SyntaxError at ast.parse

[jolaf]

Things to check first

• I have searched the existing issues and didn't find my bug already reported there

• I have checked that my bug is still present in the latest release

Typeguard version

4.0.0rc2

Python version

3.10.6

What happened?

Traceback (most recent call last):
  File "/tmp/test.py", line 4, in <module>
    import_module('A')
  File "/usr/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_importhook.py", line 106, in exec_module
    super().exec_module(module)
  File "<frozen importlib._bootstrap_external>", line 879, in exec_module
  File "<frozen importlib._bootstrap_external>", line 1017, in get_code
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_importhook.py", line 83, in source_to_code
    tree = TypeguardTransformer().visit(tree)
  File "/usr/lib/python3.10/ast.py", line 410, in visit
    return visitor(node)
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 514, in visit_Module
    self.generic_visit(node)
  File "/usr/lib/python3.10/ast.py", line 486, in generic_visit
    value = self.visit(value)
  File "/usr/lib/python3.10/ast.py", line 410, in visit
    return visitor(node)
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 559, in visit_ClassDef
    self.generic_visit(node)
  File "/usr/lib/python3.10/ast.py", line 486, in generic_visit
    value = self.visit(value)
  File "/usr/lib/python3.10/ast.py", line 410, in visit
    return visitor(node)
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 610, in visit_FunctionDef
    annotation = self._convert_annotation(copy(arg.annotation))
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 499, in _convert_annotation
    new_annotation = cast(expr, AnnotationTransformer(self).visit(annotation))
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 336, in visit
    new_node = super().visit(node)
  File "/usr/lib/python3.10/ast.py", line 410, in visit
    return visitor(node)
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 370, in visit_Subscript
    self.generic_visit(node)
  File "/usr/lib/python3.10/ast.py", line 495, in generic_visit
    new_node = self.visit(old_value)
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 336, in visit
    new_node = super().visit(node)
  File "/usr/lib/python3.10/ast.py", line 410, in visit
    return visitor(node)
  File "/usr/lib/python3.10/ast.py", line 486, in generic_visit
    value = self.visit(value)
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 336, in visit
    new_node = super().visit(node)
  File "/usr/lib/python3.10/ast.py", line 410, in visit
    return visitor(node)
  File "/home/jolaf/.local/lib/python3.10/site-packages/typeguard/_transformer.py", line 395, in visit_Constant
    expression = ast.parse(node.value, mode="eval")
  File "/usr/lib/python3.10/ast.py", line 50, in parse
    return compile(source, filename, mode, flags,
  File "<unknown>", line 1
    %
    ^
SyntaxError: invalid syntax

How can we reproduce the bug?

test.py:

from importlib import import_module
from typeguard import install_import_hook
with install_import_hook(('A',)):
    import_module('A')

A.py:

def f(a: Literal['%']):
    pass

Run:

$ python3 test.py

[agronholm]

Ok, do you have any suggestions as to how I might reproduce the bug? The stack trace gives me no clue as to what is going wrong. If you could reduce the problematic module to a minimum viable case, that would help.

[agronholm]

The problem occurs during code compilation so just remove classes and functions until you locate the piece that causes the problem. The code in the module doesn't even have to be workable for this, just syntactically correct.

[jolaf]

Oh, I've finally nailed it! Updated the description.

[agronholm]

Oof, indeed typing.Literal would trigger this since typeguard tries to aggressively resolve any forward references, and now it treats the subscript of Literal as such.

[agronholm]

I now have a test that reproduces this.

[jolaf]

Thanks! Hopefully, the fix would make it to 4.0.0 release.

[agronholm]

Of course.

[agronholm]

Could you test against latest master and report whether typeguard works with your code base now?

[jolaf]

Yep, it works now. Thanks!

[agronholm]

If nothing else comes up, I'll release v4.0.0 final this week.

[jolaf]

Amazing, thanks!