Improved error checking when defining classes and using %template.

1. When a template is instantiated via %template and uses the unary scope
operator ::, an error occurs if the instantiation is attempted within a
namespace that does not enclose the instantiated template.
For example, the following will now error as ::test::max is not enclosed within test1:

Error: '::test::max' resolves to 'test::max' and was incorrectly instantiated in
scope 'test1' instead of within scope 'test'.
  namespace test1 {
    %template(maxchar) ::test::max<char>;
  }

2. SWIG previously failed to always detect a template did not exist when using
%template. In particular when instantiating a global template incorrectly within
namespace. The code below now correctly emits an error:

Error: Template 'test5::GlobalVector' undefined.
  namespace test5 {
  }
  template<typename T> struct GlobalVector {};
  %template(GVI) test5::GlobalVector<int>;

3. Also error out if an attempt is made to define a class using the unary scope
operator ::. The following is not legal C++ and now results in an error:

Error: Using the unary scope operator :: in class definition '::Space2::B' is invalid.
  namespace Space2 {
    struct B;
  }
  struct ::Space2::B {};

10 files changed, 134 insertions, 85 deletions

diff --git a/CHANGES.current b/CHANGES.current
index ea3e81022..29f5ec67b 100644
--- a/CHANGES.current
+++ b/CHANGES.current
@@ -7,6 +7,41 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.2.0 (in progress)
 ===========================
 
+2023-03-13: wsfulton
+            Improved error checking when using %template to instantiate templates within
+            the correct scope.
+
+            1. When a template is instantiated via %template and uses the unary scope
+            operator ::, an error occurs if the instantiation is attempted within a
+            namespace that does not enclose the instantiated template.
+            For example, the following will now error as ::test::max is not enclosed within test1:
+
+            Error: '::test::max' resolves to 'test::max' and was incorrectly instantiated in
+            scope 'test1' instead of within scope 'test'.
+              namespace test1 {
+                %template(maxchar) ::test::max<char>;
+              }
+
+            2. SWIG previously failed to always detect a template did not exist when using
+            %template. In particular when instantiating a global template incorrectly within
+            namespace. The code below now correctly emits an error:
+
+            Error: Template 'test5::GlobalVector' undefined.
+              namespace test5 {
+              }
+              template<typename T> struct GlobalVector {};
+              %template(GVI) test5::GlobalVector<int>;
+
+2023-03-13: wsfulton
+            Error out if an attempt is made to define a class using the unary scope
+            operator ::. The following is not legal C++ and now results in an error:
+
+            Error: Using the unary scope operator :: in class definition '::Space2::B' is invalid.
+              namespace Space2 {
+                struct B;
+              }
+              struct ::Space2::B {};
+
 2023-03-08: wsfulton
             Fix duplicate const in generated code when template instantiation type is const
             and use of template parameter is also explicitly const, such as:
diff --git a/Examples/test-suite/errors/cpp_class_definition.i b/Examples/test-suite/errors/cpp_class_definition.i
index 22d7c1521..d6842eef1 100644
--- a/Examples/test-suite/errors/cpp_class_definition.i
+++ b/Examples/test-suite/errors/cpp_class_definition.i
@@ -24,3 +24,17 @@ namespace Space2 {
   };
 }
 
+namespace Space2 {
+    struct B;
+}
+
+struct ::Space2::B {
+    int val;
+    B() : val() {}
+};
+
+struct XX;
+// g++: error: global qualification of class name is invalid before ‘{’ token
+struct ::XX {
+  int vvv;
+};
diff --git a/Examples/test-suite/errors/cpp_class_definition.stderr b/Examples/test-suite/errors/cpp_class_definition.stderr
index 659e254c5..c467bcbcb 100644
--- a/Examples/test-suite/errors/cpp_class_definition.stderr
+++ b/Examples/test-suite/errors/cpp_class_definition.stderr
@@ -1,3 +1,5 @@
 cpp_class_definition.i:11: Warning 302: Identifier 'L' redefined (ignored),
 cpp_class_definition.i:10: Warning 302: previous definition of 'L'.
 cpp_class_definition.i:22: Error: 'Space1::A' resolves to 'Space1::A' and was incorrectly instantiated in scope 'Space2' instead of within scope 'Space1'.
+cpp_class_definition.i:31: Error: Using the unary scope operator :: in class definition '::Space2::B' is invalid.
+cpp_class_definition.i:38: Error: Using the unary scope operator :: in class definition '::XX' is invalid.
diff --git a/Examples/test-suite/errors/cpp_invalid_template.stderr b/Examples/test-suite/errors/cpp_invalid_template.stderr
index f6bfaaf7d..f39464942 100644
--- a/Examples/test-suite/errors/cpp_invalid_template.stderr
+++ b/Examples/test-suite/errors/cpp_invalid_template.stderr
@@ -1,3 +1,2 @@
-cpp_invalid_template.i:3: Error: Undefined scope 'SSS'
 cpp_invalid_template.i:3: Error: Template 'SSS::AAA' undefined.
 cpp_invalid_template.i:9: Error: 'JJJ' is not defined as a template. (classforward)
diff --git a/Examples/test-suite/errors/cpp_namespace_template_bad.i b/Examples/test-suite/errors/cpp_namespace_template_bad.i
index f41918f8e..d8a33098e 100644
--- a/Examples/test-suite/errors/cpp_namespace_template_bad.i
+++ b/Examples/test-suite/errors/cpp_namespace_template_bad.i
@@ -9,6 +9,11 @@ namespace test {
   }; 
 }
 
+namespace test1 {
+  %template(maxchar) ::test::max<char>;
+  %template(vectorchar) ::test::vector<char>;
+}
+
 namespace test2 {
   using namespace test;
   %template(maxshort) max<short>;
@@ -32,9 +37,18 @@ namespace test4 {
   %template(vectorInteger) vector<Integer>;
 }
 
-using namespace test;
 namespace test5 {
+// Empty namespace
+}
+template<typename T> struct GlobalVector {
+  void gook(T i) {}
+  void geeko(double d) {}
+  void geeky(int d) {}
+};
+%template(GlobalVectorIntPtr) test5::GlobalVector<int *>; // should fail as GlobalVector is in global namespace
+
+using namespace test;
+namespace test6 {
   %template(maxdouble) max<double>;
   %template(vectordouble) vector<double>;
 }
-
diff --git a/Examples/test-suite/errors/cpp_namespace_template_bad.stderr b/Examples/test-suite/errors/cpp_namespace_template_bad.stderr
index 8ac072d74..d6ee15d5f 100644
--- a/Examples/test-suite/errors/cpp_namespace_template_bad.stderr
+++ b/Examples/test-suite/errors/cpp_namespace_template_bad.stderr
@@ -1,9 +1,11 @@
-cpp_namespace_template_bad.i:14: Error: 'max' resolves to 'test::max' and was incorrectly instantiated in scope 'test2' instead of within scope 'test'.
-cpp_namespace_template_bad.i:15: Error: 'vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test2' instead of within scope 'test'.
-cpp_namespace_template_bad.i:21: Error: 'max' resolves to 'test::max' and was incorrectly instantiated in scope 'test3' instead of within scope 'test'.
-cpp_namespace_template_bad.i:22: Error: 'vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test3' instead of within scope 'test'.
-cpp_namespace_template_bad.i:31: Error: 'max' resolves to 'test::max' and was incorrectly instantiated in scope 'test4' instead of within scope 'test'.
-cpp_namespace_template_bad.i:32: Error: 'vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test4' instead of within scope 'test'.
-cpp_namespace_template_bad.i:37: Error: 'max' resolves to 'test::max' and was incorrectly instantiated in scope 'test5' instead of within scope 'test'.
-cpp_namespace_template_bad.i:37: Error: No matching function template 'max' found.
-cpp_namespace_template_bad.i:38: Error: 'vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test5' instead of within scope 'test'.
+cpp_namespace_template_bad.i:13: Error: '::test::max' resolves to 'test::max' and was incorrectly instantiated in scope 'test1' instead of within scope 'test'.
+cpp_namespace_template_bad.i:14: Error: '::test::vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test1' instead of within scope 'test'.
+cpp_namespace_template_bad.i:19: Error: 'max' resolves to 'test::max' and was incorrectly instantiated in scope 'test2' instead of within scope 'test'.
+cpp_namespace_template_bad.i:20: Error: 'vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test2' instead of within scope 'test'.
+cpp_namespace_template_bad.i:26: Error: 'max' resolves to 'test::max' and was incorrectly instantiated in scope 'test3' instead of within scope 'test'.
+cpp_namespace_template_bad.i:27: Error: 'vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test3' instead of within scope 'test'.
+cpp_namespace_template_bad.i:36: Error: 'max' resolves to 'test::max' and was incorrectly instantiated in scope 'test4' instead of within scope 'test'.
+cpp_namespace_template_bad.i:37: Error: 'vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test4' instead of within scope 'test'.
+cpp_namespace_template_bad.i:48: Error: Template 'test5::GlobalVector' undefined.
+cpp_namespace_template_bad.i:52: Error: 'max' resolves to 'test::max' and was incorrectly instantiated in scope 'test6' instead of within scope 'test'.
+cpp_namespace_template_bad.i:53: Error: 'vector' resolves to 'test::vector' and was incorrectly instantiated in scope 'test6' instead of within scope 'test'.
diff --git a/Examples/test-suite/errors/cpp_nested_template.stderr b/Examples/test-suite/errors/cpp_nested_template.stderr
index 363a260f6..5b107cad4 100644
--- a/Examples/test-suite/errors/cpp_nested_template.stderr
+++ b/Examples/test-suite/errors/cpp_nested_template.stderr
@@ -1,4 +1,2 @@
 cpp_nested_template.i:9: Error: 'Temply' resolves to '::Temply' and was incorrectly instantiated in scope 'A' instead of within scope ''.
-cpp_nested_template.i:9: Warning 324: Named nested template instantiations not supported. Processing as if no name was given to %template().
 cpp_nested_template.i:18: Error: 'Temply' resolves to '::Temply' and was incorrectly instantiated in scope 'B' instead of within scope ''.
-cpp_nested_template.i:18: Warning 324: Named nested template instantiations not supported. Processing as if no name was given to %template().
diff --git a/Examples/test-suite/namespace_class.i b/Examples/test-suite/namespace_class.i
index cc9940d13..17670a4ac 100644
--- a/Examples/test-suite/namespace_class.i
+++ b/Examples/test-suite/namespace_class.i
@@ -155,10 +155,8 @@ namespace test
 
 %}
 
-namespace test {
-  
-  %template(BooT_H) ::BooT<Hello>;
-}
+using test::Hello;
+%template(BooT_H) ::BooT<Hello>;
 %template(BooT_i) ::BooT<int>;
 
 
diff --git a/Examples/test-suite/template_partial_specialization.i b/Examples/test-suite/template_partial_specialization.i
index fd7c73326..3452535a9 100644
--- a/Examples/test-suite/template_partial_specialization.i
+++ b/Examples/test-suite/template_partial_specialization.i
@@ -122,24 +122,3 @@ namespace S {
 namespace S {
   %template(X2) X<int *>;
 };
-
-#if 0
-// TODO fix:
-%inline %{
-namespace Space {
-}
-template<typename T> struct Vector {
-  void gook(T i) {}
-  void geeko(double d) {}
-  void geeky(int d) {}
-};
-/*
-template<typename T> struct Vector<T *> {
-};
-*/
-%}
-
-%template(VectorIntPtr) Space::Vector<int *>; // should fail as Vector is in global namespace
-// is this a regression - no fails in 1.3.40 too
-// Note problem is removed by removing empty Space namespace!!
-#endif
diff --git a/Source/CParse/parser.y b/Source/CParse/parser.y
index b1041c0e7..325856074 100644
--- a/Source/CParse/parser.y
+++ b/Source/CParse/parser.y
@@ -267,7 +267,7 @@ static String *yyrename = 0;
 
 /* Forward renaming operator */
 
-static String *resolve_create_node_scope(String *cname, int is_class_definition);
+static String *resolve_create_node_scope(String *cname, int is_class_definition, int *errored);
 
 
 Hash *Swig_cparse_features(void) {
@@ -910,37 +910,45 @@ static Node *nscope_inner = 0;
  * The scopes required for the symbol name are resolved and/or created, if required.
  * For example AA::BB::CC as input returns CC and creates the namespace AA then inner 
  * namespace BB in the current scope. */
-static String *resolve_create_node_scope(String *cname, int is_class_definition) {
+static String *resolve_create_node_scope(String *cname_in, int is_class_definition, int *errored) {
   Symtab *gscope = 0;
   Node *cname_node = 0;
+  String *cname = cname_in;
   String *last = Swig_scopename_last(cname);
   nscope = 0;
   nscope_inner = 0;  
+  *errored = 0;
 
-  if (Strncmp(cname,"::" ,2) != 0) {
+  if (Strncmp(cname, "::", 2) == 0) {
     if (is_class_definition) {
-      /* Only lookup symbols which are in scope via a using declaration but not via a using directive.
-         For example find y via 'using x::y' but not y via a 'using namespace x'. */
-      cname_node = Swig_symbol_clookup_no_inherit(cname, 0);
-      if (!cname_node) {
-	Node *full_lookup_node = Swig_symbol_clookup(cname, 0);
-	if (full_lookup_node) {
-	 /* This finds a symbol brought into scope via both a using directive and a using declaration. */
-	  Node *last_node = Swig_symbol_clookup_no_inherit(last, 0);
-	  if (last_node == full_lookup_node)
-	    cname_node = last_node;
-	}
+      Swig_error(cparse_file, cparse_line, "Using the unary scope operator :: in class definition '%s' is invalid.\n", cname);
+      *errored = 1;
+      return last;
+    }
+    cname = NewString(Char(cname) + 2);
+  }
+  if (is_class_definition) {
+    /* Only lookup symbols which are in scope via a using declaration but not via a using directive.
+       For example find y via 'using x::y' but not y via a 'using namespace x'. */
+    cname_node = Swig_symbol_clookup_no_inherit(cname, 0);
+    if (!cname_node) {
+      Node *full_lookup_node = Swig_symbol_clookup(cname, 0);
+      if (full_lookup_node) {
+       /* This finds a symbol brought into scope via both a using directive and a using declaration. */
+	Node *last_node = Swig_symbol_clookup_no_inherit(last, 0);
+	if (last_node == full_lookup_node)
+	  cname_node = last_node;
       }
-    } else {
-      /* For %template, the template needs to be in scope via any means. */
-      cname_node = Swig_symbol_clookup(cname, 0);
     }
+  } else {
+    /* For %template, the template needs to be in scope via any means. */
+    cname_node = Swig_symbol_clookup(cname, 0);
   }
 #if RESOLVE_DEBUG
   if (!cname_node)
-    Printf(stdout, "symbol does not yet exist (%d): [%s]\n", is_class_definition, cname);
+    Printf(stdout, "symbol does not yet exist (%d): [%s]\n", is_class_definition, cname_in);
   else
-    Printf(stdout, "symbol does exist (%d): [%s]\n", is_class_definition, cname);
+    Printf(stdout, "symbol does exist (%d): [%s]\n", is_class_definition, cname_in);
 #endif
 
   if (cname_node) {
@@ -1022,8 +1030,8 @@ Printf(stdout, "comparing current: [%s] found: [%s]\n", current_scopename, found
 
 	if (fail) {
 	  String *cname_resolved = NewStringf("%s::%s", found_scopename, last);
-	  Swig_error(cparse_file, cparse_line, "'%s' resolves to '%s' and was incorrectly instantiated in scope '%s' instead of within scope '%s'.\n", cname, cname_resolved, current_scopename, found_scopename);
-	  cname = Copy(last);
+	  Swig_error(cparse_file, cparse_line, "'%s' resolves to '%s' and was incorrectly instantiated in scope '%s' instead of within scope '%s'.\n", cname_in, cname_resolved, current_scopename, found_scopename);
+	  *errored = 1;
 	  Delete(cname_resolved);
 	}
       }
@@ -1032,22 +1040,17 @@ Printf(stdout, "comparing current: [%s] found: [%s]\n", current_scopename, found
       Delete(found_scopename);
     }
   } else if (!is_class_definition) {
-    /* A template instantiation requires a template to be found in scope... fail here too?
-    Swig_error(cparse_file, cparse_line, "No template found to instantiate '%s' with %%template.\n", cname);
-     */
+    /* A template instantiation requires a template to be found in scope */
+    Swig_error(cparse_file, cparse_line, "Template '%s' undefined.\n", cname_in);
+    *errored = 1;
   }
 
-  if (Swig_scopename_check(cname)) {
+  if (*errored)
+    return last;
+
+  if (Swig_scopename_check(cname) && !*errored) {
     Node   *ns;
     String *prefix = Swig_scopename_prefix(cname);
-    if (prefix && (Strncmp(prefix,"::",2) == 0)) {
-/* I don't think we can use :: global scope to declare classes and hence neither %template. - consider reporting error instead - wsfulton. */
-      /* Use the global scope */
-      String *nprefix = NewString(Char(prefix)+2);
-      Delete(prefix);
-      prefix= nprefix;
-      gscope = set_scope_to_global();
-    }
     if (Len(prefix) == 0) {
       String *base = Copy(last);
       /* Use the global scope, but we need to add a 'global' namespace.  */
@@ -1065,10 +1068,12 @@ Printf(stdout, "comparing current: [%s] found: [%s]\n", current_scopename, found
     ns = Swig_symbol_clookup(prefix,0);
     if (!ns) {
       Swig_error(cparse_file,cparse_line,"Undefined scope '%s'\n", prefix);
+      *errored = 1;
     } else {
       Symtab *nstab = Getattr(ns,"symtab");
       if (!nstab) {
 	Swig_error(cparse_file,cparse_line, "'%s' is not defined as a valid scope.\n", prefix);
+	*errored = 1;
 	ns = 0;
       } else {
 	/* Check if the node scope is the current scope */
@@ -2814,30 +2819,32 @@ types_directive : TYPES LPAREN parms RPAREN stringbracesemi {
 
 template_directive: SWIGTEMPLATE LPAREN idstringopt RPAREN idcolonnt LESSTHAN valparms GREATERTHAN SEMI {
                   Parm *p;
-		  Node *n;
+		  Node *n = 0;
 		  Node *outer_class = currentOuterClass;
 		  Symtab *tscope = 0;
 		  String *symname = $3 ? NewString($3) : 0;
+		  int errored_flag = 0;
 
 		  $$ = 0;
 
 		  tscope = Swig_symbol_current();          /* Get the current scope */
 
 		  /* If the class name is qualified, we need to create or lookup namespace entries */
-		  $5 = resolve_create_node_scope($5, 0);
+		  $5 = resolve_create_node_scope($5, 0, &errored_flag);
 
-		  if (nscope_inner && Strcmp(nodeType(nscope_inner), "class") == 0) {
-		    outer_class	= nscope_inner;
-		  }
+		  if (!errored_flag) {
+		    if (nscope_inner && Strcmp(nodeType(nscope_inner), "class") == 0)
+		      outer_class = nscope_inner;
 
-		  /*
-		    We use the new namespace entry 'nscope' only to
-		    emit the template node. The template parameters are
-		    resolved in the current 'tscope'.
+		    /*
+		      We use the new namespace entry 'nscope' only to
+		      emit the template node. The template parameters are
+		      resolved in the current 'tscope'.
 
-		    This is closer to the C++ (typedef) behavior.
-		  */
-		  n = Swig_cparse_template_locate($5, $7, symname, tscope);
+		      This is closer to the C++ (typedef) behavior.
+		    */
+		    n = Swig_cparse_template_locate($5, $7, symname, tscope);
+		  }
 
 		  /* Patch the argument types to respect namespaces */
 		  p = $7;
@@ -3647,6 +3654,7 @@ cpp_class_decl: storage_class cpptype idcolon class_virt_specifier_opt inherit L
                    String *prefix;
                    List *bases = 0;
 		   Node *scope = 0;
+		   int errored_flag = 0;
 		   String *code;
 		   $<node>$ = new_node("class");
 		   Setline($<node>$,cparse_start_line);
@@ -3662,7 +3670,7 @@ cpp_class_decl: storage_class cpptype idcolon class_virt_specifier_opt inherit L
 		   Setattr($<node>$,"prev_symtab",Swig_symbol_current());
 		  
 		   /* If the class name is qualified.  We need to create or lookup namespace/scope entries */
-		   scope = resolve_create_node_scope($3, 1);
+		   scope = resolve_create_node_scope($3, 1, &errored_flag);
 		   /* save nscope_inner to the class - it may be overwritten in nested classes*/
 		   Setattr($<node>$, "nested:innerscope", nscope_inner);
 		   Setattr($<node>$, "nested:nscope", nscope);