[clangd] Collect the number of files referencing a symbol in the static index.

Summary:
This is an important ranking signal.
It's off for the dynamic index for now. Correspondingly, tell the index
infrastructure only to report declarations for the dynamic index.

Reviewers: ioeric, hokein

Subscribers: klimek, ilya-biryukov, jkorous-apple, cfe-commits

Differential Revision: https://reviews.llvm.org/D44315

2 files changed, 30 insertions, 1 deletions

diff --git a/clang-tools-extra/unittests/clangd/IndexTests.cpp b/clang-tools-extra/unittests/clangd/IndexTests.cpp
index 20eb4527d9f..5e5ddbfb86e 100644
--- a/clang-tools-extra/unittests/clangd/IndexTests.cpp
+++ b/clang-tools-extra/unittests/clangd/IndexTests.cpp
@@ -225,6 +225,8 @@ TEST(MergeTest, Merge) {
   L.Name = R.Name = "Foo";                    // same in both
   L.CanonicalDeclaration.FileURI = "file:///left.h"; // differs
   R.CanonicalDeclaration.FileURI = "file:///right.h";
+  L.References = 1;
+  R.References = 2;
   L.CompletionPlainInsertText = "f00";        // present in left only
   R.CompletionSnippetInsertText = "f0{$1:0}"; // present in right only
   Symbol::Details DetL, DetR;
@@ -238,6 +240,7 @@ TEST(MergeTest, Merge) {
   Symbol M = mergeSymbol(L, R, &Scratch);
   EXPECT_EQ(M.Name, "Foo");
   EXPECT_EQ(M.CanonicalDeclaration.FileURI, "file:///left.h");
+  EXPECT_EQ(M.References, 3u);
   EXPECT_EQ(M.CompletionPlainInsertText, "f00");
   EXPECT_EQ(M.CompletionSnippetInsertText, "f0{$1:0}");
   ASSERT_TRUE(M.Detail);
diff --git a/clang-tools-extra/unittests/clangd/SymbolCollectorTests.cpp b/clang-tools-extra/unittests/clangd/SymbolCollectorTests.cpp
index c6a155a4a36..76eace528f4 100644
--- a/clang-tools-extra/unittests/clangd/SymbolCollectorTests.cpp
+++ b/clang-tools-extra/unittests/clangd/SymbolCollectorTests.cpp
@@ -59,6 +59,7 @@ MATCHER_P(DefRange, Offsets, "") {
   return arg.Definition.StartOffset == Offsets.first &&
          arg.Definition.EndOffset == Offsets.second;
 }
+MATCHER_P(Refs, R, "") { return int(arg.References) == R; }
 
 namespace clang {
 namespace clangd {
@@ -201,7 +202,7 @@ TEST_F(SymbolCollectorTest, CollectSymbols) {
 TEST_F(SymbolCollectorTest, Template) {
   Annotations Header(R"(
     // Template is indexed, specialization and instantiation is not.
-    template <class T> struct [[Tmpl]] {T x = 0};
+    template <class T> struct [[Tmpl]] {T x = 0;};
     template <> struct Tmpl<int> {};
     extern template struct Tmpl<float>;
     template struct Tmpl<double>;
@@ -242,6 +243,31 @@ TEST_F(SymbolCollectorTest, Locations) {
           AllOf(QName("Z"), DeclRange(Header.offsetRange("zdecl")))));
 }
 
+TEST_F(SymbolCollectorTest, References) {
+  const std::string Header = R"(
+    class W;
+    class X {};
+    class Y;
+    class Z {}; // not used anywhere
+    Y* y = nullptr;  // used in header doesn't count
+  )";
+  const std::string Main = R"(
+    W* w = nullptr;
+    W* w2 = nullptr; // only one usage counts
+    X x();
+    class V;
+    V* v = nullptr; // Used, but not eligible for indexing.
+    class Y{}; // definition doesn't count as a reference
+  )";
+  CollectorOpts.CountReferences = true;
+  runSymbolCollector(Header, Main);
+  EXPECT_THAT(Symbols,
+              UnorderedElementsAre(AllOf(QName("W"), Refs(1)),
+                                   AllOf(QName("X"), Refs(1)),
+                                   AllOf(QName("Y"), Refs(0)),
+                                   AllOf(QName("Z"), Refs(0)), QName("y")));
+}
+
 TEST_F(SymbolCollectorTest, SymbolRelativeNoFallback) {
   runSymbolCollector("class Foo {};", /*Main=*/"");
   EXPECT_THAT(Symbols, UnorderedElementsAre(