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Lower the precedence of the as operator.

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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.
This commit is contained in:
Geoffry Song 2019-10-03 00:10:58 -07:00
parent e1c3675951
commit b63f260bbc
5 changed files with 153 additions and 45 deletions
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14
crates/ra_parser/src/grammar/expressions.rs
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@ -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 +279,10 @@ fn expr_bp(p: &mut Parser, r: Restrictions, bp: u8) -> (Option<CompletedMarker>,
if op_bp < bp {
break;
}
if p.at(T![as]) {
lhs = cast_expr(p, lhs);
continue;
}
let m = lhs.precede(p);
p.bump(op);
@ -296,6 +301,7 @@ fn lhs(p: &mut Parser, r: Restrictions) -> Option<(CompletedMarker, BlockLike)>
// fn foo() {
// let _ = &1;
// let _ = &mut &f();
// let _ = &1 as *const i32;
// }
T![&] => {
m = p.start();
@ -305,9 +311,13 @@ fn lhs(p: &mut Parser, r: Restrictions) -> Option<(CompletedMarker, BlockLike)>
}
// test unary_expr
// fn foo() {
// **&1;
// **&1 + 1;
// !!true;
// --1;
// *&1 as u64;
// *x(1);
// &x[1];
// -1..2;
// }
T![*] | T![!] | T![-] => {
m = p.start();
@ -338,6 +348,7 @@ fn lhs(p: &mut Parser, r: Restrictions) -> Option<(CompletedMarker, BlockLike)>
return Some(postfix_expr(p, lhs, blocklike, !(r.prefer_stmt && blocklike.is_block())));
}
};
// parse the interior of the unary expression
expr_bp(p, r, 255);
Some((m.complete(p, kind), BlockLike::NotBlock))
}
@ -371,7 +382,6 @@ fn postfix_expr(
}
},
T![?] => try_expr(p, lhs),
T![as] => cast_expr(p, lhs),
_ => break,
};
allow_calls = true;