A .cpp unit's depfile listed its source and headers, never the BMIs it
imports: clang's driver adds -module-file-deps to --precompile only. A
std module rebuilt in its directory, which happens whenever its source
changes under one compiler and one set of flags (a libc++ update, or
mingw-w64's under the same prefix), left every object that imports it
as it was, and the next build only relinked them. Implementation units
are now compiled with -fmodule-file-deps, so the std PCM and the
project's own PCMs are prerequisites of their objects like headers.
Depfiles written before this lack the edge, so a std module that moves
directories still needs VariantId to move with it (StdPcmKey).
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Jorijn van der Graaf
27697d06aa