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coroutine_clone: add comments #134618

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Dec 22, 2024
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coroutine_clone: add comments #134618

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5 changes: 5 additions & 0 deletions compiler/rustc_middle/src/mir/syntax.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -821,6 +821,11 @@ pub enum TerminatorKind<'tcx> {
/// continues at the `resume` basic block, with the second argument written to the `resume_arg`
/// place. If the coroutine is dropped before then, the `drop` basic block is invoked.
///
/// Note that coroutines can be (unstably) cloned under certain conditions, which means that
/// this terminator can **return multiple times**! MIR optimizations that reorder code into
/// different basic blocks needs to be aware of that.
/// See <https://github.com/rust-lang/rust/issues/95360>.
///
/// Not permitted in bodies that are not coroutine bodies, or after coroutine lowering.
///
/// **Needs clarification**: What about the evaluation order of the `resume_arg` and `value`?
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2 changes: 2 additions & 0 deletions tests/ui/coroutine/clone-impl-static.rs
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@@ -1,6 +1,8 @@
//@compile-flags: --diagnostic-width=300
// gate-test-coroutine_clone
// Verifies that static coroutines cannot be cloned/copied.
// This is important: the cloned coroutine would reference state of the original
// coroutine, leading to semantic nonsense.

#![feature(coroutines, coroutine_clone, stmt_expr_attributes)]

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16 changes: 8 additions & 8 deletions tests/ui/coroutine/clone-impl-static.stderr
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@@ -1,27 +1,27 @@
error[E0277]: the trait bound `{static coroutine@$DIR/clone-impl-static.rs:9:5: 9:19}: Copy` is not satisfied
--> $DIR/clone-impl-static.rs:12:16
error[E0277]: the trait bound `{static coroutine@$DIR/clone-impl-static.rs:11:5: 11:19}: Copy` is not satisfied
--> $DIR/clone-impl-static.rs:14:16
|
LL | check_copy(&gen);
| ---------- ^^^^ the trait `Copy` is not implemented for `{static coroutine@$DIR/clone-impl-static.rs:9:5: 9:19}`
| ---------- ^^^^ the trait `Copy` is not implemented for `{static coroutine@$DIR/clone-impl-static.rs:11:5: 11:19}`
| |
| required by a bound introduced by this call
|
note: required by a bound in `check_copy`
--> $DIR/clone-impl-static.rs:18:18
--> $DIR/clone-impl-static.rs:20:18
|
LL | fn check_copy<T: Copy>(_x: &T) {}
| ^^^^ required by this bound in `check_copy`

error[E0277]: the trait bound `{static coroutine@$DIR/clone-impl-static.rs:9:5: 9:19}: Clone` is not satisfied
--> $DIR/clone-impl-static.rs:14:17
error[E0277]: the trait bound `{static coroutine@$DIR/clone-impl-static.rs:11:5: 11:19}: Clone` is not satisfied
--> $DIR/clone-impl-static.rs:16:17
|
LL | check_clone(&gen);
| ----------- ^^^^ the trait `Clone` is not implemented for `{static coroutine@$DIR/clone-impl-static.rs:9:5: 9:19}`
| ----------- ^^^^ the trait `Clone` is not implemented for `{static coroutine@$DIR/clone-impl-static.rs:11:5: 11:19}`
| |
| required by a bound introduced by this call
|
note: required by a bound in `check_clone`
--> $DIR/clone-impl-static.rs:19:19
--> $DIR/clone-impl-static.rs:21:19
|
LL | fn check_clone<T: Clone>(_x: &T) {}
| ^^^^^ required by this bound in `check_clone`
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