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# -*-makefile-*-
# Shared/stamp-string.make
#
# Makefile fragment with rules to manage stamp strings
#
# Copyright (C) 2002 Free Software Foundation, Inc.
#
# Author: Nicola Pero <nicola@brainstorm.co.uk>
#
# This file is part of the GNUstep Makefile Package.
#
# This library is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 3
# of the License, or (at your option) any later version.
#
# You should have received a copy of the GNU General Public
# License along with this library; see the file COPYING.
# If not, write to the Free Software Foundation,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
#
# Normally, make computes dependencies basing on files' timestamps.
# You can have a target which depedends on some files. When the files
# have changed since the last time the target was built, the target
# is rebuilt.
#
# Inside gnustep-make, we have also a need for a different type of
# dependency. We create/patch some .plist files basing on the value
# of some make variables. In this case, we want some targets to
# depend on some make variables; when the variables have changed since
# the last time the target was built, the target is rebuilt.
#
# This file provides an efficient implementation of this feature. You
# can have a target be rebuilt when a certain GNUSTEP_STAMP_STRING has
# changed since the last time the target was built. By storing the
# values of some variables, in a fixed order, in the
# GNUSTEP_STAMP_STRING, you can then in practice have the result of
# having the target depend on the variable values.
#
#
# To use this file, define GNUSTEP_STAMP_STRING to be the string you
# want to depend upon. This file will store the string into a
# stamp.make; you need to provide the directory in which to store this
# file, and a rule to create the directory. In practice, you need to
# set GNUSTEP_STAMP_DIR and implement a $(GNUSTEP_STAMP_DIR): rule.
# Then, you can have a target to depend on $(GNUSTEP_STAMP_DEPEND).
# That will cause the target to store GNUSTEP_STAMP_STRING into
# $(GNUSTEP_STAMP_DIR)/stamp.make the first time it's executed, and to
# read it from the same file each time it's executed afterwards.
# Whenever the stamp string in stamp.make does not match the curret
# GNUSTEP_STAMP_STRING, the stamp file will be rebuilt, and the target
# depending on $(GNUSTEP_STAMP_DEPEND) will be forced to be rebuilt.
#
#
# Input variables:
#
# GNUSTEP_STAMP_STRING: This variable is the stamp; we check that it
# has not changed since last time the target was rebuilt. You must
# set this variable to the appropriate stamp string before including
# this file; usually the stamp string is just a concatenation of the
# values of the various variables (separated by some character you want,
# such as '-') you want to depend upon.
#
# GNUSTEP_STAMP_DIR: The directory in which you want the stamp file to
# be placed. Each time the target is rebuilt, GNUSTEP_STAMP_STRING is
# recorded into the stamp file so that next time it can be compared.
# Your code must provide a rule to build GNUSTEP_STAMP_DIR.
# Typically, GNUSTEP_STAMP_DIR is the bundle dir for a bundle, the
# application dir for an application, and so on.
#
#
# Output variables:
#
# GNUSTEP_STAMP_DEPEND: If the value of GNUSTEP_STAMP_STRING is the
# same as the value stored inside stamp.make, then this is set to ''.
# Else, this is set to shared-instance-stamp-string, and causes both
# GNUSTEP_STAMP_FILE to be regenerated, and any target depending on
# GNUSTEP_STAMP_DEPEND to be rebuilt as well.
#
#
# public targets:
#
# shared-instance-stamp-string: You do not refer this target directly;
# you should instead depend on $(GNUSTEP_STAMP_DEPEND), which will expand
# to shared-instance-stamp-string when a change in the stamp string is
# detected, and to '' when not.
#
# To read the stamp file very quickly, we use a trick: we write the
# file as a makefile fragment, and include it to read it.
# This can be considered a trick to read the file very efficiently
# without spanning a 'cat' subprocess in a subshell.
GNUSTEP_STAMP_FILE = $(GNUSTEP_STAMP_DIR)/stamp.make
# This rule tells make that GNUSTEP_STAMP_FILE is always up to date.
# Else, because it is included as a makefile, make would try
# rebuilding it, and moreover, after rebuilding it, it would run again
# using the new one! We instead manage rules manually to have control
# of it.
$(GNUSTEP_STAMP_FILE):
# By default, GNUSTEP_STAMP_DEPEND causes shared-instance-stamp-string to
# be executed, and everything depending on GNUSTEP_STAMP_DEPEND to be
# rebuilt.
GNUSTEP_STAMP_DEPEND = shared-instance-stamp-string
# We want to make sure the string put in the stamp.make is never empty.
# To make sure it is so, we add an '_' at the beginning of the string.
GNUSTEP_STAMP_ASTRING = _$(GNUSTEP_STAMP_STRING)
OLD_GNUSTEP_STAMP_ASTRING =
# Include the old stamp.make, but only if it exists.
# stamp.make contains the line
# OLD_GNUSTEP_STAMP_ASTRING = xxx
-include $(GNUSTEP_STAMP_FILE)
# If there was a stamp.make, and it contained the same
# GNUSTEP_STAMP_ASTRING, then we drop GNUSTEP_STAMP_DEPEND, and do
# nothing.
ifneq ($(OLD_GNUSTEP_STAMP_ASTRING),)
ifeq ($(OLD_GNUSTEP_STAMP_ASTRING), $(GNUSTEP_STAMP_ASTRING))
GNUSTEP_STAMP_DEPEND =
endif
endif
# The actual target building the stamp string.
.PHONY: shared-instance-stamp-string
shared-instance-stamp-string: $(GNUSTEP_STAMP_DIR)
$(ECHO_CREATING_STAMP_FILE)echo "OLD_GNUSTEP_STAMP_ASTRING = $(GNUSTEP_STAMP_ASTRING)" > $(GNUSTEP_STAMP_FILE)$(END_ECHO)
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