(fuzzer) - should the parser allow constructors in parentheses within if condition and for range?

[pczarn]

Aim

Tried to parse the following code:

fn foo() {
  let x = Bar  { baz : 1 };
  if (Bar { baz: 1 } == Bar { baz: 2 }) {
    // do something
  }
}

Expected Behavior

I know that constructors appearing directly after if and for ... in are disallowed, but I expected the code to parse and compile OK because the constructors are surrounded by parentheses.

Bug

Got parse error Expected an expression but found {.

This behavior is inconsistent with Rust lang, which allows the code to compile. Also, it does not quite make sense to disallow such syntax.

Most likely reason for the bug is the second argument to expression_with_precedence called from expression_no_constructors:

fn expression_no_constructors() -> impl ExprParser {
    recursive(|expr| {
        expression_with_precedence(Precedence::Lowest, expr.clone(), expr, false, false)
    })
    .labelled(ParsingRuleLabel::Expression)
}

Installation Method

Compiled from source

Additional Context

Found by the parser-fuzzer tool.

Would you like to submit a PR for this Issue?

Yes, possible

[pczarn]

Seems important because formal grammar is much worse with two kinds of expression inside, those allowing constructors and those that do not.

[pczarn]

I have code that may fix this.

[jfecher]

Yes, we should allow it. It was an oversight that it was not already allowed.