Don't claim template names that name non-templates are undeclared.

Author: zygoloid

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -4916,7 +4916,8 @@ def note_using_value_decl_missing_typename : Note<
   "add 'typename' to treat this using declaration as a type">;
 
 def err_template_kw_refers_to_non_template : Error<
-  "%0 following the 'template' keyword does not refer to a template">;
+  "%0%select{| following the 'template' keyword}1 "
+  "does not refer to a template">;
 def note_template_kw_refers_to_non_template : Note<
   "declared as a non-template here">;
 def err_template_kw_refers_to_dependent_non_template : Error<

clang/include/clang/Sema/Sema.h

@@ -6999,6 +6999,27 @@ class Sema final {
                                    bool AllowFunctionTemplates = true,
                                    bool AllowDependent = true);
 
+  enum TemplateNameIsRequiredTag { TemplateNameIsRequired };
+  /// Whether and why a template name is required in this lookup.
+  class RequiredTemplateKind {
+  public:
+    /// Template name is required if TemplateKWLoc is valid.
+    RequiredTemplateKind(SourceLocation TemplateKWLoc = SourceLocation())
+        : TemplateKW(TemplateKWLoc) {}
+    /// Template name is unconditionally required.
+    RequiredTemplateKind(TemplateNameIsRequiredTag) : TemplateKW() {}
+
+    SourceLocation getTemplateKeywordLoc() const {
+      return TemplateKW.getValueOr(SourceLocation());
+    }
+    bool hasTemplateKeyword() const { return getTemplateKeywordLoc().isValid(); }
+    bool isRequired() const { return TemplateKW != SourceLocation(); }
+    explicit operator bool() const { return isRequired(); }
+
+  private:
+    llvm::Optional<SourceLocation> TemplateKW;
+  };
+
   enum class AssumedTemplateKind {
     /// This is not assumed to be a template name.
     None,
@@ -7008,12 +7029,11 @@ class Sema final {
     /// functions (but no function templates).
     FoundFunctions,
   };
-  bool LookupTemplateName(LookupResult &R, Scope *S, CXXScopeSpec &SS,
-                          QualType ObjectType, bool EnteringContext,
-                          bool &MemberOfUnknownSpecialization,
-                          SourceLocation TemplateKWLoc = SourceLocation(),
-                          AssumedTemplateKind *ATK = nullptr,
-                          bool Disambiguation = false);
+  bool LookupTemplateName(
+      LookupResult &R, Scope *S, CXXScopeSpec &SS, QualType ObjectType,
+      bool EnteringContext, bool &MemberOfUnknownSpecialization,
+      RequiredTemplateKind RequiredTemplate = SourceLocation(),
+      AssumedTemplateKind *ATK = nullptr, bool AllowTypoCorrection = true);
 
   TemplateNameKind isTemplateName(Scope *S,
                                   CXXScopeSpec &SS,

clang/lib/Sema/SemaTemplate.cpp

@@ -205,7 +205,8 @@ TemplateNameKind Sema::isTemplateName(Scope *S,
   LookupResult R(*this, TName, Name.getBeginLoc(), LookupOrdinaryName);
   if (LookupTemplateName(R, S, SS, ObjectType, EnteringContext,
                          MemberOfUnknownSpecialization, SourceLocation(),
-                         &AssumedTemplate, Disambiguation))
+                         &AssumedTemplate,
+                         /*AllowTypoCorrection=*/!Disambiguation))
     return TNK_Non_template;
 
   if (AssumedTemplate != AssumedTemplateKind::None) {
@@ -371,9 +372,9 @@ bool Sema::LookupTemplateName(LookupResult &Found,
                               QualType ObjectType,
                               bool EnteringContext,
                               bool &MemberOfUnknownSpecialization,
-                              SourceLocation TemplateKWLoc,
+                              RequiredTemplateKind RequiredTemplate,
                               AssumedTemplateKind *ATK,
-                              bool Disambiguation) {
+                              bool AllowTypoCorrection) {
   if (ATK)
     *ATK = AssumedTemplateKind::None;
 
@@ -473,7 +474,8 @@ bool Sema::LookupTemplateName(LookupResult &Found,
   if (Found.isAmbiguous())
     return false;
 
-  if (ATK && SS.isEmpty() && ObjectType.isNull() && TemplateKWLoc.isInvalid()) {
+  if (ATK && SS.isEmpty() && ObjectType.isNull() &&
+      !RequiredTemplate.hasTemplateKeyword()) {
     // C++2a [temp.names]p2:
     //   A name is also considered to refer to a template if it is an
     //   unqualified-id followed by a < and name lookup finds either one or more
@@ -499,7 +501,7 @@ bool Sema::LookupTemplateName(LookupResult &Found,
     }
   }
 
-  if (Found.empty() && !IsDependent && !Disambiguation) {
+  if (Found.empty() && !IsDependent && AllowTypoCorrection) {
     // If we did not find any names, and this is not a disambiguation, attempt
     // to correct any typos.
     DeclarationName Name = Found.getLookupName();
@@ -545,9 +547,11 @@ bool Sema::LookupTemplateName(LookupResult &Found,
 
     // If a 'template' keyword was used, a lookup that finds only non-template
     // names is an error.
-    if (ExampleLookupResult && TemplateKWLoc.isValid()) {
+    if (ExampleLookupResult && RequiredTemplate) {
       Diag(Found.getNameLoc(), diag::err_template_kw_refers_to_non_template)
-        << Found.getLookupName() << SS.getRange();
+          << Found.getLookupName() << SS.getRange()
+          << RequiredTemplate.hasTemplateKeyword()
+          << RequiredTemplate.getTemplateKeywordLoc();
       Diag(ExampleLookupResult->getUnderlyingDecl()->getLocation(),
            diag::note_template_kw_refers_to_non_template)
           << Found.getLookupName();
@@ -4722,10 +4726,14 @@ TemplateNameKind Sema::ActOnTemplateName(Scope *S,
     LookupResult R(*this, DNI.getName(), Name.getBeginLoc(),
                    LookupOrdinaryName);
     bool MOUS;
-    // FIXME: If LookupTemplateName fails here, we'll have produced its
-    // diagnostics twice.
-    if (!LookupTemplateName(R, S, SS, ObjectType.get(), EnteringContext,
-                            MOUS, TemplateKWLoc) && !R.isAmbiguous()) {
+    // Tell LookupTemplateName that we require a template so that it diagnoses
+    // cases where it finds a non-template.
+    RequiredTemplateKind RTK = TemplateKWLoc.isValid()
+                                   ? RequiredTemplateKind(TemplateKWLoc)
+                                   : TemplateNameIsRequired;
+    if (!LookupTemplateName(R, S, SS, ObjectType.get(), EnteringContext, MOUS,
+                            RTK, nullptr, /*AllowTypoCorrection=*/false) &&
+        !R.isAmbiguous()) {
       if (LookupCtx)
         Diag(Name.getBeginLoc(), diag::err_no_member)
             << DNI.getName() << LookupCtx << SS.getRange();

clang/test/SemaCXX/pseudo-destructors.cpp

@@ -169,4 +169,17 @@ namespace TwoPhaseLookup {
     void h3(N::G<int> *p) { p->~G<int>(); }
     void h4(N::G<int> *p) { f(p); }
   }
+
+  namespace TemplateNamesNonTemplate {
+    int A; // expected-note 2{{non-template here}}
+    template<typename> int B; // expected-note 2{{variable template 'B' declared here}} expected-warning {{extension}}
+    using C = int; // expected-note 2{{non-template here}}
+
+    template<typename T> void f1(int *p) { p->~A<int>(); } // expected-error {{'A' does not refer to a template}}
+    template<typename T> void f2(int *p) { p->~B<int>(); } // expected-error {{template name refers to non-type template 'B'}}
+    template<typename T> void f3(int *p) { p->~C<int>(); } // expected-error {{'C' does not refer to a template}}
+    template<typename T> void f4(int *p) { p->TemplateNamesNonTemplate::C::~A<int>(); } // expected-error {{'A' does not refer to a template}}
+    template<typename T> void f5(int *p) { p->TemplateNamesNonTemplate::C::~B<int>(); } // expected-error {{template name refers to non-type template 'TemplateNamesNonTemplate::B'}}
+    template<typename T> void f6(int *p) { p->TemplateNamesNonTemplate::C::~C<int>(); } // expected-error {{'C' does not refer to a template}}
+  }
 }