Allow the use of default template arguments when forming a class

template specialization (e.g., std::vector<int> would now be
well-formed, since it relies on a default argument for the Allocator
template parameter). 

This is much less interesting than one might expect, since (1) we're
not actually using the default arguments for anything important, such
as naming an actual Decl, and (2) we'll often need to instantiate the
default arguments to check their well-formedness. The real fun will
come later.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@64310 91177308-0d34-0410-b5e6-96231b3b80d8

6 files changed, 49 insertions, 3 deletions

diff --git a/include/clang/AST/DeclTemplate.h b/include/clang/AST/DeclTemplate.h
index ccbe1288f8..334a03a439 100644
--- a/include/clang/AST/DeclTemplate.h
+++ b/include/clang/AST/DeclTemplate.h
@@ -66,9 +66,19 @@ public:
 
   unsigned size() const { return NumParams; }
 
+  /// \btief Returns the minimum number of arguments needed to form a
+  /// template specialization. This may be fewer than the number of
+  /// template parameters, if some of the parameters have default
+  /// arguments.
+  unsigned getMinRequiredArguments() const;
+
   SourceLocation getTemplateLoc() const { return TemplateLoc; }
   SourceLocation getLAngleLoc() const { return LAngleLoc; }
   SourceLocation getRAngleLoc() const { return RAngleLoc; }
+
+  SourceRange getSourceRange() const {
+    return SourceRange(TemplateLoc, RAngleLoc);
+  }
 };
 
 //===----------------------------------------------------------------------===//
diff --git a/include/clang/Basic/DiagnosticSemaKinds.def b/include/clang/Basic/DiagnosticSemaKinds.def
index 4fed9443d0..25fe8254bb 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.def
+++ b/include/clang/Basic/DiagnosticSemaKinds.def
@@ -505,6 +505,8 @@ DIAG(err_template_param_default_arg_missing, ERROR,
 // C++ Template Argument Lists
 DIAG(err_template_arg_list_different_arity, ERROR,
      "%select{too few|too many}0 template arguments for %select{class template|function template|template template parameter|template}1 %2")
+DIAG(note_template_decl_here, NOTE,
+     "template is declared here")
 DIAG(err_template_arg_must_be_type, ERROR,
      "template argument for template type parameter must be a type")
 DIAG(err_template_arg_must_be_expr, ERROR,
diff --git a/lib/AST/DeclTemplate.cpp b/lib/AST/DeclTemplate.cpp
index b297dd25cb..dccb8df075 100644
--- a/lib/AST/DeclTemplate.cpp
+++ b/lib/AST/DeclTemplate.cpp
@@ -44,6 +44,26 @@ TemplateParameterList::Create(ASTContext &C, SourceLocation TemplateLoc,
                                          NumParams, RAngleLoc);
 }
 
+unsigned TemplateParameterList::getMinRequiredArguments() const {
+  unsigned NumRequiredArgs = size();
+  iterator Param = const_cast<TemplateParameterList *>(this)->end(), 
+      ParamBegin = const_cast<TemplateParameterList *>(this)->begin();
+  while (Param != ParamBegin) {
+    --Param;
+    if (!(isa<TemplateTypeParmDecl>(*Param) && 
+          cast<TemplateTypeParmDecl>(*Param)->hasDefaultArgument()) &&
+        !(isa<NonTypeTemplateParmDecl>(*Param) &&
+          cast<NonTypeTemplateParmDecl>(*Param)->hasDefaultArgument()) &&
+        !(isa<TemplateTemplateParmDecl>(*Param) &&
+          cast<TemplateTemplateParmDecl>(*Param)->hasDefaultArgument()))
+      break;
+        
+    --NumRequiredArgs;
+  }
+
+  return NumRequiredArgs;
+}
+
 //===----------------------------------------------------------------------===//
 // TemplateDecl Implementation
 //===----------------------------------------------------------------------===//
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 86f1e2017f..b4436a2c3c 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -685,7 +685,7 @@ bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
   bool Invalid = false;
 
   if (NumArgs > NumParams ||
-      NumArgs < NumParams /*FIXME: default arguments! */) {
+      NumArgs < Params->getMinRequiredArguments()) {
     // FIXME: point at either the first arg beyond what we can handle,
     // or the '>', depending on whether we have too many or too few
     // arguments.
@@ -698,7 +698,8 @@ bool Sema::CheckTemplateArgumentList(TemplateDecl *Template,
           isa<FunctionTemplateDecl>(Template)? 1 :
           isa<TemplateTemplateParmDecl>(Template)? 2 : 3)
       << Template << Range;
-
+    Diag(Template->getLocation(), diag::note_template_decl_here)
+      << Params->getSourceRange();
     Invalid = true;
   }
   
diff --git a/test/SemaTemplate/default-arguments.cpp b/test/SemaTemplate/default-arguments.cpp
new file mode 100644
index 0000000000..94976e9735
--- /dev/null
+++ b/test/SemaTemplate/default-arguments.cpp
@@ -0,0 +1,13 @@
+// RUN: clang -fsyntax-only -verify %s
+
+template<typename T, int N = 2> struct X; // expected-note{{template is declared here}}
+
+X<int, 1> *x1;
+X<int> *x2;
+
+X<> *x3; // expected-error{{too few template arguments for class template 'X'}} \
+        // FIXME: expected-error{{expected unqualified-id}}
+
+template<typename U = float, int M> struct X;
+
+X<> *x4;
diff --git a/test/SemaTemplate/temp_arg.cpp b/test/SemaTemplate/temp_arg.cpp
index 0f69b5f4b1..b8bb279caf 100644
--- a/test/SemaTemplate/temp_arg.cpp
+++ b/test/SemaTemplate/temp_arg.cpp
@@ -2,7 +2,7 @@
 template<typename T, 
          int I, 
          template<typename> class TT>
-  class A;
+  class A; // expected-note 2 {{template is declared here}}
 
 template<typename> class X;