[clang][modules] Avoid modules diagnostics for __has_include() (llvm#71450)

After llvm#70144 Clang started resolving module maps even for
`__has_include()` expressions. This had the unintended consequence of
emitting diagnostics around header misuse. These don't make sense if you
actually don't bring contents of the header into the importer, so should
be skipped for `__has_include()`. This patch moves emission of these
diagnostics out of `Preprocessor::LookupFile()` up into
`Preprocessor::LookupHeaderIncludeOrImport()`.

(cherry picked from commit bdb309c)

Author: jansvoboda11

clang/lib/Lex/PPDirectives.cpp

@@ -953,7 +953,6 @@ OptionalFileEntryRef Preprocessor::LookupFile(
 
   Module *RequestingModule = getModuleForLocation(
       FilenameLoc, LangOpts.ModulesValidateTextualHeaderIncludes);
-  bool RequestingModuleIsModuleInterface = !SourceMgr.isInMainFile(FilenameLoc);
 
   // If the header lookup mechanism may be relative to the current inclusion
   // stack, record the parent #includes.
@@ -1029,13 +1028,8 @@ OptionalFileEntryRef Preprocessor::LookupFile(
       Filename, FilenameLoc, isAngled, FromDir, &CurDir, Includers, SearchPath,
       RelativePath, RequestingModule, SuggestedModule, IsMapped,
       IsFrameworkFound, SkipCache, BuildSystemModule, OpenFile, CacheFailures);
-  if (FE) {
-    if (SuggestedModule && !LangOpts.AsmPreprocessor)
-      HeaderInfo.getModuleMap().diagnoseHeaderInclusion(
-          RequestingModule, RequestingModuleIsModuleInterface, FilenameLoc,
-          Filename, *FE);
+  if (FE)
     return FE;
-  }
 
   const FileEntry *CurFileEnt;
   // Otherwise, see if this is a subframework header.  If so, this is relative
@@ -1046,10 +1040,6 @@ OptionalFileEntryRef Preprocessor::LookupFile(
       if (OptionalFileEntryRef FE = HeaderInfo.LookupSubframeworkHeader(
               Filename, CurFileEnt, SearchPath, RelativePath, RequestingModule,
               SuggestedModule)) {
-        if (SuggestedModule && !LangOpts.AsmPreprocessor)
-          HeaderInfo.getModuleMap().diagnoseHeaderInclusion(
-              RequestingModule, RequestingModuleIsModuleInterface, FilenameLoc,
-              Filename, *FE);
         return FE;
       }
     }
@@ -1061,10 +1051,6 @@ OptionalFileEntryRef Preprocessor::LookupFile(
         if (OptionalFileEntryRef FE = HeaderInfo.LookupSubframeworkHeader(
                 Filename, CurFileEnt, SearchPath, RelativePath,
                 RequestingModule, SuggestedModule)) {
-          if (SuggestedModule && !LangOpts.AsmPreprocessor)
-            HeaderInfo.getModuleMap().diagnoseHeaderInclusion(
-                RequestingModule, RequestingModuleIsModuleInterface,
-                FilenameLoc, Filename, *FE);
           return FE;
         }
       }
@@ -2093,12 +2079,28 @@ OptionalFileEntryRef Preprocessor::LookupHeaderIncludeOrImport(
     const FileEntry *LookupFromFile, StringRef &LookupFilename,
     SmallVectorImpl<char> &RelativePath, SmallVectorImpl<char> &SearchPath,
     ModuleMap::KnownHeader &SuggestedModule, bool isAngled) {
+  auto DiagnoseHeaderInclusion = [&](FileEntryRef FE) {
+    if (LangOpts.AsmPreprocessor)
+      return;
+
+    Module *RequestingModule = getModuleForLocation(
+        FilenameLoc, LangOpts.ModulesValidateTextualHeaderIncludes);
+    bool RequestingModuleIsModuleInterface =
+        !SourceMgr.isInMainFile(FilenameLoc);
+
+    HeaderInfo.getModuleMap().diagnoseHeaderInclusion(
+        RequestingModule, RequestingModuleIsModuleInterface, FilenameLoc,
+        Filename, FE);
+  };
+
   OptionalFileEntryRef File = LookupFile(
       FilenameLoc, LookupFilename, isAngled, LookupFrom, LookupFromFile, CurDir,
       Callbacks ? &SearchPath : nullptr, Callbacks ? &RelativePath : nullptr,
       &SuggestedModule, &IsMapped, &IsFrameworkFound);
-  if (File)
+  if (File) {
+    DiagnoseHeaderInclusion(*File);
     return File;
+  }
 
   // Give the clients a chance to silently skip this include.
   if (Callbacks && Callbacks->FileNotFound(Filename))
@@ -2117,6 +2119,7 @@ OptionalFileEntryRef Preprocessor::LookupHeaderIncludeOrImport(
         &SuggestedModule, &IsMapped,
         /*IsFrameworkFound=*/nullptr);
     if (File) {
+      DiagnoseHeaderInclusion(*File);
       Diag(FilenameTok, diag::err_pp_file_not_found_angled_include_not_fatal)
           << Filename << IsImportDecl
           << FixItHint::CreateReplacement(FilenameRange,
@@ -2147,6 +2150,7 @@ OptionalFileEntryRef Preprocessor::LookupHeaderIncludeOrImport(
         Callbacks ? &RelativePath : nullptr, &SuggestedModule, &IsMapped,
         /*IsFrameworkFound=*/nullptr);
     if (File) {
+      DiagnoseHeaderInclusion(*File);
       auto Hint =
           isAngled ? FixItHint::CreateReplacement(
                          FilenameRange, "<" + TypoCorrectionName.str() + ">")

clang/test/Modules/has_include_non_modular.c

@@ -0,0 +1,14 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+//--- module.modulemap
+module Mod { header "mod.h" }
+//--- mod.h
+#if __has_include("textual.h")
+#endif
+//--- textual.h
+
+//--- tu.c
+#include "mod.h"
+
+// RUN: %clang -fsyntax-only %t/tu.c -fmodules -fmodules-cache-path=%t/cache -Werror=non-modular-include-in-module