Improve diagnosis of unknown template name.

When an undeclared identifier in a context that requires a type is followed by
'<', only look for type templates when typo-correcting, tweak the diagnostic
text to say that a template name (not a type name) was undeclared, and parse
the template arguments when recovering from the error.

llvm-svn: 302732

Author: zygoloid

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -8188,7 +8188,9 @@ def err_undeclared_use_suggest : Error<
   "use of undeclared %0; did you mean %1?">;
 def err_undeclared_var_use_suggest : Error<
   "use of undeclared identifier %0; did you mean %1?">;
+def err_no_template : Error<"no template named %0">;
 def err_no_template_suggest : Error<"no template named %0; did you mean %1?">;
+def err_no_member_template : Error<"no template named %0 in %1">;
 def err_no_member_template_suggest : Error<
   "no template named %0 in %1; did you mean %select{|simply }2%3?">;
 def err_non_template_in_template_id : Error<

clang/include/clang/Sema/Sema.h

@@ -1593,7 +1593,7 @@ class Sema {
                                Scope *S,
                                CXXScopeSpec *SS,
                                ParsedType &SuggestedType,
-                               bool AllowClassTemplates = false);
+                               bool IsTemplateName = false);
 
   /// Attempt to behave like MSVC in situations where lookup of an unqualified
   /// type name has failed in a dependent context. In these situations, we

clang/lib/Parse/ParseDecl.cpp

@@ -2577,9 +2577,9 @@ bool Parser::ParseImplicitInt(DeclSpec &DS, CXXScopeSpec *SS,
   // and attempt to recover.
   ParsedType T;
   IdentifierInfo *II = Tok.getIdentifierInfo();
+  bool IsTemplateName = getLangOpts().CPlusPlus && NextToken().is(tok::less);
   Actions.DiagnoseUnknownTypeName(II, Loc, getCurScope(), SS, T,
-                                  getLangOpts().CPlusPlus &&
-                                      NextToken().is(tok::less));
+                                  IsTemplateName);
   if (T) {
     // The action has suggested that the type T could be used. Set that as
     // the type in the declaration specifiers, consume the would-be type
@@ -2604,6 +2604,13 @@ bool Parser::ParseImplicitInt(DeclSpec &DS, CXXScopeSpec *SS,
   DS.SetRangeEnd(Tok.getLocation());
   ConsumeToken();
 
+  // Eat any following template arguments.
+  if (IsTemplateName) {
+    SourceLocation LAngle, RAngle;
+    TemplateArgList Args;
+    ParseTemplateIdAfterTemplateName(true, LAngle, Args, RAngle);
+  }
+
   // TODO: Could inject an invalid typedef decl in an enclosing scope to
   // avoid rippling error messages on subsequent uses of the same type,
   // could be useful if #include was forgotten.

clang/lib/Sema/SemaDecl.cpp

@@ -64,29 +64,53 @@ namespace {
 
 class TypeNameValidatorCCC : public CorrectionCandidateCallback {
  public:
-  TypeNameValidatorCCC(bool AllowInvalid, bool WantClass=false,
-                       bool AllowTemplates=false)
-      : AllowInvalidDecl(AllowInvalid), WantClassName(WantClass),
-        AllowTemplates(AllowTemplates) {
-    WantExpressionKeywords = false;
-    WantCXXNamedCasts = false;
-    WantRemainingKeywords = false;
+   TypeNameValidatorCCC(bool AllowInvalid, bool WantClass = false,
+                        bool AllowTemplates = false,
+                        bool AllowNonTemplates = true)
+       : AllowInvalidDecl(AllowInvalid), WantClassName(WantClass),
+         AllowTemplates(AllowTemplates), AllowNonTemplates(AllowNonTemplates) {
+     WantExpressionKeywords = false;
+     WantCXXNamedCasts = false;
+     WantRemainingKeywords = false;
   }
 
   bool ValidateCandidate(const TypoCorrection &candidate) override {
     if (NamedDecl *ND = candidate.getCorrectionDecl()) {
+      if (!AllowInvalidDecl && ND->isInvalidDecl())
+        return false;
+
+      if (getAsTypeTemplateDecl(ND))
+        return AllowTemplates;
+
       bool IsType = isa<TypeDecl>(ND) || isa<ObjCInterfaceDecl>(ND);
-      bool AllowedTemplate = AllowTemplates && getAsTypeTemplateDecl(ND);
-      return (IsType || AllowedTemplate) &&
-             (AllowInvalidDecl || !ND->isInvalidDecl());
+      if (!IsType)
+        return false;
+
+      if (AllowNonTemplates)
+        return true;
+
+      // An injected-class-name of a class template (specialization) is valid
+      // as a template or as a non-template.
+      if (AllowTemplates) {
+        auto *RD = dyn_cast<CXXRecordDecl>(ND);
+        if (!RD || !RD->isInjectedClassName())
+          return false;
+        RD = cast<CXXRecordDecl>(RD->getDeclContext());
+        return RD->getDescribedClassTemplate() ||
+               isa<ClassTemplateSpecializationDecl>(RD);
+      }
+
+      return false;
     }
+
     return !WantClassName && candidate.isKeyword();
   }
 
  private:
   bool AllowInvalidDecl;
   bool WantClassName;
   bool AllowTemplates;
+  bool AllowNonTemplates;
 };
 
 } // end anonymous namespace
@@ -627,7 +651,7 @@ void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
                                    Scope *S,
                                    CXXScopeSpec *SS,
                                    ParsedType &SuggestedType,
-                                   bool AllowClassTemplates) {
+                                   bool IsTemplateName) {
   // Don't report typename errors for editor placeholders.
   if (II->isEditorPlaceholder())
     return;
@@ -639,28 +663,41 @@ void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
   if (TypoCorrection Corrected =
           CorrectTypo(DeclarationNameInfo(II, IILoc), LookupOrdinaryName, S, SS,
                       llvm::make_unique<TypeNameValidatorCCC>(
-                          false, false, AllowClassTemplates),
+                          false, false, IsTemplateName, !IsTemplateName),
                       CTK_ErrorRecovery)) {
+    // FIXME: Support error recovery for the template-name case.
+    bool CanRecover = !IsTemplateName;
     if (Corrected.isKeyword()) {
       // We corrected to a keyword.
-      diagnoseTypo(Corrected, PDiag(diag::err_unknown_typename_suggest) << II);
+      diagnoseTypo(Corrected,
+                   PDiag(IsTemplateName ? diag::err_no_template_suggest
+                                        : diag::err_unknown_typename_suggest)
+                       << II);
       II = Corrected.getCorrectionAsIdentifierInfo();
     } else {
       // We found a similarly-named type or interface; suggest that.
       if (!SS || !SS->isSet()) {
         diagnoseTypo(Corrected,
-                     PDiag(diag::err_unknown_typename_suggest) << II);
+                     PDiag(IsTemplateName ? diag::err_no_template_suggest
+                                          : diag::err_unknown_typename_suggest)
+                         << II, CanRecover);
       } else if (DeclContext *DC = computeDeclContext(*SS, false)) {
         std::string CorrectedStr(Corrected.getAsString(getLangOpts()));
         bool DroppedSpecifier = Corrected.WillReplaceSpecifier() &&
                                 II->getName().equals(CorrectedStr);
         diagnoseTypo(Corrected,
-                     PDiag(diag::err_unknown_nested_typename_suggest)
-                       << II << DC << DroppedSpecifier << SS->getRange());
+                     PDiag(IsTemplateName
+                               ? diag::err_no_member_template_suggest
+                               : diag::err_unknown_nested_typename_suggest)
+                         << II << DC << DroppedSpecifier << SS->getRange(),
+                     CanRecover);
       } else {
         llvm_unreachable("could not have corrected a typo here");
       }
 
+      if (!CanRecover)
+        return;
+
       CXXScopeSpec tmpSS;
       if (Corrected.getCorrectionSpecifier())
         tmpSS.MakeTrivial(Context, Corrected.getCorrectionSpecifier(),
@@ -675,7 +712,7 @@ void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
     return;
   }
 
-  if (getLangOpts().CPlusPlus) {
+  if (getLangOpts().CPlusPlus && !IsTemplateName) {
     // See if II is a class template that the user forgot to pass arguments to.
     UnqualifiedId Name;
     Name.setIdentifier(II, IILoc);
@@ -700,10 +737,13 @@ void Sema::DiagnoseUnknownTypeName(IdentifierInfo *&II,
   // (struct, union, enum) from Parser::ParseImplicitInt here, instead?
 
   if (!SS || (!SS->isSet() && !SS->isInvalid()))
-    Diag(IILoc, diag::err_unknown_typename) << II;
+    Diag(IILoc, IsTemplateName ? diag::err_no_template
+                               : diag::err_unknown_typename)
+        << II;
   else if (DeclContext *DC = computeDeclContext(*SS, false))
-    Diag(IILoc, diag::err_typename_nested_not_found)
-      << II << DC << SS->getRange();
+    Diag(IILoc, IsTemplateName ? diag::err_no_member_template
+                               : diag::err_typename_nested_not_found)
+        << II << DC << SS->getRange();
   else if (isDependentScopeSpecifier(*SS)) {
     unsigned DiagID = diag::err_typename_missing;
     if (getLangOpts().MSVCCompat && isMicrosoftMissingTypename(SS, S))

clang/lib/Sema/SemaTemplate.cpp

@@ -515,11 +515,11 @@ void Sema::diagnoseExprIntendedAsTemplateName(Scope *S, ExprResult TemplateName,
         diagnoseTypo(Corrected,
                      PDiag(diag::err_non_template_in_member_template_id_suggest)
                          << Name << LookupCtx << DroppedSpecifier
-                         << SS.getRange());
+                         << SS.getRange(), false);
       } else {
         diagnoseTypo(Corrected,
                      PDiag(diag::err_non_template_in_template_id_suggest)
-                         << Name);
+                         << Name, false);
       }
       if (Found)
         Diag(Found->getLocation(),

clang/test/SemaCXX/invalid-member-expr.cpp

@@ -53,9 +53,7 @@ namespace test3 {
 namespace rdar11293995 {
 
 struct Length {
-  explicit Length(PassRefPtr<CalculationValue>); // expected-error {{unknown type name}} \
-                    expected-error {{expected ')'}} \
-                    expected-note {{to match this '('}}
+  explicit Length(PassRefPtr<CalculationValue>); // expected-error {{no template named 'PassRefPtr}} expected-error {{undeclared identifier 'CalculationValue'}}
 };
 
 struct LengthSize {

clang/test/SemaCXX/typo-correction.cpp

@@ -524,13 +524,16 @@ namespace shadowed_template {
 template <typename T> class Fizbin {};  // expected-note {{'::shadowed_template::Fizbin' declared here}}
 class Baz {
    int Fizbin();
-   // TODO: Teach the parser to recover from the typo correction instead of
-   // continuing to treat the template name as an implicit-int declaration.
-   Fizbin<int> qux;  // expected-error {{unknown type name 'Fizbin'; did you mean '::shadowed_template::Fizbin'?}} \
-                     // expected-error {{expected member name or ';' after declaration specifiers}}
+   Fizbin<int> qux;  // expected-error {{no template named 'Fizbin'; did you mean '::shadowed_template::Fizbin'?}}
 };
 }
 
+namespace no_correct_template_id_to_non_template {
+  struct Frobnatz {}; // expected-note {{declared here}}
+  Frobnats fn; // expected-error {{unknown type name 'Frobnats'; did you mean 'Frobnatz'?}}
+  Frobnats<int> fni; // expected-error-re {{no template named 'Frobnats'{{$}}}}
+}
+
 namespace PR18852 {
 void func() {
   struct foo {

clang/test/SemaTemplate/deduction-crash.cpp

@@ -2,7 +2,7 @@
 
 // Note that the error count below doesn't matter. We just want to
 // make sure that the parser doesn't crash.
-// CHECK: 16 errors
+// CHECK: 17 errors
 
 // PR7511
 template<a>

clang/test/SemaTemplate/explicit-instantiation.cpp

@@ -95,7 +95,7 @@ namespace PR7622 {
   struct basic_streambuf;
 
   template<typename,typename>
-  struct basic_streambuf{friend bob<>()}; // expected-error{{unknown type name 'bob'}} \
+  struct basic_streambuf{friend bob<>()}; // expected-error{{no template named 'bob'}} \
                                           // expected-error{{expected member name or ';' after declaration specifiers}}
   template struct basic_streambuf<int>;
 }

clang/test/SemaTemplate/ms-lookup-template-base-classes.cpp

@@ -347,8 +347,7 @@ template <typename T> struct B : A<T> {
 };
 template <typename T> struct C : A<T> {
   // Incorrect form.
-  NameFromBase<T> m; // expected-error {{unknown type name 'NameFromBase'}}
-  //expected-error@-1 {{expected member name or ';' after declaration specifiers}}
+  NameFromBase<T> m; // expected-error {{no template named 'NameFromBase'}}
 };
 }