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Auto merge of #88087 - jesyspa:issue-87935-box, r=jackh726

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Check that a box expression's type is Sized

This resolves [issue 87935](https://github.com/rust-lang/rust/issues/87935).

This makes E0161 (move from an unsized rvalue) much less common.  I've replaced the test to use [this case](https://github.com/rust-lang/rust/blob/master/src/test/ui/object-safety/object-safety-by-value-self-use.rs), when a boxed `dyn` trait is passed by value, but that isn't an error when `unsized_locals` is enabled.  I think it may be possible to get rid of E0161 entirely by checking that case earlier, but I'm not sure if that's desirable?
This commit is contained in:
bors 2021-08-20 23:04:57 +00:00
commit 1e3d632f8f
18 changed files with 90 additions and 90 deletions
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26
compiler/rustc_error_codes/src/error_codes/E0161.md
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@ -4,11 +4,18 @@ Erroneous code example:
```compile_fail,E0161
#![feature(box_syntax)]
trait Bar {
fn f(self);
}
impl Bar for i32 {
fn f(self) {}
}
fn main() {
let array: &[isize] = &[1, 2, 3];
let _x: Box<[isize]> = box *array;
// error: cannot move a value of type [isize]: the size of [isize] cannot
let b: Box<dyn Bar> = box (0 as i32);
b.f();
// error: cannot move a value of type dyn Bar: the size of dyn Bar cannot
// be statically determined
}
```
@ -22,8 +29,17 @@ it around as usual. Example:
```
#![feature(box_syntax)]
trait Bar {
fn f(&self);
}
impl Bar for i32 {
fn f(&self) {}
}
fn main() {
let array: &[isize] = &[1, 2, 3];
let _x: Box<&[isize]> = box array; // ok!
let b: Box<dyn Bar> = box (0 as i32);
b.f();
// ok!
}
```

2
compiler/rustc_middle/src/traits/mod.rs
View File

@ -225,6 +225,8 @@ pub enum ObligationCauseCode<'tcx> {
SizedReturnType,
/// Yield type must be `Sized`.
SizedYieldType,
/// Box expression result type must be `Sized`.
SizedBoxType,
/// Inline asm operand type must be `Sized`.
InlineAsmSized,
/// `[T, ..n]` implies that `T` must be `Copy`.

4
compiler/rustc_mir/src/borrow_check/type_check/mod.rs
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@ -1893,9 +1893,7 @@ fn ensure_place_sized(&mut self, ty: Ty<'tcx>, span: Span) {
// While this is located in `nll::typeck` this error is not
// an NLL error, it's a required check to prevent creation
// of unsized rvalues in certain cases:
// * operand of a box expression
// * callee in a call expression
// of unsized rvalues in a call expression.
diag.emit();
}
}

3
compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs
View File

@ -2072,6 +2072,9 @@ fn note_obligation_cause_code<T>(
ObligationCauseCode::SizedYieldType => {
err.note("the yield type of a generator must have a statically known size");
}
ObligationCauseCode::SizedBoxType => {
err.note("the type of a box expression must have a statically known size");
}
ObligationCauseCode::AssignmentLhsSized => {
err.note("the left-hand-side of an assignment must have a statically known size");
}

1
compiler/rustc_typeck/src/check/expr.rs
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@ -313,6 +313,7 @@ fn check_expr_box(&self, expr: &'tcx hir::Expr<'tcx>, expected: Expectation<'tcx
_ => NoExpectation,
});
let referent_ty = self.check_expr_with_expectation(expr, expected_inner);
self.require_type_is_sized(referent_ty, expr.span, traits::SizedBoxType);
self.tcx.mk_box(referent_ty)
}

6
src/test/ui/dst/dst-rvalue.rs
View File

@ -4,11 +4,9 @@
pub fn main() {
let _x: Box<str> = box *"hello world";
//~^ ERROR E0161
//~^^ ERROR cannot move out of a shared reference
//~^ ERROR E0277
let array: &[isize] = &[1, 2, 3];
let _x: Box<[isize]> = box *array;
//~^ ERROR E0161
//~^^ ERROR cannot move out of type `[isize]`, a non-copy slice
//~^ ERROR E0277
}

34
src/test/ui/dst/dst-rvalue.stderr
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@ -1,31 +1,21 @@
error[E0161]: cannot move a value of type str: the size of str cannot be statically determined
error[E0277]: the size for values of type `str` cannot be known at compilation time
--> $DIR/dst-rvalue.rs:6:28
|
LL | let _x: Box<str> = box *"hello world";
| ^^^^^^^^^^^^^^
| ^^^^^^^^^^^^^^ doesn't have a size known at compile-time
|
= help: the trait `Sized` is not implemented for `str`
= note: the type of a box expression must have a statically known size
error[E0161]: cannot move a value of type [isize]: the size of [isize] cannot be statically determined
--> $DIR/dst-rvalue.rs:11:32
error[E0277]: the size for values of type `[isize]` cannot be known at compilation time
--> $DIR/dst-rvalue.rs:10:32
|
LL | let _x: Box<[isize]> = box *array;
| ^^^^^^
error[E0507]: cannot move out of a shared reference
--> $DIR/dst-rvalue.rs:6:28
| ^^^^^^ doesn't have a size known at compile-time
|
LL | let _x: Box<str> = box *"hello world";
| ^^^^^^^^^^^^^^ move occurs because value has type `str`, which does not implement the `Copy` trait
= help: the trait `Sized` is not implemented for `[isize]`
= note: the type of a box expression must have a statically known size
error[E0508]: cannot move out of type `[isize]`, a non-copy slice
--> $DIR/dst-rvalue.rs:11:32
|
LL | let _x: Box<[isize]> = box *array;
| ^^^^^^
| |
| cannot move out of here
| move occurs because `*array` has type `[isize]`, which does not implement the `Copy` trait
error: aborting due to 2 previous errors
error: aborting due to 4 previous errors
Some errors have detailed explanations: E0161, E0507, E0508.
For more information about an error, try `rustc --explain E0161`.
For more information about this error, try `rustc --explain E0277`.

8
src/test/ui/error-codes/E0161.edition.stderr
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@ -1,8 +1,8 @@
error[E0161]: cannot move a value of type [i32]: the size of [i32] cannot be statically determined
--> $DIR/E0161.rs:22:9
error[E0161]: cannot move a value of type dyn Bar: the size of dyn Bar cannot be statically determined
--> $DIR/E0161.rs:29:5
|
LL | box *x;
| ^^
LL | x.f();
| ^
error: aborting due to previous error

9
src/test/ui/error-codes/E0161.editionul.stderr
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@ -1,9 +0,0 @@
error[E0161]: cannot move a value of type [i32]: the size of [i32] cannot be statically determined
--> $DIR/E0161.rs:22:5
|
LL | box *x;
| ^^^^^^
error: aborting due to previous error
For more information about this error, try `rustc --explain E0161`.

8
src/test/ui/error-codes/E0161.migrate.stderr
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@ -1,8 +1,8 @@
error[E0161]: cannot move a value of type [i32]: the size of [i32] cannot be statically determined
--> $DIR/E0161.rs:22:9
error[E0161]: cannot move a value of type dyn Bar: the size of dyn Bar cannot be statically determined
--> $DIR/E0161.rs:29:5
|
LL | box *x;
| ^^
LL | x.f();
| ^
error: aborting due to previous error

9
src/test/ui/error-codes/E0161.migrateul.stderr
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@ -1,9 +0,0 @@
error[E0161]: cannot move a value of type [i32]: the size of [i32] cannot be statically determined
--> $DIR/E0161.rs:22:5
|
LL | box *x;
| ^^^^^^
error: aborting due to previous error
For more information about this error, try `rustc --explain E0161`.

8
src/test/ui/error-codes/E0161.nll.stderr
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@ -1,8 +1,8 @@
error[E0161]: cannot move a value of type [i32]: the size of [i32] cannot be statically determined
--> $DIR/E0161.rs:22:9
error[E0161]: cannot move a value of type dyn Bar: the size of dyn Bar cannot be statically determined
--> $DIR/E0161.rs:29:5
|
LL | box *x;
| ^^
LL | x.f();
| ^
error: aborting due to previous error

9
src/test/ui/error-codes/E0161.nllul.stderr
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@ -1,9 +0,0 @@
error[E0161]: cannot move a value of type [i32]: the size of [i32] cannot be statically determined
--> $DIR/E0161.rs:22:5
|
LL | box *x;
| ^^^^^^
error: aborting due to previous error
For more information about this error, try `rustc --explain E0161`.

14
src/test/ui/error-codes/E0161.rs
View File

@ -8,6 +8,10 @@
//[edition]edition:2018
//[zflagsul]compile-flags: -Z borrowck=migrate
//[editionul]edition:2018
//[migrateul] check-pass
//[nllul] check-pass
//[zflagsul] check-pass
//[editionul] check-pass
#![allow(incomplete_features)]
#![cfg_attr(nll, feature(nll))]
@ -16,12 +20,14 @@
#![cfg_attr(zflagsul, feature(unsized_locals))]
#![cfg_attr(nllul, feature(unsized_locals))]
#![cfg_attr(editionul, feature(unsized_locals))]
#![feature(box_syntax)]
fn foo(x: Box<[i32]>) {
box *x;
trait Bar {
fn f(self);
}
fn foo(x: Box<dyn Bar>) {
x.f();
//[migrate,nll,zflags,edition]~^ ERROR E0161
//[migrateul,nllul,zflagsul,editionul]~^^ ERROR E0161
}
fn main() {}

8
src/test/ui/error-codes/E0161.zflags.stderr
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@ -1,8 +1,8 @@
error[E0161]: cannot move a value of type [i32]: the size of [i32] cannot be statically determined
--> $DIR/E0161.rs:22:9
error[E0161]: cannot move a value of type dyn Bar: the size of dyn Bar cannot be statically determined
--> $DIR/E0161.rs:29:5
|
LL | box *x;
| ^^
LL | x.f();
| ^
error: aborting due to previous error

9
src/test/ui/error-codes/E0161.zflagsul.stderr
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@ -1,9 +0,0 @@
error[E0161]: cannot move a value of type [i32]: the size of [i32] cannot be statically determined
--> $DIR/E0161.rs:22:5
|
LL | box *x;
| ^^^^^^
error: aborting due to previous error
For more information about this error, try `rustc --explain E0161`.

10
src/test/ui/typeck/issue-87935-unsized-box-expr.rs Normal file
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@ -0,0 +1,10 @@
#![feature(box_syntax)]
// Box expression needs to be movable, and hence has to be of a Sized type.
fn main() {
let _x: Box<[u32]> = box { loop {} };
//~^ ERROR: the size for values of type `[u32]` cannot be known at compilation time
// Check that a deduced size does not cause issues.
let _y: Box<[u32]> = box [];
let _z: Box<[u32; 0]> = box { loop {} };
}

12
src/test/ui/typeck/issue-87935-unsized-box-expr.stderr Normal file
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@ -0,0 +1,12 @@
error[E0277]: the size for values of type `[u32]` cannot be known at compilation time
--> $DIR/issue-87935-unsized-box-expr.rs:4:30
|
LL | let _x: Box<[u32]> = box { loop {} };
| ^^^^^^^^^^^ doesn't have a size known at compile-time
|
= help: the trait `Sized` is not implemented for `[u32]`
= note: the type of a box expression must have a statically known size
error: aborting due to previous error
For more information about this error, try `rustc --explain E0277`.