From 3b03f920e7ac69924e816c1951c9027514432bdd Mon Sep 17 00:00:00 2001
From: Olly Betts <olly@survex.com>
Date: Sun, 20 Jan 2019 12:24:45 +1300
Subject: [PATCH] Suppress warnings about PyCFunction casts

These remaining warnings are due to the design of Python's C API,
so suppress them by casting via void(*)(void) (which GCC documents
as the way to suppress this warning).

Closes #1259.
---
 CHANGES.current           |  7 +++----
 Source/Modules/python.cxx | 18 ++++++++++++++----
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/CHANGES.current b/CHANGES.current
index 27eb7d1c5..18d694a16 100644
--- a/CHANGES.current
+++ b/CHANGES.current
@@ -468,10 +468,9 @@ Version 4.0.0 (in progress)
 
 2018-06-11: olly
             [Python] Fix new GCC8 warnings in generated code by avoiding casts
-            between incompatible function types where possible (when keyword
-            args are in use, it is not possible to avoid such warnings as they
-            are inherent in the design of Python's C API in that particular
-            case).  Fixes #1259.
+            between incompatible function types where possible, and by
+            suppressing the warning when it's due to the design of Python's C
+            API.  Fixes #1259.
 
 2018-06-08: philippkraft
 	    [Python] Stop exposing <CLASS>_swigregister to Python.  It's not
diff --git a/Source/Modules/python.cxx b/Source/Modules/python.cxx
index d58e21ba7..fe681f768 100755
--- a/Source/Modules/python.cxx
+++ b/Source/Modules/python.cxx
@@ -2343,7 +2343,10 @@ public:
 	Printf(methods, "\t { \"%s\", %s, METH_VARARGS, ", name, function);
       }
     } else {
-      Printf(methods, "\t { \"%s\", (PyCFunction)%s, METH_VARARGS|METH_KEYWORDS, ", name, function);
+      // Cast via void(*)(void) to suppress GCC -Wcast-function-type warning.
+      // Python should always call the function correctly, but the Python C API
+      // requires us to store it in function pointer of a different type.
+      Printf(methods, "\t { \"%s\", (PyCFunction)(void(*)(void))%s, METH_VARARGS|METH_KEYWORDS, ", name, function);
     }
 
     if (!n) {
@@ -4503,7 +4506,11 @@ public:
 	int argcount = Getattr(n, "python:argcount") ? atoi(Char(Getattr(n, "python:argcount"))) : 2;
 	String *ds = have_docstring(n) ? cdocstring(n, AUTODOC_METHOD) : NewString("");
 	if (check_kwargs(n)) {
-	  Printf(builtin_methods, "  { \"%s\", (PyCFunction)%s, METH_VARARGS|METH_KEYWORDS, \"%s\" },\n", symname, wname, ds);
+	  // Cast via void(*)(void) to suppress GCC -Wcast-function-type
+	  // warning.  Python should always call the function correctly, but
+	  // the Python C API requires us to store it in function pointer of a
+	  // different type.
+	  Printf(builtin_methods, "  { \"%s\", (PyCFunction)(void(*)(void))%s, METH_VARARGS|METH_KEYWORDS, \"%s\" },\n", symname, wname, ds);
 	} else if (argcount == 0) {
 	  Printf(builtin_methods, "  { \"%s\", %s, METH_NOARGS, \"%s\" },\n", symname, wname, ds);
 	} else if (argcount == 1) {
@@ -4603,12 +4610,15 @@ public:
 	  Append(pyflags, "METH_O");
 	else
 	  Append(pyflags, "METH_VARARGS");
+	// Cast via void(*)(void) to suppress GCC -Wcast-function-type warning.
+	// Python should always call the function correctly, but the Python C
+	// API requires us to store it in function pointer of a different type.
 	if (have_docstring(n)) {
 	  String *ds = cdocstring(n, AUTODOC_STATICFUNC);
-	  Printf(builtin_methods, "  { \"%s\", (PyCFunction)%s, %s, \"%s\" },\n", symname, wname, pyflags, ds);
+	  Printf(builtin_methods, "  { \"%s\", (PyCFunction)(void(*)(void))%s, %s, \"%s\" },\n", symname, wname, pyflags, ds);
 	  Delete(ds);
 	} else {
-	  Printf(builtin_methods, "  { \"%s\", (PyCFunction)%s, %s, \"\" },\n", symname, wname, pyflags);
+	  Printf(builtin_methods, "  { \"%s\", (PyCFunction)(void(*)(void))%s, %s, \"\" },\n", symname, wname, pyflags);
 	}
 	Delete(fullname);
 	Delete(wname);