Feature or enhancement

There's already a similar rule:

But, it has two problems:

1. It does not work for cases likeas a.b, becausea matchesNAME
2. It does not show rich error message, only a static one:invalid pattern target

My proposed change:

    | or_pattern 'as' a=expression {        RAISE_SYNTAX_ERROR_KNOWN_LOCATION(            a, "cannot use pattern target as %s", _PyPegen_get_expr_name(a)) }

Why is it safe?

Here's how the parent rule is defined:

as_pattern[pattern_ty]:    | pattern=or_pattern 'as' target=pattern_capture_target {        _PyAST_MatchAs(pattern, target->v.Name.id, EXTRA) }    | invalid_as_pattern

So, ifpattern=or_pattern 'as' target=pattern_capture_target with a valid'as' NAME is matched, we won't fall to the nextinvalid_ rule.

Proposed result:

>>>match1:...casexasa.b: ......File"<python-input-0>",line2casexasa.b: ...^^^SyntaxError:cannotusepatterntargetasattribute

Refs#123440

Linked PRs

• gh-123562: ImproveSyntaxError message forcase ... as a.b #123563