# vpath.rules: rules for using the vpath-mechanism of make

#
# The purpose of vpath-Makefiles is to generate object files in
# another directory than a source file directory. This mechanism 
# is supported by the internal Make VPATH variable, which tells
# make where to search for source files, in addition to the
# current directory. A change of directory to the object directory
# is encoded in the rule below which also sets VPATH to point to
# the source file directory where make execution is invoked.
#

#
# This file provides a (default) target `chdir' and expects an empty 
# rule with a corresponding target `vpath_chdir' and `real' targets 
# as dependencies in the Makefile of the source file directory 
# (or Makefile.rules) which includes this rules file, by the rule
# below that same Makefile is invoked from the object directory
# to make the `real' target objects.
#

# Thus the general usage is:
#
# all:  chdir
#
# include $(MAKE_ROOT)/make/vpath.rules
#
# vpath_chdir: <true targets>
#
# Where `all' is the default target and <true targets> a list of targets which
# should be made in the object directory, usually a list of libraries or
# executables.
#

# 
# The default target name `chdir' is set here as the value of the variable
# VPATH_TARGET which may also be set to another value, in this case the
# target `vpath_chdir' must be substituted accordingly, it is named
# vpath_$(VPATH_TARGET) here. Using different target names is necessary
# for including this vpath rules file multiple times.
#
# The variable VPATH_MAKEDIR specifys the directory where make shall be
# executed. By default, this is set to OBJ_PATH.
# VPATH_MAKEDIR is the dependency of the VPATH_TARGET. As a consequence
# of the make's makefile parsing behaviour, it has to be set BEFORE including
# vpath.rules . The including makefile has to take care of the existence/creation
# of VPATH_MAKEDIR, i.e. this directory either has to exist or there must be a rule
# for creating this directory somewhere else.
# For the default VPATH_MAKEDIR=OBJ_PATH, there is such a rule in obj.rules .
#

ifndef	BINPWD
BINPWD=/bin/pwd
endif

MAKECWD=--no-print-directory

ifndef	VPATH_TARGET
VPATH_TARGET=chdir
endif

ifndef	VPATH_MAKEDIR
VPATH_MAKEDIR=$(OBJ_PATH)
endif


$(VPATH_TARGET): $(VPATH_MAKEDIR) 
	@$(MAKE) $(MAKECWD) -C $< -f `$(BINPWD)`/GNUmakefile vpath_$@ VPATH=`$(BINPWD)`/ $(PARALLELFLAGS)