fix(env): expose Devbox profile share dir via XDG_DATA_DIRS so package completions work

[mikeland73]

Summary

Fixes #2776.

Package-provided shell completions were never active inside a Devbox shell. For
example, on a fresh Ubuntu + bash setup, kubectl <TAB> does nothing even though
the kubectl Nix package ships a completion script.

Root cause

Nix packages install their bash completions under
share/bash-completion/completions/<cmd>, and bash-completion's dynamic loader
discovers them by scanning the bash-completion/completions subdirectory of
every entry in XDG_DATA_DIRS at completion time.

When computing the environment (internal/devbox/devbox.go), Devbox only
preserved the host's original XDG_DATA_DIRS:

if !envOpts.Pure {
    // preserve the original XDG_DATA_DIRS by prepending to it
    env["XDG_DATA_DIRS"] = envpath.JoinPathLists(env["XDG_DATA_DIRS"], os.Getenv("XDG_DATA_DIRS"))
}

It never added the Devbox profile's own share directory
(.devbox/nix/profile/default/share), which is where all of a project's
installed packages aggregate their data files. As a result the completions — and
other XDG data such as man pages and icons — shipped by those packages were
invisible to the shell.

Fix

Prepend the profile's share directory to XDG_DATA_DIRS while computing the
environment:

profileShareDir := filepath.Join(d.projectDir, nix.ProfilePath, "share")
env["XDG_DATA_DIRS"] = envpath.JoinPathLists(profileShareDir, env["XDG_DATA_DIRS"])

• Done for both regular and --pure environments, so completions keep working
  in pure shells too.
• envpath.JoinPathLists cleans, dedupes, and drops empty/relative segments, so
  this is a no-op if the entry is already present and it never introduces a
  duplicate or an unsafe relative path.
• This mirrors how nix-env / home-manager expose the same data via
  XDG_DATA_DIRS.

How was it tested?

• go build ./... and go vet ./internal/devbox/ — clean.
• Added testscripts/run/xdg_data_dirs.test.txt, which asserts that
  devbox run echo '$XDG_DATA_DIRS' includes
  .devbox/nix/profile/default/share.

Manual verification of the underlying mechanism: with the profile's share
directory on XDG_DATA_DIRS, bash-completion's __load_completion finds
share/bash-completion/completions/kubectl in the Devbox profile and activates
kubectl <TAB> completion; the change is additive and does not alter any other
environment variable.

/cc @gberche-orange (issue reporter) — thanks for the clear report and the
upstream package links.

Community Contribution License

All community contributions in this pull request are licensed to the project
maintainers under the terms of the
Apache 2 License.

By creating this pull request, I represent that I have the right to license the
contributions to the project maintainers under the Apache 2 License as stated in
the
Community Contribution License.

🤖 Generated with Claude Code

https://claude.ai/code/session_01EuAos6xjPuVdUWNEVvCYh1

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Generated by Claude Code

[Copilot]

Pull request overview

This PR fixes missing package-provided shell completions (and other XDG data like man pages/icons) inside Devbox environments by ensuring the project profile’s share/ directory is discoverable via XDG_DATA_DIRS.

Changes:

• Prepend .devbox/nix/profile/default/share to XDG_DATA_DIRS when computing the Devbox environment (including --pure).
• Add a run testscript that asserts XDG_DATA_DIRS includes the profile share/ directory.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
internal/devbox/devbox.go	Prepends the Devbox profile share dir to XDG_DATA_DIRS during environment computation.
testscripts/run/xdg_data_dirs.test.txt	Adds coverage to ensure XDG_DATA_DIRS exposes the profile share directory.

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