee = self.infer.method_resolution(call_id)?;
+                let callee = match self.infer.method_resolution(call_id) {
+                    Some(callee) => callee,
+                    None => return,
+                };
                 let sig = db.callable_item_signature(callee.into()).value;
 
                 (sig, args)
             }
-            _ => return None,
+            _ => return,
         };
 
         if sig.is_varargs {
-            return None;
+            return;
         }
 
         let params = sig.params();
@@ -213,8 +278,6 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
                 });
             }
         }
-
-        None
     }
 
     fn validate_match(
@@ -318,14 +381,11 @@ impl<'a, 'b> ExprValidator<'a, 'b> {
             _ => return,
         };
 
-        let core_result_ctor = TypeCtor::Adt(AdtId::EnumId(core_result_enum));
-        let core_option_ctor = TypeCtor::Adt(AdtId::EnumId(core_option_enum));
-
-        let (params, required) = match &mismatch.expected {
-            Ty::Apply(ApplicationTy { ctor, parameters }) if ctor == &core_result_ctor => {
+        let (params, required) = match mismatch.expected {
+            Ty::Adt(AdtId::EnumId(enum_id), ref parameters) if enum_id == core_result_enum => {
                 (parameters, "Ok".to_string())
             }
-            Ty::Apply(ApplicationTy { ctor, parameters }) if ctor == &core_option_ctor => {
+            Ty::Adt(AdtId::EnumId(enum_id), ref parameters) if enum_id == core_option_enum => {
                 (parameters, "Some".to_string())
             }
             _ => return,
diff --git a/crates/hir_ty/src/diagnostics/match_check.rs b/crates/hir_ty/src/diagnostics/match_check.rs
index fbe760c39..86fee0050 100644
--- a/crates/hir_ty/src/diagnostics/match_check.rs
+++ b/crates/hir_ty/src/diagnostics/match_check.rs
@@ -227,7 +227,7 @@ use hir_def::{
 use la_arena::Idx;
 use smallvec::{smallvec, SmallVec};
 
-use crate::{db::HirDatabase, ApplicationTy, InferenceResult, Ty, TypeCtor};
+use crate::{db::HirDatabase, InferenceResult, Ty};
 
 #[derive(Debug, Clone, Copy)]
 /// Either a pattern from the source code being analyzed, represented as
@@ -627,14 +627,12 @@ pub(super) fn is_useful(
     // - `!` type
     // In those cases, no match arm is useful.
     match cx.infer[cx.match_expr].strip_references() {
-        Ty::Apply(ApplicationTy { ctor: TypeCtor::Adt(AdtId::EnumId(enum_id)), .. }) => {
+        Ty::Adt(AdtId::EnumId(enum_id), ..) => {
             if cx.db.enum_data(*enum_id).variants.is_empty() {
                 return Ok(Usefulness::NotUseful);
             }
         }
-        Ty::Apply(ApplicationTy { ctor: TypeCtor::Never, .. }) => {
-            return Ok(Usefulness::NotUseful);
-        }
+        Ty::Never => return Ok(Usefulness::NotUseful),
         _ => (),
     }
 
@@ -1495,6 +1493,20 @@ fn main(f: Foo) {
         );
     }
 
+    #[test]
+    fn internal_or() {
+        check_diagnostics(
+            r#"
+fn main() {
+    enum Either { A(bool), B }
+    match Either::B {
+        //^^^^^^^^^ Missing match arm
+        Either::A(true | false) => (),
+    }
+}
+"#,
+        );
+    }
     mod false_negatives {
         //! The implementation of match checking here is a work in progress. As we roll this out, we
         //! prefer false negatives to false positives (ideally there would be no false positives). This
@@ -1521,20 +1533,5 @@ fn main() {
 "#,
             );
         }
-
-        #[test]
-        fn internal_or() {
-            // We do not currently handle patterns with internal `or`s.
-            check_diagnostics(
-                r#"
-fn main() {
-    enum Either { A(bool), B }
-    match Either::B {
-        Either::A(true | false) => (),
-    }
-}
-"#,
-            );
-        }
     }
 }
diff --git a/crates/hir_ty/src/diagnostics/unsafe_check.rs b/crates/hir_ty/src/diagnostics/unsafe_check.rs
index 6dc862826..e77a20fea 100644
--- a/crates/hir_ty/src/diagnostics/unsafe_check.rs
+++ b/crates/hir_ty/src/diagnostics/unsafe_check.rs
@@ -11,10 +11,7 @@ use hir_def::{
 };
 use hir_expand::diagnostics::DiagnosticSink;
 
-use crate::{
-    db::HirDatabase, diagnostics::MissingUnsafe, lower::CallableDefId, ApplicationTy,
-    InferenceResult, Ty, TypeCtor,
-};
+use crate::{db::HirDatabase, diagnostics::MissingUnsafe, InferenceResult, Ty};
 
 pub(super) struct UnsafeValidator<'a, 'b: 'a> {
     owner: DefWithBodyId,
@@ -87,13 +84,8 @@ fn walk_unsafe(
 ) {
     let expr = &body.exprs[current];
     match expr {
-        Expr::Call { callee, .. } => {
-            let ty = &infer[*callee];
-            if let &Ty::Apply(ApplicationTy {
-                ctor: TypeCtor::FnDef(CallableDefId::FunctionId(func)),
-                ..
-            }) = ty
-            {
+        &Expr::Call { callee, .. } => {
+            if let Some(func) = infer[callee].as_fn_def() {
                 if db.function_data(func).is_unsafe {
                     unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
                 }
@@ -118,7 +110,7 @@ fn walk_unsafe(
             }
         }
         Expr::UnaryOp { expr, op: UnaryOp::Deref } => {
-            if let Ty::Apply(ApplicationTy { ctor: TypeCtor::RawPtr(..), .. }) = &infer[*expr] {
+            if let Ty::Raw(..) = &infer[*expr] {
                 unsafe_exprs.push(UnsafeExpr { expr: current, inside_unsafe_block });
             }
         }