compile(): `func_type` mode is not documented

In 2019, compile() got a new mode="func_type" used to parse the signature of a function as AST:

• commit dcfcd146f8e6fc5c2fc16a4c192a0c5f5ca8c53c
• issue gh-79947

>>> compile('() -> int', '<string>', 'func_type', flags=ast.PyCF_ONLY_AST)
FunctionType(argtypes=[], returns=Name(id='int', ctx=Load()))

>>> import ast; ast.parse('() -> int', '<string>', 'func_type')
FunctionType(argtypes=[], returns=Name(id='int', ctx=Load()))

It's tested by test_type_comments using ast.parse() function.

The 'func_type' mode is documented in ast.parse() documentation:

In addition, if mode is 'func_type', the input syntax is modified to correspond to PEP 484 “signature type comments”, e.g. (str, int) -> List[str].

But it's not documented in the compile() function documentation. Should it be documented there as well? Maybe at least by redirecting to ast.parse()?

Linked PRs

• gh-153542
• gh-153561

Compare the compile() function documentation with the existing ast.parse() documentation linked in the issue, focusing on the undocumented 'func_type' mode. Done means the compile() documentation either describes this mode or clearly redirects readers to the ast.parse() explanation; check linked PRs gh-153542 and gh-153561 before starting.