`codeql-action/init` Makes Metal Toolchain Unavailable on macOS 26 Runners

[PSchmiedmayer]

Description

Swift/iOS builds fail after github/codeql-action/init with Xcode 26 on macOS 26 GitHub-hosted runners when the build needs the Metal toolchain.

The failing build error is:

error: error: cannot execute tool 'metal' due to missing Metal Toolchain; use: xcodebuild -downloadComponent MetalToolchain
Command CompileMetalFile failed with a nonzero exit code

This was originally discussed in actions/runner-images:

• Runner-images issue: Metal Toolchain on macOS 26 Runners with Xcode 26 actions/runner-images#13014
• Maintainer repro: xcrun metal -v works after Xcode selection, then fails after codeql-action/init: Metal Toolchain on macOS 26 Runners with Xcode 26 actions/runner-images#13014 (comment)
• See comment by @v-sergei-pyshnoi , pointing to an issue here: Metal Toolchain on macOS 26 Runners with Xcode 26 actions/runner-images#13014 (comment)

Reproduction outline

jobs:
  codeql-metal-repro:
    runs-on: macos-26
    permissions:
      contents: read
      security-events: write
    steps:
      - uses: actions/checkout@v4
      - name: Select Xcode
        uses: maxim-lobanov/setup-xcode@v1
        with:
          xcode-version: latest-stable
      - name: Check Metal before CodeQL init
        run: |
          xcodebuild -version
          xcrun --find metal
          xcrun metal -v
      - name: Initialize CodeQL
        uses: github/codeql-action/init@v4
        with:
          languages: swift
          build-mode: manual
      - name: Check Metal after CodeQL init
        run: |
          xcrun --find metal
          xcrun metal -v
      - name: Build
        run: |
          # Run the normal xcodebuild command for an iOS app target that compiles Metal files.
          xcodebuild ...

Expected: xcrun metal -v and the xcodebuild invocation continue to find the selected Xcode’s Metal toolchain after CodeQL initialization.

Actual: after codeql-action/init, xcrun metal -v / CompileMetalFile can fail with “missing Metal Toolchain”, even though the runner image appears to have the toolchain available before CodeQL initialization.

Note: Xcode 26 changed Metal Toolchain distribution/visibility, and MacPorts documented extra steps sometimes needed to make the toolchain visible to all users:
https://trac.macports.org/wiki/TahoeProblems#MetaltoolchainisnolongerbundledinXcode

[mbg]

Hi @PSchmiedmayer 👋🏻

Thanks for opening this issue. My first thought here is that this could be a Rosetta issue. One of the things that the codeql-action/init step does is to initialise the CodeQL tracer which injects itself into certain processes to observe how the project is built. This does not natively support ARM-based architectures, and so runs through Rosetta on macOS. Subsequently, all processes it intercepted then also run under Rosetta. My hypothesis would therefore be that in the example run, Metal is installed for the ARM-based host, but not for the Intel-based process tree that runs after the CodeQL tracer intercepted the command.

I'll pass this on to the team that looks after Swift support in CodeQL who'll know best and whether there's anything we can do on our end to address this.

[PSchmiedmayer]

Thank you @mbg for the quick response; greatly appreciated and thank you for looking into this!