gh-145019: improve SyntaxError when match patterns bind different names

[picnixz]

• Issue: Improve SyntaxError message for inconsistent name binding in OR-patterns #145019

[picnixz]

Thanks Hugo for the review! I am unavailable this week-end so I will address this next week. If you want to apply your changes, feel free to do so! Otherwise I will do it once I have my laptop.

[picnixz]

@hugovk @pablogsal Thanks for the comments! I decided not to compute the exclusive variable names because it's a bit annoying to do so. In pure Python it would be easy as I just need to do x_control = [c for c in control if c not in mismatch_names] and vice-versa. But then we need to distinguish when control is empty to print "nothing" or when x_control is empty (in which case "nothing" isn't the appropriate word so yet another message). For instance, ideally, we want to have:

>>> match 1:
...     case (y, z) | (x, y, z): pass
SyntaxError: pattern 1 does not bind "x" but pattern 3 does

instead of

>>> match 1:
...     case (y, z) | (x, y, z): pass
SyntaxError: pattern 1 binds ['y', 'z'] but pattern 3 binds ['x', 'y', 'z']

It would be annoying to do so and unledss there are hundreds of variables, I think it's ok to read it from the list. Please tell me whether you want a more precise solution though.