leanprover / leanprover/lean4

[cmake] Not using clang when LLVM=ON is specified

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Description

Description

When building using cmake -B build -DLLVM=ON, stage1 fails to build when the default compiler is gcc.

Workaround

Set environment variable CC=clang and CXX=clang++ before using cmake

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the failure with cmake -B build -DLLVM=ON while the default compiler is gcc, then compare it with the CC=clang and CXX=clang++ workaround. Trace the CMake configuration for the LLVM option and stage1 build; done means stage1 builds successfully without manually setting those environment variables.

Written by the indexing model from the issue text.

Assessment

Tech stack
cmake
Domain
build-system
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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