The check fell into "this matcher equals vector selector's name" case when vector selector doesn't have a name and the matcher is an explicit matcher for an empty __name__ label.
To provide some context about why this is important: some downstream projects use the promql.Parse(expr.String()) to clone an expression's AST, and with this bug that matcher disappears in the cloning.
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
4b7a44c7a0