core.mk: Allow to take erlang.mk from an alternate Git repository

core/core.mk

@@ -173,13 +173,15 @@ core_ls = $(filter-out $(1),$(shell echo $(1)))
 
 # Automated update.
 
+ERLANG_MK_REPO ?= https://github.com/ninenines/erlang.mk
+ERLANG_MK_COMMIT ?=
 ERLANG_MK_BUILD_CONFIG ?= build.config
 ERLANG_MK_BUILD_DIR ?= .erlang.mk.build
 
 erlang-mk:
-	git clone https://github.com/ninenines/erlang.mk $(ERLANG_MK_BUILD_DIR)
+	git clone $(ERLANG_MK_REPO) $(ERLANG_MK_BUILD_DIR)
 	if [ -f $(ERLANG_MK_BUILD_CONFIG) ]; then cp $(ERLANG_MK_BUILD_CONFIG) $(ERLANG_MK_BUILD_DIR)/build.config; fi
-	cd $(ERLANG_MK_BUILD_DIR) && $(MAKE)
+	cd $(ERLANG_MK_BUILD_DIR) && $(if $(ERLANG_MK_COMMIT),git checkout $(ERLANG_MK_COMMIT) &&) $(MAKE)
 	cp $(ERLANG_MK_BUILD_DIR)/erlang.mk ./erlang.mk
 	rm -rf $(ERLANG_MK_BUILD_DIR)
 

test/Makefile

@@ -1323,7 +1323,7 @@ $(CORE_APP_CLEAN_TARGETS):
 
 # Core: Erlang.mk upgrade.
 
-CORE_UPGRADE_CASES = no-config custom-config renamed-config custom-build-dir
+CORE_UPGRADE_CASES = alt-erlangmk-repo no-config custom-config renamed-config custom-build-dir
 CORE_UPGRADE_TARGETS = $(addprefix core-upgrade-,$(CORE_UPGRADE_CASES))
 CORE_UPGRADE_CLEAN_TARGETS = $(addprefix clean-,$(CORE_UPGRADE_TARGETS))
 
@@ -1331,6 +1331,34 @@ CORE_UPGRADE_CLEAN_TARGETS = $(addprefix clean-,$(CORE_UPGRADE_TARGETS))
 
 core-upgrade: $(CORE_UPGRADE_TARGETS)
 
+core-upgrade-alt-erlangmk-repo: build clean-core-upgrade-alt-erlangmk-repo
+
+	$i "Bootstrap a new OTP library named $(APP)"
+	$t mkdir $(APP)/
+	$t cp ../erlang.mk $(APP)/
+	$t $(MAKE) -C $(APP) -f erlang.mk bootstrap-lib $v
+
+	$i "Fork erlang.mk locally and modify it"
+	$t git clone -q file://$(abspath $(CURDIR)/..) $(APP)/alt-erlangmk-repo
+	$t sed -i.bak '1i\
+# Copyright (c) erlang.mk Testsuite!\
+' $(APP)/alt-erlangmk-repo/core/core.mk
+	$t (cd $(APP)/alt-erlangmk-repo && \
+		git checkout -q -b test-copyright && \
+		git commit -q -a -m 'Add Testsuite copyright')
+
+	$i "Point application to an alternate erlang.mk repository"
+	$t sed -i.bak '2i\
+ERLANG_MK_REPO = file://$(abspath $(APP)/alt-erlangmk-repo)\
+ERLANG_MK_COMMIT = test-copyright\
+' $(APP)/Makefile
+
+	$i "Update erlang.mk"
+	$t $(MAKE) -C $(APP) erlang-mk $v
+
+	$i "Check our modification is there"
+	$t grep -q "# Copyright (c) erlang.mk Testsuite!" $(APP)/erlang.mk
+
 core-upgrade-no-config: build clean-core-upgrade-no-config
 
 	$i "Bootstrap a new OTP library named $(APP)"