[PATCH] D108647: [clang][deps] Use top-level modules as precompiled dependencies

[Jan Svoboda via Phabricator via cfe-commits]

jansvoboda11 created this revision.
jansvoboda11 added reviewers: Bigcheese, dexonsmith, arphaman.
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The `ASTReader` populates `Module::PresumedModuleMapFile` only for top-level modules, not submodules. To avoid generating empty `-fmodule-map-file=` arguments, make discovered modules depend on top-level precompiled modules. The granularity of submodules is not important here.

The documentation of `Module::PresumedModuleMapFile` says this field is non-empty only when building from preprocessed source. This means there can still be cases where the dependency scanner generates empty `-fmodule-map-file=` arguments. That's being addressed in separate patch: D108544 <https://reviews.llvm.org/D108544>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D108647

Files:
  clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
  clang/test/ClangScanDeps/Inputs/modules-pch-common-submodule/cdb_pch.json
  clang/test/ClangScanDeps/Inputs/modules-pch-common-submodule/cdb_tu.json
  clang/test/ClangScanDeps/Inputs/modules-pch-common-submodule/mod_common.h
  clang/test/ClangScanDeps/Inputs/modules-pch-common-submodule/mod_common_sub.h
  clang/test/ClangScanDeps/Inputs/modules-pch-common-submodule/mod_tu.h
  clang/test/ClangScanDeps/Inputs/modules-pch-common-submodule/module.modulemap
  clang/test/ClangScanDeps/Inputs/modules-pch-common-submodule/pch.h
  clang/test/ClangScanDeps/Inputs/modules-pch-common-submodule/tu.c
  clang/test/ClangScanDeps/modules-pch-common-submodule.c

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