Wrap friend functions that are defined or declared within a namespace

Previously unqualified friend definitions/declarations in a namespace were
ignored.

CHANGES.current

@@ -7,6 +7,15 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.2.1 (in progress)
 ===========================
 
+2024-01-15: wsfulton
+            https://sourceforge.net/p/swig/bugs/807/
+            Wrap friend functions that are defined or declared within a namespace.
+            Previously unqualified friend definitions/declarations in a namespace were
+            ignored.
+
+            The visibility of unqualified friend functions in C++ is somewhat quirky
+            and the documentation has been enhanced to aid wrapping of friends.
+
 2024-01-12: wsfulton
             #2749 Fix seg fault handling friend constructor/destructor declarations.
 

Examples/test-suite/csharp/friends_runme.cs

@@ -2,6 +2,11 @@ using System;
 using friendsNamespace;
 
 public class friends_runme {
+  private static void check_equal(int a, int b) {
+    if (a != b)
+      throw new Exception("Not equal " + a + " != " + b);
+  }
+
   public static void Main() {
     A a = new A(2);
 
@@ -43,6 +48,17 @@ public class friends_runme {
       throw new Exception("failed");
     if (friends.mate_blah() != 4321)
       throw new Exception("failed");
+
+    Foe foe = new Foe(111);
+    check_equal(friends.friend_definition(), 10);
+    check_equal(friends.friend_declaration(), 11);
+    check_equal(friends.friend_args_definition(foe), 111);
+    check_equal(friends.friend_args_declaration(foe), 111);
+
+    check_equal(friends.friend_definition_compiler(), 20);
+    check_equal(friends.friend_declaration_compiler(), 21);
+    check_equal(friends.friend_args_definition_compiler(foe), 111);
+    check_equal(friends.friend_args_declaration_compiler(foe), 111);
   }
 }
 

Examples/test-suite/friends.i

@@ -5,7 +5,6 @@
 
 %warnfilter(SWIGWARN_LANG_IDENTIFIER) operator<<;
 %warnfilter(SWIGWARN_LANG_IDENTIFIER) operator>>;
-%warnfilter(SWIGWARN_LANG_IDENTIFIER) ns1::ns2::bar; // This warning suppression is hiding a bug when using namespaces and friends, warning should not be issued
 
 #if defined(SWIGOCTAVE)
 %warnfilter(SWIGWARN_IGNORE_OPERATOR_LSHIFT_MSG) operator<<;
@@ -141,9 +140,7 @@
     };
 
   namespace ns1 {
-
     void bas() {}
-
     void baz() {}
   }
 }
@@ -208,16 +205,45 @@ void Mate::private_function() { this->val = 4321; }
 %}
 
 
+// Foe class tests friend definitions/declarations in a namespace
 %inline %{
   namespace ns1 {
     namespace ns2 {
-      class Foo {
+      class Foe {
+        int val;
       public:
-	Foo() {}
-	friend void bar();
-	friend void ns1::baz();	
+	Foe() : val() {}
+	Foe(int val) : val(val) {}
+        // Unqualified friends visible to SWIG in outer scope
+	friend int friend_definition() { return Foe(10).val; }
+	friend int friend_declaration();
+	friend int friend_args_definition(Foe &foe) { return foe.val; }
+	friend int friend_args_declaration(Foe &foe);
+
+        // Unqualified friends only visible to C++ compiler in outer scope
+	friend int friend_definition_compiler() { return Foe(20).val; }
+	friend int friend_declaration_compiler();
+	friend int friend_args_definition_compiler(Foe &foe) { return foe.val; }
+	friend int friend_args_declaration_compiler(Foe &foe);
+
+        // Qualified friend (silently ignored)
+	friend void ns1::baz();
       };
-      void bar() {}    
+      int friend_definition();
+      int friend_declaration() { return Foe(11).val; }
+      int friend_args_definition(Foe &foe);
+      int friend_args_declaration(Foe &foe) { return foe.val; }
+    }
+  }
+%}
+
+%{
+  namespace ns1 {
+    namespace ns2 {
+      int friend_definition_compiler();
+      int friend_declaration_compiler() { return Foe(21).val; }
+   // int friend_args_definition_compiler(Foe &foe); // ADL is used to find this, so no declaration is needed
+      int friend_args_declaration_compiler(Foe &foe) { return foe.val; }
     }
   }
 %}

Examples/test-suite/java/friends_runme.java

@@ -11,6 +11,11 @@ public class friends_runme {
     }
   }
 
+  private static void check_equal(int a, int b) {
+    if (a != b)
+      throw new RuntimeException("Not equal " + a + " != " + b);
+  }
+
   public static void main(String argv[]) throws Throwable
   {
     A a = new A(2);
@@ -53,6 +58,17 @@ public class friends_runme {
       throw new RuntimeException("failed");
     if (friends.mate_blah() != 4321)
       throw new RuntimeException("failed");
+
+    Foe foe = new Foe(111);
+    check_equal(friends.friend_definition(), 10);
+    check_equal(friends.friend_declaration(), 11);
+    check_equal(friends.friend_args_definition(foe), 111);
+    check_equal(friends.friend_args_declaration(foe), 111);
+
+    check_equal(friends.friend_definition_compiler(), 20);
+    check_equal(friends.friend_declaration_compiler(), 21);
+    check_equal(friends.friend_args_definition_compiler(foe), 111);
+    check_equal(friends.friend_args_declaration_compiler(foe), 111);
   }
 }
 

Examples/test-suite/php/friends_runme.php

@@ -2,8 +2,8 @@
 
 require "tests.php";
 
-check::functions(array('globalscope','mix','get_val2','get_val3','bas','baz','bar','get_val1','set','chum_blah','mate_blah'));
-check::classes(array('friends','Foo','A','B','D_i','D_d','CModelParameterCompartment','CModelParameterSpecies','Chum','Mate'));
+check::functions(array('globalscope','mix','get_val2','get_val3','bas','baz','get_val1','set','chum_blah','mate_blah','friend_definition','friend_declaration','friend_args_definition','friend_args_declaration','friend_definition_compiler','friend_declaration_compiler','friend_args_definition_compiler','friend_args_declaration_compiler'));
+check::classes(array('friends','Foe','A','B','D_i','D_d','CModelParameterCompartment','CModelParameterSpecies','Chum','Mate'));
 // No new vars
 check::globals(array());
 
@@ -37,4 +37,15 @@ check::equal(get_val1($dd), 1.3);
 check::equal(chum_blah(), 1234);
 check::equal(mate_blah(), 4321);
 
+$foe = new Foe(111);
+check::equal(friend_definition(), 10);
+check::equal(friend_declaration(), 11);
+check::equal(friend_args_definition($foe), 111);
+check::equal(friend_args_declaration($foe), 111);
+
+check::equal(friend_definition_compiler(), 20);
+check::equal(friend_declaration_compiler(), 21);
+check::equal(friend_args_definition_compiler($foe), 111);
+check::equal(friend_args_declaration_compiler($foe), 111);
+
 check::done();

Examples/test-suite/python/friends_runme.py

@@ -1,5 +1,9 @@
 import friends
 
+def check_equal(a, b):
+    if a != b:
+        raise RuntimeError("Not equal {} != {}".format(a, b))
+
 a = friends.A(2)
 
 if friends.get_val1(a) != 2:
@@ -40,3 +44,14 @@ if friends.chum_blah() != 1234:
   raise RuntimeError("failed")
 if friends.mate_blah() != 4321:
   raise RuntimeError("failed")
+
+foe = friends.Foe(111)
+check_equal(friends.friend_definition(), 10)
+check_equal(friends.friend_declaration(), 11)
+check_equal(friends.friend_args_definition(foe), 111)
+check_equal(friends.friend_args_declaration(foe), 111)
+
+check_equal(friends.friend_definition_compiler(), 20)
+check_equal(friends.friend_declaration_compiler(), 21)
+check_equal(friends.friend_args_definition_compiler(foe), 111)
+check_equal(friends.friend_args_declaration_compiler(foe), 111)

Source/CParse/parser.y

@@ -411,7 +411,6 @@ static void add_symbols(Node *n) {
   }
   while (n) {
     String *symname = 0;
-    /* for friends, we need to pop the scope once */
     String *old_prefix = 0;
     Symtab *old_scope = 0;
     int isfriend = inclass && Checkattr(n, "storage", "friend");
@@ -421,26 +420,17 @@ static void add_symbols(Node *n) {
     if (inclass) {
       String *name = Getattr(n, "name");
       if (isfriend) {
-	/* for friends, we need to add the scopename if needed */
+	/* For friends, set the scope to the same as the class that the friend is defined/declared in, that is, pop scope once */
 	String *prefix = name ? Swig_scopename_prefix(name) : 0;
 	old_prefix = Namespaceprefix;
 	old_scope = Swig_symbol_popscope();
 	Namespaceprefix = Swig_symbol_qualifiedscopename(0);
 	if (!prefix) {
 	  if (name && !is_operator(name) && Namespaceprefix) {
-	    String *nname = NewStringf("%s::%s", Namespaceprefix, name);
-	    Setattr(n,"name",nname);
-	    Delete(nname);
+	    String *friendusing = NewStringf("using namespace %s;", Namespaceprefix);
+	    Setattr(n, "friendusing", friendusing);
+	    Delete(friendusing);
 	  }
-	} else {
-	  Symtab *st = Swig_symbol_getscope(prefix);
-	  String *ns = st ? Getattr(st,"name") : prefix;
-	  String *base  = Swig_scopename_last(name);
-	  String *nname = NewStringf("%s::%s", ns, base);
-	  Setattr(n,"name",nname);
-	  Delete(nname);
-	  Delete(base);
-	  Delete(prefix);
 	}
 	Namespaceprefix = 0;
       } else if (Equal(nodeType(n), "using")) {

Source/Modules/lang.cxx

@@ -1166,7 +1166,20 @@ int Language::globalfunctionHandler(Node *n) {
   String *extendname = Getattr(n, "extendname");
   String *call = Swig_cfunction_call(extendname ? extendname : name, parms);
   String *cres = Swig_cresult(type, Swig_cresult_name(), call);
-  Setattr(n, "wrap:action", cres);
+  String *friendusing = Getattr(n, "friendusing");
+  if (friendusing) {
+    // Add a using directive to avoid having to possibly fully qualify the call to the friend function.
+    // Unconventional for SWIG generation, but the alternative is to implement Argument Dependent Lookup
+    // as friend functions are quirky and not visible, except for ADL. An ADL implementation would be needed
+    // in order to work out when the friend function is visible or not, in order to determine whether to
+    // rely on ADL (with no qualification) or to fully qualify the call to the friend function made
+    // visible via a matching declaration at namespace scope.
+    String *action = NewStringf("%s\n%s", friendusing, cres);
+    Setattr(n, "wrap:action", action);
+    Delete(action);
+  } else {
+    Setattr(n, "wrap:action", cres);
+  }
   Delete(cres);
   Delete(call);
   functionWrapper(n);