[clang-format] Add MacroUnexpander.

MacroUnexpander applies the structural formatting of expanded lines into
UnwrappedLines to the corresponding unexpanded macro calls, resulting in
UnwrappedLines for the macro calls the user typed.

Differential Revision: https://reviews.llvm.org/D88299

clang/lib/Format/CMakeLists.txt

@@ -8,6 +8,7 @@ add_clang_library(clangFormat
   Format.cpp
   FormatToken.cpp
   FormatTokenLexer.cpp
+  MacroCallReconstructor.cpp
   MacroExpander.cpp
   NamespaceEndCommentsFixer.cpp
   QualifierAlignmentFixer.cpp

clang/lib/Format/FormatToken.h

@@ -497,6 +497,15 @@ struct FormatToken {
   // in a configured macro expansion.
   llvm::Optional<MacroExpansion> MacroCtx;
 
+  /// When macro expansion introduces nodes with children, those are marked as
+  /// \c MacroParent.
+  /// FIXME: The formatting code currently hard-codes the assumption that
+  /// child nodes are introduced by blocks following an opening brace.
+  /// This is deeply baked into the code and disentangling this will require
+  /// signficant refactorings. \c MacroParent allows us to special-case the
+  /// cases in which we treat parents as block-openers for now.
+  bool MacroParent = false;
+
   bool is(tok::TokenKind Kind) const { return Tok.is(Kind); }
   bool is(TokenType TT) const { return getType() == TT; }
   bool is(const IdentifierInfo *II) const {