Add to AST location info for compound exception headers or keywords

[iritkatriel]

The location information in the AST for a compound statement spans the whole body.

For example:

>>> src = """with A as cm:
...     1
...     2
...     3
...     """

Output:

"Module(body=[With(items=[withitem(context_expr=Name(id='A', ctx=Load(), lineno=1, col_offset=5, end_lineno=1, end_col_offset=6), optional_vars=Name(id='cm', ctx=Store(), lineno=1, col_offset=10, end_lineno=1, end_col_offset=12))], body=[Expr(value=Constant(value=1, lineno=2, col_offset=4, end_lineno=2, end_col_offset=5), lineno=2, col_offset=4, end_lineno=2, end_col_offset=5), Expr(value=Constant(value=2, lineno=3, col_offset=4, end_lineno=3, end_col_offset=5), lineno=3, col_offset=4, end_lineno=3, end_col_offset=5), Expr(value=Constant(value=3, lineno=4, col_offset=4, end_lineno=4, end_col_offset=5), lineno=4, col_offset=4, end_lineno=4, end_col_offset=5)], lineno=1, col_offset=0, end_lineno=4, end_col_offset=5)])"

If __enter__ or __exit__ of the context manager raises an exception, we don't want the location of the exception to span the entire body. Ideally it would be the location of the with keyword (my view) or the entire with x as y statement (@ericsnowcurrently's view). However, we don't have those locations in the AST so currently we hilight the location of the expression that creates the context manager:

>>> class C:
...     def __enter__(self): 1/0
...     def __exit__(*args): pass
...     
>>> with C() as c: pass
... 
Traceback (most recent call last):
  File "<python-input-11>", line 1, in <module>
    with C() as c: pass
         ~^^
  File "<python-input-10>", line 2, in __enter__
    def __enter__(self): 1/0
                         ~^~
ZeroDivisionError: division by zero

We have similar issue with except blocks and class definitions.

Can we add location information of the keywords, or of the header of a compound expression, to the AST?

@pablogsal @lysnikolaou

Linked PRs

• gh-129157: Change the location of with statement AST nodes to spawn the first line #129162

[pablogsal]

On it

[pablogsal]

Let's settle on this one first and I will take the other in other PRs

[JelleZijlstra]

There's an analogous issue with for loops:

>>> class X:
...     def __iter__(self): return self
...     def __next__(self): 1/0
...     
>>> for f in X():
...     pass
...     
Traceback (most recent call last):
  File "<python-input-9>", line 1, in <module>
    for f in X():
             ~^^
  File "<python-input-8>", line 3, in __next__
    def __next__(self): 1/0
                        ~^~
ZeroDivisionError: division by zero