diff options
| -rw-r--r-- | clippy_lints/src/unused_async.rs | 50 | ||||
| -rw-r--r-- | tests/ui/unused_async.rs | 20 | ||||
| -rw-r--r-- | tests/ui/unused_async.stderr | 25 |
3 files changed, 84 insertions, 11 deletions
diff --git a/clippy_lints/src/unused_async.rs b/clippy_lints/src/unused_async.rs index 55651a28be9..117dda09222 100644 --- a/clippy_lints/src/unused_async.rs +++ b/clippy_lints/src/unused_async.rs @@ -1,5 +1,5 @@ -use clippy_utils::diagnostics::span_lint_and_help; -use rustc_hir::intravisit::{walk_expr, walk_fn, FnKind, Visitor}; +use clippy_utils::diagnostics::span_lint_and_then; +use rustc_hir::intravisit::{walk_body, walk_expr, walk_fn, FnKind, Visitor}; use rustc_hir::{Body, Expr, ExprKind, FnDecl, YieldSource}; use rustc_lint::{LateContext, LateLintPass}; use rustc_middle::hir::nested_filter; @@ -42,6 +42,10 @@ declare_lint_pass!(UnusedAsync => [UNUSED_ASYNC]); struct AsyncFnVisitor<'a, 'tcx> { cx: &'a LateContext<'tcx>, found_await: bool, + /// Also keep track of `await`s in nested async blocks so we can mention + /// it in a note + await_in_async_block: Option<Span>, + async_depth: usize, } impl<'a, 'tcx> Visitor<'tcx> for AsyncFnVisitor<'a, 'tcx> { @@ -49,7 +53,11 @@ impl<'a, 'tcx> Visitor<'tcx> for AsyncFnVisitor<'a, 'tcx> { fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) { if let ExprKind::Yield(_, YieldSource::Await { .. }) = ex.kind { - self.found_await = true; + if self.async_depth == 1 { + self.found_await = true; + } else if self.await_in_async_block.is_none() { + self.await_in_async_block = Some(ex.span); + } } walk_expr(self, ex); } @@ -57,6 +65,20 @@ impl<'a, 'tcx> Visitor<'tcx> for AsyncFnVisitor<'a, 'tcx> { fn nested_visit_map(&mut self) -> Self::Map { self.cx.tcx.hir() } + + fn visit_body(&mut self, b: &'tcx Body<'tcx>) { + let is_async_block = matches!(b.generator_kind, Some(rustc_hir::GeneratorKind::Async(_))); + + if is_async_block { + self.async_depth += 1; + } + + walk_body(self, b); + + if is_async_block { + self.async_depth -= 1; + } + } } impl<'tcx> LateLintPass<'tcx> for UnusedAsync { @@ -70,16 +92,30 @@ impl<'tcx> LateLintPass<'tcx> for UnusedAsync { def_id: LocalDefId, ) { if !span.from_expansion() && fn_kind.asyncness().is_async() { - let mut visitor = AsyncFnVisitor { cx, found_await: false }; + let mut visitor = AsyncFnVisitor { + cx, + found_await: false, + async_depth: 0, + await_in_async_block: None, + }; walk_fn(&mut visitor, fn_kind, fn_decl, body.id(), def_id); if !visitor.found_await { - span_lint_and_help( + span_lint_and_then( cx, UNUSED_ASYNC, span, "unused `async` for function with no await statements", - None, - "consider removing the `async` from this function", + |diag| { + diag.help("consider removing the `async` from this function"); + + if let Some(span) = visitor.await_in_async_block { + diag.span_note( + span, + "`await` used in an async block, which does not require \ + the enclosing function to be `async`", + ); + } + }, ); } } diff --git a/tests/ui/unused_async.rs b/tests/ui/unused_async.rs index 4ca7f29b34c..bfaa5dadfa5 100644 --- a/tests/ui/unused_async.rs +++ b/tests/ui/unused_async.rs @@ -3,6 +3,26 @@ use std::future::Future; use std::pin::Pin; +mod issue10800 { + #![allow(dead_code, unused_must_use, clippy::no_effect)] + + use std::future::ready; + + async fn async_block_await() { + async { + ready(()).await; + }; + } + + async fn normal_block_await() { + { + { + ready(()).await; + } + } + } +} + async fn foo() -> i32 { 4 } diff --git a/tests/ui/unused_async.stderr b/tests/ui/unused_async.stderr index cff3eccbd32..8ac2066a6b2 100644 --- a/tests/ui/unused_async.stderr +++ b/tests/ui/unused_async.stderr @@ -1,5 +1,23 @@ error: unused `async` for function with no await statements - --> $DIR/unused_async.rs:6:1 + --> $DIR/unused_async.rs:11:5 + | +LL | / async fn async_block_await() { +LL | | async { +LL | | ready(()).await; +LL | | }; +LL | | } + | |_____^ + | + = help: consider removing the `async` from this function +note: `await` used in an async block, which does not require the enclosing function to be `async` + --> $DIR/unused_async.rs:13:23 + | +LL | ready(()).await; + | ^^^^^ + = note: `-D clippy::unused-async` implied by `-D warnings` + +error: unused `async` for function with no await statements + --> $DIR/unused_async.rs:26:1 | LL | / async fn foo() -> i32 { LL | | 4 @@ -7,10 +25,9 @@ LL | | } | |_^ | = help: consider removing the `async` from this function - = note: `-D clippy::unused-async` implied by `-D warnings` error: unused `async` for function with no await statements - --> $DIR/unused_async.rs:17:5 + --> $DIR/unused_async.rs:37:5 | LL | / async fn unused(&self) -> i32 { LL | | 1 @@ -19,5 +36,5 @@ LL | | } | = help: consider removing the `async` from this function -error: aborting due to 2 previous errors +error: aborting due to 3 previous errors |