[clangd] Don't index template specializations.

[sammccall]

Summary

These have different USRs than the underlying entity, but are not typically
interesting in their own right and can be numerous (e.g. generated traits).

[sammccall]

merge matchers

[sammccall]

verify that we don't emit extra symbols in other template-related cases

[ioeric]

lgtm

unittests/clangd/SymbolCollectorTests.cpp

200

nit: I'd probably also check the range, just in case...

clangd/index/SymbolCollector.cpp

if (ND->isInAnonymousNamespace())
     return true;
 
   // We only want:
   //   * symbols in namespaces or translation unit scopes (e.g. no class
   //     members)
   //   * enum constants in unscoped enum decl (e.g. "red" in "enum {red};")
   auto InTopLevelScope = hasDeclContext(
       anyOf(namespaceDecl(), translationUnitDecl(), linkageSpecDecl()));
+  // Don't index template specializations.
+  auto IsSpecialization =
+      anyOf(functionDecl(isExplicitTemplateSpecialization()),
+            cxxRecordDecl(isExplicitTemplateSpecialization()),
+            varDecl(isExplicitTemplateSpecialization()));
   if (match(decl(allOf(unless(isExpansionInMainFile()),
                        anyOf(InTopLevelScope,
                              hasDeclContext(enumDecl(InTopLevelScope,
-                                                     unless(isScoped())))))),
+                                                     unless(isScoped())))),
+                       unless(IsSpecialization))),
             *ND, *ASTCtx)
           .empty())
     return true;
 
   return false;
 }
 
 // We only collect #include paths for symbols that are suitable for global code

unittests/clangd/SymbolCollectorTests.cpp

const std::string Header = R"(
     class Foo {
       void f();
     };
     void f1();
     inline void f2() {}
     static const int KInt = 2;
     const char* kStr = "123";
 
+    // Template is indexed, specialization is not.
+    template <class T> struct Tmpl;
+    template <> struct Tmpl<int> {};
+
     namespace {
     void ff() {} // ignore
     }
 
     void f1() {}
 
     namespace foo {
     // Type alias
const std::string Header = R"(
 
     // FIXME: using declaration is not supported as the IndexAction will ignore
     // implicit declarations (the implicit using shadow declaration) by default,
     // and there is no way to customize this behavior at the moment.
     using bar::v2;
     } // namespace foo
   )";
   runSymbolCollector(Header, /*Main=*/"");
-  EXPECT_THAT(Symbols,
-              UnorderedElementsAreArray(
-                  {QName("Foo"), QName("f1"), QName("f2"), QName("KInt"),
-                   QName("kStr"), QName("foo"), QName("foo::bar"),
-                   QName("foo::int32"), QName("foo::int32_t"), QName("foo::v1"),
-                   QName("foo::bar::v2"), QName("foo::baz")}));
+  EXPECT_THAT(
+      Symbols,
+          {QName("Foo"), QName("f1"), QName("f2"), QName("KInt"), QName("Tmpl"),
+           QName("kStr"), QName("foo"), QName("foo::bar"), QName("foo::int32"),
+           QName("foo::int32_t"), QName("foo::v1"), QName("foo::bar::v2"),
+           QName("foo::baz")}));
 }
 
 TEST_F(SymbolCollectorTest, Locations) {
   Annotations Header(R"cpp(
     // Declared in header, defined in main.
     extern int $xdecl[[X]];
     class $clsdecl[[Cls]];
     void $printdecl[[print]]();