Add CCACHE_FOUND=OFF to default CMake flags

[matteosecli]

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As discussed with @SMillerDev in https://github.com/orgs/Homebrew/discussions/6920, some formulae fail to build if ccache is installed. Simple example:

docker run --rm -it ghcr.io/homebrew/ubuntu24.04:main \
bash -lc 'brew install --yes ccache && brew install --yes --build-from-source ada-url'

This is due to the fact that ccache integration in several formulae is typically handled as e.g.:

find_program(CCACHE_FOUND ccache)
if(CCACHE_FOUND)
  message(STATUS "Ccache found: using it as compiler launcher.")
  set(CMAKE_C_COMPILER_LAUNCHER ccache)
  set(CMAKE_CXX_COMPILER_LAUNCHER ccache)
endif()

instead of e.g.:

find_program(CCACHE_FOUND ccache)
if(CCACHE_FOUND)
  message(STATUS "Using ccache: ${CCACHE_FOUND}")
  set(CMAKE_C_COMPILER_LAUNCHER ${CCACHE_FOUND})
  set(CMAKE_CXX_COMPILER_LAUNCHER ${CCACHE_FOUND})
endif()

So, if ccache is not on $PATH, the build will fail.

This is certainly an upstream problem. However, as a matter of fact, it currently affects at least 20 Homebrew formulae (minimum, these are just the ones I could find): ada-url, apache-arrow, cppinsights, exiv2, kingfisher, libff, librealsense, libwbxml, lief, merve, musikcube, osrm-backend, ppsspp, rapidjson, rocksdb, rtags, taglib, tdlib, vectorscan, yalantinglibs.

As the CMake snippets above seem to be a fairly standard approach even for formulae not currently packaged by Homebrew, as it can be quickly verified by a code search, this PR proposes to add -DCCACHE_FOUND=OFF to the standard CMake flags. For the same formula as before, this will now work if using the proposed additional flag:

docker run --rm -it ghcr.io/homebrew/ubuntu24.04:main \
bash -lc 'set -euo pipefail; export HOMEBREW_NO_AUTO_UPDATE=1; curl -fsSL https://raw.githubusercontent.com/matteosecli/brew/344b6d838de7caf9457c4c58db879b8481d929b8/Library/Homebrew/formula.rb > "$(brew --repository)/Library/Homebrew/formula.rb"; brew install --yes ccache && brew install --yes --build-from-source ada-url'

Adding this flag will also be beneficial if other formulae, in the future, decide to include the same CMake snippet or to enable ccache discovery by default in their CMake files, or if newer CI build images will happen to ship with ccache preinstalled.

[Copilot]

Pull request overview

This PR updates Homebrew’s shared std_cmake_args (used by formulae that invoke CMake) to explicitly disable projects’ ad-hoc ccache detection via a commonly used find_program(CCACHE_FOUND ccache) pattern, avoiding build failures when ccache is discoverable at configure-time but not reliably invokable at build-time.

Changes:

• Add -DCCACHE_FOUND=OFF to the default CMake arguments returned by Formula#std_cmake_args.

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[carlocab]

I'm not opposed to this, but I am slightly hesitant because it only affects local source builds.

Does doing brew unlink ccache not prevent cmake from finding your ccache installation when building from source?

[matteosecli]

Hi @carlocab, thanks for taking a look.

Does doing brew unlink ccache not prevent cmake from finding your ccache installation when building from source?

Yes, unlinking ccache does avoid this specific failure when ccache was installed by Homebrew.

However, I don’t think that is an ideal solution from a user’s point of view: if ccache happens to be installed, I would still expect brew install --build-from-source <formula> to work without having to know that I first need to unlink another formula.

It also only fixes the Homebrew-installed ccache case. If ccache comes from outside Homebrew, CMake can still find it and use it. For example, this succeeds:

docker run --rm -it ghcr.io/homebrew/ubuntu24.04:main \
bash -lc 'sudo apt update && sudo apt install --yes ccache && brew install --yes --build-from-source --verbose ada-url'

However, it succeeds because /usr/bin/ccache is on the system PATH: CMake finds it, and the verbose build shows compilation going through ccache. That still seems contrary to Homebrew’s own best practices: brew builds are not meant to rely on ccache, since it can prevent some software from compiling.

The proposed change makes the default behavior consistent: Homebrew CMake builds should not accidentally discover and use ccache just because it happens to be installed somewhere.

[MikeMcQuaid]

Makes sense to me, thanks!