Improve out of project tree builds

For the out of the project tree builds there is no need to replicate
under TOP_BUILD_DIR whole directory stack leading to the actual project
directory.  This is now removed and the project is built now right under
TOP_BUILD_DIR.  In addition:
- OBJ_PATH has been optimized (no need for constant TOP_BUILD_DIR testing)
- clean targets has been corrected
- echo_cmd also has been corrected

mk/def_rules.mk

@@ -29,7 +29,11 @@ COLOR_TTY := $(shell [ `tput colors` -gt 2 ] && echo true)
 endif
 
 ifneq ($(VERBOSE),true)
-strip_top = $(subst $(TOP)/,,$(subst $(TOP_BUILD_DIR),,$(1)))
+ifneq ($(strip $(TOP_BUILD_DIR)),)
+  strip_top = $(subst $(TOP_BUILD_DIR)/,,$(1))
+else
+  strip_top = $(subst $(TOP)/,,$(1))
+endif
 ifeq ($(COLOR_TTY),true)
 echo_prog := $(shell if echo -e | grep -q -- -e; then echo echo; else echo echo -e; fi)
 echo_cmd = @$(echo_prog) "$(COLOR)$(call strip_top,$(1))$(NOCOLOR)";

mk/footer.mk

@@ -65,7 +65,7 @@ dist_clean_$(d) :
 else
 dist_clean_$(d) : clean_extra_$(d)
 endif
-	rm -rf $(TOP_BUILD_DIR)$(subst dist_clean_,,$@)/$(firstword $(subst /, ,$(OBJDIR)))
+	rm -rf $(DIST_CLEAN_DIR)
 endif
 
 ########################################################################
@@ -78,7 +78,7 @@ clean_$(d) :
 else
 clean_$(d) : clean_extra_$(d)
 endif
-	rm -f $(TOP_BUILD_DIR)$(subst clean_,,$@)/$(OBJDIR)/*
+	rm -f $(CLEAN_DIR)/*
 
 # clean_extra is meant for the extra output that is generated in source
 # directory (e.g. generated source from lex/yacc) so I'm not using

mk/skel.mk

@@ -150,8 +150,16 @@ OBJDIR := $(if $(BUILD_MODE),obj/$(BUILD_MODE),obj)
 # By default OBJDIR is relative to the directory of the corresponding Rules.mk
 # however you can use TOP_BUILD_DIR to build all objects outside of your
 # project tree.
-#TOP_BUILD_DIR := /tmp/make-builddir
-OBJPATH = $(if $(TOP_BUILD_DIR),$(TOP_BUILD_DIR)$(d),$(d))/$(OBJDIR)
+#TOP_BUILD_DIR := /tmp/make-builddir/project_name
+ifneq ($(strip $(TOP_BUILD_DIR)),)
+  OBJPATH = $(TOP_BUILD_DIR)$(subst $(TOP),,$(d))/$(OBJDIR)
+  CLEAN_DIR = $(TOP_BUILD_DIR)$(subst $(TOP),,$(subst clean_,,$@))/$(OBJDIR)
+  DIST_CLEAN_DIR = $(TOP_BUILD_DIR)$(subst $(TOP),,$(subst dist_clean_,,$@))/$(firstword $(subst /, ,$(OBJDIR)))
+else
+  OBJPATH = $(d)/$(OBJDIR)
+  CLEAN_DIR = $(subst clean_,,$@)/$(OBJDIR)
+  DIST_CLEAN_DIR = $(subst dist_clean_,,$@)/$(firstword $(subst /, ,$(OBJDIR)))
+endif
 
 # This variable contains a list of subdirectories where to look for
 # sources.  That is if you have some/dir/Rules.mk where you name object
@@ -231,7 +239,7 @@ endef
 # have dist_clean on per directory level and the one below is enough
 ifneq ($(strip $(TOP_BUILD_DIR)),)
 dist_clean :
-	rm -rf $(TOP_BUILD_DIR)$(TOP)
+	rm -rf $(TOP_BUILD_DIR)
 endif
 
 # Suck in the default rules