[clang][modules] Only avoid pruning module maps when asked to (#89428)

Pruning non-affecting module maps is useful even when passing module
maps explicitly via `-fmodule-map-file=<path>`. For this situation, this
patch reinstates the behavior we had prior to #87849. For the situation
where the explicit module map file arguments were generated by the
dependency scanner (which already pruned the non-affecting ones), this
patch introduces new `-cc1` flag
`-fno-modules-prune-non-affecting-module-map-files` that avoids the
extra work.

1 files changed, 5 insertions, 0 deletions

diff --git a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
index e19f19b2..f46324e 100644
--- a/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
+++ b/clang/lib/Tooling/DependencyScanning/ModuleDepCollector.cpp
@@ -179,6 +179,11 @@ makeCommonInvocationForModuleBuild(CompilerInvocation CI) {
   CI.resetNonModularOptions();
   CI.clearImplicitModuleBuildOptions();
 
+  // The scanner takes care to avoid passing non-affecting module maps to the
+  // explicit compiles. No need to do extra work just to find out there are no
+  // module map files to prune.
+  CI.getHeaderSearchOpts().ModulesPruneNonAffectingModuleMaps = false;
+
   // Remove options incompatible with explicit module build or are likely to
   // differ between identical modules discovered from different translation
   // units.