Feature: pixi-unpack --from-extracted <dir> to run post-processing only

[joe-cho]

Feature request: pixi-unpack --from-extracted <dir> to run post-processing only

Problem

On Windows, when antivirus software is enabled, pixi-unpack can be very slow because it:

1. Creates a system temp directory (tempfile::tempdir() → typically %TEMP% / %TMP%), which antivirus often scans.
2. Extracts the tar archive into that temp dir.
3. Runs post-processing (validate metadata, create conda cache, install packages, write activation script) — all under that same temp path.

Plain tar extraction (e.g. with 7-zip or another tool) in a user-chosen directory is fast; the slowdown is largely from doing extraction and post-processing under a system temp path that is heavily monitored.

Proposed solution

Add a mode that skips tar extraction and uses an already-extracted pack directory as input. This allows callers to:

• Extract the tar with a fast method (e.g. Node tar, 7-zip, or system tar) into a directory they control (e.g. app-local, outside system temp).
• Run pixi-unpack only for the post-processing step, with all I/O under that directory (or another app-local path).

Suggested interface

pixi-unpack --from-extracted <dir> -o <output_dir>

Behavior:

• Do not create a temp dir or unarchive anything.
• Treat <dir> as the already-extracted pack root (same layout as after tar -xf environment.tar: pixi-pack.json, channel/, optional pypi/, etc.).
• Run only:
  1. Validate metadata (pixi-pack.json).
  2. Create prefix: read repodata, build cache (e.g. under <dir>/cache or a configurable path), install conda packages into output_dir/env.
  3. If present, install PyPI packages from <dir>/pypi/.
  4. Write activate.sh / activate.bat under output_dir.

The tar format and pack layout stay the same; this is purely a different “entry point” that assumes the tar has already been extracted.

Example usage (caller side)

# 1. Extract with any fast tool (e.g. tar, 7-zip, Node tar)
tar -xf env-win-64.tar -C .pixi-src

# 2. Run post-processing only
pixi-unpack --from-extracted .pixi-src -o .

Benefits

• Performance on Windows: Avoids system temp for extraction; callers can extract to an app-local directory that antivirus may not scan as aggressively.
• Flexibility: Callers can choose their own extractor (e.g. for speed or to avoid touching system temp at all).
• Same format: The pack remains the same conda-packed tar; no change to how pixi-pack produces it.

Possible implementation notes

• In unpack.rs, the new code path would skip tempfile::tempdir() and unarchive(), and would set unpack_dir = PathBuf::from(<dir>) (and optionally keep cache under that dir or under -o).
• The rest of the pipeline (validate metadata → create_prefix → install_pypi_packages → create_activation_script) can likely be reused as-is, with the only difference being the source of unpack_dir.

Alternative names

• --extract-to could mean “extract the tar into this dir, then run post-processing there” (extract + post-process in one shot, but to a chosen path instead of system temp). That would also help with the antivirus issue. The request above is specifically “post-processing only” so that extraction can be done by an external tool.

Thank you for considering this feature.

[e8035669]

Is this feature request similar to #245 ?

[joe-cho]

Is this feature request similar to #245 ?

Yes, quite similar.