gh-138294: Fix Misleading error for ((a) := 1)

[dbXD320]

This PR fixes a corner-case in assignment expressions (walrus operator :=) where using parentheses around a target name incorrectly compiles, e.g., ((x) := 1).

• Issue: Misleading error for ((a) := 1) #138294

[dbXD320]

@pablogsal @lysnikolaou Hi, I’ve added the grammar change for raising a SyntaxError when a walrus target is parenthesized.
I think the test could go in Lib/test/test_syntax.py, but I’m not entirely sure about the exact location or structure. Could you confirm or suggest a better place?

[pablogsal]

@pablogsal @lysnikolaou Hi, I’ve added the grammar change for raising a SyntaxError when a walrus target is parenthesized.

I think the test could go in Lib/test/test_syntax.py, but I’m not entirely sure about the exact location or structure. Could you confirm or suggest a better place?

It should go in test_syntax. Find a zone where we test similar errors and add a new one respecting the structure of the other examples.

If you are not sure just put it somewhere you thing is good and we can guide you from there :)

[dbXD320]

@pablogsal I’ve added the test in test_syntax.py. Please review it and let me know if any adjustments are needed.

[lysnikolaou]

Thanks a lot @dbXD320! The PR looks good! 🚀

Left just one comment for where I think the test should go.

[lysnikolaou]

I think it'd be best if this went in the docstring at the top of the file instead of a separate test. It can probably go at the very bottom of that docstring with a short description of the error being tested, something along the lines of Invalid parenthesization inside assignment expressions.

[pablogsal]

@dbXD320 You can add a new section like this:

cpython/Lib/test/test_syntax.py

Line 2471 in 921f61b

Invalid expressions in type scopes:

[StanFromIreland]

LGTM

thanks for applying my patch!