Add to AST location info for compound exception headers or keywords

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-129162

No se nombran archivos fuente ni pruebas. Empieza revisando el comportamiento de las ubicaciones del AST descrito aquí y en el PR enlazado gh-129162, y después compara los issues relacionados con los bloques except y las definiciones de clases. Se considera terminado cuando los encabezados o las palabras clave de las sentencias compuestas tienen ubicaciones del AST utilizables, sin atribuir las excepciones de los gestores de contexto al cuerpo completo.