GHC 8.10.7 on Mac, but LLVM12 is disabled?

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Hi! Recently the CI (GitHub Actions) for my library has started failing for GHC 8.10.7 on macOS.

GHC 8.10.7 depends on LLVM versions strictly less than 13.

Until now, I had explicitly installed an older version of LLVM (llvm@12) through homebrew, but Homebrew have disabled the package on 2025-07-01. Thus, all 8.10.7+macOS CI has been failing for me since that date.

Would anybody have quick solutions to this? Ideally, I want to keep supporting 8.10.7 in my package and CI since there’s nothing in code that explicitly breaks support. If I have to build LLVM from scratch etc, that’d be quite a pain.

The CI log is available here: Update discord-haskell upper bound to include 1.18.0 · yutotakano/discord-haskell-voice@68b3521 · GitHub

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Solution: you can forcefully override the disabled status by retrieving the llvm@12 formula locally, modifying the formula file to remove the ‘disable’ line, and installing from that file.

- brew install llvm@12
+ # Download the llvm@12 formula and patch it to remove the disabled reason
+ brew update
+ brew fetch --formula llvm@12
+ FORMULA_PATH="$(brew --repo homebrew/core)/Formula/l/llvm@12.rb"
+ # Remove the 'disable!' line
+ sed -i.bak '/^  disable!/d' "$FORMULA_PATH"
+ # Install ignoring the disabled status
+ HOMEBREW_NO_INSTALL_FROM_API=1 brew install llvm@12
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