treefmt --stdin doesn't work if file name has no extension

[manuelteillet]

Describe the bug

When using treefmt in stdin mode on a justfile, I get a warning "no formatter for path".

To Reproduce

Here is my example:

echo "set quiet := true

# print this message
help:
    just --list --list-submodules --unsorted

# interactive recipes launcher
choose:
    just --choose --unsorted



mod init 'just/init.just'
mod bootstrap 'just/bootstrap.just'
mod apply 'just/apply.just'
"|treefmt --stdin justfile

and my result:

WARN no formatter for path: 1621644870
set quiet := true

# print this message
help:
    just --list --list-submodules --unsorted

# interactive recipes launcher
choose:
    just --choose --unsorted



mod init 'just/init.just'
mod bootstrap 'just/bootstrap.just'
mod apply 'just/apply.just'

traversed 1 files
emitted 0 files for processing
formatted 0 files (0 changed) in 18ms

Expected behavior

The same example just adding a . in front of justfile:

echo "set quiet := true

# print this message
help:
    just --list --list-submodules --unsorted

# interactive recipes launcher
choose:
    just --choose --unsorted



mod init 'just/init.just'
mod bootstrap 'just/bootstrap.just'
mod apply 'just/apply.just'
"|treefmt --stdin .justfile

works flawlessly:

set quiet := true

# print this message
help:
    just --list --list-submodules --unsorted

# interactive recipes launcher
choose:
    just --choose --unsorted

mod init 'just/init.just'
mod bootstrap 'just/bootstrap.just'
mod apply 'just/apply.just'
traversed 1 files
emitted 1 files for processing
formatted 1 files (1 changed) in 21ms

Possible explanation

I suspect that the copy of stdin to a file with the same extension as the original file doesn't work well if original file has no extension:

treefmt/walk/stdin.go

Line 28 in a6ea040

// read stdin into a temporary file with the same file extension