Fix pointless warnings 330 for empty template instantiations

Appearing recently since 8c8e27d246.
Fixes warnings in test cases:
complextest, li_std_pair_extra, std_containers, template_nested_typemaps

Also attempts to instantiate a template for an unsupported nested template class
now have a separate new warning number 331 (SWIGWARN_PARSE_TEMPLATE_NESTED).

Closes #2965

Doc/Manual/Warnings.html

@@ -415,7 +415,8 @@ example.i(4) : Syntax error in input(1).
 <li>327. Extern template ignored.
 <li>328. Value assigned to <em>name</em> not used due to limited parsing implementation.
 <li>329. Using declaration '<em>name</em>' for inheriting constructors uses base '<em>name</em>' which is not an immediate base of '<em>name</em>'.
-<li>330. Template forward class instantiation '<em>templ</em>' with name '<em>name</em>' is ineffective.
+<li>330. Template forward class '<em>name</em>' cannot be used to instantiate a full template class with name '<em>name</em>'.
+<li>331. Unsupported template nested class '<em>name</em>' cannot be used to instantiate a full template class with name '<em>name</em>'.
 <li>340. Lambda expressions and closures are not fully supported yet.
 <li>344. Unable to deduce decltype for '<em>expr</em>'.
 <li>345. Unable to deduce auto return type for '<em>name</em>' (ignored).

Examples/test-suite/errors/cpp_nested_class_template.i

@@ -0,0 +1,15 @@
+%module xxx
+
+namespace ns {
+  class OuterClass {
+  public:
+    template <class T> struct Inner1 {
+    };
+    Inner1<int> useInner1(const Inner1<int>& inner) { return inner; }
+
+#ifdef SWIG
+    %template(T_OuterClassInner1Double) Inner1<double>;
+#endif
+    int iii;
+  };
+}

Examples/test-suite/errors/cpp_nested_class_template.stderr

@@ -0,0 +1,2 @@
+cpp_nested_class_template.i:7: Warning 325: Nested struct not currently supported (Inner1 ignored)
+cpp_nested_class_template.i:11: Warning 331: Unsupported template nested class 'ns::OuterClass::Inner1< double >' cannot be used to instantiate a full template class with name 'T_OuterClassInner1Double'.

Examples/test-suite/errors/cpp_template_forward.stderr

@@ -1,4 +1,4 @@
-cpp_template_forward.i:6: Warning 330: Template forward class instantiation 'Space::ForwardDeclaredTemplate< double >' with name 'ForwardDeclaredTemplate_double' is ineffective.
-cpp_template_forward.i:9: Warning 330: Template forward class instantiation 'Space::ForwardDeclaredSpecialized< int >' with name 'ForwardDeclaredTemplate_int' is ineffective.
-cpp_template_forward.i:10: Warning 330: Template forward class instantiation 'Space::ForwardDeclaredSpecialized< double >' with name 'ForwardDeclaredTemplate_double' is ineffective.
-cpp_template_forward.i:16: Warning 330: Template forward class instantiation 'Space::ForwardDeclaredMisplacedPrimary< double >' with name 'ForwardDeclaredTemplate_double' is ineffective.
+cpp_template_forward.i:6: Warning 330: Template forward class 'Space::ForwardDeclaredTemplate< double >' cannot be used to instantiate a full template class with name 'ForwardDeclaredTemplate_double'.
+cpp_template_forward.i:9: Warning 330: Template forward class 'Space::ForwardDeclaredSpecialized< int >' cannot be used to instantiate a full template class with name 'ForwardDeclaredTemplate_int'.
+cpp_template_forward.i:10: Warning 330: Template forward class 'Space::ForwardDeclaredSpecialized< double >' cannot be used to instantiate a full template class with name 'ForwardDeclaredTemplate_double'.
+cpp_template_forward.i:16: Warning 330: Template forward class 'Space::ForwardDeclaredMisplacedPrimary< double >' cannot be used to instantiate a full template class with name 'ForwardDeclaredTemplate_double'.

Examples/test-suite/template_nested.i

@@ -4,6 +4,8 @@
 
 #if !defined(SWIGCSHARP) && !defined(SWIGJAVA)
 #pragma SWIG nowarn=SWIGWARN_PARSE_NAMED_NESTED_CLASS
+%warnfilter(SWIGWARN_PARSE_TEMPLATE_NESTED) ns::OuterClass::Inner1;
+%warnfilter(SWIGWARN_PARSE_TEMPLATE_NESTED) ns::OuterClass::Inner2;
 #endif
 
 namespace ns {

Source/CParse/parser.y

@@ -1242,6 +1242,7 @@ static Node *nested_forward_declaration(const String *storage, const String *kin
     Setattr(n, "name", sname);
     Setattr(n, "storage", storage);
     Setattr(n, "sym:weak", "1");
+    SetFlag(n, "nested:forward");
     add_symbols(n);
     nn = n;
   }
@@ -2960,10 +2961,13 @@ template_directive: SWIGTEMPLATE LPAREN idstringopt RPAREN idcolonnt LESSTHAN va
 			  }
                           add_symbols_copy(templnode);
 
-			  if (Equal(nodeType(templnode), "classforward")) {
+			  if (Equal(nodeType(templnode), "classforward") && !(GetFlag(templnode, "feature:ignore") || GetFlag(templnode, "hidden"))) {
 			    SWIG_WARN_NODE_BEGIN(templnode);
 			    /* A full template class definition is required in order to wrap a template class as a proxy class so this %template is ineffective. */
-			    Swig_warning(WARN_PARSE_TEMPLATE_FORWARD, cparse_file, cparse_line, "Template forward class instantiation '%s' with name '%s' is ineffective.\n", Swig_name_decl(templnode), Getattr(templnode, "sym:name"));
+			    if (GetFlag(templnode, "nested:forward"))
+			      Swig_warning(WARN_PARSE_TEMPLATE_NESTED, cparse_file, cparse_line, "Unsupported template nested class '%s' cannot be used to instantiate a full template class with name '%s'.\n", Swig_name_decl(templnode), Getattr(templnode, "sym:name"));
+			    else
+			      Swig_warning(WARN_PARSE_TEMPLATE_FORWARD, cparse_file, cparse_line, "Template forward class '%s' cannot be used to instantiate a full template class with name '%s'.\n", Swig_name_decl(templnode), Getattr(templnode, "sym:name"));
 			    SWIG_WARN_NODE_END(templnode);
 			  }
 

Source/Include/swigwarn.h

@@ -97,6 +97,7 @@
 #define WARN_PARSE_ASSIGNED_VALUE     328
 #define WARN_PARSE_USING_CONSTRUCTOR  329
 #define WARN_PARSE_TEMPLATE_FORWARD   330
+#define WARN_PARSE_TEMPLATE_NESTED    331
 
 #define WARN_CPP11_LAMBDA             340
 /* Unused since 3.0.11: #define WARN_CPP11_ALIAS_DECLARATION  341 */