Use $(if) instead of ifeq and add a test for RELX_TAR=0

plugins/relx.mk

@@ -42,18 +42,10 @@ $(RELX):
 	$(verbose) chmod +x $(RELX)
 
 relx-rel: $(RELX) rel-deps app
-ifeq ($(RELX_TAR),1)
-	$(verbose) $(RELX) -c $(RELX_CONFIG) $(RELX_OPTS) release tar
-else
-	$(verbose) $(RELX) -c $(RELX_CONFIG) $(RELX_OPTS) release
-endif
+	$(verbose) $(RELX) -c $(RELX_CONFIG) $(RELX_OPTS) release $(if $(filter 1,$(RELX_TAR)),tar)
 
 relx-relup: $(RELX) rel-deps app
-ifeq ($(RELX_TAR),1)
-	$(verbose) $(RELX) -c $(RELX_CONFIG) $(RELX_OPTS) release relup tar
-else
-	$(verbose) $(RELX) -c $(RELX_CONFIG) $(RELX_OPTS) release relup
-endif
+	$(verbose) $(RELX) -c $(RELX_CONFIG) $(RELX_OPTS) release relup $(if $(filter 1,$(RELX_TAR)),tar)
 
 distclean-relx-rel:
 	$(gen_verbose) rm -rf $(RELX_OUTPUT_DIR)

test/plugin_relx.mk

@@ -184,6 +184,12 @@ relx-tar: build clean
 	$t cp ../erlang.mk $(APP)/
 	$t $(MAKE) -C $(APP) -f erlang.mk bootstrap bootstrap-rel $v
 
+	$i "Build the release without a tarball"
+	$t $(MAKE) -C $(APP) RELX_TAR=0 $v
+
+	$i "Check that tarball doesn't exist"
+	$t test ! -e $(APP)/_rel/$(APP)_release/$(APP)_release-1.tar.gz
+
 	$i "Build the release as a tarball"
 	$t $(MAKE) -C $(APP) $v