Rollup merge of #80160 - diondokter:move_async_fix, r=davidtwco

Implemented a compiler diagnostic for move async mistake

Fixes #79694

First time contributing, so I hope I'm doing everything right.
(If not, please correct me!)

This code performs a check when a move capture clause is parsed. The check is to detect if the user has reversed the async move keywords and to provide a diagnostic with a suggestion to fix it.

Checked code:
```rust
fn main() {
    move async { };
}
```

Previous output:
```txt
PS C:\Repos\move_async_test> cargo build
   Compiling move_async_test v0.1.0 (C:\Repos\move_async_test)
error: expected one of `|` or `||`, found keyword `async`
 --> src\main.rs:2:10
  |
2 |     move async { };
  |          ^^^^^ expected one of `|` or `||`

error: aborting due to previous error

error: could not compile `move_async_test`
```

New output:
```txt
PS C:\Repos\move_async_test> cargo +dev build
   Compiling move_async_test v0.1.0 (C:\Repos\move_async_test)
error: the order of `move` and `async` is incorrect
 --> src\main.rs:2:13
  |
2 |     let _ = move async { };
  |             ^^^^^^^^^^
  |
help: try switching the order
  |
2 |     let _ = async move { };
  |             ^^^^^^^^^^

error: aborting due to previous error

error: could not compile `move_async_test`
```

Is there a file/module where these kind of things are tested?
Would love some feedback 😄

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -1912,4 +1912,22 @@ impl<'a> Parser<'a> {
  *self = snapshot;
  Err(err)
  }
+
+ /// Get the diagnostics for the cases where `move async` is found.
+ ///
+ /// `move_async_span` starts at the 'm' of the move keyword and ends with the 'c' of the async keyword
+ pub(super) fn incorrect_move_async_order_found(
+ &self,
+ move_async_span: Span,
+ ) -> DiagnosticBuilder<'a> {
+ let mut err =
+ self.struct_span_err(move_async_span, "the order of `move` and `async` is incorrect");
+ err.span_suggestion_verbose(
+ move_async_span,
+ "try switching the order",
+ "async move".to_owned(),
+ Applicability::MaybeIncorrect,
+ );
+ err
+ }
 }

compiler/rustc_parse/src/parser/expr.rs

@@ -1603,7 +1603,7 @@ impl<'a> Parser<'a> {
  self.sess.gated_spans.gate(sym::async_closure, span);
  }
 
- let capture_clause = self.parse_capture_clause();
+ let capture_clause = self.parse_capture_clause()?;
  let decl = self.parse_fn_block_decl()?;
  let decl_hi = self.prev_token.span;
  let body = match decl.output {
@@ -1626,8 +1626,18 @@ impl<'a> Parser<'a> {
  }
 
  /// Parses an optional `move` prefix to a closure-like construct.
- fn parse_capture_clause(&mut self) -> CaptureBy {
- if self.eat_keyword(kw::Move) { CaptureBy::Value } else { CaptureBy::Ref }
+ fn parse_capture_clause(&mut self) -> PResult<'a, CaptureBy> {
+ if self.eat_keyword(kw::Move) {
+ // Check for `move async` and recover
+ if self.check_keyword(kw::Async) {
+ let move_async_span = self.token.span.with_lo(self.prev_token.span.data().lo);
+ Err(self.incorrect_move_async_order_found(move_async_span))
+ } else {
+ Ok(CaptureBy::Value)
+ }
+ } else {
+ Ok(CaptureBy::Ref)
+ }
  }
 
  /// Parses the `|arg, arg|` header of a closure.
@@ -2019,7 +2029,7 @@ impl<'a> Parser<'a> {
  fn parse_async_block(&mut self, mut attrs: AttrVec) -> PResult<'a, P<Expr>> {
  let lo = self.token.span;
  self.expect_keyword(kw::Async)?;
- let capture_clause = self.parse_capture_clause();
+ let capture_clause = self.parse_capture_clause()?;
  let (iattrs, body) = self.parse_inner_attrs_and_block()?;
  attrs.extend(iattrs);
  let kind = ExprKind::Async(capture_clause, DUMMY_NODE_ID, body);

src/test/ui/parser/incorrect-move-async-order-issue-79694.fixed

@@ -0,0 +1,8 @@
+// run-rustfix
+// edition:2018
+
+// Regression test for issue 79694
+
+fn main() {
+ let _ = async move { }; //~ ERROR 7:13: 7:23: the order of `move` and `async` is incorrect
+}

src/test/ui/parser/incorrect-move-async-order-issue-79694.rs

@@ -0,0 +1,8 @@
+// run-rustfix
+// edition:2018
+
+// Regression test for issue 79694
+
+fn main() {
+ let _ = move async { }; //~ ERROR 7:13: 7:23: the order of `move` and `async` is incorrect
+}

src/test/ui/parser/incorrect-move-async-order-issue-79694.stderr

@@ -0,0 +1,13 @@
+error: the order of `move` and `async` is incorrect
+ --> $DIR/incorrect-move-async-order-issue-79694.rs:7:13
+ |
+LL | let _ = move async { };
+ | ^^^^^^^^^^
+ |
+help: try switching the order
+ |
+LL | let _ = async move { };
+ | ^^^^^^^^^^
+
+error: aborting due to previous error
+