Index: clangd/global-symbol-builder/GlobalSymbolBuilderMain.cpp
===================================================================
--- clangd/global-symbol-builder/GlobalSymbolBuilderMain.cpp
+++ clangd/global-symbol-builder/GlobalSymbolBuilderMain.cpp
@@ -83,6 +83,7 @@
     IndexOpts.IndexFunctionLocals = false;
     auto CollectorOpts = SymbolCollector::Options();
     CollectorOpts.FallbackDir = AssumedHeaderDir;
+    CollectorOpts.Revision = Ctx->getRevision();
     return new WrappedIndexAction(
         std::make_shared<SymbolCollector>(std::move(CollectorOpts)), IndexOpts,
         Ctx);
Index: clangd/index/Index.h
===================================================================
--- clangd/index/Index.h
+++ clangd/index/Index.h
@@ -126,6 +126,10 @@
   //     (not a definition), which is usually declared in ".h" file.
   SymbolLocation CanonicalDeclaration;
 
+  // The source control symbol's revision number from which the symbol is
+  // indexed.
+  llvm::StringRef Revision;
+
   /// A brief description of the symbol that can be displayed in the completion
   /// candidate list. For example, "Foo(X x, Y y) const" is a labal for a
   /// function.
Index: clangd/index/Index.cpp
===================================================================
--- clangd/index/Index.cpp
+++ clangd/index/Index.cpp
@@ -55,6 +55,7 @@
   Intern(S.Name);
   Intern(S.Scope);
   Intern(S.CanonicalDeclaration.FilePath);
+  Intern(S.Revision);
 
   Intern(S.CompletionLabel);
   Intern(S.CompletionFilterText);
Index: clangd/index/SymbolCollector.h
===================================================================
--- clangd/index/SymbolCollector.h
+++ clangd/index/SymbolCollector.h
@@ -34,6 +34,9 @@
     // VFS that does not have absolute path), combine the fallback directory
     // with symbols' paths to get absolute paths. This must be an absolute path.
     std::string FallbackDir;
+    // The source control symbol's revision number on which SymbolCollector
+    // runs.
+    std::string Revision;
   };
 
   SymbolCollector(Options Opts);
Index: clangd/index/SymbolCollector.cpp
===================================================================
--- clangd/index/SymbolCollector.cpp
+++ clangd/index/SymbolCollector.cpp
@@ -204,6 +204,8 @@
     std::string FilePath;
     S.CanonicalDeclaration = GetSymbolLocation(ND, SM, Opts.FallbackDir, FilePath);
 
+    S.Revision = Opts.Revision;
+
     // Add completion info.
     assert(ASTCtx && PP.get() && "ASTContext and Preprocessor must be set.");
     CodeCompletionResult SymbolCompletion(ND, 0);
Index: clangd/index/SymbolYAML.cpp
===================================================================
--- clangd/index/SymbolYAML.cpp
+++ clangd/index/SymbolYAML.cpp
@@ -97,6 +97,7 @@
     IO.mapRequired("Name", Sym.Name);
     IO.mapRequired("Scope", Sym.Scope);
     IO.mapRequired("SymInfo", Sym.SymInfo);
+    IO.mapRequired("Revision", Sym.Revision);
     IO.mapRequired("CanonicalDeclaration", Sym.CanonicalDeclaration);
     IO.mapRequired("CompletionLabel", Sym.CompletionLabel);
     IO.mapRequired("CompletionFilterText", Sym.CompletionFilterText);
Index: unittests/clangd/SymbolCollectorTests.cpp
===================================================================
--- unittests/clangd/SymbolCollectorTests.cpp
+++ unittests/clangd/SymbolCollectorTests.cpp
@@ -47,6 +47,7 @@
 }
 MATCHER_P(QName, Name, "") { return (arg.Scope + arg.Name).str() == Name; }
 MATCHER_P(CPath, P, "") { return arg.CanonicalDeclaration.FilePath == P; }
+MATCHER_P(Revision, R, "") { return arg.Revision == R; }
 MATCHER_P(LocationOffsets, Offsets, "") {
   // Offset range in SymbolLocation is [start, end] while in Clangd is [start,
   // end).
@@ -167,9 +168,11 @@
 
 TEST_F(SymbolCollectorTest, SymbolRelativeNoFallback) {
   CollectorOpts.IndexMainFiles = false;
+  CollectorOpts.Revision = "1234";
   runSymbolCollector("class Foo {};", /*Main=*/"");
   EXPECT_THAT(Symbols,
-              UnorderedElementsAre(AllOf(QName("Foo"), CPath("symbols.h"))));
+              UnorderedElementsAre(AllOf(QName("Foo"), CPath("symbols.h"),
+                                         Revision(CollectorOpts.Revision))));
 }
 
 TEST_F(SymbolCollectorTest, SymbolRelativeWithFallback) {
@@ -434,6 +437,7 @@
   StartOffset:     0
   EndOffset:       1
   FilePath:        /path/foo.h
+Revision: 1234
 CompletionLabel:    'Foo1-label'
 CompletionFilterText:    'filter'
 CompletionPlainInsertText:    'plain'
@@ -454,6 +458,7 @@
   StartOffset:     10
   EndOffset:       12
   FilePath:        /path/foo.h
+Revision: 1234
 CompletionLabel:    'Foo2-label'
 CompletionFilterText:    'filter'
 CompletionPlainInsertText:    'plain'
@@ -462,11 +467,13 @@
 )";
 
   auto Symbols1 = SymbolFromYAML(YAML1);
-  EXPECT_THAT(Symbols1, UnorderedElementsAre(
-                            AllOf(QName("clang::Foo1"), Labeled("Foo1-label"),
-                                  Doc("Foo doc"), Detail("int"))));
+  EXPECT_THAT(Symbols1,
+              UnorderedElementsAre(AllOf(QName("clang::Foo1"), Revision("1234"),
+                                         Labeled("Foo1-label"), Doc("Foo doc"),
+                                         Detail("int"))));
   auto Symbols2 = SymbolFromYAML(YAML2);
   EXPECT_THAT(Symbols2, UnorderedElementsAre(AllOf(QName("clang::Foo2"),
+                                                   Revision("1234"),
                                                    Labeled("Foo2-label"),
                                                    Not(HasDetail()))));