Python `type_comments`

[maximiliankaul]

Investigate and make it work.

ast.parse = parse(source, filename='<unknown>', mode='exec', *, type_comments=False, feature_version=None)
    Parse the source into an AST node.
    Equivalent to compile(source, filename, mode, PyCF_ONLY_AST).
    Pass type_comments=True to get back type comments where the syntax allows.

[oxisto]

After some investigation, it seems that type comments are mainly used in backporting type functionality into Python 2. Python 3 uses type annotations and we actually already use them at least for function return types and argument types.

Example for a type comment (This is parsed as an Assign with type_comment:

a = 42 # type int

Example for a type annotation on variable (this is parsed as an AnnAssign with annotation:

a: int = 42

Example for type annotation on function (this is parsed as returns on the FunctionDef as well as annotation on the arg):

def bar(x: int) -> int: ...

We currently only support parsing the last one, but in order to get as much type information as possible we should probably support all.

[oxisto]

Let's keep this issue specifically about type comments. I created an umbrella issues for everything in PEP-484