[C++20] [Modules] Introduce ForceCheckCXX20ModulesInputFiles options for

C++20 modules

Previously, we banned the check for input files from C++20 modules since
we thought the BMI from C++20 modules should be a standalone artifact.

However, during the recent experiment with clangd for modules, I find
it is necessary to tell whether or not a BMI is out-of-date by checking the
input files especially for language servers.

So this patch brings a header search option
ForceCheckCXX20ModulesInputFiles to allow the tools (concretly, clangd)
to check the input files from BMI.

1 files changed, 5 insertions, 1 deletions

diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index a4753f52..167db521 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -550,12 +550,16 @@ public:
   bool ReadHeaderSearchOptions(const HeaderSearchOptions &HSOpts,
                                StringRef SpecificModuleCachePath,
                                bool Complain) override {
-    // Preserve previously set header search paths.
+    // llvm::SaveAndRestore doesn't support bit field.
+    auto ForceCheckCXX20ModulesInputFiles =
+        this->HSOpts.ForceCheckCXX20ModulesInputFiles;
     llvm::SaveAndRestore X(this->HSOpts.UserEntries);
     llvm::SaveAndRestore Y(this->HSOpts.SystemHeaderPrefixes);
     llvm::SaveAndRestore Z(this->HSOpts.VFSOverlayFiles);
 
     this->HSOpts = HSOpts;
+    this->HSOpts.ForceCheckCXX20ModulesInputFiles =
+        ForceCheckCXX20ModulesInputFiles;
 
     return false;
   }