macOS: make the deployment target overridable, and raise it to 13.0

[cbjeukendrup]

The macOS deployment target was hardcoded in SetupBuildEnvironment.cmake, as a normal variable, after project(). That has two problems:

• a normal variable shadows the cache entry of the same name, so -DCMAKE_OSX_DEPLOYMENT_TARGET=... or a cacheVariables entry in a CMake preset was silently ignored (the cache said one thing, the build used another);
• after project() is too late anyway: CMAKE_OSX_DEPLOYMENT_TARGET is initialised by project() and used for the compiler checks it performs.

It is now set as a cache variable in a new SetupMacOSDeploymentTarget.cmake, which both this repo and MuseScore Studio include before project(). The default can be overridden on the command line, in a preset, or through the MACOSX_DEPLOYMENT_TARGET environment variable that CMake picks up by itself.

The separate MACOSX_DEPLOYMENT_TARGET variable is gone. It was not a CMake variable at all (it shares its name with Apple's environment variable) and was only consumed by LSMinimumSystemVersion in the Info.plist template, which now uses CMAKE_OSX_DEPLOYMENT_TARGET directly, so there is a single source of truth.

The second commit raises the default from 10.15.4 to 13.0.

Notes

• The emptiness check combined with FORCE is deliberate: build directories configured before this change contain an empty CMAKE_OSX_DEPLOYMENT_TARGET cache entry (CMake creates one in Platform/Darwin-Initialize.cmake when the variable is not set before project()), and a non-FORCE set(... CACHE ...) on an existing entry does nothing. Without it, those build directories would end up with no -mmacosx-version-min flag at all.
• Build directories that already hold a value keep it; run cmake -U CMAKE_OSX_DEPLOYMENT_TARGET <dir> to pick up the new default.
• Checked on a configured MuseScore Studio build directory: the default, a -D override and an environment variable override all end up in both -mmacosx-version-min and the LSMinimumSystemVersion of the app bundle and the QuickLook extension.

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• buildscripts/ci/macos/install_qt.sh
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📝 Walkthrough

Walkthrough

The build defines framework paths and includes the macOS deployment target setup before project(). A new module defaults CMAKE_OSX_DEPLOYMENT_TARGET to 13.0 when no target is configured. The previous macOS-specific deployment settings are removed from SetupBuildEnvironment.cmake. The macOS Info.plist template now uses CMAKE_OSX_DEPLOYMENT_TARGET.

Priority: ⬇️ Low

Merge Risk: 🟡 Moderate · up to 6cb15

Some existing or environment-configured macOS builds can omit the intended deployment target rather than using 13.0, producing artifacts without the expected compatibility setting. Resolve empty values before merging.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description gives a clear motivation, implementation summary, override behavior, migration details, and validation notes. However, it omits the required issue reference, checklist confirmations, a…	Add the Resolves: #NNNNN`` issue reference, complete every required checklist item with accurate [x] or `[ ]` values, and include or explicitly remove the Build configuration section according to repository requirements.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main changes: configurable macOS deployment targets and a new default of 13.0.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Description check

Explanation

The description gives a clear motivation, implementation summary, override behavior, migration details, and validation notes. However, it omits the required issue reference, checklist confirmations, and build configuration section from the repository template.

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Actionable comments posted: 1

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Inline comments:
In `@buildscripts/cmake/SetupMacOSDeploymentTarget.cmake`:
- Around line 33-34: Update the guard around CMAKE_OSX_DEPLOYMENT_TARGET so an
empty cache value is resolved using the non-empty MACOSX_DEPLOYMENT_TARGET
environment value when available, otherwise defaulting to 13.0. Preserve any
non-empty command-line or preset CMAKE_OSX_DEPLOYMENT_TARGET unchanged.

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📒 Files selected for processing (4)

• CMakeLists.txt
• buildscripts/cmake/SetupBuildEnvironment.cmake
• buildscripts/cmake/SetupMacOSDeploymentTarget.cmake
• buildscripts/packaging/macOS/Info.plist.in

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• buildscripts/cmake/SetupBuildEnvironment.cmake

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[cbjeukendrup]

This was motivated by the fact that it is no longer possible to compile for macOS <11.0 using Xcode 27, and that a deployment target bump is likely required for musescore/MuseScore#34896.

Also, it is bad practice to override standard CMake cache variables with normal variables; it should be possible to override those via the CMake command line.

[cbjeukendrup]

@igorkorsukov I think you can now close #278