SBOMs break bottle reproducibility about brew

[Bo98]

Yes, for tabs we don't store this stuff in the bottles - we store them in GitHub Packages manifest annotations instead.

[MikeMcQuaid]

Except that the download location (and checksum) is not for the version indicated (20.13.1). Instead, it points to the location and checksum of 20.13.0. Which kinda makes sense, because you can't really write a file containing the checksum of the bottle inside the bottle. (Or I could just be very confused about what's going on here, which is also a possibility.)

This also should be removed at bottling time and restored at install time.

[carlocab]

CC @SMillerDev

[SMillerDev]

I'll have to find where this is ignored for tabs since we can't really make sure it's the same. I can probably fix the build date though

[carlocab]

I'll have to find where this is ignored for tabs since we can't really make sure it's the same.

Yup, they will indeed be different. It isn't ignored for tabs -- they're just not stored in the bottle, so they don't affect the bottle checksum.

[MikeMcQuaid]

Yes, for tabs we don't store this stuff in the bottles - we store them in GitHub Packages manifest annotations instead.

We should do the same thing for SBOMs dates/times as we do for Tab runtime dependencies: update them after installation (based on the dates/times from the tab):

brew/Library/Homebrew/formula_installer.rb

Lines 825 to 830 in 1e4d119

	# Update tab with actual runtime dependencies
	tab = keg.tab
	Tab.clear_cache
	f_runtime_deps = formula.runtime_dependencies(read_from_tab: false)
	tab.runtime_dependencies = Tab.runtime_deps_hash(formula, f_runtime_deps)
	tab.write

[SMillerDev]

Not sure how to resolve this. We could not write the field if the compiler is the system one maybe? Or, which affects the usefulness iyam, we could drop the bottle inclusion of the file and only write it on install.

[MikeMcQuaid]

I think in an ideal world we'd detect if the compiler was actually used somehow e.g. write a temporary file on first usage of one of the compiler shims.

In cases like this, it's pretty clear that the compiler isn't actually used or a dependency.

[Bo98]

If compiler information needs to be available in the bottle archive via brew fetch (though this archive isn't necessarily representative of a complete install as it's pre-relocation): avoiding system compiler makes sense

If compiler information only needs to be available in the Cellar after brew install: SBOM already fetches the compiler from the tab, so we can exclude it and attach it back again on install.

[MikeMcQuaid]

If compiler information only needs to be available in the Cellar after brew install: SBOM already fetches the compiler from the tab, so we can exclude it and attach it back again on install.

Yes, this seems best for now.

[carlocab]

If compiler information only needs to be available in the Cellar after brew install: SBOM already fetches the compiler from the tab, so we can exclude it and attach it back again on install.

Yes, this seems best for now.

This is fine, but it might not be enough. The sbom.spdx.json files also reference bottle checksum of dependencies, which in general be different across OS versions even for existing :all bottles. Unless this information is generated during brew fetch?

[carlocab]

Confusingly, the SBOM also seems to contain this snippet:

    {
      "SPDXID": "SPDXRef-Bottle-node@20",
      "name": "node@20",
      "versionInfo": "20.13.1",
      "filesAnalyzed": false,
      "licenseDeclared": "NOASSERTION",
      "builtDate": "2024-05-09 05:20:38 -0400",
      "licenseConcluded": "MIT",
      "downloadLocation": "https://ghcr.io/v2/homebrew/core/node/20/blobs/sha256:a865d16c32d50cdffe26e341fb6a8d52b7c3f95daf10e2a390fb988c4fba0ab3",
      "copyrightText": "NOASSERTION",
      "externalRefs": [
        {
          "referenceCategory": "PACKAGE-MANAGER",
          "referenceLocator": "pkg:brew/homebrew/core/node@[email protected]",
          "referenceType": "purl"
        }
      ],
      "checksums": [
        {
          "algorithm": "SHA256",
          "checksumValue": "a865d16c32d50cdffe26e341fb6a8d52b7c3f95daf10e2a390fb988c4fba0ab3"
        }
      ]
    }

Except that the download location (and checksum) is not for the version indicated (20.13.1). Instead, it points to the location and checksum of 20.13.0. Which kinda makes sense, because you can't really write a file containing the checksum of the bottle inside the bottle. (Or I could just be very confused about what's going on here, which is also a possibility.)

[MikeMcQuaid]

Confirmed rebottling in Homebrew/homebrew-core#171540 post #17284 fixes the bottles 🎉

[carlocab]

Thanks @MikeMcQuaid ❤️