Proto extension support Buf formatter

[06kellyjac]

Check for existing issues

• Completed

Misc notes

It'd be nice, in addition to having buf lsp support (#1928) to also have buf formatter support.

There are a few upstream blockers to this

• Format accepts input from stdin bufbuild/buf#1035
• Potentially the fact buf wants to be relative to the files it scans, this could be addressed by the above PR too

---

For now you can hack in support for buf formatting like so (use at your own risk):

  "languages": {
    "Proto": {
      "formatter": {
        "external": {
          "command": "bash",
          "arguments": [
            "-c",
            "INPUT=\"$(cat)\";TMPFILE=\"$(mktemp -u -p /tmp).proto\";echo \"$INPUT\" > $TMPFILE;trap 'rm -rf -- \"$TMPFILE\"' EXIT;cd /tmp;buf format --path $TMPFILE;"
          ]
        }
      }
    }
  },

It executes into bash with a script that:

• captures stdin, being the file content
• prepares a filename to use in /tmp
  • -u for dryrun because we need to add a suffix
  • .proto needs to be the suffix or buf format --path doesn't actually read it/run
• dump the stdin capture to the tmpfile location
• create a trap so when bash exits it'll clean up the tmpfile
  • this also helps if buf crashes or doesn't exist
• cd into /tmp because buf wants to be relative to the file
• run buf pointing at the single file with --path

I imagine this should work on Mac but it certainly works for me on Linux.
I think the mktemp usage could be cleaned up a bit but I wanted to avoid using too many features in-case they're GNU mktemp specific.
Maybe there should be a check that $TMPFILE gets written to just to double check the right file is being targeted for deletion.