Merge #1951

1951: Lower the precedence of the `as` operator. r=matklad a=goffrie

Previously, the `as` operator was being parsed like a postfix expression, and
therefore being given the highest possible precedence. That caused it to bind
more tightly than prefix operators, which it should not. Instead, parse it
somewhat like a normal binary expression with some special-casing.

Fixes #1851.

Co-authored-by: Geoffry Song <[email protected]>

1 files changed, 10 insertions, 1 deletions

diff --git a/crates/ra_parser/src/grammar/expressions.rs b/crates/ra_parser/src/grammar/expressions.rs
index 74b23e2f7..45f2e3de4 100644
--- a/crates/ra_parser/src/grammar/expressions.rs
+++ b/crates/ra_parser/src/grammar/expressions.rs
@@ -250,6 +250,7 @@ fn current_op(p: &Parser) -> (u8, SyntaxKind) {
         T![!] if p.at(T![!=])  => (5,  T![!=]),
         T![-] if p.at(T![-=])  => (1,  T![-=]),
         T![-]                  => (10, T![-]),
+        T![as]                 => (12, T![as]),
 
         _                      => NOT_AN_OP
     }
@@ -278,6 +279,14 @@ fn expr_bp(p: &mut Parser, r: Restrictions, bp: u8) -> (Option<CompletedMarker>,
         if op_bp < bp {
             break;
         }
+        // test as_precedence
+        // fn foo() {
+        //     let _ = &1 as *const i32;
+        // }
+        if p.at(T![as]) {
+            lhs = cast_expr(p, lhs);
+            continue;
+        }
         let m = lhs.precede(p);
         p.bump(op);
 
@@ -344,6 +353,7 @@ fn lhs(p: &mut Parser, r: Restrictions) -> Option<(CompletedMarker, BlockLike)>
             ));
         }
     };
+    // parse the interior of the unary expression
     expr_bp(p, r, 255);
     Some((m.complete(p, kind), BlockLike::NotBlock))
 }
@@ -378,7 +388,6 @@ fn postfix_expr(
                 }
             },
             T![?] => try_expr(p, lhs),
-            T![as] => cast_expr(p, lhs),
             _ => break,
         };
         allow_calls = true;