include: add TestHostCommand and SetupHostCommand macros

Those macros allow testing various commands on the host system, also process the
prereq tests in the order they're declared.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

SVN-Revision: 44269

include/prereq.mk

@@ -1,5 +1,5 @@
 # 
-# Copyright (C) 2006-2007 OpenWrt.org
+# Copyright (C) 2006-2015 OpenWrt.org
 #
 # This is free software, licensed under the GNU General Public License v2.
 # See /LICENSE for more information.
@@ -20,12 +20,16 @@ prereq:
 .SILENT: prereq
 endif
 
+PREREQ_PREV=
+
+# 1: display name
+# 2: error message
 define Require
   export PREREQ_CHECK=1
   ifeq ($$(CHECK_$(1)),)
     prereq: prereq-$(1)
 
-    prereq-$(1): FORCE
+    prereq-$(1): $(if $(PREREQ_PREV),prereq-$(PREREQ_PREV)) FORCE
 		echo -n "Checking '$(1)'... "
 		if $(NO_TRACE_MAKE) -f $(firstword $(MAKEFILE_LIST)) check-$(1) >/dev/null 2>/dev/null; then \
 			echo 'ok.'; \
@@ -41,6 +45,8 @@ define Require
     .SILENT: prereq-$(1) check-$(1)
     .NOTPARALLEL:
   endif
+
+  PREREQ_PREV=$(1)
 endef
 
 
@@ -60,3 +66,41 @@ define RequireHeader
   $$(eval $$(call Require,$(1),$(2)))
 endef
 
+define QuoteHostCommand
+'$(subst ','"'"',$(strip $(1)))'
+endef
+
+# 1: display name
+# 2: failure message
+# 3: test
+define TestHostCommand
+  define Require/$(1)
+	($(3)) >/dev/null 2>/dev/null
+  endef
+
+  $$(eval $$(call Require,$(1),$(2)))
+endef
+
+# 1: canonical name
+# 2: failure message
+# 3+: candidates
+define SetupHostCommand
+  define Require/$(1)
+	for cmd in $(call QuoteHostCommand,$(3)) $(call QuoteHostCommand,$(4)) \
+	           $(call QuoteHostCommand,$(5)) $(call QuoteHostCommand,$(6)) \
+	           $(call QuoteHostCommand,$(7)) $(call QuoteHostCommand,$(8)); do \
+		if [ -n "$$$$$$$$cmd" ]; then \
+			bin="$$$$$$$$(PATH="$(subst $(space),:,$(filter-out $(STAGING_DIR_HOST)/%,$(subst :,$(space),$(PATH))))" \
+				which "$$$$$$$${cmd%% *}")"; \
+			if [ -x "$$$$$$$$bin" ] && eval "$$$$$$$$cmd" >/dev/null 2>/dev/null; then \
+				mkdir -p "$(STAGING_DIR_HOST)/bin"; \
+				ln -sf "$$$$$$$$bin" "$(STAGING_DIR_HOST)/bin/$(strip $(1))"; \
+				exit 0; \
+			fi; \
+		fi; \
+	done; \
+	exit 1
+  endef
+
+  $$(eval $$(call Require,$(1),$(if $(2),$(2),Missing $(1) command)))
+endef