diff --git a/compiler/rustc_typeck/src/check/pat.rs b/compiler/rustc_typeck/src/check/pat.rs index f45b94bcdff45..e1ec9f13cd166 100644 --- a/compiler/rustc_typeck/src/check/pat.rs +++ b/compiler/rustc_typeck/src/check/pat.rs @@ -663,6 +663,46 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { ast::Mutability::Not => "", }; + let mut_var_suggestion = 'block: { + if !matches!(mutbl, ast::Mutability::Mut) { + break 'block None; + } + + let ident_kind = match binding_parent { + hir::Node::Param(_) => "parameter", + hir::Node::Local(_) => "variable", + hir::Node::Arm(_) => "binding", + + // Provide diagnostics only if the parent pattern is struct-like, + // i.e. where `mut binding` makes sense + hir::Node::Pat(Pat { kind, .. }) => match kind { + PatKind::Struct(..) + | PatKind::TupleStruct(..) + | PatKind::Or(..) + | PatKind::Tuple(..) + | PatKind::Slice(..) => "binding", + + PatKind::Wild + | PatKind::Binding(..) + | PatKind::Path(..) + | PatKind::Box(..) + | PatKind::Ref(..) + | PatKind::Lit(..) + | PatKind::Range(..) => break 'block None, + }, + + // Don't provide suggestions in other cases + _ => break 'block None, + }; + + Some(( + pat.span, + format!("to declare a mutable {ident_kind} use"), + format!("mut {binding}"), + )) + + }; + match binding_parent { // Check that there is explicit type (ie this is not a closure param with inferred type) // so we don't suggest moving something to the type that does not exist @@ -675,6 +715,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { ], Applicability::MachineApplicable ); + + if let Some((sp, msg, sugg)) = mut_var_suggestion { + err.span_note(sp, format!("{msg}: `{sugg}`")); + } } hir::Node::Param(_) | hir::Node::Arm(_) | hir::Node::Pat(_) => { // rely on match ergonomics or it might be nested `&&pat` @@ -684,6 +728,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { "", Applicability::MaybeIncorrect, ); + + if let Some((sp, msg, sugg)) = mut_var_suggestion { + err.span_note(sp, format!("{msg}: `{sugg}`")); + } + } + _ if let Some((sp, msg, sugg)) = mut_var_suggestion => { + err.span_suggestion(sp, msg, sugg, Applicability::MachineApplicable); } _ => {} // don't provide suggestions in other cases #55175 } diff --git a/src/test/ui/mismatched_types/ref-pat-suggestions.fixed b/src/test/ui/mismatched_types/ref-pat-suggestions.fixed index ab8483eef49fa..d50acd1ac62d2 100644 --- a/src/test/ui/mismatched_types/ref-pat-suggestions.fixed +++ b/src/test/ui/mismatched_types/ref-pat-suggestions.fixed @@ -21,4 +21,17 @@ fn main() { let _ = |&mut _a: &mut u32| (); //~ ERROR mismatched types let _ = |&_a: &u32| (); //~ ERROR mismatched types let _ = |&mut _a: &mut u32| (); //~ ERROR mismatched types + + #[allow(unused_mut)] + { + struct S(u8); + + let mut _a = 0; //~ ERROR mismatched types + let S(_b) = S(0); //~ ERROR mismatched types + let (_c,) = (0,); //~ ERROR mismatched types + + match 0 { + _d => {} //~ ERROR mismatched types + } + } } diff --git a/src/test/ui/mismatched_types/ref-pat-suggestions.rs b/src/test/ui/mismatched_types/ref-pat-suggestions.rs index 7e55539aa3d1b..1a77f68769224 100644 --- a/src/test/ui/mismatched_types/ref-pat-suggestions.rs +++ b/src/test/ui/mismatched_types/ref-pat-suggestions.rs @@ -21,4 +21,17 @@ fn main() { let _ = |&mut &_a: &mut u32| (); //~ ERROR mismatched types let _ = |&&mut _a: &u32| (); //~ ERROR mismatched types let _ = |&mut &mut _a: &mut u32| (); //~ ERROR mismatched types + + #[allow(unused_mut)] + { + struct S(u8); + + let &mut _a = 0; //~ ERROR mismatched types + let S(&mut _b) = S(0); //~ ERROR mismatched types + let (&mut _c,) = (0,); //~ ERROR mismatched types + + match 0 { + &mut _d => {} //~ ERROR mismatched types + } + } } diff --git a/src/test/ui/mismatched_types/ref-pat-suggestions.stderr b/src/test/ui/mismatched_types/ref-pat-suggestions.stderr index 0e8f8853fb751..d9501a9bbc61e 100644 --- a/src/test/ui/mismatched_types/ref-pat-suggestions.stderr +++ b/src/test/ui/mismatched_types/ref-pat-suggestions.stderr @@ -24,6 +24,11 @@ LL | fn _f1(&mut _a: u32) {} | = note: expected type `u32` found mutable reference `&mut _` +note: to declare a mutable parameter use: `mut _a` + --> $DIR/ref-pat-suggestions.rs:4:8 + | +LL | fn _f1(&mut _a: u32) {} + | ^^^^^^^ help: to take parameter `_a` by reference, move `&mut` to the type | LL - fn _f1(&mut _a: u32) {} @@ -122,6 +127,11 @@ LL | let _: fn(u32) = |&mut _a| (); | = note: expected type `u32` found mutable reference `&mut _` +note: to declare a mutable parameter use: `mut _a` + --> $DIR/ref-pat-suggestions.rs:12:23 + | +LL | let _: fn(u32) = |&mut _a| (); + | ^^^^^^^ help: consider removing `&mut` from the pattern | LL - let _: fn(u32) = |&mut _a| (); @@ -222,6 +232,11 @@ LL | let _ = |&mut _a: u32| (); | = note: expected type `u32` found mutable reference `&mut _` +note: to declare a mutable parameter use: `mut _a` + --> $DIR/ref-pat-suggestions.rs:19:14 + | +LL | let _ = |&mut _a: u32| (); + | ^^^^^^^ help: to take parameter `_a` by reference, move `&mut` to the type | LL - let _ = |&mut _a: u32| (); @@ -292,6 +307,81 @@ LL - let _ = |&mut &mut _a: &mut u32| (); LL + let _ = |&mut _a: &mut u32| (); | -error: aborting due to 18 previous errors +error[E0308]: mismatched types + --> $DIR/ref-pat-suggestions.rs:29:13 + | +LL | let &mut _a = 0; + | ^^^^^^^ - this expression has type `{integer}` + | | + | expected integer, found `&mut _` + | help: to declare a mutable variable use: `mut _a` + | + = note: expected type `{integer}` + found mutable reference `&mut _` + +error[E0308]: mismatched types + --> $DIR/ref-pat-suggestions.rs:30:15 + | +LL | let S(&mut _b) = S(0); + | ^^^^^^^ ---- this expression has type `S` + | | + | expected `u8`, found `&mut _` + | + = note: expected type `u8` + found mutable reference `&mut _` +note: to declare a mutable binding use: `mut _b` + --> $DIR/ref-pat-suggestions.rs:30:15 + | +LL | let S(&mut _b) = S(0); + | ^^^^^^^ +help: consider removing `&mut` from the pattern + | +LL - let S(&mut _b) = S(0); +LL + let S(_b) = S(0); + | + +error[E0308]: mismatched types + --> $DIR/ref-pat-suggestions.rs:31:14 + | +LL | let (&mut _c,) = (0,); + | ^^^^^^^ ---- this expression has type `({integer},)` + | | + | expected integer, found `&mut _` + | + = note: expected type `{integer}` + found mutable reference `&mut _` +note: to declare a mutable binding use: `mut _c` + --> $DIR/ref-pat-suggestions.rs:31:14 + | +LL | let (&mut _c,) = (0,); + | ^^^^^^^ +help: consider removing `&mut` from the pattern + | +LL - let (&mut _c,) = (0,); +LL + let (_c,) = (0,); + | + +error[E0308]: mismatched types + --> $DIR/ref-pat-suggestions.rs:34:13 + | +LL | match 0 { + | - this expression has type `{integer}` +LL | &mut _d => {} + | ^^^^^^^ expected integer, found `&mut _` + | + = note: expected type `{integer}` + found mutable reference `&mut _` +note: to declare a mutable binding use: `mut _d` + --> $DIR/ref-pat-suggestions.rs:34:13 + | +LL | &mut _d => {} + | ^^^^^^^ +help: consider removing `&mut` from the pattern + | +LL - &mut _d => {} +LL + _d => {} + | + +error: aborting due to 22 previous errors For more information about this error, try `rustc --explain E0308`. diff --git a/src/test/ui/pattern/for-loop-bad-item.stderr b/src/test/ui/pattern/for-loop-bad-item.stderr index ad737f7bd15e1..f064a25a9c9a4 100644 --- a/src/test/ui/pattern/for-loop-bad-item.stderr +++ b/src/test/ui/pattern/for-loop-bad-item.stderr @@ -8,6 +8,11 @@ LL | for ((_, _), (&mut c, _)) in &mut map { | = note: expected type `char` found mutable reference `&mut _` +note: to declare a mutable binding use: `mut c` + --> $DIR/for-loop-bad-item.rs:7:19 + | +LL | for ((_, _), (&mut c, _)) in &mut map { + | ^^^^^^ help: consider removing `&mut` from the pattern | LL - for ((_, _), (&mut c, _)) in &mut map {