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Auto merge of rust-lang#127097 - compiler-errors:async-closure-lint, …
…r=oli-obk
Implement simple, unstable lint to suggest turning closure-of-async-block into async-closure
We want to eventually suggest people to turn `|| async {}` to `async || {}`. This begins doing that. It's a pretty rudimentary lint, but I wanted to get something down so I wouldn't lose the code.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,129 @@ | ||
| use rustc_hir as hir; | ||
| use rustc_macros::{LintDiagnostic, Subdiagnostic}; | ||
| use rustc_session::{declare_lint, declare_lint_pass}; | ||
| use rustc_span::Span; | ||
|
|
||
| use crate::{LateContext, LateLintPass}; | ||
|
|
||
| declare_lint! { | ||
| /// The `closure_returning_async_block` lint detects cases where users | ||
| /// write a closure that returns an async block. | ||
| /// | ||
| /// ### Example | ||
| /// | ||
| /// ```rust | ||
| /// #![warn(closure_returning_async_block)] | ||
| /// let c = |x: &str| async {}; | ||
| /// ``` | ||
| /// | ||
| /// {{produces}} | ||
| /// | ||
| /// ### Explanation | ||
| /// | ||
| /// Using an async closure is preferable over a closure that returns an | ||
| /// async block, since async closures are less restrictive in how its | ||
| /// captures are allowed to be used. | ||
| /// | ||
| /// For example, this code does not work with a closure returning an async | ||
| /// block: | ||
| /// | ||
| /// ```rust,compile_fail | ||
| /// async fn callback(x: &str) {} | ||
| /// | ||
| /// let captured_str = String::new(); | ||
| /// let c = move || async { | ||
| /// callback(&captured_str).await; | ||
| /// }; | ||
| /// ``` | ||
| /// | ||
| /// But it does work with async closures: | ||
| /// | ||
| /// ```rust | ||
| /// #![feature(async_closure)] | ||
| /// | ||
| /// async fn callback(x: &str) {} | ||
| /// | ||
| /// let captured_str = String::new(); | ||
| /// let c = async move || { | ||
| /// callback(&captured_str).await; | ||
| /// }; | ||
| /// ``` | ||
| pub CLOSURE_RETURNING_ASYNC_BLOCK, | ||
| Allow, | ||
| "closure that returns `async {}` could be rewritten as an async closure", | ||
| @feature_gate = async_closure; | ||
| } | ||
|
|
||
| declare_lint_pass!( | ||
| /// Lint for potential usages of async closures and async fn trait bounds. | ||
| AsyncClosureUsage => [CLOSURE_RETURNING_ASYNC_BLOCK] | ||
| ); | ||
|
|
||
| impl<'tcx> LateLintPass<'tcx> for AsyncClosureUsage { | ||
| fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) { | ||
| let hir::ExprKind::Closure(&hir::Closure { | ||
| body, | ||
| kind: hir::ClosureKind::Closure, | ||
| fn_decl_span, | ||
| .. | ||
| }) = expr.kind | ||
| else { | ||
| return; | ||
| }; | ||
|
|
||
| let mut body = cx.tcx.hir().body(body).value; | ||
|
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||
| // Only peel blocks that have no expressions. | ||
| while let hir::ExprKind::Block(&hir::Block { stmts: [], expr: Some(tail), .. }, None) = | ||
| body.kind | ||
| { | ||
| body = tail; | ||
| } | ||
|
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||
| let hir::ExprKind::Closure(&hir::Closure { | ||
| kind: | ||
| hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared( | ||
| hir::CoroutineDesugaring::Async, | ||
| hir::CoroutineSource::Block, | ||
| )), | ||
| fn_decl_span: async_decl_span, | ||
| .. | ||
| }) = body.kind | ||
| else { | ||
| return; | ||
| }; | ||
|
|
||
| let deletion_span = cx.tcx.sess.source_map().span_extend_while_whitespace(async_decl_span); | ||
|
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||
| cx.tcx.emit_node_span_lint( | ||
| CLOSURE_RETURNING_ASYNC_BLOCK, | ||
| expr.hir_id, | ||
| fn_decl_span, | ||
| ClosureReturningAsyncBlock { | ||
| async_decl_span, | ||
| sugg: AsyncClosureSugg { | ||
| deletion_span, | ||
| insertion_span: fn_decl_span.shrink_to_lo(), | ||
| }, | ||
| }, | ||
| ); | ||
| } | ||
| } | ||
|
|
||
| #[derive(LintDiagnostic)] | ||
| #[diag(lint_closure_returning_async_block)] | ||
| struct ClosureReturningAsyncBlock { | ||
| #[label] | ||
| async_decl_span: Span, | ||
| #[subdiagnostic] | ||
| sugg: AsyncClosureSugg, | ||
| } | ||
|
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||
| #[derive(Subdiagnostic)] | ||
| #[multipart_suggestion(lint_suggestion, applicability = "maybe-incorrect")] | ||
| struct AsyncClosureSugg { | ||
| #[suggestion_part(code = "")] | ||
| deletion_span: Span, | ||
| #[suggestion_part(code = "async ")] | ||
| insertion_span: Span, | ||
| } |
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21 changes: 21 additions & 0 deletions
21
tests/ui/async-await/async-closures/lint-closure-returning-async-block.rs
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,21 @@ | ||
| //@ edition: 2021 | ||
|
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||
| #![feature(async_closure)] | ||
| #![deny(closure_returning_async_block)] | ||
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| fn main() { | ||
| let x = || async {}; | ||
| //~^ ERROR closure returning async block can be made into an async closure | ||
|
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| let x = || async move {}; | ||
| //~^ ERROR closure returning async block can be made into an async closure | ||
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||
| let x = move || async move {}; | ||
| //~^ ERROR closure returning async block can be made into an async closure | ||
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||
| let x = move || async {}; | ||
| //~^ ERROR closure returning async block can be made into an async closure | ||
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||
| let x = || {{ async {} }}; | ||
| //~^ ERROR closure returning async block can be made into an async closure | ||
| } |
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