fix(stablediffusion): embed Metal library (#11531)

The Darwin workflow passes BUILD_TYPE=metal but does not define OS=Darwin. The backend therefore omitted its Metal CMake flags and shipped the runtime source path instead of the embedded library.

Map the requested build type directly to the Metal flags and guard the build contract with a dry-run regression test.

Assisted-by: Codex:gpt-5

Co-authored-by: localai-org-maint-bot <306269227+localai-org-maint-bot@users.noreply.github.com>

backend/go/stablediffusion-ggml/Makefile

@@ -42,13 +42,9 @@ else ifeq ($(BUILD_TYPE),hipblas)
 	CMAKE_ARGS+=-DSD_HIPBLAS=ON -DGGML_HIPBLAS=ON -DAMDGPU_TARGETS=$(AMDGPU_TARGETS)
 else ifeq ($(BUILD_TYPE),vulkan)
 	CMAKE_ARGS+=-DSD_VULKAN=ON -DGGML_VULKAN=ON
-else ifeq ($(OS),Darwin)
-	ifneq ($(BUILD_TYPE),metal)
-		CMAKE_ARGS+=-DSD_METAL=OFF -DGGML_METAL=OFF
-	else
-		CMAKE_ARGS+=-DSD_METAL=ON -DGGML_METAL=ON
-		CMAKE_ARGS+=-DGGML_METAL_EMBED_LIBRARY=ON
-	endif
+else ifeq ($(BUILD_TYPE),metal)
+	CMAKE_ARGS+=-DSD_METAL=ON -DGGML_METAL=ON
+	CMAKE_ARGS+=-DGGML_METAL_EMBED_LIBRARY=ON
 endif
 
 ifeq ($(BUILD_TYPE),sycl_f16)
@@ -72,7 +68,6 @@ sources/stablediffusion-ggml.cpp:
 	git checkout $(STABLEDIFFUSION_GGML_VERSION) && \
 	git submodule update --init --recursive --depth 1 --single-branch
 
-# Detect OS
 UNAME_S := $(shell uname -s)
 
 # Only build CPU variants on Linux
@@ -134,4 +129,4 @@ libgosd-custom: CMakeLists.txt cpp/gosd.cpp cpp/gosd.h
 	(mv build-$(SO_TARGET)/libgosd.so ./$(SO_TARGET) 2>/dev/null || \
 	 mv build-$(SO_TARGET)/libgosd.dylib ./$(SO_TARGET) 2>/dev/null)
 
-all: stablediffusion-ggml package
+all: stablediffusion-ggml package

scripts/build/stablediffusion-metal-build_test.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+CURDIR=$(dirname "$(realpath "$0")")
+BACKEND_DIR="$CURDIR/../../backend/go/stablediffusion-ggml"
+
+build_commands=$(make -Bn -C "$BACKEND_DIR" \
+  BUILD_TYPE=metal \
+  libgosd-fallback.so)
+
+for expected_flag in \
+  -DSD_METAL=ON \
+  -DGGML_METAL=ON \
+  -DGGML_METAL_EMBED_LIBRARY=ON; do
+  if ! grep -Fq -- "$expected_flag" <<<"$build_commands"; then
+    echo "FAIL: Darwin Metal build omitted $expected_flag"
+    exit 1
+  fi
+done
+
+echo "PASS: stablediffusion-ggml embeds its Darwin Metal library"