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Document everybody_loops #82617

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Mar 14, 2021
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Document everybody_loops #82617

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28 changes: 18 additions & 10 deletions compiler/rustc_interface/src/util.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -712,16 +712,24 @@ pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> {
std::fs::rename(src, dst)
}

// Note: Also used by librustdoc, see PR #43348. Consider moving this struct elsewhere.
//
// FIXME: Currently the `everybody_loops` transformation is not applied to:
// * `const fn`, due to issue #43636 that `loop` is not supported for const evaluation. We are
// waiting for miri to fix that.
// * `impl Trait`, due to issue #43869 that functions returning impl Trait cannot be diverging.
// Solving this may require `!` to implement every trait, which relies on the an even more
// ambitious form of the closed RFC #1637. See also [#34511].
//
// [#34511]: https://github.com/rust-lang/rust/issues/34511#issuecomment-322340401
/// Replaces function bodies with `loop {}` (an infinite loop). This gets rid of
/// all semantic errors in the body while still satisfying the return type,
/// except in certain cases, see below for more.
///
/// This pass is known as `everybody_loops`. Very punny.
///
/// As of March 2021, `everybody_loops` is only used for the
/// `-Z unpretty=everybody_loops` debugging option.
///
/// FIXME: Currently the `everybody_loops` transformation is not applied to:
/// * `const fn`; support could be added, but hasn't. Originally `const fn`
/// was skipped due to issue #43636 that `loop` was not supported for
/// const evaluation.
Comment on lines +725 to +727
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Do you want to add support here? I think it would be as simple as removing within_static_or_const and https://github.com/rust-lang/rust/blob/bd203dfe0a70bd4c5fe3927b16ed75d3d0e13b2c/compiler/rustc_interface/src/util.rs#L865.

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Probably makes sense to do that in a separate PR since it would require signoff on the change.

/// * `impl Trait`, due to issue #43869 that functions returning impl Trait cannot be diverging.
/// Solving this may require `!` to implement every trait, which relies on the an even more
/// ambitious form of the closed RFC #1637. See also [#34511].
///
/// [#34511]: https://github.com/rust-lang/rust/issues/34511#issuecomment-322340401
pub struct ReplaceBodyWithLoop<'a, 'b> {
within_static_or_const: bool,
nested_blocks: Option<Vec<ast::Block>>,
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