Index: clangd/index/IndexAction.h
===================================================================
--- clangd/index/IndexAction.h
+++ clangd/index/IndexAction.h
@@ -21,9 +21,8 @@
 // Only a subset of SymbolCollector::Options are respected:
 //   - include paths are always collected, and canonicalized appropriately
 //   - references are always counted
-//   - main-file refs are collected (if RefsCallback is non-null)
+//   - all references are collected (if RefsCallback is non-null)
 //   - the symbol origin is always Static
-// FIXME: refs from headers should also be collected.
 std::unique_ptr<FrontendAction>
 createStaticIndexingAction(SymbolCollector::Options Opts,
                            std::function<void(SymbolSlab)> SymbolsCallback,
Index: clangd/index/IndexAction.cpp
===================================================================
--- clangd/index/IndexAction.cpp
+++ clangd/index/IndexAction.cpp
@@ -66,8 +66,10 @@
   Opts.CollectIncludePath = true;
   Opts.CountReferences = true;
   Opts.Origin = SymbolOrigin::Static;
-  if (RefsCallback != nullptr)
+  if (RefsCallback != nullptr) {
     Opts.RefFilter = RefKind::All;
+    Opts.RefsInHeaders = true;
+  }
   auto Includes = llvm::make_unique<CanonicalIncludes>();
   addSystemHeadersMapping(Includes.get());
   Opts.Includes = Includes.get();
Index: clangd/index/SymbolCollector.h
===================================================================
--- clangd/index/SymbolCollector.h
+++ clangd/index/SymbolCollector.h
@@ -57,6 +57,11 @@
     /// The symbol ref kinds that will be collected.
     /// If not set, SymbolCollector will not collect refs.
     RefKind RefFilter = RefKind::Unknown;
+    /// If set to true, SymbolCollector will collect all refs (from main file
+    /// and included headers); otherwise, only refs from main file will be
+    /// collected.
+    /// This flag is only meaningful when RefFilter is set.
+    bool RefsInHeaders = false;
     // Every symbol collected will be stamped with this origin.
     SymbolOrigin Origin = SymbolOrigin::Unknown;
     /// Collect macros.
Index: clangd/index/SymbolCollector.cpp
===================================================================
--- clangd/index/SymbolCollector.cpp
+++ clangd/index/SymbolCollector.cpp
@@ -19,6 +19,7 @@
 #include "clang/AST/DeclBase.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclTemplate.h"
+#include "clang/Basic/SourceLocation.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/Specifiers.h"
 #include "clang/Index/IndexSymbol.h"
@@ -354,7 +355,8 @@
     return true;
   if (!shouldCollectSymbol(*ND, *ASTCtx, Opts))
     return true;
-  if (CollectRef && SM.getFileID(SpellingLoc) == SM.getMainFileID())
+  if (CollectRef &&
+      (Opts.RefsInHeaders || SM.getFileID(SpellingLoc) == SM.getMainFileID()))
     DeclRefs[ND].emplace_back(SpellingLoc, Roles);
   // Don't continue indexing if this is a mere reference.
   if (IsOnlyRef)
@@ -474,26 +476,43 @@
   }
 
   const auto &SM = ASTCtx->getSourceManager();
-  auto* MainFileEntry = SM.getFileEntryForID(SM.getMainFileID());
+  llvm::DenseMap<FileID, std::string> URICache;
+  auto GetURI = [&](FileID FID) -> llvm::Optional<std::string> {
+    auto Found = URICache.find(FID);
+    if (Found == URICache.end()) {
+      // Ignore cases where we can not find a corresponding file entry
+      // for the loc, thoses are not interesting, e.g. symbols formed
+      // via macro concatenation.
+      if (auto *FileEntry = SM.getFileEntryForID(FID)) {
+        auto FileURI = toURI(SM, FileEntry->getName(), Opts);
+        if (!FileURI) {
+          log("Failed to create URI for file: {0}\n", FileEntry);
+          FileURI = ""; // reset to empty as we also want to cache this case.
+        }
+        Found = URICache.insert({FID, *FileURI}).first;
+      }
+    }
+    return Found->second;
+  };
 
-  if (auto MainFileURI = toURI(SM, MainFileEntry->getName(), Opts)) {
-    std::string MainURI = *MainFileURI;
+  if (auto MainFileURI = GetURI(SM.getMainFileID())) {
     for (const auto &It : DeclRefs) {
       if (auto ID = getSymbolID(It.first)) {
         for (const auto &LocAndRole : It.second) {
-          Ref R;
-          auto Range =
-              getTokenRange(LocAndRole.first, SM, ASTCtx->getLangOpts());
-          R.Location.Start = Range.first;
-          R.Location.End = Range.second;
-          R.Location.FileURI = MainURI;
-          R.Kind = toRefKind(LocAndRole.second);
-          Refs.insert(*ID, R);
+          auto FileID = SM.getFileID(LocAndRole.first);
+          if (auto FileURI = GetURI(FileID)) {
+            auto Range =
+                getTokenRange(LocAndRole.first, SM, ASTCtx->getLangOpts());
+            Ref R;
+            R.Location.Start = Range.first;
+            R.Location.End = Range.second;
+            R.Location.FileURI = *FileURI;
+            R.Kind = toRefKind(LocAndRole.second);
+            Refs.insert(*ID, R);
+          }
         }
       }
     }
-  } else {
-    log("Failed to create URI for main file: {0}", MainFileEntry->getName());
   }
 
   ReferencedDecls.clear();
Index: unittests/clangd/SymbolCollectorTests.cpp
===================================================================
--- unittests/clangd/SymbolCollectorTests.cpp
+++ unittests/clangd/SymbolCollectorTests.cpp
@@ -479,6 +479,17 @@
   EXPECT_THAT(Refs, Not(Contains(Pair(findSymbol(MainSymbols, "c").ID, _))));
 }
 
+TEST_F(SymbolCollectorTest, RefsInHeaders) {
+  CollectorOpts.RefFilter = RefKind::All;
+  CollectorOpts.RefsInHeaders = true;
+  Annotations Header(R"(
+  class [[Foo]] {};
+  )");
+  runSymbolCollector(Header.code(), "");
+  EXPECT_THAT(Refs, Contains(Pair(findSymbol(Symbols, "Foo").ID,
+                                  HaveRanges(Header.ranges()))));
+}
+
 TEST_F(SymbolCollectorTest, References) {
   const std::string Header = R"(
     class W;