diff --git a/clang-tools-extra/clangd/SourceCode.cpp b/clang-tools-extra/clangd/SourceCode.cpp
index fb1183a..d991164 100644
--- a/clang-tools-extra/clangd/SourceCode.cpp
+++ b/clang-tools-extra/clangd/SourceCode.cpp
@@ -328,6 +328,10 @@
   return FileRange;
 }
 
+bool isInsideMainFile(SourceLocation Loc, const SourceManager &SM) {
+  return Loc.isValid() && SM.isWrittenInMainFile(SM.getExpansionLoc(Loc));
+}
+
 llvm::Optional<SourceRange> toHalfOpenFileRange(const SourceManager &SM,
                                                 const LangOptions &LangOpts,
                                                 SourceRange R) {