Handle scripts with no file extension

[zimbatm]

Problem statement

Scripts often don't have a file extension. This means that the files = [] attribute won't be able to target them efficiently. The user would have to manually pass all of the filenames in there.

Proposed solution

If a file has the executable bit set, open the file and look at the shebang. This will make the detection more expensive but I don't really see a way around it.

In the formatter config, add a files_executable = [] section that lists all of the shebang executables the formatter should match on.

In cases where #!/usr/bin/env is being used, it should strip that and look at the next argument to find the executable name. Otherwise, it looks at the basename of the first argument.

[sellout]

shfmt does this internally (I don’t know if that is visible via treefmt or if the interface always passes specific files or what).

An shfmt --find or something will return a list of the files it would have formatted, so it exposes the ability to find shebangs … but it doesn’t let you specify what you might want to find on the shebang, so you’re restricted to shell scripts.