Add AllowRebuild parameter to ASTUnit::Reparse()

[ibronstein]

Summary

An idea behind the commit is to have an option (AllowRebuild = false) in ASTUnit::Reparse() which will disallow rebuilding the precompiled preamble.

[ibronstein]

lib/Frontend/ASTUnit.cpp

2068

Can we leave ASTUnit in such state?

include/clang/Frontend/ASTUnit.h

static ASTUnit *LoadFromCommandLine(
       std::unique_ptr<ASTUnit> *ErrAST = nullptr);
 
   /// \brief Reparse the source files using the same command-line options that
   /// were originally used to produce this translation unit.
   ///
   /// \returns True if a failure occurred that causes the ASTUnit not to
   /// contain any translation-unit information, false otherwise.
   bool Reparse(std::shared_ptr<PCHContainerOperations> PCHContainerOps,
-               ArrayRef<RemappedFile> RemappedFiles = None);
+               ArrayRef<RemappedFile> RemappedFiles = None,
+               bool AllowRebuild = true);
 
   /// \brief Perform code completion at the given file, line, and
   /// column within this translation unit.
   ///
   /// \param File The file in which code completion will occur.
   ///
   /// \param Line The line at which code completion will occur.
   ///

lib/Frontend/ASTUnit.cpp

if (AST->LoadFromCompilerInvocation(std::move(PCHContainerOps),
     }
     return nullptr;
   }
 
   return AST.release();
 }
 
 bool ASTUnit::Reparse(std::shared_ptr<PCHContainerOperations> PCHContainerOps,
-                      ArrayRef<RemappedFile> RemappedFiles) {
+                      ArrayRef<RemappedFile> RemappedFiles,
+                      bool AllowRebuild) {
   if (!Invocation)
     return true;
 
   clearFileLevelDecls();
   
   SimpleTimer ParsingTimer(WantTiming);
   ParsingTimer.setOutput("Reparsing " + getMainFileName());
 
   // Remap files.
   PreprocessorOptions &PPOpts = Invocation->getPreprocessorOpts();
   for (const auto &RB : PPOpts.RemappedFileBuffers)
     delete RB.second;
 
   Invocation->getPreprocessorOpts().clearRemappedFiles();
   for (const auto &RemappedFile : RemappedFiles) {
     Invocation->getPreprocessorOpts().addRemappedFile(RemappedFile.first,
                                                       RemappedFile.second);
   }
 
   // If we have a preamble file lying around, or if we might try to
   // build a precompiled preamble, do so now.
   std::unique_ptr<llvm::MemoryBuffer> OverrideMainBuffer;
-  if (!getPreambleFile(this).empty() || PreambleRebuildCounter > 0)
+  if (!getPreambleFile(this).empty() || PreambleRebuildCounter > 0) {
     OverrideMainBuffer =
-        getMainBufferWithPrecompiledPreamble(PCHContainerOps, *Invocation);
+        getMainBufferWithPrecompiledPreamble(PCHContainerOps, *Invocation, AllowRebuild);
+    if (!AllowRebuild && !OverrideMainBuffer)
+      return false;
+  }
 
   // Clear out the diagnostics state.
   FileMgr.reset();
   getDiagnostics().Reset();
   ProcessWarningOptions(getDiagnostics(), Invocation->getDiagnosticOpts());
   if (OverrideMainBuffer)
     getDiagnostics().setNumWarnings(NumWarningsInPreamble);