[stable/20230725] Split incremental-extensions

The preprocessor `IncrementalProcessing` option was being used to
control whether or not to teardown the lexer or run the end of
translation unit action. In D127284 this was merged with
`-fincremental-extensions`, which also changes top level parsing.

Split these again so that the former behavior can be achieved without
the latter (ie. to allow managing lifetime without also changing
parsing).

Resolves rdar://113406310.

Author: bnbarham

clang/include/clang/Lex/Preprocessor.h

@@ -281,6 +281,9 @@ class Preprocessor {
   /// Empty line handler.
   EmptylineHandler *Emptyline = nullptr;
 
+  /// True to avoid tearing down the lexer etc on EOF
+  bool IncrementalProcessing = false;
+
 public:
   /// The kind of translation unit we are processing.
   const TranslationUnitKind TUKind;
@@ -1925,14 +1928,11 @@ class Preprocessor {
   void recomputeCurLexerKind();
 
   /// Returns true if incremental processing is enabled
-  bool isIncrementalProcessingEnabled() const {
-    return getLangOpts().IncrementalExtensions;
-  }
+  bool isIncrementalProcessingEnabled() const { return IncrementalProcessing; }
 
   /// Enables the incremental processing
   void enableIncrementalProcessing(bool value = true) {
-    // FIXME: Drop this interface.
-    const_cast<LangOptions &>(getLangOpts()).IncrementalExtensions = value;
+    IncrementalProcessing = value;
   }
 
   /// Specify the point at which code-completion will be performed.

clang/lib/Lex/PPLexerChange.cpp

@@ -545,7 +545,7 @@ bool Preprocessor::HandleEndOfFile(Token &Result, bool isEndOfMacro) {
   Result.startToken();
   CurLexer->BufferPtr = EndPos;
 
-  if (isIncrementalProcessingEnabled()) {
+  if (getLangOpts().IncrementalExtensions) {
     CurLexer->FormTokenWithChars(Result, EndPos, tok::annot_repl_input_end);
     Result.setAnnotationEndLoc(Result.getLocation());
     Result.setAnnotationValue(nullptr);

clang/lib/Lex/Preprocessor.cpp

@@ -147,6 +147,10 @@ Preprocessor::Preprocessor(std::shared_ptr<PreprocessorOptions> PPOpts,
     Ident_AbnormalTermination = nullptr;
   }
 
+  // Default incremental processing to -fincremental-extensions, clients can
+  // override with `enableIncrementalProcessing` if desired.
+  IncrementalProcessing = LangOpts.IncrementalExtensions;
+
   // If using a PCH where a #pragma hdrstop is expected, start skipping tokens.
   if (usingPCHWithPragmaHdrStop())
     SkippingUntilPragmaHdrStop = true;

clang/lib/Parse/Parser.cpp

@@ -623,6 +623,11 @@ bool Parser::ParseTopLevelDecl(DeclGroupPtrTy &Result,
                                Sema::ModuleImportState &ImportState) {
   DestroyTemplateIdAnnotationsRAIIObj CleanupRAII(*this);
 
+  // Skip over the EOF token, flagging end of previous input for incremental
+  // processing
+  if (PP.isIncrementalProcessingEnabled() && Tok.is(tok::eof))
+    ConsumeToken();
+
   Result = nullptr;
   switch (Tok.getKind()) {
   case tok::annot_pragma_unused:
@@ -714,7 +719,8 @@ bool Parser::ParseTopLevelDecl(DeclGroupPtrTy &Result,
 
     // Late template parsing can begin.
     Actions.SetLateTemplateParser(LateTemplateParserCallback, nullptr, this);
-    Actions.ActOnEndOfTranslationUnit();
+    if (!PP.isIncrementalProcessingEnabled())
+      Actions.ActOnEndOfTranslationUnit();
     //else don't tell Sema that we ended parsing: more input might come.
     return true;
 
@@ -1039,7 +1045,7 @@ Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
       ConsumeToken();
       return nullptr;
     }
-    if (PP.isIncrementalProcessingEnabled() &&
+    if (getLangOpts().IncrementalExtensions &&
         !isDeclarationStatement(/*DisambiguatingWithExpression=*/true))
       return ParseTopLevelStmtDecl();