Improve handling of text decoding errors when scanning imports

[fraser-langton]

Can't offer too much more info unfortunately, I literally opened my laptop up in the morning and the same command won't run, quite baffling

> lint-imports --verbose
=============
Import Linter
=============

Verbose mode.
'charmap' codec can't decode byte 0x8d in position 622: character maps to <undefined>

[fraser-langton]

found the culprit using this script

from pathlib import Path

def check_files_for_charmap_error(glob_pattern):
    # Use glob to filter files based on the provided pattern in the current directory
    for file_path in Path().glob(glob_pattern):  # Use the glob pattern to find matching files
        if file_path.is_file():  # Ensure it's a file
            if ".venv" in file_path.parts:  # Exclude files in .venv directory
                continue

            try:
                with file_path.open(encoding="cp1252") as f:  # Windows default encoding
                    f.read()
            except UnicodeDecodeError as e:
                print(f"Error decoding {file_path}: {e}")
            except Exception as e:
                print(f"An error occurred with {file_path}: {e}")

if __name__ == "__main__":
    glob_pattern = "**/*.py"
    check_files_for_charmap_error(glob_pattern)

[fraser-langton]

And this single char was the culprit: Í

[seddonym]

Thanks for the bug report. While it's a bit difficult to get a file in that state, Import Linter should handle it better - I think, by emitting an error that it could not decode that particular file.

To reproduce, we need create a file in a Python codebase that has an Import Linter contract (I used Import Linter itself). This explicitly tells Python what file encoding to expect.

# -*- coding: cp1252 -*-

Then open up a Python REPL to write the invalid byte to the end of that file:

>>> with open("src/importlinter/foo.py", mode="ab") as file:
...   file.write(b"\x8d")

Finally, run lint-imports.

$ lint-imports
=============
Import Linter
=============

'charmap' codec can't decode byte 0x8d in position 25: character maps to <undefined>

The source of the problem can be seen by running the command in debug mode:

$ lint-imports --debug
...
File ".../grimp/application/usecases.py", line 133, in _scan_packages
    direct_imports = import_scanner.scan_for_imports(
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../grimp/adaptors/importscanner.py", line 36, in scan_for_imports
    module_contents = self._read_module_contents(module_filename)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../grimp/adaptors/importscanner.py", line 109, in _read_module_contents
    return self.file_system.read(module_filename)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".../grimp/adaptors/filesystem.py", line 33, in read
    return file.read()
           ^^^^^^^^^^^
  File ".../python3.12/encodings/cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
UnicodeDecodeError: 'charmap' codec can't decode byte 0x8d in position 25: character maps to <undefined>

I think the fix would be to catch the UnicodeDecodeError within scan_for_imports and resurface it as a more helpful error, including the filename.

[fraser-langton]

Yep I think just emitting the filename will work :)

[fraser-langton]

@seddonym I think I misled you a bit! It was the config that had emojis in it 😂

I also didn't know about the --debug flag I was just using --verbose

Traceback (most recent call last):
  File "C:\Users\fraser\AppData\Roaming\uv\python\cpython-3.8.20-windows-x86_64-none\lib\runpy.py", line 194, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Users\fraser\AppData\Roaming\uv\python\cpython-3.8.20-windows-x86_64-none\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "C:\Users\fraser\Render\render-services\.venv\Scripts\lint-imports.exe\__main__.py", line 7, in <module>
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\click\core.py", line 1120, in __call__
    return self.main(*args, **kwargs)
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\click\core.py", line 1041, in main
    rv = self.invoke(ctx)
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\click\core.py", line 1395, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\click\core.py", line 750, in invoke
    return __callback(*args, **kwargs)
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\importlinter\cli.py", line 52, in lint_imports_command
    exit_code = lint_imports(
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\importlinter\cli.py", line 99, in lint_imports
    passed = use_cases.lint_imports(
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\importlinter\application\use_cases.py", line 57, in lint_imports
    raise e
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\importlinter\application\use_cases.py", line 52, in lint_imports
    user_options = read_user_options(config_filename=config_filename)
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\importlinter\application\use_cases.py", line 87, in read_user_options
    options = reader.read_options(config_filename=config_filename)
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\importlinter\adapters\user_options.py", line 32, in read_options
    options = self._read_config_filename(config_filename)
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\importlinter\adapters\user_options.py", line 53, in _read_config_filename
    file_contents = settings.FILE_SYSTEM.read(config_filename)
  File "C:\Users\fraser\Render\render-services\.venv\lib\site-packages\importlinter\adapters\filesystem.py", line 16, in read
    return file.read()
  File "C:\Users\fraser\AppData\Roaming\uv\python\cpython-3.8.20-windows-x86_64-none\lib\encodings\cp1252.py", line 23, in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
UnicodeDecodeError: 'charmap' codec can't decode byte 0x8d in position 622: character maps to <undefined>
``

[seddonym]

Ah right, thanks! Well, there are obviously a few places where it would be good to surface encoding problems in a friendlier way.

[seddonym]

@dandiggas has kindly offered to look at this one.