Bad error handling on wildcard pattern within expression

I tried this code:

fn test() {
    let _ = 42;
    let a = _ + 123;
}

I expected to see this happen:

error: expected expression, found reserved identifier `_`
 --> test.rs:3:13
  |
3 |     let a = _ + 123;
  |             ^ expected expression

Instead, this happened:

test.rs:3:13: error: found unexpected token ‘_’ in null denotation
    3 |     let a = _ + 123;
      |             ^
test.rs:3:15: error: failed to parse expression in let statement
    3 |     let a = _ + 123;
      |               ^
test.rs:3:5: error: failed to parse statement or expression without block in block expression
    3 |     let a = _ + 123;
      |     ^
test.rs:4:1: error: unrecognised token ‘}’ for start of item
    4 | }
      | ^
test.rs:4:1: error: failed to parse item in crate
test.rs:4:1: error: attempted to get string for ‘}’, which has no string. returning empty string instead

Meta

• What version of Rust GCC were you using, git sha if possible. 69f6be3ee483c9895b4b5187a44b3e1c8be2ba63

Start by reproducing the Rust snippet from the issue and trace how the parser handles _ in expression position and reports the resulting errors. Done means the invalid wildcard expression produces the expected primary diagnostic without the cascade of follow-on errors shown here.