[clang][lex] Add PragmaOnce callback to PPCallbacks

[KyleFromKitware]

Rebased onto main for D141000.

clang/include/clang/Lex/PPCallbacks.h

public:
   virtual void PragmaAssumeNonNullBegin(PragmaIntroducer Introducer,
                                         SourceLocation Loc) {}
 
   /// Callback invoked when a \#pragma clang assume_nonnull end directive
   /// is read.
   virtual void PragmaAssumeNonNullEnd(PragmaIntroducer Introducer,
                                       SourceLocation Loc) {}
 
+  /// Callback invoked when a \#pragma once directive is read.
+  virtual void PragmaOnce(PragmaIntroducer Introducer, SourceLocation Loc) {}
+
   /// Called by Preprocessor::HandleMacroExpandedIdentifier when a
   /// macro invocation is found.
   virtual void MacroExpands(const Token &MacroNameTok,
                             const MacroDefinition &MD, SourceRange Range,
                             const MacroArgs *Args) {}
 
   /// Hook called whenever a macro definition is seen.
   virtual void MacroDefined(SourceLocation HashLoc, const Token &MacroNameTok,
public:
   }
 
   void PragmaAssumeNonNullEnd(PragmaIntroducer Introducer,
                               SourceLocation Loc) override {
     First->PragmaAssumeNonNullEnd(Introducer, Loc);
     Second->PragmaAssumeNonNullEnd(Introducer, Loc);
   }
 
+  void PragmaOnce(PragmaIntroducer Introducer, SourceLocation Loc) override {
+    First->PragmaOnce(Introducer, Loc);
+    Second->PragmaOnce(Introducer, Loc);
+  }
+
   void MacroExpands(const Token &MacroNameTok, const MacroDefinition &MD,
                     SourceRange Range, const MacroArgs *Args) override {
     First->MacroExpands(MacroNameTok, MD, Range, Args);
     Second->MacroExpands(MacroNameTok, MD, Range, Args);
   }
 
   void MacroDefined(SourceLocation HashLoc, const Token &MacroNameTok,
                     const MacroDirective *MD) override {

clang/include/clang/Lex/Preprocessor.h

private:
   void HandleElseDirective(Token &Result, const Token &HashToken);
   void HandleElifFamilyDirective(Token &ElifToken, const Token &HashToken,
                                  tok::PPKeywordKind Kind);
 
   // Pragmas.
   void HandlePragmaDirective(PragmaIntroducer Introducer);
 
 public:
-  void HandlePragmaOnce(Token &OnceTok);
+  void HandlePragmaOnce(PragmaIntroducer Introducer, Token &OnceTok);
   void HandlePragmaMark(PragmaIntroducer Introducer, Token &MarkTok);
   void HandlePragmaPoison();
   void HandlePragmaSystemHeader(Token &SysHeaderTok);
   void HandlePragmaDependency(Token &DependencyTok);
   void HandlePragmaPushMacro(Token &Tok);
   void HandlePragmaPopMacro(Token &Tok);
   void HandlePragmaIncludeAlias(Token &Tok);
   void HandlePragmaModuleBuild(Token &Tok);

clang/lib/Lex/Pragma.cpp

void Preprocessor::HandleMicrosoft__pragma(Token &Tok) {
   // With everything set up, lex this as a #pragma directive.
   HandlePragmaDirective({PIK___pragma, PragmaLoc});
 
   // Finally, return whatever came after the pragma directive.
   return Lex(Tok);
 }
 
 /// HandlePragmaOnce - Handle \#pragma once.  OnceTok is the 'once'.
-void Preprocessor::HandlePragmaOnce(Token &OnceTok) {
+void Preprocessor::HandlePragmaOnce(PragmaIntroducer Introducer, Token &OnceTok) {
   // Don't honor the 'once' when handling the primary source file, unless
   // this is a prefix to a TU, which indicates we're generating a PCH file, or
   // when the main file is a header (e.g. when -xc-header is provided on the
   // commandline).
   if (isInPrimaryFile() && TUKind != TU_Prefix && !getLangOpts().IsHeaderFile) {
     Diag(OnceTok, diag::pp_pragma_once_in_main_file);
     return;
   }
 
   // Get the current file lexer we're looking at.  Ignore _Pragma 'files' etc.
   // Mark the file as a once-only file now.
   HeaderInfo.MarkFileIncludeOnce(getCurrentFileLexer()->getFileEntry());
+
+  if (Callbacks)
+    Callbacks->PragmaOnce(Introducer, OnceTok.getLocation());
 }
 
 void Preprocessor::HandlePragmaMark(PragmaIntroducer Introducer,
                                     Token &MarkTok) {
   assert(CurPPLexer && "No current lexer?");
 
   SmallString<64> Buffer;
   CurLexer->ReadToEndOfLine(&Buffer);

 
 /// PragmaOnceHandler - "\#pragma once" marks the file as atomically included.
 struct PragmaOnceHandler : public PragmaHandler {
   PragmaOnceHandler() : PragmaHandler("once") {}
 
   void HandlePragma(Preprocessor &PP, PragmaIntroducer Introducer,
                     Token &OnceTok) override {
     PP.CheckEndOfDirective("pragma once");
-    PP.HandlePragmaOnce(OnceTok);
+    PP.HandlePragmaOnce(Introducer, OnceTok);
   }
 };
 
 /// PragmaMarkHandler - "\#pragma mark ..." is ignored by the compiler, and the
 /// rest of the line is not lexed.
 struct PragmaMarkHandler : public PragmaHandler {
   PragmaMarkHandler() : PragmaHandler("mark") {}