Fix clang analyzer ObjC lifetime warnings in non-ARC case

In general those warnings were uncritical, leaks could
only happen in the Metal backend when shader creation
failed, because the error path didn't properly
release all objects before returning a failure.

sokol_gfx.h

@@ -9744,11 +9744,9 @@ _SOKOL_PRIVATE void _sg_d3d11_update_image(_sg_image_t* img, const sg_image_data
 #if __has_feature(objc_arc)
 #define _SG_OBJC_RETAIN(obj) { }
 #define _SG_OBJC_RELEASE(obj) { obj = nil; }
-#define _SG_OBJC_RELEASE_WITH_NULL(obj) { obj = [NSNull null]; }
 #else
 #define _SG_OBJC_RETAIN(obj) { [obj retain]; }
 #define _SG_OBJC_RELEASE(obj) { [obj release]; obj = nil; }
-#define _SG_OBJC_RELEASE_WITH_NULL(obj) { [obj release]; obj = [NSNull null]; }
 #endif
 
 /*-- enum translation functions ----------------------------------------------*/
@@ -10144,6 +10142,7 @@ _SOKOL_PRIVATE int _sg_mtl_add_resource(id res) {
         return _SG_MTL_INVALID_SLOT_INDEX;
     }
     const int slot_index = _sg_mtl_alloc_pool_slot();
+    // NOTE: the NSMutableArray will take ownership of its items
     SOKOL_ASSERT([NSNull null] == _sg.mtl.idpool.pool[(NSUInteger)slot_index]);
     _sg.mtl.idpool.pool[(NSUInteger)slot_index] = res;
     return slot_index;
@@ -10183,8 +10182,11 @@ _SOKOL_PRIVATE void _sg_mtl_garbage_collect(uint32_t frame_index) {
         /* safe to release this resource */
         const int slot_index = _sg.mtl.idpool.release_queue[_sg.mtl.idpool.release_queue_back].slot_index;
         SOKOL_ASSERT((slot_index > 0) && (slot_index < _sg.mtl.idpool.num_slots));
+        /* note: the NSMutableArray takes ownership of its items, assigning an NSNull object will
+           release the object, no matter if using ARC or not
+        */
         SOKOL_ASSERT(_sg.mtl.idpool.pool[(NSUInteger)slot_index] != [NSNull null]);
-        _SG_OBJC_RELEASE_WITH_NULL(_sg.mtl.idpool.pool[(NSUInteger)slot_index]);
+        _sg.mtl.idpool.pool[(NSUInteger)slot_index] = [NSNull null];
         /* put the now free pool index back on the free queue */
         _sg_mtl_free_pool_slot(slot_index);
         /* reset the release queue slot and advance the back index */
@@ -10249,6 +10251,7 @@ _SOKOL_PRIVATE int _sg_mtl_create_sampler(id<MTLDevice> mtl_device, const sg_ima
         id<MTLSamplerState> mtl_sampler = [mtl_device newSamplerStateWithDescriptor:mtl_desc];
         _SG_OBJC_RELEASE(mtl_desc);
         int sampler_handle = _sg_mtl_add_resource(mtl_sampler);
+        _SG_OBJC_RELEASE(mtl_sampler);
         _sg_smpcache_add_item(&_sg.mtl.sampler_cache, img_desc, (uintptr_t)sampler_handle);
         return sampler_handle;
     }
@@ -10518,6 +10521,7 @@ _SOKOL_PRIVATE sg_resource_state _sg_mtl_create_buffer(_sg_buffer_t* buf, const
             }
         }
         buf->mtl.buf[slot] = _sg_mtl_add_resource(mtl_buf);
+        _SG_OBJC_RELEASE(mtl_buf);
     }
     return SG_RESOURCESTATE_VALID;
 }
@@ -10695,6 +10699,7 @@ _SOKOL_PRIVATE sg_resource_state _sg_mtl_create_image(_sg_image_t* img, const sg
         id<MTLTexture> tex = [_sg.mtl.device newTextureWithDescriptor:mtl_desc];
         SOKOL_ASSERT(nil != tex);
         img->mtl.depth_tex = _sg_mtl_add_resource(tex);
+        _SG_OBJC_RELEASE(tex);
     }
     else {
         /* create the color texture
@@ -10721,6 +10726,7 @@ _SOKOL_PRIVATE sg_resource_state _sg_mtl_create_image(_sg_image_t* img, const sg
                 }
             }
             img->mtl.tex[slot] = _sg_mtl_add_resource(tex);
+            _SG_OBJC_RELEASE(tex);
         }
 
         /* if MSAA color render target, create an additional MSAA render-surface texture */
@@ -10728,6 +10734,7 @@ _SOKOL_PRIVATE sg_resource_state _sg_mtl_create_image(_sg_image_t* img, const sg
             _sg_mtl_init_texdesc_rt_msaa(mtl_desc, img);
             id<MTLTexture> tex = [_sg.mtl.device newTextureWithDescriptor:mtl_desc];
             img->mtl.msaa_tex = _sg_mtl_add_resource(tex);
+            _SG_OBJC_RELEASE(tex);
         }
 
         /* create (possibly shared) sampler state */
@@ -10778,18 +10785,18 @@ _SOKOL_PRIVATE sg_resource_state _sg_mtl_create_shader(_sg_shader_t* shd, const
     _sg_shader_common_init(&shd->cmn, desc);
 
     /* create metal libray objects and lookup entry functions */
-    id<MTLLibrary> vs_lib;
-    id<MTLLibrary> fs_lib;
-    id<MTLFunction> vs_func;
-    id<MTLFunction> fs_func;
+    id<MTLLibrary> vs_lib = nil;
+    id<MTLLibrary> fs_lib = nil;
+    id<MTLFunction> vs_func = nil;
+    id<MTLFunction> fs_func = nil;
     const char* vs_entry = desc->vs.entry;
     const char* fs_entry = desc->fs.entry;
     if (desc->vs.bytecode.ptr && desc->fs.bytecode.ptr) {
         /* separate byte code provided */
         vs_lib = _sg_mtl_library_from_bytecode(desc->vs.bytecode.ptr, desc->vs.bytecode.size);
         fs_lib = _sg_mtl_library_from_bytecode(desc->fs.bytecode.ptr, desc->fs.bytecode.size);
-        if (nil == vs_lib || nil == fs_lib) {
-            return SG_RESOURCESTATE_FAILED;
+        if ((nil == vs_lib) || (nil == fs_lib)) {
+            goto failed;
         }
         vs_func = [vs_lib newFunctionWithName:[NSString stringWithUTF8String:vs_entry]];
         fs_func = [fs_lib newFunctionWithName:[NSString stringWithUTF8String:fs_entry]];
@@ -10798,29 +10805,47 @@ _SOKOL_PRIVATE sg_resource_state _sg_mtl_create_shader(_sg_shader_t* shd, const
         /* separate sources provided */
         vs_lib = _sg_mtl_compile_library(desc->vs.source);
         fs_lib = _sg_mtl_compile_library(desc->fs.source);
-        if (nil == vs_lib || nil == fs_lib) {
-            return SG_RESOURCESTATE_FAILED;
+        if ((nil == vs_lib) || (nil == fs_lib)) {
+            goto failed;
         }
         vs_func = [vs_lib newFunctionWithName:[NSString stringWithUTF8String:vs_entry]];
         fs_func = [fs_lib newFunctionWithName:[NSString stringWithUTF8String:fs_entry]];
     }
     else {
-        return SG_RESOURCESTATE_FAILED;
+        goto failed;
     }
     if (nil == vs_func) {
         SOKOL_LOG("vertex shader entry function not found\n");
-        return SG_RESOURCESTATE_FAILED;
+        goto failed;
     }
     if (nil == fs_func) {
         SOKOL_LOG("fragment shader entry function not found\n");
-        return SG_RESOURCESTATE_FAILED;
+        goto failed;
     }
     /* it is legal to call _sg_mtl_add_resource with a nil value, this will return a special 0xFFFFFFFF index */
     shd->mtl.stage[SG_SHADERSTAGE_VS].mtl_lib  = _sg_mtl_add_resource(vs_lib);
+    _SG_OBJC_RELEASE(vs_lib);
     shd->mtl.stage[SG_SHADERSTAGE_FS].mtl_lib  = _sg_mtl_add_resource(fs_lib);
+    _SG_OBJC_RELEASE(fs_lib);
     shd->mtl.stage[SG_SHADERSTAGE_VS].mtl_func = _sg_mtl_add_resource(vs_func);
+    _SG_OBJC_RELEASE(vs_func);
     shd->mtl.stage[SG_SHADERSTAGE_FS].mtl_func = _sg_mtl_add_resource(fs_func);
+    _SG_OBJC_RELEASE(fs_func);
     return SG_RESOURCESTATE_VALID;
+failed:
+    if (vs_lib != nil) {
+        _SG_OBJC_RELEASE(vs_lib);
+    }
+    if (fs_lib != nil) {
+        _SG_OBJC_RELEASE(fs_lib);
+    }
+    if (vs_func != nil) {
+        _SG_OBJC_RELEASE(vs_func);
+    }
+    if (fs_func != nil) {
+        _SG_OBJC_RELEASE(fs_func);
+    }
+    return SG_RESOURCESTATE_FAILED;
 }
 
 _SOKOL_PRIVATE void _sg_mtl_destroy_shader(_sg_shader_t* shd) {
@@ -10947,7 +10972,9 @@ _SOKOL_PRIVATE sg_resource_state _sg_mtl_create_pipeline(_sg_pipeline_t* pip, _s
     id<MTLDepthStencilState> mtl_dss = [_sg.mtl.device newDepthStencilStateWithDescriptor:ds_desc];
     _SG_OBJC_RELEASE(ds_desc);
     pip->mtl.rps = _sg_mtl_add_resource(mtl_rps);
+    _SG_OBJC_RELEASE(mtl_rps);
     pip->mtl.dss = _sg_mtl_add_resource(mtl_dss);
+    _SG_OBJC_RELEASE(mtl_dss);
     return SG_RESOURCESTATE_VALID;
 }