Improve documentation, use ternary

Author: jansvoboda11

clang/include/clang/Serialization/ASTWriter.h

@@ -659,10 +659,13 @@ class ASTWriter : public ASTDeserializationListener,
   /// include timestamps in the output file.
   time_t getTimestampForOutput(const FileEntry *E) const;
 
-  /// Write a precompiled header for the given semantic analysis.
+  /// Write a precompiled header or a module with the AST produced by the
+  /// \c Sema object, or a dependency scanner module with the preprocessor state
+  /// produced by the \c Preprocessor object.
   ///
-  /// \param Subject The object that processed the input to be written into the
-  /// AST file.
+  /// \param Subject The \c Sema object that processed the AST to be written, or
+  /// in the case of a dependency scanner module the \c Preprocessor that holds
+  /// the state.
   ///
   /// \param WritingModule The module that we are writing. If null, we are
   /// writing a precompiled header.

clang/lib/Serialization/ASTWriter.cpp

@@ -4868,11 +4868,8 @@ ASTWriter::WriteAST(llvm::PointerUnion<Sema *, Preprocessor *> Subject,
   WritingAST = true;
 
   Sema *SemaPtr = Subject.dyn_cast<Sema *>();
-  Preprocessor &PPRef = [&]() -> Preprocessor & {
-    if (SemaPtr)
-      return SemaPtr->getPreprocessor();
-    return *Subject.get<Preprocessor *>();
-  }();
+  Preprocessor &PPRef =
+      SemaPtr ? SemaPtr->getPreprocessor() : *Subject.get<Preprocessor *>();
 
   ASTHasCompilerErrors = PPRef.getDiagnostics().hasUncompilableErrorOccurred();