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Rollup merge of #108000 - y21:no-zero-init-for-uninhabited, r=jackh726
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lint: don't suggest MaybeUninit::assume_init for uninhabited types

Creating a zeroed uninhabited type such as `!` or an empty enum with `mem::zeroed()` (or transmuting `()` to `!`) currently triggers this lint:
```rs
warning: the type `!` does not permit zero-initialization
 --> test.rs:5:23
  |
5 |         let _val: ! = mem::zeroed();
  |                       ^^^^^^^^^^^^^
  |                       |
  |                       this code causes undefined behavior when executed
  |                       help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
  |
  = note: the `!` type has no valid value
```
The `MaybeUninit` suggestion in the help message seems confusing/useless for uninhabited types, as such a type cannot be fully initialized in the first place (as the note implies).
This PR limits this help message to inhabited types which can be initialized
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@Dylan-DPC
Dylan-DPC authored Feb 21, 2023
2 parents f715e43 + 0610df9 commit 4dea3a2
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Showing 6 changed files with 32 additions and 59 deletions.
8 changes: 7 additions & 1 deletion compiler/rustc_lint/src/builtin.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2635,7 +2635,13 @@ impl<'tcx> LateLintPass<'tcx> for InvalidValue {
cx.emit_spanned_lint(
INVALID_VALUE,
expr.span,
BuiltinUnpermittedTypeInit { msg, ty: conjured_ty, label: expr.span, sub },
BuiltinUnpermittedTypeInit {
msg,
ty: conjured_ty,
label: expr.span,
sub,
tcx: cx.tcx,
},
);
}
}
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13 changes: 11 additions & 2 deletions compiler/rustc_lint/src/lints.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,9 @@ use rustc_errors::{
};
use rustc_hir::def_id::DefId;
use rustc_macros::{LintDiagnostic, Subdiagnostic};
use rustc_middle::ty::{PolyExistentialTraitRef, Predicate, Ty, TyCtxt};
use rustc_middle::ty::{
inhabitedness::InhabitedPredicate, PolyExistentialTraitRef, Predicate, Ty, TyCtxt,
};
use rustc_session::parse::ParseSess;
use rustc_span::{edition::Edition, sym, symbol::Ident, Span, Symbol};

Expand Down Expand Up @@ -419,6 +421,7 @@ pub struct BuiltinUnpermittedTypeInit<'a> {
pub ty: Ty<'a>,
pub label: Span,
pub sub: BuiltinUnpermittedTypeInitSub,
pub tcx: TyCtxt<'a>,
}

impl<'a> DecorateLint<'a, ()> for BuiltinUnpermittedTypeInit<'_> {
Expand All @@ -428,7 +431,13 @@ impl<'a> DecorateLint<'a, ()> for BuiltinUnpermittedTypeInit<'_> {
) -> &'b mut rustc_errors::DiagnosticBuilder<'a, ()> {
diag.set_arg("ty", self.ty);
diag.span_label(self.label, fluent::lint_builtin_unpermitted_type_init_label);
diag.span_label(self.label, fluent::lint_builtin_unpermitted_type_init_label_suggestion);
if let InhabitedPredicate::True = self.ty.inhabited_predicate(self.tcx) {
// Only suggest late `MaybeUninit::assume_init` initialization if the type is inhabited.
diag.span_label(
self.label,
fluent::lint_builtin_unpermitted_type_init_label_suggestion,
);
}
self.sub.add_to_diagnostic(diag);
diag
}
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10 changes: 2 additions & 8 deletions tests/ui/consts/const-eval/validate_uninhabited_zsts.32bit.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,10 +2,7 @@ warning: the type `!` does not permit zero-initialization
--> $DIR/validate_uninhabited_zsts.rs:4:14
|
LL | unsafe { std::mem::transmute(()) }
| ^^^^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
= note: the `!` type has no valid value
= note: `#[warn(invalid_value)]` on by default
Expand Down Expand Up @@ -40,10 +37,7 @@ warning: the type `empty::Empty` does not permit zero-initialization
--> $DIR/validate_uninhabited_zsts.rs:21:42
|
LL | const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];
| ^^^^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
note: in this struct field
--> $DIR/validate_uninhabited_zsts.rs:16:22
Expand Down
10 changes: 2 additions & 8 deletions tests/ui/consts/const-eval/validate_uninhabited_zsts.64bit.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,10 +2,7 @@ warning: the type `!` does not permit zero-initialization
--> $DIR/validate_uninhabited_zsts.rs:4:14
|
LL | unsafe { std::mem::transmute(()) }
| ^^^^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
= note: the `!` type has no valid value
= note: `#[warn(invalid_value)]` on by default
Expand Down Expand Up @@ -40,10 +37,7 @@ warning: the type `empty::Empty` does not permit zero-initialization
--> $DIR/validate_uninhabited_zsts.rs:21:42
|
LL | const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];
| ^^^^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
note: in this struct field
--> $DIR/validate_uninhabited_zsts.rs:16:22
Expand Down
40 changes: 8 additions & 32 deletions tests/ui/lint/invalid_value.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -61,54 +61,39 @@ error: the type `!` does not permit zero-initialization
--> $DIR/invalid_value.rs:65:23
|
LL | let _val: ! = mem::zeroed();
| ^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
= note: the `!` type has no valid value

error: the type `!` does not permit being left uninitialized
--> $DIR/invalid_value.rs:66:23
|
LL | let _val: ! = mem::uninitialized();
| ^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
= note: the `!` type has no valid value

error: the type `(i32, !)` does not permit zero-initialization
--> $DIR/invalid_value.rs:68:30
|
LL | let _val: (i32, !) = mem::zeroed();
| ^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
= note: the `!` type has no valid value

error: the type `(i32, !)` does not permit being left uninitialized
--> $DIR/invalid_value.rs:69:30
|
LL | let _val: (i32, !) = mem::uninitialized();
| ^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
= note: integers must be initialized

error: the type `Void` does not permit zero-initialization
--> $DIR/invalid_value.rs:71:26
|
LL | let _val: Void = mem::zeroed();
| ^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
note: enums with no inhabited variants have no valid value
--> $DIR/invalid_value.rs:12:1
Expand All @@ -120,10 +105,7 @@ error: the type `Void` does not permit being left uninitialized
--> $DIR/invalid_value.rs:72:26
|
LL | let _val: Void = mem::uninitialized();
| ^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
note: enums with no inhabited variants have no valid value
--> $DIR/invalid_value.rs:12:1
Expand Down Expand Up @@ -405,10 +387,7 @@ error: the type `TwoUninhabited` does not permit zero-initialization
--> $DIR/invalid_value.rs:104:36
|
LL | let _val: TwoUninhabited = mem::zeroed();
| ^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
note: enums with no inhabited variants have no valid value
--> $DIR/invalid_value.rs:42:1
Expand All @@ -420,10 +399,7 @@ error: the type `TwoUninhabited` does not permit being left uninitialized
--> $DIR/invalid_value.rs:105:36
|
LL | let _val: TwoUninhabited = mem::uninitialized();
| ^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
note: enums with no inhabited variants have no valid value
--> $DIR/invalid_value.rs:42:1
Expand Down
10 changes: 2 additions & 8 deletions tests/ui/statics/uninhabited-static.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -53,10 +53,7 @@ warning: the type `Void` does not permit zero-initialization
--> $DIR/uninhabited-static.rs:12:31
|
LL | static VOID2: Void = unsafe { std::mem::transmute(()) };
| ^^^^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
note: enums with no inhabited variants have no valid value
--> $DIR/uninhabited-static.rs:4:1
Expand All @@ -75,10 +72,7 @@ warning: the type `Void` does not permit zero-initialization
--> $DIR/uninhabited-static.rs:16:32
|
LL | static NEVER2: Void = unsafe { std::mem::transmute(()) };
| ^^^^^^^^^^^^^^^^^^^^^^^
| |
| this code causes undefined behavior when executed
| help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
| ^^^^^^^^^^^^^^^^^^^^^^^ this code causes undefined behavior when executed
|
note: enums with no inhabited variants have no valid value
--> $DIR/uninhabited-static.rs:4:1
Expand Down

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