Makefile: simplify provisioner and builder selection

1 files changed, 15 insertions, 11 deletions

diff --git a/Makefile b/Makefile
index d1f8426..e878aac 100644
--- a/Makefile
+++ b/Makefile
@@ -24,19 +24,23 @@ BUILDER_VIRTUALBOX_PROV := virtualbox-ovf
 
 BUILDERS                := QEMU VMWARE VIRTUALBOX
 
-ifndef BUILDER
-    $(foreach cur, $(BUILDERS),\
-        $(if $(shell command -v $(BUILDER_$(cur)_EXE)),\
-            $(eval AVAILABLE_BUILDERS += $(BUILDER_$(cur)_NAME))))
 
-    BUILDER := $(firstword $(AVAILABLE_BUILDERS))
-endif
+$(foreach cur, $(BUILDERS),\
+    $(if $(shell command -v $(BUILDER_$(cur)_EXE)),\
+        $(eval AVAILABLE_BUILDERS += $(cur))))
 
-ifndef PROVISIONER
-    $(foreach cur, $(BUILDERS),\
-        $(if $(filter $(BUILDER),$(BUILDER_$(cur)_NAME)),\
-            $(eval PROVISIONER := $(BUILDER_$(cur)_PROV))))
-endif
+
+# If now BUILDER or PROVISIONER was specified on the command line, take the
+# first available one; otherwise use that specified one.
+BUILDER_SELECTED     := $(strip $(if $(filter $(BUILDER),$(AVAILABLE_BUILDERS)),\
+                                    $(BUILDER),\
+                                    $(firstword $(AVAILABLE_BUILDERS))))
+PROVISIONER_SELECTED := $(strip $(if $(filter $(PROVISIONER),$(AVAILABLE_BUILDERS)),\
+                                    $(PROVISIONER),\
+                                    $(BUILDER_SELECTED)))
+
+override BUILDER     = $(BUILDER_$(BUILDER_SELECTED)_NAME)
+override PROVISIONER = $(BUILDER_$(PROVISIONER_SELECTED)_PROV)
 
 
 # The packer templates, detected as *.json (excluding base.json)