[ZTJun]

brew outdated crashes for formulae installed from HEAD whose head spec
is not a VCS URL:

Error: undefined method 'last_commit' for an instance of CurlDownloadStrategy

Formula#latest_head_pkg_version calls downloader.last_commit
unconditionally, but that method only exists on VCSDownloadStrategy. A
formula's head can point to a plain archive URL (e.g.
fredowski/pspp/pspp uses head ".../latest-source.tar.gz"), which gives
a CurlDownloadStrategy.

The crash triggers whenever a HEAD keg is deemed outdated without
--fetch-HEAD: after the formula's stable version is bumped past the one
recorded in the keg's tab, head_version_outdated? returns true via the
stable comparison and the unguarded last_commit call runs. Verbose
output is the default in interactive shells, so plain brew outdated
hits this too. Introduced by #20940.

To reproduce: brew install --HEAD a formula whose head is an archive
URL, wait until its stable version is bumped (or lower the "stable"
version recorded in the keg's INSTALL_RECEIPT.json), then run
brew outdated in a terminal or brew outdated -v anywhere.

When head_spec.downloader is not a VCSDownloadStrategy there is no
upstream commit to report, so return the installed HEAD version and let
verbose output fall back to printing latest HEAD, as it did before
#20940. Adds a regression test.

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---

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Drafted with AI assistance (Devin, SWE-2); code, tests and prose reviewed by me before submission.

[coderabbitai]

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• Library/Homebrew/formula.rb
• Library/Homebrew/test/formula_spec.rb

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Summary

Summary by CodeRabbit

• Bug Fixes
  • Corrected package version reporting for installed HEAD builds that use non-version-control download sources.

Changes

The HEAD package version method now returns the latest installed version when the HEAD downloader is not a VCS downloader. A test checks that this returns package version HEAD with revision 0 when the installed tab records stable version 1.0.

HEAD package version handling

Layer / File(s)	Summary
Handle non-VCS HEAD versions Library/Homebrew/formula.rb, Library/Homebrew/test/formula_spec.rb	The method returns the latest installed version for non-VCS HEAD downloaders. The test checks the HEAD package version and revision 0 when the installed tab records stable version 1.0. VCS downloaders retain the existing commit-based version calculation.

Merge Risk: Minimal · up to 680aa

The non-VCS HEAD fallback and regression coverage are aligned with the stated fix.

Pre-merge checks: 4

Check name	Status	Explanation
Title check		The title "formula: handle non-VCS head in outdated" matches the main change. The PR makes Formula#latest_head_pkg_version return the installed HEAD version when the HEAD downloader is not a VCSDownlo…
Description check		The description explains the crash in brew outdated for formulae whose head spec is a plain archive URL. It names the cause (an unguarded downloader.last_commit call), gives reproduction steps, and de…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title "formula: handle non-VCS head in outdated" matches the main change. The PR makes Formula#latest_head_pkg_version return the installed HEAD version when the HEAD downloader is not a VCSDownloadStrategy, which stops the brew outdated crash. The title is specific and concise, and it names the affected area.

Full details: Description check

Explanation

The description explains the crash in brew outdated for formulae whose head spec is a plain archive URL. It names the cause (an unguarded downloader.last_commit call), gives reproduction steps, and describes the fix and the regression test. It is directly related to the changeset.

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[MikeMcQuaid]

Thanks for the PR! Why use a non-VCS head URL? Want to figure out what makes most sense, particularly given this has been broken for a year and you're first to complain.

[ZTJun]

Thanks for the PR! Why use a non-VCS head URL? Want to figure out what makes most sense, particularly given this has been broken for a year and you're first to complain.

I think it's not a choice on my end — fredowski/pspp/pspp (a third-party tap) declares head ".../latest-source.tar.gz", a rolling source tarball rather than a VCS checkout. I've seen that the DSL permits it, audit doesn't flag it, and installs that already exist carry it regardless.

Probably nobody hit it before because it needs a narrow combination: a non-VCS head, a --HEAD install, a stable bump afterwards, and verbose or interactive output. pspp only started crashing for me when its stable went 2.1.2 → 2.1.3.

On direction: for a non-VCS downloader there is no upstream commit to report, and fetching the archive would defeat --fetch-HEAD. Returning the installed version restores the pre-#20940 latest HEAD output, matching the existing VCSDownloadStrategy guards in head_version_outdated?/update_head_version.
Displaying the bumped stable version instead (e.g. < 2.1.3) was the other option, but brew upgrade still targets HEAD for these kegs, so latest HEAD is the honest output even if it carries less information, I think.
Maybe to pair this with an audit deprecation of non-VCS heads or take a different fallback if you prefer. But I am convinced the guard seems needed either way, so outdated doesn't NoMethodError on existing installs.

[MikeMcQuaid]

Thanks!