[modules] Fix findDirectiveAtLoc to not call a member function on a null pointer.

This is exercised by existing tests, and fixes a failure with -fsanitize=null.
No observable change otherwise; the code happened to do the right thing in
practice under recent versions of Clang and GCC because
MacroDirective::getDefinition happens to check whether this == null.

llvm-svn: 240691

1 files changed, 3 insertions, 1 deletions

diff --git a/clang/include/clang/Lex/Preprocessor.h b/clang/include/clang/Lex/Preprocessor.h
index 439a28041e2..f02364a385e 100644
--- a/clang/include/clang/Lex/Preprocessor.h
+++ b/clang/include/clang/Lex/Preprocessor.h
@@ -454,7 +454,9 @@ class Preprocessor : public RefCountedBase<Preprocessor> {
     MacroDirective::DefInfo findDirectiveAtLoc(SourceLocation Loc,
                                                SourceManager &SourceMgr) const {
       // FIXME: Incorporate module macros into the result of this.
-      return getLatest()->findDirectiveAtLoc(Loc, SourceMgr);
+      if (auto *Latest = getLatest())
+        return Latest->findDirectiveAtLoc(Loc, SourceMgr);
+      return MacroDirective::DefInfo();
     }
 
     void overrideActiveModuleMacros(Preprocessor &PP, IdentifierInfo *II) {