Import aliases configured for ICN001 can cause syntax errors

[dscorbett]

Ruff 0.8.0 does not validate the aliases in lint.flake8-import-conventions.extend-aliases for unconventional-import-alias (ICN001).

$ cat icn001.py
import sys

$ ruff check --select ICN001 --config 'lint.flake8-import-conventions.extend-aliases = {"sys" = "def"}' --isolated --unsafe-fixes --fix icn001.py

error: Fix introduced a syntax error. Reverting all changes.

This indicates a bug in Ruff. If you could open an issue at:

    https://github.com/astral-sh/ruff/issues/new?title=%5BFix%20error%5D

...quoting the contents of `icn001.py`, the rule codes ICN001, along with the `pyproject.toml` settings and executed command, we'd be very appreciative!

icn001.py:1:8: ICN001 `sys` should be imported as `def`
  |
1 | import sys
  |        ^^^ ICN001
  |
  = help: Alias `sys` to `def`

Found 1 error.
[*] 1 fixable with the --fix option.

The extra aliases should be validated like the ones in lint.flake8-import-conventions.aliases (#14477).

$ ruff check --select ICN001 --config 'lint.flake8-import-conventions.aliases = {"sys" = "def"}' --isolated --unsafe-fixes --fix icn001.py
error: invalid value 'lint.flake8-import-conventions.aliases = {"sys" = "def"}' for '--config <CONFIG_OPTION>'

  tip: A `--config` flag must either be a path to a `.toml` configuration file
       or a TOML `<KEY> = <VALUE>` pair overriding a specific configuration
       option

Could not parse the supplied argument as a `ruff.toml` configuration option:

invalid value: string "def", expected a Python identifier
in `lint`

For more information, try '--help'.

There is still one problem with lint.flake8-import-conventions.aliases, and therefore also extend-aliases: they allow __debug__ as an alias, but that is a syntax error.

$ ruff check --select ICN001 --config 'lint.flake8-import-conventions.aliases = {"sys" = "__debug__"}' --isolated --unsafe-fixes --fix icn001.py
Found 1 error (1 fixed, 0 remaining).

$ cat icn001.py
import sys as __debug__

$ python icn001.py
  File "icn001.py", line 1
    import sys as __debug__
    ^^^^^^^^^^^^^^^^^^^^^^^
SyntaxError: cannot assign to __debug__

[AlexWaygood]

Cc. @dylwil3, if you're interested in this one!