[clangd] Heuristic resolution for dependent type and template names

Fixes https://github.com/clangd/clangd/issues/543

Differential Revision: https://reviews.llvm.org/D88469

clang-tools-extra/clangd/FindTarget.cpp

@@ -125,6 +125,10 @@ const auto StaticFilter = [](const NamedDecl *D) {
   return !D->isCXXInstanceMember();
 };
 const auto ValueFilter = [](const NamedDecl *D) { return isa<ValueDecl>(D); };
+const auto TypeFilter = [](const NamedDecl *D) { return isa<TypeDecl>(D); };
+const auto TemplateFilter = [](const NamedDecl *D) {
+  return isa<TemplateDecl>(D);
+};
 
 // Given the type T of a dependent expression that appears of the LHS of a
 // "->", heuristically find a corresponding pointee type in whose scope we
@@ -219,19 +223,45 @@ std::vector<const NamedDecl *> resolveExprToDecls(const Expr *E) {
   return {};
 }
 
-// Try to heuristically resolve the type of a possibly-dependent expression `E`.
-const Type *resolveExprToType(const Expr *E) {
-  std::vector<const NamedDecl *> Decls = resolveExprToDecls(E);
+const Type *resolveDeclsToType(const std::vector<const NamedDecl *> &Decls) {
   if (Decls.size() != 1) // Names an overload set -- just bail.
     return nullptr;
   if (const auto *TD = dyn_cast<TypeDecl>(Decls[0])) {
     return TD->getTypeForDecl();
-  } else if (const auto *VD = dyn_cast<ValueDecl>(Decls[0])) {
+  }
+  if (const auto *VD = dyn_cast<ValueDecl>(Decls[0])) {
     return VD->getType().getTypePtrOrNull();
   }
   return nullptr;
 }
 
+// Try to heuristically resolve the type of a possibly-dependent expression `E`.
+const Type *resolveExprToType(const Expr *E) {
+  return resolveDeclsToType(resolveExprToDecls(E));
+}
+
+// Try to heuristically resolve the type of a possibly-dependent nested name
+// specifier.
+const Type *resolveNestedNameSpecifierToType(const NestedNameSpecifier *NNS) {
+  if (!NNS)
+    return nullptr;
+
+  switch (NNS->getKind()) {
+  case NestedNameSpecifier::TypeSpec:
+  case NestedNameSpecifier::TypeSpecWithTemplate:
+    return NNS->getAsType();
+  case NestedNameSpecifier::Identifier: {
+    return resolveDeclsToType(getMembersReferencedViaDependentName(
+        resolveNestedNameSpecifierToType(NNS->getPrefix()),
+        [&](const ASTContext &) { return NNS->getAsIdentifier(); },
+        TypeFilter));
+  }
+  default:
+    break;
+  }
+  return nullptr;
+}
+
 const NamedDecl *getTemplatePattern(const NamedDecl *D) {
   if (const CXXRecordDecl *CRD = dyn_cast<CXXRecordDecl>(D)) {
     if (const auto *Result = CRD->getTemplateInstantiationPattern())
@@ -291,10 +321,8 @@ const NamedDecl *getTemplatePattern(const NamedDecl *D) {
 //    and both are lossy. We must know upfront what the caller ultimately wants.
 //
 // FIXME: improve common dependent scope using name lookup in primary templates.
-// We currently handle DependentScopeDeclRefExpr and
-// CXXDependentScopeMemberExpr, but some other constructs remain to be handled:
-//  - DependentTemplateSpecializationType,
-//  - DependentNameType
+// We currently handle several dependent constructs, but some others remain to
+// be handled:
 //  - UnresolvedUsingTypenameDecl
 struct TargetFinder {
   using RelSet = DeclRelationSet;
@@ -536,6 +564,23 @@ public:
         if (auto *TD = DTST->getTemplateName().getAsTemplateDecl())
           Outer.add(TD->getTemplatedDecl(), Flags | Rel::TemplatePattern);
       }
+      void VisitDependentNameType(const DependentNameType *DNT) {
+        for (const NamedDecl *ND : getMembersReferencedViaDependentName(
+                 resolveNestedNameSpecifierToType(DNT->getQualifier()),
+                 [DNT](ASTContext &) { return DNT->getIdentifier(); },
+                 TypeFilter)) {
+          Outer.add(ND, Flags);
+        }
+      }
+      void VisitDependentTemplateSpecializationType(
+          const DependentTemplateSpecializationType *DTST) {
+        for (const NamedDecl *ND : getMembersReferencedViaDependentName(
+                 resolveNestedNameSpecifierToType(DTST->getQualifier()),
+                 [DTST](ASTContext &) { return DTST->getIdentifier(); },
+                 TemplateFilter)) {
+          Outer.add(ND, Flags);
+        }
+      }
       void VisitTypedefType(const TypedefType *TT) {
         Outer.add(TT->getDecl(), Flags);
       }
@@ -591,17 +636,16 @@ public:
       return;
     debug(*NNS, Flags);
     switch (NNS->getKind()) {
-    case NestedNameSpecifier::Identifier:
-      return;
     case NestedNameSpecifier::Namespace:
       add(NNS->getAsNamespace(), Flags);
       return;
     case NestedNameSpecifier::NamespaceAlias:
       add(NNS->getAsNamespaceAlias(), Flags);
       return;
+    case NestedNameSpecifier::Identifier:
     case NestedNameSpecifier::TypeSpec:
     case NestedNameSpecifier::TypeSpecWithTemplate:
-      add(QualType(NNS->getAsType(), 0), Flags);
+      add(QualType(resolveNestedNameSpecifierToType(NNS), 0), Flags);
       return;
     case NestedNameSpecifier::Global:
       // This should be TUDecl, but we can't get a pointer to it!

clang-tools-extra/clangd/unittests/FindTargetTests.cpp

@@ -728,6 +728,54 @@ TEST_F(TargetDeclTest, DependentExprs) {
                "template <typename T> T convert() const");
 }
 
+TEST_F(TargetDeclTest, DependentTypes) {
+  Flags = {"-fno-delayed-template-parsing"};
+
+  // Heuristic resolution of dependent type name
+  Code = R"cpp(
+        template <typename>
+        struct A { struct B {}; };
+
+        template <typename T>
+        void foo(typename A<T>::[[B]]);
+      )cpp";
+  EXPECT_DECLS("DependentNameTypeLoc", "struct B");
+
+  // Heuristic resolution of dependent type name which doesn't get a TypeLoc
+  Code = R"cpp(
+        template <typename>
+        struct A { struct B { struct C {}; }; };
+
+        template <typename T>
+        void foo(typename A<T>::[[B]]::C);
+      )cpp";
+  EXPECT_DECLS("NestedNameSpecifierLoc", "struct B");
+
+  // Heuristic resolution of dependent type name whose qualifier is also
+  // dependent
+  Code = R"cpp(
+        template <typename>
+        struct A { struct B { struct C {}; }; };
+
+        template <typename T>
+        void foo(typename A<T>::B::[[C]]);
+      )cpp";
+  EXPECT_DECLS("DependentNameTypeLoc", "struct C");
+
+  // Heuristic resolution of dependent template name
+  Code = R"cpp(
+        template <typename>
+        struct A {
+          template <typename> struct B {};
+        };
+
+        template <typename T>
+        void foo(typename A<T>::template [[B]]<int>);
+      )cpp";
+  EXPECT_DECLS("DependentTemplateSpecializationTypeLoc",
+               "template <typename> struct B");
+}
+
 TEST_F(TargetDeclTest, ObjC) {
   Flags = {"-xobjective-c"};
   Code = R"cpp(