Fix crash when reporting a lib2to3 parse error - #1317
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FormatErrorMsg assumed every non-SyntaxError, non-TokenError exception
carried a (filename, lineno, column) tuple in e.args[1], but
parse.ParseError builds its message through a plain
Exception.__init__(msg) call, so e.args is just a one-element tuple
holding that string. Indexing e.args[1] on it raises IndexError before
the real error ever gets reported.
This surfaces most easily on Python 3.12+, where PEP 701 relaxed the
rules around quote characters inside f-strings. yapf's own lib2to3
based grammar doesn't parse that construct yet, so something like
f"{tab["key"]}" is valid to the real interpreter but makes yapf's
parser raise ParseError, and formatting that error is what used to
crash with the unrelated IndexError instead of telling you what
actually went wrong.
ParseError already tracks the position it failed at as e.context
(a (prefix, (lineno, column)) pair), so use that directly instead of
assuming a shape the exception was never built with.
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Fixes #1303.
The crash isn't really about the f-string itself, it's in how yapf reports the parse failure.
FormatErrorMsgassumes any exception that isn't aSyntaxErrorortokenize.TokenErrorcarries a(filename, lineno, column)tuple ase.args[1], butparse.ParseErrorbuilds its message through a plainException.__init__(msg)call, soe.argsends up being a one-element tuple with just that string in it. Indexinge.args[1]on it raisesIndexErrorbefore the actual parse error message ever gets shown.The repro from the issue triggers this because of PEP 701 (Python 3.12):
f"{tab["SOME_STRING"]}"reuses the outer quote character inside the f-string expression, which the real interpreter accepts but yapf's own lib2to3-based grammar doesn't parse yet, so it raises aParseErrorinternally. That part is a separate, bigger piece of work (teaching the grammar about PEP 701), this PR is just about not crashing with a confusing, unrelated error when that (or any other)ParseErrorhappens.ParseErroralready stores where it failed ase.context, a(prefix, (lineno, column))pair, so I used that instead of guessing at a tuple shape the exception was never actually constructed with. After the fix, the example from the issue reports cleanly:instead of crashing.
Added a regression test in the existing
BadInputTestclass, skipped on Python < 3.12 since the repro needs PEP 701 to even be valid syntax. Ran the full test suite locally (612 tests, all green).