Trying to use a non-existent fromfile with a leading special character panics instead of giving nice error

[MeGaGiGaGon]

Summary

For example, trying to use a fromfile named !.txt (a valid file name) that doesn't exist panics instead of giving a nice error message.

$ uvx ruff check '@!.txt'

thread 'main' panicked at crates/ruff/src/main.rs:42:90:
called `Result::unwrap()` on an `Err` value: Custom { kind: NotFound, error: Error { kind: OpenFile, source: Os { code: 2, kind: NotFound, message: "No such file or directory" }, path: "!.txt" } }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Old issue description

If a file's name starts with @ and you try to specify it on the command line, it will fail. Checking works fine if the file is gotten automatically, ie by checking .

If the file name has no special characters after the @, ruff will act like no argument was given on powershell, or act like . was given on WSL
If the file name has a special character after the @, checking will fail completely.

Powershell demo

PS ~\...\issue>ls

    Directory: C:\...\issue

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a---           9/30/2025  4:44 PM              2 @!.py
-a---           9/30/2025  4:42 PM              2 @.py
-a---           9/30/2025  4:41 PM              2 @issue.py
-a---           9/30/2025  4:40 PM              2 issue.py

PS ~\...\issue>uvx ruff check "issue.py"
All checks passed!
PS ~\...\issue>uvx ruff check "@issue.py"
error: a value is required for '[FILES]...' but none was supplied

For more information, try '--help'.
PS ~\...\issue>uvx ruff check "@.py"

thread 'main' panicked at crates\ruff\src\main.rs:42:90:
called `Result::unwrap()` on an `Err` value: Custom { kind: NotFound, error: Error { kind: OpenFile, source: Os { code: 2, kind: NotFound, message: "The system cannot find the file specified." }, path: ".py" } }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

WSL demo

user@DESKTOP-44VGRD0:~/issue$ ls
@.py  @issue.py  issue.py  issue@.py
user@DESKTOP-44VGRD0:~/issue$ uvx ruff check issue.py
All checks passed!
user@DESKTOP-44VGRD0:~/issue$ uvx ruff check @issue.py -v
[2025-09-30][17:07:22][ruff::resolve][DEBUG] Using Ruff default settings
[2025-09-30][17:07:22][ruff_workspace::resolver][DEBUG] Included path via `include`: "/home/user/issue/@issue.py"
[2025-09-30][17:07:22][ruff_workspace::resolver][DEBUG] Included path via `include`: "/home/user/issue/issue.py"
[2025-09-30][17:07:22][ruff_workspace::resolver][DEBUG] Included path via `include`: "/home/user/issue/@.py"
[2025-09-30][17:07:22][ignore::gitignore][DEBUG] opened gitignore file: /home/user/issue/.ruff_cache/.gitignore
[2025-09-30][17:07:22][ruff_workspace::resolver][DEBUG] Included path via `include`: "/home/user/issue/issue@.py"
[2025-09-30][17:07:22][ruff_workspace::resolver][DEBUG] Ignored path via `exclude`: "/home/user/issue/.ruff_cache"
[2025-09-30][17:07:22][ruff::commands::check][DEBUG] Identified files to lint in: 4.4311ms
[2025-09-30][17:07:22][ruff::commands::check][DEBUG] Checked 4 files in: 161.7µs
All checks passed!
user@DESKTOP-44VGRD0:~/issue$ uvx ruff check @.py

thread 'main' panicked at crates/ruff/src/main.rs:42:90:
called `Result::unwrap()` on an `Err` value: Custom { kind: NotFound, error: Error { kind: OpenFile, source: Os { code: 2, kind: NotFound, message: "No such file or directory" }, path: ".py" } }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Version

ruff 0.13.2 (b0bdf03 2025-09-25)

[charliermarsh]

Note that @ is indicative of a fromfile. Whatever you pass there gets read and expanded as command-line arguments. Similar to https://docs.python.org/3/library/argparse.html#fromfile-prefix-chars.

[MeGaGiGaGon]

Interesting, I wasn't aware that existed, so I guess you have to do /@<file name> instead. Is that anywhere in the docs?

So I guess that isn't a problem, but there is still a different one, where you get a panic instead of a nice error message

[TaKO8Ki]

i will take this one.