Auto merge of #14222 - Veykril:pat-mismatch-diags, r=Veykril

Show pattern mismatch diagnostics

12 files changed, 354 insertions, 242 deletions

diff --git a/crates/hir-def/src/resolver.rs b/crates/hir-def/src/resolver.rs
index 36d8b24e9c3..fdb236c1114 100644
--- a/crates/hir-def/src/resolver.rs
+++ b/crates/hir-def/src/resolver.rs
@@ -85,7 +85,7 @@ pub enum ResolveValueResult {
     Partial(TypeNs, usize),
 }
 
-#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 pub enum ValueNs {
     ImplSelf(ImplId),
     LocalBinding(PatId),
diff --git a/crates/hir-expand/src/lib.rs b/crates/hir-expand/src/lib.rs
index a52716cc02c..e4719237a2a 100644
--- a/crates/hir-expand/src/lib.rs
+++ b/crates/hir-expand/src/lib.rs
@@ -771,6 +771,15 @@ impl<T> InFile<Option<T>> {
     }
 }
 
+impl<L, R> InFile<Either<L, R>> {
+    pub fn transpose(self) -> Either<InFile<L>, InFile<R>> {
+        match self.value {
+            Either::Left(l) => Either::Left(InFile::new(self.file_id, l)),
+            Either::Right(r) => Either::Right(InFile::new(self.file_id, r)),
+        }
+    }
+}
+
 impl<'a> InFile<&'a SyntaxNode> {
     pub fn ancestors_with_macros(
         self,
diff --git a/crates/hir-ty/src/infer.rs b/crates/hir-ty/src/infer.rs
index c77a5e07375..f229bf2f644 100644
--- a/crates/hir-ty/src/infer.rs
+++ b/crates/hir-ty/src/infer.rs
@@ -144,44 +144,6 @@ impl Default for BindingMode {
     }
 }
 
-/// Used to generalize patterns and assignee expressions.
-trait PatLike: Into<ExprOrPatId> + Copy {
-    type BindingMode: Copy;
-
-    fn infer(
-        this: &mut InferenceContext<'_>,
-        id: Self,
-        expected_ty: &Ty,
-        default_bm: Self::BindingMode,
-    ) -> Ty;
-}
-
-impl PatLike for ExprId {
-    type BindingMode = ();
-
-    fn infer(
-        this: &mut InferenceContext<'_>,
-        id: Self,
-        expected_ty: &Ty,
-        _: Self::BindingMode,
-    ) -> Ty {
-        this.infer_assignee_expr(id, expected_ty)
-    }
-}
-
-impl PatLike for PatId {
-    type BindingMode = BindingMode;
-
-    fn infer(
-        this: &mut InferenceContext<'_>,
-        id: Self,
-        expected_ty: &Ty,
-        default_bm: Self::BindingMode,
-    ) -> Ty {
-        this.infer_pat(id, expected_ty, default_bm)
-    }
-}
-
 #[derive(Debug)]
 pub(crate) struct InferOk<T> {
     value: T,
@@ -389,18 +351,15 @@ impl InferenceResult {
     pub fn type_mismatch_for_pat(&self, pat: PatId) -> Option<&TypeMismatch> {
         self.type_mismatches.get(&pat.into())
     }
+    pub fn type_mismatches(&self) -> impl Iterator<Item = (ExprOrPatId, &TypeMismatch)> {
+        self.type_mismatches.iter().map(|(expr_or_pat, mismatch)| (*expr_or_pat, mismatch))
+    }
     pub fn expr_type_mismatches(&self) -> impl Iterator<Item = (ExprId, &TypeMismatch)> {
         self.type_mismatches.iter().filter_map(|(expr_or_pat, mismatch)| match *expr_or_pat {
             ExprOrPatId::ExprId(expr) => Some((expr, mismatch)),
             _ => None,
         })
     }
-    pub fn pat_type_mismatches(&self) -> impl Iterator<Item = (PatId, &TypeMismatch)> {
-        self.type_mismatches.iter().filter_map(|(expr_or_pat, mismatch)| match *expr_or_pat {
-            ExprOrPatId::PatId(pat) => Some((pat, mismatch)),
-            _ => None,
-        })
-    }
 }
 
 impl Index<ExprId> for InferenceResult {
@@ -584,7 +543,7 @@ impl<'a> InferenceContext<'a> {
             let ty = self.insert_type_vars(ty);
             let ty = self.normalize_associated_types_in(ty);
 
-            self.infer_pat(*pat, &ty, BindingMode::default());
+            self.infer_top_pat(*pat, &ty);
         }
         let error_ty = &TypeRef::Error;
         let return_ty = if data.has_async_kw() {
diff --git a/crates/hir-ty/src/infer/expr.rs b/crates/hir-ty/src/infer/expr.rs
index e169cbef497..6f20f0dc893 100644
--- a/crates/hir-ty/src/infer/expr.rs
+++ b/crates/hir-ty/src/infer/expr.rs
@@ -25,7 +25,9 @@ use syntax::ast::RangeOp;
 use crate::{
     autoderef::{self, Autoderef},
     consteval,
-    infer::{coerce::CoerceMany, find_continuable, BreakableKind},
+    infer::{
+        coerce::CoerceMany, find_continuable, pat::contains_explicit_ref_binding, BreakableKind,
+    },
     lower::{
         const_or_path_to_chalk, generic_arg_to_chalk, lower_to_chalk_mutability, ParamLoweringMode,
     },
@@ -39,8 +41,8 @@ use crate::{
 };
 
 use super::{
-    coerce::auto_deref_adjust_steps, find_breakable, BindingMode, BreakableContext, Diverges,
-    Expectation, InferenceContext, InferenceDiagnostic, TypeMismatch,
+    coerce::auto_deref_adjust_steps, find_breakable, BreakableContext, Diverges, Expectation,
+    InferenceContext, InferenceDiagnostic, TypeMismatch,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -111,7 +113,7 @@ impl<'a> InferenceContext<'a> {
             }
             &Expr::Let { pat, expr } => {
                 let input_ty = self.infer_expr(expr, &Expectation::none());
-                self.infer_pat(pat, &input_ty, BindingMode::default());
+                self.infer_top_pat(pat, &input_ty);
                 self.result.standard_types.bool_.clone()
             }
             Expr::Block { statements, tail, label, id: _ } => {
@@ -223,7 +225,7 @@ impl<'a> InferenceContext<'a> {
                 let pat_ty =
                     self.resolve_associated_type(into_iter_ty, self.resolve_iterator_item());
 
-                self.infer_pat(pat, &pat_ty, BindingMode::default());
+                self.infer_top_pat(pat, &pat_ty);
                 self.with_breakable_ctx(BreakableKind::Loop, self.err_ty(), label, |this| {
                     this.infer_expr(body, &Expectation::HasType(TyBuilder::unit()));
                 });
@@ -298,7 +300,7 @@ impl<'a> InferenceContext<'a> {
 
                 // Now go through the argument patterns
                 for (arg_pat, arg_ty) in args.iter().zip(sig_tys) {
-                    self.infer_pat(*arg_pat, &arg_ty, BindingMode::default());
+                    self.infer_top_pat(*arg_pat, &arg_ty);
                 }
 
                 let prev_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
@@ -395,7 +397,8 @@ impl<'a> InferenceContext<'a> {
 
                 for arm in arms.iter() {
                     self.diverges = Diverges::Maybe;
-                    let _pat_ty = self.infer_pat(arm.pat, &input_ty, BindingMode::default());
+                    let input_ty = self.resolve_ty_shallow(&input_ty);
+                    self.infer_top_pat(arm.pat, &input_ty);
                     if let Some(guard_expr) = arm.guard {
                         self.infer_expr(
                             guard_expr,
@@ -1142,27 +1145,33 @@ impl<'a> InferenceContext<'a> {
                     let decl_ty = type_ref
                         .as_ref()
                         .map(|tr| self.make_ty(tr))
-                        .unwrap_or_else(|| self.err_ty());
-
-                    // Always use the declared type when specified
-                    let mut ty = decl_ty.clone();
+                        .unwrap_or_else(|| self.table.new_type_var());
 
-                    if let Some(expr) = initializer {
-                        let actual_ty =
-                            self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()));
-                        if decl_ty.is_unknown() {
-                            ty = actual_ty;
+                    let ty = if let Some(expr) = initializer {
+                        let ty = if contains_explicit_ref_binding(&self.body, *pat) {
+                            self.infer_expr(*expr, &Expectation::has_type(decl_ty.clone()))
+                        } else {
+                            self.infer_expr_coerce(*expr, &Expectation::has_type(decl_ty.clone()))
+                        };
+                        if type_ref.is_some() {
+                            decl_ty
+                        } else {
+                            ty
                         }
-                    }
+                    } else {
+                        decl_ty
+                    };
+
+                    self.infer_top_pat(*pat, &ty);
 
                     if let Some(expr) = else_branch {
+                        let previous_diverges = mem::replace(&mut self.diverges, Diverges::Maybe);
                         self.infer_expr_coerce(
                             *expr,
                             &Expectation::HasType(self.result.standard_types.never.clone()),
                         );
+                        self.diverges = previous_diverges;
                     }
-
-                    self.infer_pat(*pat, &ty, BindingMode::default());
                 }
                 Statement::Expr { expr, .. } => {
                     self.infer_expr(*expr, &Expectation::none());
diff --git a/crates/hir-ty/src/infer/pat.rs b/crates/hir-ty/src/infer/pat.rs
index 2c935733c06..3d03c2a527c 100644
--- a/crates/hir-ty/src/infer/pat.rs
+++ b/crates/hir-ty/src/infer/pat.rs
@@ -4,7 +4,8 @@ use std::iter::repeat_with;
 
 use chalk_ir::Mutability;
 use hir_def::{
-    expr::{BindingAnnotation, Expr, Literal, Pat, PatId},
+    body::Body,
+    expr::{BindingAnnotation, Expr, ExprId, ExprOrPatId, Literal, Pat, PatId, RecordFieldPat},
     path::Path,
 };
 use hir_expand::name::Name;
@@ -17,7 +18,43 @@ use crate::{
     static_lifetime, Interner, Scalar, Substitution, Ty, TyBuilder, TyExt, TyKind,
 };
 
-use super::PatLike;
+/// Used to generalize patterns and assignee expressions.
+pub(super) trait PatLike: Into<ExprOrPatId> + Copy {
+    type BindingMode: Copy;
+
+    fn infer(
+        this: &mut InferenceContext<'_>,
+        id: Self,
+        expected_ty: &Ty,
+        default_bm: Self::BindingMode,
+    ) -> Ty;
+}
+
+impl PatLike for ExprId {
+    type BindingMode = ();
+
+    fn infer(
+        this: &mut InferenceContext<'_>,
+        id: Self,
+        expected_ty: &Ty,
+        (): Self::BindingMode,
+    ) -> Ty {
+        this.infer_assignee_expr(id, expected_ty)
+    }
+}
+
+impl PatLike for PatId {
+    type BindingMode = BindingMode;
+
+    fn infer(
+        this: &mut InferenceContext<'_>,
+        id: Self,
+        expected_ty: &Ty,
+        default_bm: Self::BindingMode,
+    ) -> Ty {
+        this.infer_pat(id, expected_ty, default_bm)
+    }
+}
 
 impl<'a> InferenceContext<'a> {
     /// Infers type for tuple struct pattern or its corresponding assignee expression.
@@ -110,6 +147,7 @@ impl<'a> InferenceContext<'a> {
         ellipsis: Option<usize>,
         subs: &[T],
     ) -> Ty {
+        let expected = self.resolve_ty_shallow(expected);
         let expectations = match expected.as_tuple() {
             Some(parameters) => &*parameters.as_slice(Interner),
             _ => &[],
@@ -143,12 +181,11 @@ impl<'a> InferenceContext<'a> {
             .intern(Interner)
     }
 
-    pub(super) fn infer_pat(
-        &mut self,
-        pat: PatId,
-        expected: &Ty,
-        mut default_bm: BindingMode,
-    ) -> Ty {
+    pub(super) fn infer_top_pat(&mut self, pat: PatId, expected: &Ty) {
+        self.infer_pat(pat, expected, BindingMode::default());
+    }
+
+    fn infer_pat(&mut self, pat: PatId, expected: &Ty, mut default_bm: BindingMode) -> Ty {
         let mut expected = self.resolve_ty_shallow(expected);
 
         if is_non_ref_pat(self.body, pat) {
@@ -183,30 +220,17 @@ impl<'a> InferenceContext<'a> {
                 self.infer_tuple_pat_like(&expected, default_bm, *ellipsis, args)
             }
             Pat::Or(pats) => {
-                if let Some((first_pat, rest)) = pats.split_first() {
-                    let ty = self.infer_pat(*first_pat, &expected, default_bm);
-                    for pat in rest {
-                        self.infer_pat(*pat, &expected, default_bm);
-                    }
-                    ty
-                } else {
-                    self.err_ty()
+                for pat in pats.iter() {
+                    self.infer_pat(*pat, &expected, default_bm);
                 }
+                expected.clone()
             }
-            Pat::Ref { pat, mutability } => {
-                let mutability = lower_to_chalk_mutability(*mutability);
-                let expectation = match expected.as_reference() {
-                    Some((inner_ty, _lifetime, exp_mut)) => {
-                        if mutability != exp_mut {
-                            // FIXME: emit type error?
-                        }
-                        inner_ty.clone()
-                    }
-                    _ => self.result.standard_types.unknown.clone(),
-                };
-                let subty = self.infer_pat(*pat, &expectation, default_bm);
-                TyKind::Ref(mutability, static_lifetime(), subty).intern(Interner)
-            }
+            &Pat::Ref { pat, mutability } => self.infer_ref_pat(
+                pat,
+                lower_to_chalk_mutability(mutability),
+                &expected,
+                default_bm,
+            ),
             Pat::TupleStruct { path: p, args: subpats, ellipsis } => self
                 .infer_tuple_struct_pat_like(
                     p.as_deref(),
@@ -226,62 +250,10 @@ impl<'a> InferenceContext<'a> {
                 self.infer_path(&resolver, path, pat.into()).unwrap_or_else(|| self.err_ty())
             }
             Pat::Bind { mode, name: _, subpat } => {
-                let mode = if mode == &BindingAnnotation::Unannotated {
-                    default_bm
-                } else {
-                    BindingMode::convert(*mode)
-                };
-                self.result.pat_binding_modes.insert(pat, mode);
-
-                let inner_ty = match subpat {
-                    Some(subpat) => self.infer_pat(*subpat, &expected, default_bm),
-                    None => expected,
-                };
-                let inner_ty = self.insert_type_vars_shallow(inner_ty);
-
-                let bound_ty = match mode {
-                    BindingMode::Ref(mutability) => {
-                        TyKind::Ref(mutability, static_lifetime(), inner_ty.clone())
-                            .intern(Interner)
-                    }
-                    BindingMode::Move => inner_ty.clone(),
-                };
-                self.write_pat_ty(pat, bound_ty);
-                return inner_ty;
+                return self.infer_bind_pat(pat, *mode, default_bm, *subpat, &expected);
             }
             Pat::Slice { prefix, slice, suffix } => {
-                let elem_ty = match expected.kind(Interner) {
-                    TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
-                    _ => self.err_ty(),
-                };
-
-                for &pat_id in prefix.iter().chain(suffix.iter()) {
-                    self.infer_pat(pat_id, &elem_ty, default_bm);
-                }
-
-                if let &Some(slice_pat_id) = slice {
-                    let rest_pat_ty = match expected.kind(Interner) {
-                        TyKind::Array(_, length) => {
-                            let len = try_const_usize(length);
-                            let len = len.and_then(|len| {
-                                len.checked_sub((prefix.len() + suffix.len()) as u128)
-                            });
-                            TyKind::Array(
-                                elem_ty.clone(),
-                                usize_const(self.db, len, self.resolver.krate()),
-                            )
-                        }
-                        _ => TyKind::Slice(elem_ty.clone()),
-                    }
-                    .intern(Interner);
-                    self.infer_pat(slice_pat_id, &rest_pat_ty, default_bm);
-                }
-
-                match expected.kind(Interner) {
-                    TyKind::Array(_, const_) => TyKind::Array(elem_ty, const_.clone()),
-                    _ => TyKind::Slice(elem_ty),
-                }
-                .intern(Interner)
+                self.infer_slice_pat(&expected, prefix, slice, suffix, default_bm)
             }
             Pat::Wild => expected.clone(),
             Pat::Range { start, end } => {
@@ -289,27 +261,10 @@ impl<'a> InferenceContext<'a> {
                 self.infer_expr(*end, &Expectation::has_type(start_ty))
             }
             &Pat::Lit(expr) => {
-                // FIXME: using `Option` here is a workaround until we can use if-let chains in stable.
-                let mut pat_ty = None;
-
-                // Like slice patterns, byte string patterns can denote both `&[u8; N]` and `&[u8]`.
-                if let Expr::Literal(Literal::ByteString(_)) = self.body[expr] {
-                    if let Some((inner, ..)) = expected.as_reference() {
-                        let inner = self.resolve_ty_shallow(inner);
-                        if matches!(inner.kind(Interner), TyKind::Slice(_)) {
-                            let elem_ty = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
-                            let slice_ty = TyKind::Slice(elem_ty).intern(Interner);
-                            let ty = TyKind::Ref(Mutability::Not, static_lifetime(), slice_ty)
-                                .intern(Interner);
-                            self.write_expr_ty(expr, ty.clone());
-                            pat_ty = Some(ty);
-                        }
-                    }
-                }
-
-                pat_ty.unwrap_or_else(|| {
-                    self.infer_expr(expr, &Expectation::has_type(expected.clone()))
-                })
+                // Don't emit type mismatches again, the expression lowering already did that.
+                let ty = self.infer_lit_pat(expr, &expected);
+                self.write_pat_ty(pat, ty.clone());
+                return ty;
             }
             Pat::Box { inner } => match self.resolve_boxed_box() {
                 Some(box_adt) => {
@@ -338,7 +293,8 @@ impl<'a> InferenceContext<'a> {
         };
         // use a new type variable if we got error type here
         let ty = self.insert_type_vars_shallow(ty);
-        if !self.unify(&ty, &expected) {
+        // FIXME: This never check is odd, but required with out we do inference right now
+        if !expected.is_never() && !self.unify(&ty, &expected) {
             self.result
                 .type_mismatches
                 .insert(pat.into(), TypeMismatch { expected, actual: ty.clone() });
@@ -346,6 +302,109 @@ impl<'a> InferenceContext<'a> {
         self.write_pat_ty(pat, ty.clone());
         ty
     }
+
+    fn infer_ref_pat(
+        &mut self,
+        pat: PatId,
+        mutability: Mutability,
+        expected: &Ty,
+        default_bm: BindingMode,
+    ) -> Ty {
+        let expectation = match expected.as_reference() {
+            Some((inner_ty, _lifetime, _exp_mut)) => inner_ty.clone(),
+            _ => self.result.standard_types.unknown.clone(),
+        };
+        let subty = self.infer_pat(pat, &expectation, default_bm);
+        TyKind::Ref(mutability, static_lifetime(), subty).intern(Interner)
+    }
+
+    fn infer_bind_pat(
+        &mut self,
+        pat: PatId,
+        mode: BindingAnnotation,
+        default_bm: BindingMode,
+        subpat: Option<PatId>,
+        expected: &Ty,
+    ) -> Ty {
+        let mode = if mode == BindingAnnotation::Unannotated {
+            default_bm
+        } else {
+            BindingMode::convert(mode)
+        };
+        self.result.pat_binding_modes.insert(pat, mode);
+
+        let inner_ty = match subpat {
+            Some(subpat) => self.infer_pat(subpat, &expected, default_bm),
+            None => expected.clone(),
+        };
+        let inner_ty = self.insert_type_vars_shallow(inner_ty);
+
+        let bound_ty = match mode {
+            BindingMode::Ref(mutability) => {
+                TyKind::Ref(mutability, static_lifetime(), inner_ty.clone()).intern(Interner)
+            }
+            BindingMode::Move => inner_ty.clone(),
+        };
+        self.write_pat_ty(pat, bound_ty);
+        return inner_ty;
+    }
+
+    fn infer_slice_pat(
+        &mut self,
+        expected: &Ty,
+        prefix: &[PatId],
+        slice: &Option<PatId>,
+        suffix: &[PatId],
+        default_bm: BindingMode,
+    ) -> Ty {
+        let elem_ty = match expected.kind(Interner) {
+            TyKind::Array(st, _) | TyKind::Slice(st) => st.clone(),
+            _ => self.err_ty(),
+        };
+
+        for &pat_id in prefix.iter().chain(suffix.iter()) {
+            self.infer_pat(pat_id, &elem_ty, default_bm);
+        }
+
+        if let &Some(slice_pat_id) = slice {
+            let rest_pat_ty = match expected.kind(Interner) {
+                TyKind::Array(_, length) => {
+                    let len = try_const_usize(length);
+                    let len =
+                        len.and_then(|len| len.checked_sub((prefix.len() + suffix.len()) as u128));
+                    TyKind::Array(elem_ty.clone(), usize_const(self.db, len, self.resolver.krate()))
+                }
+                _ => TyKind::Slice(elem_ty.clone()),
+            }
+            .intern(Interner);
+            self.infer_pat(slice_pat_id, &rest_pat_ty, default_bm);
+        }
+
+        match expected.kind(Interner) {
+            TyKind::Array(_, const_) => TyKind::Array(elem_ty, const_.clone()),
+            _ => TyKind::Slice(elem_ty),
+        }
+        .intern(Interner)
+    }
+
+    fn infer_lit_pat(&mut self, expr: ExprId, expected: &Ty) -> Ty {
+        // Like slice patterns, byte string patterns can denote both `&[u8; N]` and `&[u8]`.
+        if let Expr::Literal(Literal::ByteString(_)) = self.body[expr] {
+            if let Some((inner, ..)) = expected.as_reference() {
+                let inner = self.resolve_ty_shallow(inner);
+                if matches!(inner.kind(Interner), TyKind::Slice(_)) {
+                    let elem_ty = TyKind::Scalar(Scalar::Uint(UintTy::U8)).intern(Interner);
+                    let slice_ty = TyKind::Slice(elem_ty).intern(Interner);
+                    let ty =
+                        TyKind::Ref(Mutability::Not, static_lifetime(), slice_ty).intern(Interner);
+                    self.write_expr_ty(expr, ty.clone());
+                    return ty;
+                }
+            }
+        }
+
+        self.infer_expr(expr, &Expectation::has_type(expected.clone()))
+    }
 }
 
 fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
@@ -370,3 +429,41 @@ fn is_non_ref_pat(body: &hir_def::body::Body, pat: PatId) -> bool {
         Pat::Wild | Pat::Bind { .. } | Pat::Ref { .. } | Pat::Box { .. } | Pat::Missing => false,
     }
 }
+
+pub(super) fn contains_explicit_ref_binding(body: &Body, pat_id: PatId) -> bool {
+    let mut res = false;
+    walk_pats(body, pat_id, &mut |pat| {
+        res |= matches!(pat, Pat::Bind { mode: BindingAnnotation::Ref, .. })
+    });
+    res
+}
+
+fn walk_pats(body: &Body, pat_id: PatId, f: &mut impl FnMut(&Pat)) {
+    let pat = &body[pat_id];
+    f(pat);
+    match pat {
+        Pat::Range { .. }
+        | Pat::Lit(..)
+        | Pat::Path(..)
+        | Pat::ConstBlock(..)
+        | Pat::Wild
+        | Pat::Missing => {}
+        &Pat::Bind { subpat, .. } => {
+            if let Some(subpat) = subpat {
+                walk_pats(body, subpat, f);
+            }
+        }
+        Pat::Or(args) | Pat::Tuple { args, .. } | Pat::TupleStruct { args, .. } => {
+            args.iter().copied().for_each(|p| walk_pats(body, p, f));
+        }
+        Pat::Ref { pat, .. } => walk_pats(body, *pat, f),
+        Pat::Slice { prefix, slice, suffix } => {
+            let total_iter = prefix.iter().chain(slice.iter()).chain(suffix.iter());
+            total_iter.copied().for_each(|p| walk_pats(body, p, f));
+        }
+        Pat::Record { args, .. } => {
+            args.iter().for_each(|RecordFieldPat { pat, .. }| walk_pats(body, *pat, f));
+        }
+        Pat::Box { inner } => walk_pats(body, *inner, f),
+    }
+}
diff --git a/crates/hir-ty/src/tests.rs b/crates/hir-ty/src/tests.rs
index ba5d9c24126..ab848a18eb3 100644
--- a/crates/hir-ty/src/tests.rs
+++ b/crates/hir-ty/src/tests.rs
@@ -191,30 +191,11 @@ fn check_impl(ra_fixture: &str, allow_none: bool, only_types: bool, display_sour
             }
         }
 
-        for (pat, mismatch) in inference_result.pat_type_mismatches() {
-            let node = match pat_node(&body_source_map, pat, &db) {
-                Some(value) => value,
-                None => continue,
-            };
-            let range = node.as_ref().original_file_range(&db);
-            let actual = format!(
-                "expected {}, got {}",
-                mismatch.expected.display_test(&db),
-                mismatch.actual.display_test(&db)
-            );
-            match mismatches.remove(&range) {
-                Some(annotation) => assert_eq!(actual, annotation),
-                None => format_to!(unexpected_type_mismatches, "{:?}: {}\n", range.range, actual),
-            }
-        }
-        for (expr, mismatch) in inference_result.expr_type_mismatches() {
-            let node = match body_source_map.expr_syntax(expr) {
-                Ok(sp) => {
-                    let root = db.parse_or_expand(sp.file_id).unwrap();
-                    sp.map(|ptr| ptr.to_node(&root).syntax().clone())
-                }
-                Err(SyntheticSyntax) => continue,
-            };
+        for (expr_or_pat, mismatch) in inference_result.type_mismatches() {
+            let Some(node) = (match expr_or_pat {
+                hir_def::expr::ExprOrPatId::ExprId(expr) => expr_node(&body_source_map, expr, &db),
+                hir_def::expr::ExprOrPatId::PatId(pat) => pat_node(&body_source_map, pat, &db),
+            }) else { continue; };
             let range = node.as_ref().original_file_range(&db);
             let actual = format!(
                 "expected {}, got {}",
diff --git a/crates/hir-ty/src/tests/patterns.rs b/crates/hir-ty/src/tests/patterns.rs
index 9333e269352..be67329fee4 100644
--- a/crates/hir-ty/src/tests/patterns.rs
+++ b/crates/hir-ty/src/tests/patterns.rs
@@ -953,9 +953,9 @@ fn main() {
             42..51 'true | ()': bool
             49..51 '()': ()
             57..59 '{}': ()
-            68..80 '(() | true,)': ((),)
+            68..80 '(() | true,)': (bool,)
             69..71 '()': ()
-            69..78 '() | true': ()
+            69..78 '() | true': bool
             74..78 'true': bool
             74..78 'true': bool
             84..86 '{}': ()
@@ -964,19 +964,15 @@ fn main() {
             96..102 '_ | ()': bool
             100..102 '()': ()
             108..110 '{}': ()
-            119..128 '(() | _,)': ((),)
+            119..128 '(() | _,)': (bool,)
             120..122 '()': ()
-            120..126 '() | _': ()
+            120..126 '() | _': bool
             125..126 '_': bool
             132..134 '{}': ()
             49..51: expected bool, got ()
-            68..80: expected (bool,), got ((),)
             69..71: expected bool, got ()
-            69..78: expected bool, got ()
             100..102: expected bool, got ()
-            119..128: expected (bool,), got ((),)
             120..122: expected bool, got ()
-            120..126: expected bool, got ()
         "#]],
     );
 }
@@ -1092,3 +1088,19 @@ fn my_fn(foo: ...) {}
 "#,
     );
 }
+
+#[test]
+fn ref_pat_mutability() {
+    check(
+        r#"
+fn foo() {
+    let &() = &();
+    let &mut () = &mut ();
+    let &mut () = &();
+      //^^^^^^^ expected &(), got &mut ()
+    let &() = &mut ();
+      //^^^ expected &mut (), got &()
+}
+"#,
+    );
+}
diff --git a/crates/hir/src/diagnostics.rs b/crates/hir/src/diagnostics.rs
index 54d43fa8dc7..3b2591e8a10 100644
--- a/crates/hir/src/diagnostics.rs
+++ b/crates/hir/src/diagnostics.rs
@@ -178,8 +178,7 @@ pub struct MissingMatchArms {
 
 #[derive(Debug)]
 pub struct TypeMismatch {
-    // FIXME: add mismatches in patterns as well
-    pub expr: InFile<AstPtr<ast::Expr>>,
+    pub expr_or_pat: Either<InFile<AstPtr<ast::Expr>>, InFile<AstPtr<ast::Pat>>>,
     pub expected: Type,
     pub actual: Type,
 }
diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 26f678e5a9b..846ad4007ce 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -1413,14 +1413,22 @@ impl DefWithBody {
                 }
             }
         }
-        for (expr, mismatch) in infer.expr_type_mismatches() {
-            let expr = match source_map.expr_syntax(expr) {
-                Ok(expr) => expr,
-                Err(SyntheticSyntax) => continue,
+        for (pat_or_expr, mismatch) in infer.type_mismatches() {
+            let expr_or_pat = match pat_or_expr {
+                ExprOrPatId::ExprId(expr) => source_map.expr_syntax(expr).map(Either::Left),
+                ExprOrPatId::PatId(pat) => source_map.pat_syntax(pat).map(Either::Right),
             };
+            let expr_or_pat = match expr_or_pat {
+                Ok(Either::Left(expr)) => Either::Left(expr),
+                Ok(Either::Right(InFile { file_id, value: Either::Left(pat) })) => {
+                    Either::Right(InFile { file_id, value: pat })
+                }
+                Ok(Either::Right(_)) | Err(SyntheticSyntax) => continue,
+            };
+
             acc.push(
                 TypeMismatch {
-                    expr,
+                    expr_or_pat,
                     expected: Type::new(db, DefWithBodyId::from(self), mismatch.expected.clone()),
                     actual: Type::new(db, DefWithBodyId::from(self), mismatch.actual.clone()),
                 }
diff --git a/crates/ide-diagnostics/src/handlers/missing_match_arms.rs b/crates/ide-diagnostics/src/handlers/missing_match_arms.rs
index c24430ce604..6594eed26d1 100644
--- a/crates/ide-diagnostics/src/handlers/missing_match_arms.rs
+++ b/crates/ide-diagnostics/src/handlers/missing_match_arms.rs
@@ -273,15 +273,20 @@ enum Either2 { C, D }
 fn main() {
     match Either::A {
         Either2::C => (),
+     // ^^^^^^^^^^  error: expected Either, found Either2
         Either2::D => (),
+     // ^^^^^^^^^^  error: expected Either, found Either2
     }
     match (true, false) {
         (true, false, true) => (),
+     // ^^^^^^^^^^^^^^^^^^^  error: expected (bool, bool), found (bool, bool, bool)
         (true) => (),
       // ^^^^  error: expected (bool, bool), found bool
     }
     match (true, false) { (true,) => {} }
+                       // ^^^^^^^  error: expected (bool, bool), found (bool,)
     match (0) { () => () }
+             // ^^  error: expected i32, found ()
     match Unresolved::Bar { Unresolved::Baz => () }
 }
         "#,
@@ -295,7 +300,9 @@ fn main() {
             r#"
 fn main() {
     match false { true | () => {} }
+                      // ^^  error: expected bool, found ()
     match (false,) { (true | (),) => {} }
+                          // ^^  error: expected bool, found ()
 }
 "#,
         );
@@ -1038,12 +1045,12 @@ fn main() {
         #[test]
         fn reference_patterns_in_fields() {
             cov_mark::check_count!(validate_match_bailed_out, 2);
-
             check_diagnostics(
                 r#"
 fn main() {
     match (&false,) {
         (true,) => {}
+     // ^^^^^^^  error: expected (&bool,), found (bool,)
     }
     match (&false,) {
         (&true,) => {}
diff --git a/crates/ide-diagnostics/src/handlers/type_mismatch.rs b/crates/ide-diagnostics/src/handlers/type_mismatch.rs
index 2adae165e4d..2026a2d4b8a 100644
--- a/crates/ide-diagnostics/src/handlers/type_mismatch.rs
+++ b/crates/ide-diagnostics/src/handlers/type_mismatch.rs
@@ -1,8 +1,9 @@
-use hir::{db::AstDatabase, HirDisplay, Type};
+use either::Either;
+use hir::{db::AstDatabase, HirDisplay, InFile, Type};
 use ide_db::{famous_defs::FamousDefs, source_change::SourceChange};
 use syntax::{
     ast::{self, BlockExpr, ExprStmt},
-    AstNode,
+    AstNode, AstPtr,
 };
 use text_edit::TextEdit;
 
@@ -10,19 +11,23 @@ use crate::{adjusted_display_range, fix, Assist, Diagnostic, DiagnosticsContext}
 
 // Diagnostic: type-mismatch
 //
-// This diagnostic is triggered when the type of an expression does not match
+// This diagnostic is triggered when the type of an expression or pattern does not match
 // the expected type.
 pub(crate) fn type_mismatch(ctx: &DiagnosticsContext<'_>, d: &hir::TypeMismatch) -> Diagnostic {
-    let display_range = adjusted_display_range::<ast::BlockExpr>(
-        ctx,
-        d.expr.clone().map(|it| it.into()),
-        &|block| {
-            let r_curly_range = block.stmt_list()?.r_curly_token()?.text_range();
-            cov_mark::hit!(type_mismatch_on_block);
-            Some(r_curly_range)
-        },
-    );
-
+    let display_range = match &d.expr_or_pat {
+        Either::Left(expr) => adjusted_display_range::<ast::BlockExpr>(
+            ctx,
+            expr.clone().map(|it| it.into()),
+            &|block| {
+                let r_curly_range = block.stmt_list()?.r_curly_token()?.text_range();
+                cov_mark::hit!(type_mismatch_on_block);
+                Some(r_curly_range)
+            },
+        ),
+        Either::Right(pat) => {
+            ctx.sema.diagnostics_display_range(pat.clone().map(|it| it.into())).range
+        }
+    };
     let mut diag = Diagnostic::new(
         "type-mismatch",
         format!(
@@ -42,10 +47,15 @@ pub(crate) fn type_mismatch(ctx: &DiagnosticsContext<'_>, d: &hir::TypeMismatch)
 fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::TypeMismatch) -> Option<Vec<Assist>> {
     let mut fixes = Vec::new();
 
-    add_reference(ctx, d, &mut fixes);
-    add_missing_ok_or_some(ctx, d, &mut fixes);
-    remove_semicolon(ctx, d, &mut fixes);
-    str_ref_to_owned(ctx, d, &mut fixes);
+    match &d.expr_or_pat {
+        Either::Left(expr_ptr) => {
+            add_reference(ctx, d, expr_ptr, &mut fixes);
+            add_missing_ok_or_some(ctx, d, expr_ptr, &mut fixes);
+            remove_semicolon(ctx, d, expr_ptr, &mut fixes);
+            str_ref_to_owned(ctx, d, expr_ptr, &mut fixes);
+        }
+        Either::Right(_pat_ptr) => {}
+    }
 
     if fixes.is_empty() {
         None
@@ -57,9 +67,10 @@ fn fixes(ctx: &DiagnosticsContext<'_>, d: &hir::TypeMismatch) -> Option<Vec<Assi
 fn add_reference(
     ctx: &DiagnosticsContext<'_>,
     d: &hir::TypeMismatch,
+    expr_ptr: &InFile<AstPtr<ast::Expr>>,
     acc: &mut Vec<Assist>,
 ) -> Option<()> {
-    let range = ctx.sema.diagnostics_display_range(d.expr.clone().map(|it| it.into())).range;
+    let range = ctx.sema.diagnostics_display_range(expr_ptr.clone().map(|it| it.into())).range;
 
     let (_, mutability) = d.expected.as_reference()?;
     let actual_with_ref = Type::reference(&d.actual, mutability);
@@ -71,7 +82,7 @@ fn add_reference(
 
     let edit = TextEdit::insert(range.start(), ampersands);
     let source_change =
-        SourceChange::from_text_edit(d.expr.file_id.original_file(ctx.sema.db), edit);
+        SourceChange::from_text_edit(expr_ptr.file_id.original_file(ctx.sema.db), edit);
     acc.push(fix("add_reference_here", "Add reference here", source_change, range));
     Some(())
 }
@@ -79,10 +90,11 @@ fn add_reference(
 fn add_missing_ok_or_some(
     ctx: &DiagnosticsContext<'_>,
     d: &hir::TypeMismatch,
+    expr_ptr: &InFile<AstPtr<ast::Expr>>,
     acc: &mut Vec<Assist>,
 ) -> Option<()> {
-    let root = ctx.sema.db.parse_or_expand(d.expr.file_id)?;
-    let expr = d.expr.value.to_node(&root);
+    let root = ctx.sema.db.parse_or_expand(expr_ptr.file_id)?;
+    let expr = expr_ptr.value.to_node(&root);
     let expr_range = expr.syntax().text_range();
     let scope = ctx.sema.scope(expr.syntax())?;
 
@@ -109,7 +121,7 @@ fn add_missing_ok_or_some(
     builder.insert(expr.syntax().text_range().start(), format!("{variant_name}("));
     builder.insert(expr.syntax().text_range().end(), ")".to_string());
     let source_change =
-        SourceChange::from_text_edit(d.expr.file_id.original_file(ctx.sema.db), builder.finish());
+        SourceChange::from_text_edit(expr_ptr.file_id.original_file(ctx.sema.db), builder.finish());
     let name = format!("Wrap in {variant_name}");
     acc.push(fix("wrap_in_constructor", &name, source_change, expr_range));
     Some(())
@@ -118,10 +130,11 @@ fn add_missing_ok_or_some(
 fn remove_semicolon(
     ctx: &DiagnosticsContext<'_>,
     d: &hir::TypeMismatch,
+    expr_ptr: &InFile<AstPtr<ast::Expr>>,
     acc: &mut Vec<Assist>,
 ) -> Option<()> {
-    let root = ctx.sema.db.parse_or_expand(d.expr.file_id)?;
-    let expr = d.expr.value.to_node(&root);
+    let root = ctx.sema.db.parse_or_expand(expr_ptr.file_id)?;
+    let expr = expr_ptr.value.to_node(&root);
     if !d.actual.is_unit() {
         return None;
     }
@@ -136,7 +149,7 @@ fn remove_semicolon(
 
     let edit = TextEdit::delete(semicolon_range);
     let source_change =
-        SourceChange::from_text_edit(d.expr.file_id.original_file(ctx.sema.db), edit);
+        SourceChange::from_text_edit(expr_ptr.file_id.original_file(ctx.sema.db), edit);
 
     acc.push(fix("remove_semicolon", "Remove this semicolon", source_change, semicolon_range));
     Some(())
@@ -145,24 +158,26 @@ fn remove_semicolon(
 fn str_ref_to_owned(
     ctx: &DiagnosticsContext<'_>,
     d: &hir::TypeMismatch,
+    expr_ptr: &InFile<AstPtr<ast::Expr>>,
     acc: &mut Vec<Assist>,
 ) -> Option<()> {
     let expected = d.expected.display(ctx.sema.db);
     let actual = d.actual.display(ctx.sema.db);
 
+    // FIXME do this properly
     if expected.to_string() != "String" || actual.to_string() != "&str" {
         return None;
     }
 
-    let root = ctx.sema.db.parse_or_expand(d.expr.file_id)?;
-    let expr = d.expr.value.to_node(&root);
+    let root = ctx.sema.db.parse_or_expand(expr_ptr.file_id)?;
+    let expr = expr_ptr.value.to_node(&root);
     let expr_range = expr.syntax().text_range();
 
     let to_owned = format!(".to_owned()");
 
     let edit = TextEdit::insert(expr.syntax().text_range().end(), to_owned);
     let source_change =
-        SourceChange::from_text_edit(d.expr.file_id.original_file(ctx.sema.db), edit);
+        SourceChange::from_text_edit(expr_ptr.file_id.original_file(ctx.sema.db), edit);
     acc.push(fix("str_ref_to_owned", "Add .to_owned() here", source_change, expr_range));
 
     Some(())
@@ -595,4 +610,21 @@ fn f() -> i32 {
 "#,
         );
     }
+
+    #[test]
+    fn type_mismatch_pat_smoke_test() {
+        check_diagnostics(
+            r#"
+fn f() {
+    let &() = &mut ();
+      //^^^ error: expected &mut (), found &()
+    match &() {
+        &9 => ()
+      //^^ error: expected &(), found &i32
+       //^ error: expected (), found i32
+    }
+}
+"#,
+        );
+    }
 }
diff --git a/crates/ide/src/inlay_hints/adjustment.rs b/crates/ide/src/inlay_hints/adjustment.rs
index 188eb7f977b..729780fa0c9 100644
--- a/crates/ide/src/inlay_hints/adjustment.rs
+++ b/crates/ide/src/inlay_hints/adjustment.rs
@@ -606,14 +606,13 @@ fn a() {
     }
 
     #[test]
-    fn bug() {
+    fn let_stmt_explicit_ty() {
         check_with_config(
             InlayHintsConfig { adjustment_hints: AdjustmentHints::Always, ..DISABLED_CONFIG },
             r#"
 fn main() {
-    // These should be identical, but they are not...
-
     let () = return;
+           //^^^^^^<never-to-any>
     let (): () = return;
                //^^^^^^<never-to-any>
 }