Merge #996

996: Allow attributes on top level expressions r=matklad a=pcpthm

This PR modifies parser to allow outer attributes on top level expression. Here, top level expression means either
- Expression statement e.g. `foo();`
- Last expression in a block without semicolon `bar()` in `{ foo(); bar() }`.

Except for binary operation expressions and `if` expressions, which are errors (feature gated) in rustc.
Attributes on inner expressions like `foo(#[a] 1)` are not implemented.

I first tried to implement this by passing `Maker` to expression parsers. However, this implementation couldn't parse `#[attr] foo()` correctly as `CallExpr(Attr(..), PathExpr(..), ArgList(..))` and instead parsed incorrectly as `CallExpr(PathExpr(Attr(..), ..), ArgList(..))` due to the way left recursion is handled.
In the end, I introduce `undo_completion` method. Which is not the suggested approach, but it seems not very bad.

Fix #759.


Co-authored-by: pcpthm <[email protected]>

1 files changed, 2 insertions, 2 deletions

diff --git a/crates/ra_parser/src/grammar/expressions/atom.rs b/crates/ra_parser/src/grammar/expressions/atom.rs
index d933288cd..a23977bfb 100644
--- a/crates/ra_parser/src/grammar/expressions/atom.rs
+++ b/crates/ra_parser/src/grammar/expressions/atom.rs
@@ -392,9 +392,9 @@ fn match_arm(p: &mut Parser) -> BlockLike {
         match_guard(p);
     }
     p.expect(FAT_ARROW);
-    let ret = expr_stmt(p);
+    let blocklike = expr_stmt(p).1;
     m.complete(p, MATCH_ARM);
-    ret
+    blocklike
 }
 
 // test match_guard