Fix: mesonbuild/msubprojects.py line 723: source_dir =... - #16093
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bonzini
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Aug 10, 2026
| @@ -0,0 +1,59 @@ | |||
| #!/usr/bin/env python3 | |||
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this is not how you do testcases.
Replace the standalone check_relpath_fix.py script (rejected by maintainer review as not the project's testing convention) with a test method in unittests/machinefiletests.py, following the existing TestCase style in that file. The test monkeypatches os.path.relpath to raise ValueError, simulating the Windows cross-mount/UNC scenario, and verifies msubprojects.run() handles it gracefully instead of crashing.
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Summary
Wrapped the os.path.relpath(...) call in try/except ValueError, falling back to the already-computed realpath (absolute path) when relpath raises due to a cross-mount/UNC situation.
Problem
mesonbuild/meson issue reference: #13814 - Meson throws exception updating subprojects
Root Cause
mesonbuild/msubprojects.py line 723: source_dir = os.path.relpath(os.path.realpath(options.sourcedir)) calls relpath with no start=, defaulting to os.getcwd(). On Windows, ntpath.relpath raises ValueError when the two paths are on different drives/UNC mounts, and this was unhandled, surfacing as an internal Meson exception instead of a graceful error.
Testing
PASS - exit 0 with fix applied; empirically verified exit 1 (uncaught ValueError) on unfixed code via git stash before committing.
Related Issue
#13814 - Meson throws exception updating subprojects