Default constructor detection fix for templated constructors

Don't generate a default constructor wrapper when a class has a
templated constructor, as there isn't actually an implied default
constructor. For example:

  struct TConstructor3 {
    template<typename T> TConstructor3(T val) {}
  };

Previously wrappers were generated for a non-existent default
constructor which failed to compile.

CHANGES.current

@@ -7,6 +7,18 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.2.0 (in progress)
 ===========================
 
+2023-07-21: wsfulton
+            Don't generate a default constructor wrapper when a class has a
+            templated constructor, as there isn't actually an implied default
+            constructor. For example:
+
+              struct TConstructor3 {
+                template<typename T> TConstructor3(T val) {}
+              };
+
+            Previously wrappers were generated for a non-existent default
+            constructor which failed to compile.
+
 2023-07-15: wsfulton
             C++11 using declarations for inheriting constructors has now been
             extended to support the directors feature.

Examples/test-suite/template_templated_constructors.i

@@ -16,6 +16,20 @@ public:
   ~TConstructor2() {}
 };
 
+class TConstructor3 {
+public:
+  // No implicit default constructor available
+  template<typename T> TConstructor3(T val) {}
+  ~TConstructor3() {}
+};
+
+class TConstructor4 {
+public:
+  // No constructors available from wrappers when there is no %template to instantiate templated constructor
+  template<typename T> TConstructor4() {}
+  ~TConstructor4() {}
+};
+
 template<typename T> class TClass1 {
 public:
   template<typename Y> TClass1(Y t) {}

Source/Modules/allocate.cxx

@@ -1123,6 +1123,15 @@ Allocate():
     return SWIG_OK;
   }
 
+  virtual int templateDeclaration(Node *n) {
+    String *ttype = Getattr(n, "templatetype");
+    if (Equal(ttype, "constructor")) {
+      // Templated constructors need to be taken account of even if not instantiated with %template
+      constructorDeclaration(n);
+    }
+    return SWIG_OK;
+  }
+
   virtual int constructorDeclaration(Node *n) {
     if (!inclass)
       return SWIG_OK;

Source/Swig/typesys.c

@@ -1497,7 +1497,7 @@ int SwigType_type(const SwigType *t) {
  *
  * This is the default behavior unless:
  *
- *  1.- swig detects a default_constructor and 'setallocate:default_constructor'
+ *  1.- swig detects a default_constructor and 'allocate:default_constructor'
  *      attribute.
  *
  *  2.- swig doesn't mark 'type' as non-assignable.