[clangd] Include Cleaner: suppress unused warnings for IWYU pragma: export

[kbobyrev]

Summary

Add limited support for "IWYU pragma: export" - for now it just supresses the
warning similar to "IWYU pragma: keep".

[kbobyrev]

Use strlen for performance.

[sammccall]

clang-tools-extra/clangd/Headers.cpp

26

or just drop to IWYUPragma and hardcode "keep" and "export" at the sites? up to you

151

why not just if (!Text.consume_front(IWYUPragmaKeep) && !Text.consume_front(IWYUPragmaExport))?

strlen makes me wary and also seems more verbose

[kbobyrev]

Resolve comment.

clang-tools-extra/clangd/Headers.cpp

 #include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/PPCallbacks.h"
 #include "clang/Lex/Preprocessor.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Path.h"
+#include <cstring>
 
 namespace clang {
 namespace clangd {
 
 const char IWYUPragmaKeep[] = "// IWYU pragma: keep";
+const char IWYUPragmaExport[] = "// IWYU pragma: export";
 
 class IncludeStructure::RecordHeaders : public PPCallbacks,
                                         public CommentHandler {
 public:
   RecordHeaders(const CompilerInstance &CI, IncludeStructure *Out)
       : SM(CI.getSourceManager()),
         HeaderInfo(CI.getPreprocessor().getHeaderSearchInfo()), Out(Out) {}
 
public:
   // #include "bar.h" // IWYU pragma: keep
   //
   // The order in which the callbacks will be triggered:
   //
   // 1. InclusionDirective("foo.h")
   // 2. HandleComment("// IWYU pragma: keep")
   // 3. InclusionDirective("bar.h")
   //
-  // HandleComment will store the last location of "IWYU pragma: keep" comment
-  // in the main file, so that when InclusionDirective is called, it will know
-  // that the next inclusion is behind the IWYU pragma.
+  // HandleComment will store the last location of "IWYU pragma: keep" (or
+  // export) comment in the main file, so that when InclusionDirective is
+  // called, it will know that the next inclusion is behind the IWYU pragma.
   bool HandleComment(Preprocessor &PP, SourceRange Range) override {
     if (!inMainFile() || Range.getBegin().isMacroID())
       return false;
     bool Err = false;
     llvm::StringRef Text = SM.getCharacterData(Range.getBegin(), &Err);
-    if (Err || !Text.consume_front(IWYUPragmaKeep))
+    if (Err && !Text.consume_front(IWYUPragmaKeep) &&
+        !Text.consume_front(IWYUPragmaExport))
       return false;
     unsigned Offset = SM.getFileOffset(Range.getBegin());
     LastPragmaKeepInMainFileLine =
         SM.getLineNumber(SM.getFileID(Range.getBegin()), Offset) - 1;
     return false;
   }
 
 private:
   // Keeps track of include depth for the current file. It's 1 for main file.

clang-tools-extra/clangd/unittests/IncludeCleanerTests.cpp

TEST(IncludeCleaner, NonSelfContainedHeaders) {
   EXPECT_THAT(ReferencedFileNames.keys(),
               UnorderedElementsAre(testPath("foo.h")));
 }
 
 TEST(IncludeCleaner, IWYUPragmas) {
   TestTU TU;
   TU.Code = R"cpp(
     #include "behind_keep.h" // IWYU pragma: keep
+    #include "exported.h" // IWYU pragma: export
     #include "public.h"
 
     void bar() { foo(); }
     )cpp";
   TU.AdditionalFiles["behind_keep.h"] = guard("");
+  TU.AdditionalFiles["exported.h"] = guard("");
   TU.AdditionalFiles["public.h"] = guard("#include \"private.h\"");
   TU.AdditionalFiles["private.h"] = guard(R"cpp(
     // IWYU pragma: private, include "public.h"
     void foo() {}
   )cpp");
   ParsedAST AST = TU.build();
 
   auto ReferencedFiles = findReferencedFiles(