Add warning for ineffective %template instantiations

on forward template class declarations. A full template class definition is
required in order to wrap a template class as a proxy class.

Also tidyup handling of classforward code (no observable changes in
test-suite).

Doc/Manual/Warnings.html

@@ -415,6 +415,7 @@ 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>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_invalid_template.i

@@ -7,3 +7,8 @@ namespace UUU {
 }
 
 %template(xxx) UUU::JJJ<int>;
+
+%template(TTT_int) VVV::TTT<int>; // needs to be after template is parsed
+namespace VVV {
+  template<typename T> struct TTT {};
+}

Examples/test-suite/errors/cpp_invalid_template.stderr

@@ -1,2 +1,3 @@
 cpp_invalid_template.i:3: Error: Template 'SSS::AAA' undefined.
 cpp_invalid_template.i:9: Error: 'JJJ' is not defined as a template. (classforward)
+cpp_invalid_template.i:11: Error: Template 'VVV::TTT' undefined.

Examples/test-suite/errors/cpp_template_forward.i

@@ -0,0 +1,20 @@
+%module xxx
+
+
+namespace Space {
+  template <typename T> struct ForwardDeclaredTemplate;
+  %template(ForwardDeclaredTemplate_double) ForwardDeclaredTemplate<double>;
+
+  template <typename T> struct ForwardDeclaredSpecialized;
+  %template(ForwardDeclaredTemplate_int) ForwardDeclaredSpecialized<int>; // no primary defined
+  %template(ForwardDeclaredTemplate_double) ForwardDeclaredSpecialized<double>; // needs to be after the specialized template definition.
+  template <> struct ForwardDeclaredSpecialized<double> {
+    void specialized(const ForwardDeclaredSpecialized& other) { }
+  };
+
+  template <typename T> struct ForwardDeclaredMisplacedPrimary;
+  %template(ForwardDeclaredTemplate_double) ForwardDeclaredMisplacedPrimary<double>; // needs to be after the primary template definition.
+  template <typename T> struct ForwardDeclaredMisplacedPrimary {
+    void primary(const ForwardDeclaredMisplacedPrimary& other) { }
+  };
+}

Examples/test-suite/errors/cpp_template_forward.stderr

@@ -0,0 +1,4 @@
+cpp_template_forward.i:6: Warning 330: Template instantiation of forward class declaration 'Space::ForwardDeclaredTemplate< double >' with name 'ForwardDeclaredTemplate_double' is ineffective.
+cpp_template_forward.i:9: Warning 330: Template instantiation of forward class declaration 'Space::ForwardDeclaredSpecialized< int >' with name 'ForwardDeclaredTemplate_int' is ineffective.
+cpp_template_forward.i:10: Warning 330: Template instantiation of forward class declaration 'Space::ForwardDeclaredSpecialized< double >' with name 'ForwardDeclaredTemplate_double' is ineffective.
+cpp_template_forward.i:16: Warning 330: Template instantiation of forward class declaration 'Space::ForwardDeclaredMisplacedPrimary< double >' with name 'ForwardDeclaredTemplate_double' is ineffective.

Examples/test-suite/template_specialization.i

@@ -3,6 +3,8 @@
 %rename(not1) *::operator!() const;
 %rename(negate) *::operator-() const;
 
+%warnfilter(SWIGWARN_PARSE_TEMPLATE_FORWARD) vfncs::OnlySpecialized<double>;
+
 %inline %{
   
   namespace vfncs {
@@ -45,7 +47,7 @@ namespace vfncs {
   %template(OnlySpecialized_int) OnlySpecialized<int>;
 
   // Primary instantiation with only primary template forward declaration
-  %template(OnlySpecialized_double) OnlySpecialized<double>; // silently ignored - probably should warn
+  %template(OnlySpecialized_double) OnlySpecialized<double>; // ignored with a warning
 }
 
 %{

Source/CParse/parser.y

@@ -2905,7 +2905,7 @@ template_directive: SWIGTEMPLATE LPAREN idstringopt RPAREN idcolonnt LESSTHAN va
                       if (GetFlag(nn, "instantiate")) {
 			Delattr(nn, "instantiate");
 			{
-			  int nnisclass = (Strcmp(Getattr(nn, "templatetype"), "class") == 0); /* if not a class template it is a function template */
+			  int nnisclass = (Strcmp(Getattr(nn, "templatetype"), "class") == 0); /* class template not a classforward nor function template */
 			  Parm *tparms = Getattr(nn, "templateparms");
 			  int specialized = !tparms; /* fully specialized (an explicit specialization) */
 			  String *tname = Copy(idcolonnt);
@@ -2960,6 +2960,13 @@ template_directive: SWIGTEMPLATE LPAREN idstringopt RPAREN idcolonnt LESSTHAN va
 			  }
                           add_symbols_copy(templnode);
 
+			  if (Equal(nodeType(templnode), "classforward")) {
+			    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"));
+			    SWIG_WARN_NODE_END(templnode);
+			  }
+
                           if (Strcmp(nodeType(templnode),"class") == 0) {
 
                             /* Identify pure abstract methods */

Source/CParse/templ.c

@@ -223,6 +223,8 @@ static void cparse_template_expand(Node *templnode, Node *n, String *tname, Stri
 	cn = nextSibling(cn);
       }
     }
+  } else if (Equal(nodeType, "classforward")) {
+    /* Nothing to expand */
   } else if (Equal(nodeType, "constructor")) {
     if (!(Getattr(n, "templatetype"))) {
       String *symname = Getattr(n, "sym:name");
@@ -1172,12 +1174,10 @@ Node *Swig_cparse_template_locate(String *name, Parm *instantiated_parms, String
 
   if (n) {
     String *nodeType = nodeType(n);
-    int isclass = 0;
     assert(Equal(nodeType, "template"));
-    (void)nodeType;
+    String *templatetype = Getattr(n, "templatetype");
-    isclass = (Equal(Getattr(n, "templatetype"), "class"));
 
-    if (isclass) {
+    if (Equal(templatetype, "class") || Equal(templatetype, "classforward")) {
       Node *primary = Getattr(n, "primarytemplate");
       Parm *tparmsfound = Getattr(primary ? primary : n, "templateparms");
       int specialized = !tparmsfound; /* fully specialized (an explicit specialization) */
@@ -1361,8 +1361,8 @@ static void expand_defaults(ParmList *expanded_templateparms) {
 
 ParmList *Swig_cparse_template_parms_expand(ParmList *instantiated_parms, Node *primary, Node *templ) {
   ParmList *expanded_templateparms = CopyParmList(instantiated_parms);
-
   String *templatetype = Getattr(primary, "templatetype");
+
   if (Equal(templatetype, "class") || Equal(templatetype, "classforward")) {
     /* Class template */
     ParmList *templateparms = Getattr(primary, "templateparms");
@@ -1400,8 +1400,9 @@ ParmList *Swig_cparse_template_parms_expand(ParmList *instantiated_parms, Node *
 
 ParmList *Swig_cparse_template_partialargs_expand(ParmList *partially_specialized_parms, Node *primary, ParmList *templateparms) {
   ParmList *expanded_templateparms = CopyParmList(partially_specialized_parms);
+  String *templatetype = Getattr(primary, "templatetype");
 
-  if (Equal(Getattr(primary, "templatetype"), "class")) {
+  if (Equal(templatetype, "class") || Equal(templatetype, "classforward")) {
     /* Class template */
     int variadic = ParmList_variadic_parm(templateparms) ? 1 : 0;
     /* Add default arguments from primary template */

Source/Include/swigwarn.h

@@ -96,6 +96,7 @@
 #define WARN_PARSE_EXTERN_TEMPLATE    327
 #define WARN_PARSE_ASSIGNED_VALUE     328
 #define WARN_PARSE_USING_CONSTRUCTOR  329
+#define WARN_PARSE_TEMPLATE_FORWARD   330
 
 #define WARN_CPP11_LAMBDA             340
 /* Unused since 3.0.11: #define WARN_CPP11_ALIAS_DECLARATION  341 */