Refine Kconfig integration and build system

This converts tools/kconfig to git submodule pointing to the refined
one [1], integrates Kbuild toolchain detection functions for automatic
dependency checking, and tweaks build system to prevent unnecessary
compilation when invalid targets are specified.
- Add Kbuild $(success,...) functions to detect SDL2, Pixman, libpng,
  libjpeg
- Add dependency clauses to backend and loader options

[1] https://github.com/sysprog21/Kconfiglib

Author: jserv

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "tools/kconfig"]
+	path = tools/kconfig
+	url = https://github.com/sysprog21/Kconfiglib

Makefile

@@ -7,7 +7,7 @@ $(error You must first run 'make config')
 endif
 endif
 
-# Rules
+# Target variables initialization
 
 target-y :=
 target.o-y :=
@@ -58,11 +58,12 @@ libtwin.a_includes-y := \
 	include \
 	src
 
-# Features
+# Optional features
+
 libtwin.a_files-$(CONFIG_LOGGING) += src/log.c
 libtwin.a_files-$(CONFIG_CURSOR) += src/cursor.c
 
-# Renderer
+# Rendering backends
 libtwin.a_files-$(CONFIG_RENDERER_BUILTIN) += src/draw-builtin.c
 libtwin.a_files-$(CONFIG_RENDERER_PIXMAN) += src/draw-pixman.c
 libtwin.a_cflags-$(CONFIG_RENDERER_PIXMAN) += $(shell pkg-config --cflags pixman-1)
@@ -156,28 +157,32 @@ demo-$(BACKEND)_ldflags-y := \
 	$(TARGET_LIBS)
 endif
 
+# Font editor tool
+
 ifeq ($(CONFIG_TOOLS), y)
 target-$(CONFIG_TOOL_FONTEDIT) += font-edit
 font-edit_files-y = \
-    tools/font-edit/sfit.c \
-    tools/font-edit/font-edit.c
+	tools/font-edit/sfit.c \
+	tools/font-edit/font-edit.c
 font-edit_includes-y := tools/font-edit
 font-edit_cflags-y := \
-    $(shell pkg-config --cflags cairo) \
-    $(shell sdl2-config --cflags)
+	$(shell pkg-config --cflags cairo) \
+	$(shell sdl2-config --cflags)
 font-edit_ldflags-y := \
-    $(shell pkg-config --libs cairo) \
-    $(shell sdl2-config --libs)
+	$(shell pkg-config --libs cairo) \
+	$(shell sdl2-config --libs)
 endif
 
+# Build system integration
+
 CFLAGS += -include config.h
 
-check_goal := $(strip $(MAKECMDGOALS))
+# Only include build rules when not running config target
 ifneq ($(check_goal), config)
 include mk/common.mk
 endif
 
-# Menuconfig
+# Configuration target
 .PHONY: config
 config: configs/Kconfig
 	@tools/kconfig/menuconfig.py $<

configs/Kconfig

@@ -4,6 +4,19 @@ config CONFIGURED
     bool
     default y
 
+# Dependency detection using Kbuild toolchain functions
+config HAVE_SDL2
+    def_bool $(success,pkg-config --exists sdl2)
+
+config HAVE_PIXMAN
+    def_bool $(success,pkg-config --exists pixman-1)
+
+config HAVE_LIBPNG
+    def_bool $(success,pkg-config --exists libpng)
+
+config HAVE_LIBJPEG
+    def_bool $(success,pkg-config --exists libjpeg)
+
 choice
     prompt "Backend Selection"
     default BACKEND_SDL
@@ -14,6 +27,7 @@ config BACKEND_FBDEV
 
 config BACKEND_SDL
     bool "SDL video output support"
+    depends on HAVE_SDL2
 
 config BACKEND_VNC
     bool "VNC server output support"
@@ -28,6 +42,7 @@ config RENDERER_BUILTIN
 
 config RENDERER_PIXMAN
     bool "Pixman based rendering"
+    depends on HAVE_PIXMAN
 
 endchoice
 
@@ -83,10 +98,12 @@ menu "Image Loaders"
 
 config LOADER_PNG
     bool "Enable PNG loader"
+    depends on HAVE_LIBPNG
     default y
 
 config LOADER_JPEG
     bool "Enable JPEG loader"
+    depends on HAVE_LIBJPEG
     default y
 
 config LOADER_GIF
@@ -131,7 +148,7 @@ config DEMO_LINE
     depends on DEMO_APPLICATIONS
 
 config DEMO_SPLINE
-    bool "Build spline demp"
+    bool "Build spline demo"
     default y
     depends on DEMO_APPLICATIONS 
 

mk/common.mk

@@ -678,6 +678,17 @@ clean: __FORCE
 __FORCE:
 	@true
 
-ifneq "$(MAKECMDGOALS)" "clean"
--include $(target-depends)
+# Only include dependencies when building known targets
+build-goals := all clean $(target-builds)
+ifneq ($(MAKECMDGOALS),)
+    # MAKECMDGOALS is not empty, check if it's a known target
+    ifneq ($(filter $(MAKECMDGOALS),$(build-goals)),)
+        # Known target, include dependencies (except for clean)
+        ifneq "$(MAKECMDGOALS)" "clean"
+            -include $(target-depends)
+        endif
+    endif
+else
+    # Empty MAKECMDGOALS means building 'all', include dependencies
+    -include $(target-depends)
 endif