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better error for bad LHS in binop-assign

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This commit is contained in:
Michael Goulet 2022-03-04 23:17:31 -08:00
parent a5c4f4cc4b
commit b26580f214
6 changed files with 47 additions and 14 deletions
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2
compiler/rustc_typeck/src/check/expr.rs
View File

@ -1058,6 +1058,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
self.check_lhs_assignable(lhs, "E0070", span, |err| {
let rhs_ty = self.check_expr(&rhs);
// FIXME: This could be done any time lhs_ty is DerefMut into something that
// is compatible with rhs_ty, and not _just_ `&mut`
if let ty::Ref(_, lhs_inner_ty, hir::Mutability::Mut) = lhs_ty.kind() {
if self.can_coerce(rhs_ty, *lhs_inner_ty) {
err.span_suggestion_verbose(

24
compiler/rustc_typeck/src/check/op.rs
View File

@ -41,7 +41,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
return_ty
};
self.check_lhs_assignable(lhs, "E0067", op.span, |_| {});
self.check_lhs_assignable(lhs, "E0067", op.span, |err| {
if let Ref(_, rty, hir::Mutability::Mut) = lhs_ty.kind() {
if self
.lookup_op_method(*rty, Some(rhs_ty), Some(rhs), Op::Binary(op, IsAssign::Yes))
.is_ok()
{
// Suppress this error, since we already emitted
// a deref suggestion in check_overloaded_binop
err.delay_as_bug();
}
}
});
ty
}
@ -404,8 +415,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
(err, missing_trait, use_output)
}
};
if let Ref(_, rty, _) = lhs_ty.kind() {
if self.infcx.type_is_copy_modulo_regions(self.param_env, *rty, lhs_expr.span)
if let Ref(_, rty, mutability) = lhs_ty.kind() {
let is_copy =
self.infcx.type_is_copy_modulo_regions(self.param_env, *rty, lhs_expr.span);
// We should suggest `a + b` => `*a + b` if `a` is copy, and suggest
// `a += b` => `*a += b` if a is a mut ref.
// FIXME: This could be done any time lhs_ty is DerefMut into something that
// is compatible with rhs_ty, and not _just_ `&mut` (for IsAssign::Yes).
if ((is_assign == IsAssign::No && is_copy)
|| (is_assign == IsAssign::Yes && *mutability == hir::Mutability::Mut))
&& self
.lookup_op_method(
*rty,

5
src/test/ui/issues/issue-5239-1.stderr
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@ -5,11 +5,6 @@ LL | let x = |ref x: isize| { x += 1; };
| -^^^^^
| |
| cannot use `+=` on type `&isize`
|
help: `+=` can be used on `isize`, you can dereference `x`
|
LL | let x = |ref x: isize| { *x += 1; };
| +
error: aborting due to previous error

4
src/test/ui/typeck/assign-non-lval-mut-ref.fixed
View File

@ -2,6 +2,8 @@
fn main() {
let mut x = vec![1usize];
*x.last_mut().unwrap() = 2usize;
*x.last_mut().unwrap() = 2;
//~^ ERROR invalid left-hand side of assignment
*x.last_mut().unwrap() += 1;
//~^ ERROR binary assignment operation `+=` cannot be applied to type `&mut usize`
}

4
src/test/ui/typeck/assign-non-lval-mut-ref.rs
View File

@ -2,6 +2,8 @@
fn main() {
let mut x = vec![1usize];
x.last_mut().unwrap() = 2usize;
x.last_mut().unwrap() = 2;
//~^ ERROR invalid left-hand side of assignment
x.last_mut().unwrap() += 1;
//~^ ERROR binary assignment operation `+=` cannot be applied to type `&mut usize`
}

22
src/test/ui/typeck/assign-non-lval-mut-ref.stderr
View File

@ -1,16 +1,30 @@
error[E0070]: invalid left-hand side of assignment
--> $DIR/assign-non-lval-mut-ref.rs:5:27
|
LL | x.last_mut().unwrap() = 2usize;
LL | x.last_mut().unwrap() = 2;
| --------------------- ^
| |
| cannot assign to this expression
|
help: consider dereferencing here to assign to the mutable borrowed piece of memory
|
LL | *x.last_mut().unwrap() = 2usize;
LL | *x.last_mut().unwrap() = 2;
| +
error: aborting due to previous error
error[E0368]: binary assignment operation `+=` cannot be applied to type `&mut usize`
--> $DIR/assign-non-lval-mut-ref.rs:7:5
|
LL | x.last_mut().unwrap() += 1;
| ---------------------^^^^^
| |
| cannot use `+=` on type `&mut usize`
|
help: `+=` can be used on `usize`, you can dereference `x.last_mut().unwrap()`
|
LL | *x.last_mut().unwrap() += 1;
| +
For more information about this error, try `rustc --explain E0070`.
error: aborting due to 2 previous errors
Some errors have detailed explanations: E0070, E0368.
For more information about an error, try `rustc --explain E0070`.