Improve recovery for template-ids whose template-name doesn't actually

name a template, when they occur in a base-specifier. This is one of
the (few) places where we know for sure that an identifier followed by
a '<' must be a template name, so we can diagnose and recover well:

test/SemaTemplate/dependent-base-classes.cpp:9:16: error: missing
'template'
      keyword prior to dependent template name 'T::apply'
struct X1 : T::apply<U> { }; // expected-error{{missing 'template' ...
               ^
               template 
test/SemaTemplate/dependent-base-classes.cpp:12:13: error: unknown
template name
      'vector'
struct X2 : vector<T> { }; // expected-error{{unknown template name
'vector'}}
            ^
2 diagnostics generated.

llvm-svn: 93257

3 files changed, 77 insertions, 6 deletions

diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 61a494193c7..90040c54bfb 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -490,18 +490,57 @@ Parser::TypeResult Parser::ParseClassName(SourceLocation &EndLocation,
     return true;
   }
 
+  IdentifierInfo *Id = Tok.getIdentifierInfo();
+  SourceLocation IdLoc = ConsumeToken();
+
+  if (Tok.is(tok::less)) {
+    // It looks the user intended to write a template-id here, but the
+    // template-name was wrong. Try to fix that.
+    TemplateNameKind TNK = TNK_Type_template;
+    TemplateTy Template;
+    if (!Actions.DiagnoseUnknownTemplateName(*Id, IdLoc, CurScope,
+                                             SS, Template, TNK)) {
+      Diag(IdLoc, diag::err_unknown_template_name)
+        << Id;
+    }
+    
+    if (!Template)
+      return true;
+
+    // Form the template name 
+    UnqualifiedId TemplateName;
+    TemplateName.setIdentifier(Id, IdLoc);
+    
+    // Parse the full template-id, then turn it into a type.
+    if (AnnotateTemplateIdToken(Template, TNK, SS, TemplateName,
+                                SourceLocation(), true))
+      return true;
+    if (TNK == TNK_Dependent_template_name)
+      AnnotateTemplateIdTokenAsType(SS);
+    
+    // If we didn't end up with a typename token, there's nothing more we
+    // can do.
+    if (Tok.isNot(tok::annot_typename))
+      return true;
+    
+    // Retrieve the type from the annotation token, consume that token, and
+    // return.
+    EndLocation = Tok.getAnnotationEndLoc();
+    TypeTy *Type = Tok.getAnnotationValue();
+    ConsumeToken();
+    return Type;
+  }
+
   // We have an identifier; check whether it is actually a type.
-  TypeTy *Type = Actions.getTypeName(*Tok.getIdentifierInfo(),
-                                     Tok.getLocation(), CurScope, SS,
-                                     true);
-  if (!Type) {
-    Diag(Tok, DestrExpected ? diag::err_destructor_class_name
+  TypeTy *Type = Actions.getTypeName(*Id, IdLoc, CurScope, SS, true);
+  if (!Type) {    
+    Diag(IdLoc, DestrExpected ? diag::err_destructor_class_name
                             : diag::err_expected_class_name);
     return true;
   }
 
   // Consume the identifier.
-  EndLocation = ConsumeToken();
+  EndLocation = IdLoc;
   return Type;
 }
 
diff --git a/clang/lib/Sema/Sema.h b/clang/lib/Sema/Sema.h
index d46bfc6cffd..d06cecc4678 100644
--- a/clang/lib/Sema/Sema.h
+++ b/clang/lib/Sema/Sema.h
@@ -2367,6 +2367,14 @@ public:
                                           TypeTy *ObjectType,
                                           bool EnteringContext,
                                           TemplateTy &Template);
+  
+  virtual bool DiagnoseUnknownTemplateName(const IdentifierInfo &II, 
+                                           SourceLocation IILoc,
+                                           Scope *S,
+                                           const CXXScopeSpec *SS,
+                                           TemplateTy &SuggestedTemplate,
+                                           TemplateNameKind &SuggestedKind);
+    
   bool DiagnoseTemplateParameterShadow(SourceLocation Loc, Decl *PrevDecl);
   TemplateDecl *AdjustDeclIfTemplate(DeclPtrTy &Decl);
 
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index d11bf3c0645..e75277e823e 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -143,6 +143,30 @@ TemplateNameKind Sema::isTemplateName(Scope *S,
   return TemplateKind;
 }
 
+bool Sema::DiagnoseUnknownTemplateName(const IdentifierInfo &II, 
+                                       SourceLocation IILoc,
+                                       Scope *S,
+                                       const CXXScopeSpec *SS,
+                                       TemplateTy &SuggestedTemplate,
+                                       TemplateNameKind &SuggestedKind) {
+  // We can't recover unless there's a dependent scope specifier preceding the
+  // template name.
+  if (!SS || !SS->isSet() || !isDependentScopeSpecifier(*SS) ||
+      computeDeclContext(*SS))
+    return false;
+  
+  // The code is missing a 'template' keyword prior to the dependent template
+  // name.
+  NestedNameSpecifier *Qualifier = (NestedNameSpecifier*)SS->getScopeRep();
+  Diag(IILoc, diag::err_template_kw_missing)
+    << Qualifier << II.getName()
+    << CodeModificationHint::CreateInsertion(IILoc, "template ");
+  SuggestedTemplate 
+    = TemplateTy::make(Context.getDependentTemplateName(Qualifier, &II));
+  SuggestedKind = TNK_Dependent_template_name;
+  return true;
+}
+
 void Sema::LookupTemplateName(LookupResult &Found,
                               Scope *S, const CXXScopeSpec &SS,
                               QualType ObjectType,