Index: clangd/ClangdServer.cpp
===================================================================
--- clangd/ClangdServer.cpp
+++ clangd/ClangdServer.cpp
@@ -305,7 +305,8 @@
                             llvm::Expected<InputsAndAST> InpAST) {
     if (!InpAST)
       return CB(InpAST.takeError());
-    CB(clangd::findDefinitions(InpAST->AST, Pos, Index));
+    CB(clangd::findDefinitions(InpAST->AST, Pos, *FSProvider.getFileSystem(),
+                               Index));
   };
 
   WorkScheduler.runWithAST("Definitions", File, Bind(Action, std::move(CB)));
Index: clangd/XRefs.h
===================================================================
--- clangd/XRefs.h
+++ clangd/XRefs.h
@@ -24,6 +24,7 @@
 
 /// Get definition of symbol at a specified \p Pos.
 std::vector<Location> findDefinitions(ParsedAST &AST, Position Pos,
+                                      const vfs::FileSystem &VFS,
                                       const SymbolIndex *Index = nullptr);
 
 /// Returns highlights for all usages of a symbol at \p Pos.
Index: clangd/XRefs.cpp
===================================================================
--- clangd/XRefs.cpp
+++ clangd/XRefs.cpp
@@ -174,11 +174,17 @@
   return {DeclMacrosFinder.takeDecls(), DeclMacrosFinder.takeMacroInfos()};
 }
 
-llvm::Optional<std::string>
-getAbsoluteFilePath(const FileEntry *F, const SourceManager &SourceMgr) {
+llvm::Optional<std::string> getAbsoluteFilePath(const FileEntry *F,
+                                                const SourceManager &SourceMgr,
+                                                const vfs::FileSystem &VFS) {
   SmallString<64> FilePath = F->tryGetRealPathName();
-  if (FilePath.empty())
-    FilePath = F->getName();
+
+  if (FilePath.empty()) {
+    if (VFS.getRealPath(F->getName(), FilePath) != std::error_code()) {
+      FilePath = F->getName();
+    }
+  }
+
   if (!llvm::sys::path::is_absolute(FilePath)) {
     if (!SourceMgr.getFileManager().makeAbsolutePath(FilePath)) {
       log("Could not turn relative path to absolute: " + FilePath);
@@ -188,8 +194,9 @@
   return FilePath.str().str();
 }
 
-llvm::Optional<Location>
-makeLocation(ParsedAST &AST, const SourceRange &ValSourceRange) {
+llvm::Optional<Location> makeLocation(ParsedAST &AST,
+                                      const SourceRange &ValSourceRange,
+                                      const vfs::FileSystem &VFS) {
   const SourceManager &SourceMgr = AST.getASTContext().getSourceManager();
   const LangOptions &LangOpts = AST.getASTContext().getLangOpts();
   SourceLocation LocStart = ValSourceRange.getBegin();
@@ -205,7 +212,7 @@
   Range R = {Begin, End};
   Location L;
 
-  auto FilePath = getAbsoluteFilePath(F, SourceMgr);
+  auto FilePath = getAbsoluteFilePath(F, SourceMgr, VFS);
   if (!FilePath) {
     log("failed to get path!");
     return llvm::None;
@@ -227,6 +234,7 @@
 } // namespace
 
 std::vector<Location> findDefinitions(ParsedAST &AST, Position Pos,
+                                      const vfs::FileSystem &VFS,
                                       const SymbolIndex *Index) {
   const SourceManager &SourceMgr = AST.getASTContext().getSourceManager();
   SourceLocation SourceLocationBeg =
@@ -247,7 +255,7 @@
 
   for (auto Item : Symbols.Macros) {
     auto Loc = Item.Info->getDefinitionLoc();
-    auto L = makeLocation(AST, SourceRange(Loc, Loc));
+    auto L = makeLocation(AST, SourceRange(Loc, Loc), VFS);
     if (L)
       Result.push_back(*L);
   }
@@ -290,7 +298,7 @@
 
     auto &Candidate = ResultCandidates[Key];
     auto Loc = findNameLoc(D);
-    auto L = makeLocation(AST, SourceRange(Loc, Loc));
+    auto L = makeLocation(AST, SourceRange(Loc, Loc), VFS);
     // The declaration in the identified symbols is a definition if possible
     // otherwise it is declaration.
     bool IsDef = GetDefinition(D) == D;
@@ -309,7 +317,7 @@
     std::string HintPath;
     const FileEntry *FE =
         SourceMgr.getFileEntryForID(SourceMgr.getMainFileID());
-    if (auto Path = getAbsoluteFilePath(FE, SourceMgr))
+    if (auto Path = getAbsoluteFilePath(FE, SourceMgr, VFS))
       HintPath = *Path;
     // Query the index and populate the empty slot.
     Index->lookup(
Index: unittests/clangd/TestTU.h
===================================================================
--- unittests/clangd/TestTU.h
+++ unittests/clangd/TestTU.h
@@ -44,7 +44,7 @@
   std::string HeaderCode;
   std::string HeaderFilename = "TestTU.h";
 
-  ParsedAST build() const;
+  ParsedAST build(IntrusiveRefCntPtr<vfs::FileSystem> *OutFS = nullptr) const;
   SymbolSlab headerSymbols() const;
   std::unique_ptr<SymbolIndex> index() const;
 };
Index: unittests/clangd/TestTU.cpp
===================================================================
--- unittests/clangd/TestTU.cpp
+++ unittests/clangd/TestTU.cpp
@@ -19,7 +19,7 @@
 namespace clangd {
 using namespace llvm;
 
-ParsedAST TestTU::build() const {
+ParsedAST TestTU::build(IntrusiveRefCntPtr<vfs::FileSystem> *OutFS) const {
   std::string FullFilename = testPath(Filename),
               FullHeaderName = testPath(HeaderFilename);
   std::vector<const char *> Cmd = {"clang", FullFilename.c_str()};
@@ -29,11 +29,12 @@
     Cmd.push_back("-include");
     Cmd.push_back(FullHeaderName.c_str());
   }
-  auto AST = ParsedAST::Build(
-      createInvocationFromCommandLine(Cmd), nullptr,
-      MemoryBuffer::getMemBufferCopy(Code),
-      std::make_shared<PCHContainerOperations>(),
-      buildTestFS({{FullFilename, Code}, {FullHeaderName, HeaderCode}}));
+  auto FS = buildTestFS({{FullFilename, Code}, {FullHeaderName, HeaderCode}});
+  if (OutFS)
+    *OutFS = FS;
+  auto AST = ParsedAST::Build(createInvocationFromCommandLine(Cmd), nullptr,
+                              MemoryBuffer::getMemBufferCopy(Code),
+                              std::make_shared<PCHContainerOperations>(), FS);
   if (!AST.hasValue()) {
     ADD_FAILURE() << "Failed to build code:\n" << Code;
     llvm_unreachable("Failed to build TestTU!");
Index: unittests/clangd/XRefsTests.cpp
===================================================================
--- unittests/clangd/XRefsTests.cpp
+++ unittests/clangd/XRefsTests.cpp
@@ -114,8 +114,9 @@
   TU.HeaderCode = SymbolHeader.code();
   auto Index = TU.index();
   auto runFindDefinitionsWithIndex = [&Index](const Annotations &Main) {
-    auto AST = TestTU::withCode(Main.code()).build();
-    return clangd::findDefinitions(AST, Main.point(), Index.get());
+    IntrusiveRefCntPtr<vfs::FileSystem> FS;
+    auto AST = TestTU::withCode(Main.code()).build(&FS);
+    return clangd::findDefinitions(AST, Main.point(), *FS, Index.get());
   };
 
   Annotations Test(R"cpp(// only declaration in AST.
@@ -301,11 +302,12 @@
   };
   for (const char *Test : Tests) {
     Annotations T(Test);
-    auto AST = TestTU::withCode(T.code()).build();
+    IntrusiveRefCntPtr<vfs::FileSystem> FS;
+    auto AST = TestTU::withCode(T.code()).build(&FS);
     std::vector<Matcher<Location>> ExpectedLocations;
     for (const auto &R : T.ranges())
       ExpectedLocations.push_back(RangeIs(R));
-    EXPECT_THAT(findDefinitions(AST, T.point()),
+    EXPECT_THAT(findDefinitions(AST, T.point(), *FS),
                 ElementsAreArray(ExpectedLocations))
         << Test;
   }