Remove Lua 5.0 from the build system and improve lua-detect.mk

Lua doesn't include an official pkg-config file, therefore we can't rely on
pkg-config variables like "V" or "major_version" - on my system, it detected
the 5.3 library/cflags and used the 5.1 lua/luac binaries (I have both installed
and there was a fallback to 5.1 if it couldn't query these variables from
pkg-config).

build/lua-detect.mk

@@ -3,7 +3,7 @@
 # It uses pkg-config to do this, but will fail if you have liblua, but
 # not the corresponding interpreter/compiler. Let's say you have liblua5.2
 # but want to build with liblua5.1 (for which you have the lib, interpreter
-# and compiler), you can override by setting LUA_VERSION=5.0 when invoking
+# and compiler), you can override by setting LUA_VERSION=5.1 when invoking
 # make.
 #
 # If successful, sets the following variables:
@@ -12,25 +12,69 @@
 #  * LUA_INCLUDES (can be appended to CFLAGS directly)
 #  * LUA (full path to lua interpreter)
 #  * LUAC (full path to lua compiler)
+#
+# If unsuccessful, you can set these manually.
+
+ifndef LUA
+
+# first off, some helper functions to $(call) - this one executes lua/luac to match it's version
+lua_ver_match_bin = $(shell $2 -v 2>&1 | grep -qFo $1. && echo 1)
+# this one is like which(1), which isn't portable - from the gmake manual
+pathsearch = $(firstword $(wildcard $(addsuffix /$(1),$(subst :, ,$(PATH)))))
+# Extract "5.x" from lua -v
+lua_ver_extract = $(shell $1 -v 2>&1 | cut -f2 -d' ' | cut -f-2 -d.)
+
+# Lua does not provide an official .pc file, so finding one at all is tricky,
+# and there won't be any guarantees it looks the same as elsewhere.
+# We try the package names lua$(ver), lua-$(ver) for all candidate versions in
+# descending order and last but not least "lua" here.
+PKG_CONFIG_ALL_PACKAGES:= $(shell pkg-config --list-all | cut -f1 -d' ')
+
+# these are in order of preference
+LUA_CANDIDATES:=		$(or $(LUA_VERSION),5.3 5.2 5.1)
+LUA_BIN_CANDIDATES:=		$(foreach ver,$(LUA_CANDIDATES),lua$(ver) lua-$(ver))
+LUAC_BIN_CANDIDATES:=		$(foreach ver,$(LUA_CANDIDATES),luac$(ver) luac-$(ver))
+
+# the binaries might of course also just be called lua and luac
+ifndef LUA_VERSION
+LUA_BIN_CANDIDATES+=		lua
+LUAC_BIN_CANDIDATES+=		luac
+endif
 
-LUA_VERSIONS_CANDIDATES = $(or $(LUA_VERSION),5.3 5.2 5.1 5.0)
+# find pkg-config packages in the same order of preference
+PKG_CONFIG_LUA_PACKAGES:= 	$(foreach lua,$(LUA_BIN_CANDIDATES),$(filter $(lua),$(PKG_CONFIG_ALL_PACKAGES)))
+PKG_CONFIG_LUA:=		$(firstword $(PKG_CONFIG_LUA_PACKAGES))
 
-LUA_PKG := $(firstword $(foreach ver,$(LUA_VERSIONS_CANDIDATES),$(shell \
-       ($(PKG_CONFIG) --exists lua-$(ver)     && echo lua-$(ver)) \
-    || ($(PKG_CONFIG) --exists lua$(ver:5.0=) && echo lua$(ver:5.0=)))))
+ifeq ($(PKG_CONFIG_LUA),)
+$(error It seems that pkg-config is not aware of your lua package. Make sure \
+	the -dev package is installed along with a .pc file within the       \
+	pkg-config search-path. Alternatively, you can set the following     \
+	variables manually: LUA LUAC LUA_VERSION LUA_LIBS LUA_INCLUDES)
+endif
+
+PKG_CONFIG_LUA_VERSION:=	$(shell pkg-config --modversion $(PKG_CONFIG_LUA) | cut -d. -f-2)
+
+$(info >> pkg-config found Lua $(PKG_CONFIG_LUA_VERSION) (available: $(PKG_CONFIG_LUA_PACKAGES:=)).)
+
+LUA_LIBS=	$(shell pkg-config --libs $(PKG_CONFIG_LUA))
+LUA_INCLUDES=	$(shell pkg-config --cflags $(PKG_CONFIG_LUA))
+LUA_VERSION?=	$(PKG_CONFIG_LUA_VERSION)
 
-ifeq ($(LUA_PKG),)
-    $(error Could not find $(or $(LUA_VERSION),any) lua version. (Did you install the -dev package?))
+LUA=		$(firstword $(foreach bin,$(LUA_BIN_CANDIDATES),$(call pathsearch,$(bin))))
+LUAC=		$(firstword $(foreach bin,$(LUAC_BIN_CANDIDATES),$(call pathsearch,$(bin))))
+
+$(info >> Lua $(LUA_VERSION) binary is $(LUA) and luac is $(LUAC))
+
+ifneq ($(call lua_ver_match_bin,$(LUA_VERSION),$(LUA)),1)
+$(error $(LUA) should be $(LUA_VERSION) but is $(call lua_ver_extract,$(LUA)))
 endif
 
-ifeq ($(LUA_VERSION),)
-LUA_VERSION := $(or $(shell $(PKG_CONFIG) --variable=V $(LUA_PKG)),$(or $(shell $(PKG_CONFIG) --variable=major_version $(LUA_PKG)),5.0))
+ifneq ($(call lua_ver_match_bin,$(LUA_VERSION),$(LUAC)),1)
+$(error $(LUAC) should be $(LUA_VERSION) but is $(call lua_ver_extract,$(LUAC)))
 endif
 
-# prior to 5.1 the lib didn't include version in name.
-LUA_SUFFIX := $(if $(findstring $(LUA_VERSION),5.0),,$(LUA_VERSION))
+endif
 
-LUA_LIBS     := $(or $(shell $(PKG_CONFIG) --libs $(LUA_PKG)), $(error "pkg-config couldn't find linker flags for lua$(LUA_SUFFIX)!"))
-LUA_INCLUDES := $(shell $(PKG_CONFIG) --cflags $(LUA_PKG))
-LUA          := $(or $(shell which lua$(LUA_SUFFIX)),          $(shell which lua),  $(error No lua$(LUA_SUFFIX) interpreter found!))
-LUAC         := $(or $(shell which luac$(LUA_SUFFIX)),         $(shell which luac), $(error No lua$(LUA_SUFFIX) compiler found!))
+# this is necessary, otherwise the rest of the build process keeps calling
+# pkg-config and all these other programs up there
+export LUA_VERSION LUA_INCLUDES LUA_LIBS LUA LUAC