[preprocessor] Add an opportunity to retain excluded conditional blocks

It is handy for clang tooling, for instance, in source to source transformation.

Reviewers: vpykhtin (Valery Pykhtin), erichkeane (Erich Keane)

Subscribers: rsmith (Richard Smith), akyrtzi (Argyrios Kyrtzidis)

Tags: #clang

Differential Revision: https://reviews.llvm.org/D66597

llvm-svn: 370123

3 files changed, 11 insertions, 1 deletions

diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
index 74badac740b..bdce233ce8b 100644
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -1356,7 +1356,12 @@ enum CXTranslationUnit_Flags {
    * the case where these warnings are not of interest, as for an IDE for
    * example, which typically shows only the diagnostics in the main file.
    */
-  CXTranslationUnit_IgnoreNonErrorsFromIncludedFiles = 0x4000
+  CXTranslationUnit_IgnoreNonErrorsFromIncludedFiles = 0x4000,
+
+  /**
+   * Tells the preprocessor not to skip excluded conditional blocks.
+   */
+  CXTranslationUnit_RetainExcludedConditionalBlocks = 0x8000,
 };
 
 /**
diff --git a/clang/include/clang/Frontend/ASTUnit.h b/clang/include/clang/Frontend/ASTUnit.h
index 08cc91946eb..a36655150d4 100644
--- a/clang/include/clang/Frontend/ASTUnit.h
+++ b/clang/include/clang/Frontend/ASTUnit.h
@@ -832,6 +832,7 @@ public:
           SkipFunctionBodiesScope::None,
       bool SingleFileParse = false, bool UserFilesAreVolatile = false,
       bool ForSerialization = false,
+      bool RetainExcludedConditionalBlocks = false,
       llvm::Optional<StringRef> ModuleFormat = llvm::None,
       std::unique_ptr<ASTUnit> *ErrAST = nullptr,
       IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS = nullptr);
diff --git a/clang/include/clang/Lex/PreprocessorOptions.h b/clang/include/clang/Lex/PreprocessorOptions.h
index 1480548c7fb..8824f0a51d0 100644
--- a/clang/include/clang/Lex/PreprocessorOptions.h
+++ b/clang/include/clang/Lex/PreprocessorOptions.h
@@ -142,6 +142,9 @@ public:
   /// compiler invocation and its buffers will be reused.
   bool RetainRemappedFileBuffers = false;
 
+  /// When enabled, excluded conditional blocks retain in the main file.
+  bool RetainExcludedConditionalBlocks = false;
+
   /// The Objective-C++ ARC standard library that we should support,
   /// by providing appropriate definitions to retrofit the standard library
   /// with support for lifetime-qualified pointers.
@@ -201,6 +204,7 @@ public:
     RetainRemappedFileBuffers = true;
     PrecompiledPreambleBytes.first = 0;
     PrecompiledPreambleBytes.second = false;
+    RetainExcludedConditionalBlocks = false;
   }
 };