`--config` doesn't accept VFS files

describe your issue

I ran the following on bash:

pre-commit run --config <(cat .pre-commit-config.yaml <(echo "fail_fast: true"))

I expected this to be valid since <() creates a temporary file descriptor on vfs and expose it normally on devfs as /dev/fd/<fd identifier> and cat will append to the created temporary file descriptor the configuration file and the fail_fast: true.

Although this is reproducible in bash, this bug can be expanded if anyone wants to pipe a file descriptor to a child process using procfs since devfs and procfs are both virtual file systems.

pre-commit --version

pre-commit 2.15.0

.pre-commit-config.yaml

# Pretty much any configuration
repos:
-   repo: https://github.com/pre-commit/pre-commit-hooks
    rev: v4.0.1
    hooks:
    -   id: trailing-whitespace
    -   id: end-of-file-fixer

~/.cache/pre-commit/pre-commit.log (if present)

version information

pre-commit version: 2.15.0
sys.version:
    3.9.7 (default, Aug 31 2021, 13:28:12) 
    [GCC 11.1.0]
sys.executable: /home/luis/Workspace/Programming/Repos/tempcollab/github/pre-commit/pre-commit/env/bin/python3
os.name: posix
sys.platform: linux

error information

An error has occurred: InvalidConfigError: 
=====> ../../../../../../../../../dev/fd/63 is not a file

Traceback (most recent call last):
  File "/home/luis/Workspace/Programming/Repos/tempcollab/github/pre-commit/pre-commit/pre_commit/error_handler.py", line 65, in error_handler
    yield
  File "/home/luis/Workspace/Programming/Repos/tempcollab/github/pre-commit/pre-commit/pre_commit/main.py", line 400, in main
    return run(args.config, store, args)
  File "/home/luis/Workspace/Programming/Repos/tempcollab/github/pre-commit/pre-commit/pre_commit/commands/run.py", line 401, in run
    config = load_config(config_file)
  File "/home/luis/Workspace/Programming/Repos/tempcollab/github/pre-commit/pre-commit/env/lib/python3.9/site-packages/cfgv.py", line 411, in load_from_filename
    return apply_defaults(data, schema)
  File "/usr/lib/python3.9/contextlib.py", line 137, in __exit__
    self.gen.throw(typ, value, traceback)
  File "/home/luis/Workspace/Programming/Repos/tempcollab/github/pre-commit/pre-commit/env/lib/python3.9/site-packages/cfgv.py", line 43, in reraise_as
    raise tp(e).with_traceback(tb) from None
  File "/home/luis/Workspace/Programming/Repos/tempcollab/github/pre-commit/pre-commit/env/lib/python3.9/site-packages/cfgv.py", line 40, in reraise_as
    yield
  File "/home/luis/Workspace/Programming/Repos/tempcollab/github/pre-commit/pre-commit/env/lib/python3.9/site-packages/cfgv.py", line 396, in load_from_filename
    raise ValidationError(f'{filename} is not a file')
pre_commit.clientlib.InvalidConfigError: 
=====> ../../../../../../../../../dev/fd/63 is not a file

[ljmf00]

just use a normal file instead

This is not ideal. A user to use a temporary configuration file doesn’t need to use I/O or have tmpfs mounted. Writing to disk to read it right after is a workaround to how a UNIX-based system should work.

[asottile]

pre-commit needs a normal, writable file – a FIFO is not an acceptable substitute