Updated Comfignat to version 1.1.

1 files changed, 429 insertions, 99 deletions

diff --git a/comfignat.mk b/comfignat.mk
index aea3103..07ae8d2 100644
--- a/comfignat.mk
+++ b/comfignat.mk
@@ -11,6 +11,11 @@
 # modified is included with the above copyright notice.
 
 
+# This file is part of Comfignat – common, convenient, command-line-controlled
+# compile-time configuration of software built with the GNAT tools. For more
+# information about Comfignat, see http://www.Rombobeorn.se/Comfignat/.
+
+
 # This file contains generic Make code. It is designed to be included by other
 # makefiles, called containing makefiles, which add information specific to the
 # project at hand. Builds are controlled by GNAT project files which import the
@@ -19,7 +24,7 @@
 # system. Usage projects and the Comfignat project will be preprocessed with
 # Gnatprep. (Build projects may also be preprocessed.)
 #
-# If a directory project is provided, then the project files will get the
+# If a directories project is provided, then the project files will get the
 # directory variables from there, otherwise the Make variables will be used.
 #
 # This file may not work with other Make clones than GNU Make. (Reusable Make
@@ -39,17 +44,28 @@ GNAT_BUILDER ?= gprbuild
 # If GNAT_BUILDER looks like it will invoke Gnatmake, then make the default
 # value of GNATFLAGS compatible with Gnatmake. Otherwise make it suitable for
 # building multi-language projects with GPRbuild.
-ifeq ($(findstring gnatmake,${notdir ${lastword ${GNAT_BUILDER}}}),)
-   GNATFLAGS ?= ${GNAT_BUILDER_FLAGS} \
-                -cargs:Ada ${ADAFLAGS} -cargs:C ${CFLAGS} \
-                -cargs:C++ ${CXXFLAGS} -cargs:Fortran ${FFLAGS} \
-                -largs ${LDFLAGS}
-else
-   GNATFLAGS ?= ${GNAT_BUILDER_FLAGS} -cargs ${ADAFLAGS} -largs ${LDFLAGS}
-endif
+GNATFLAGS ?= ${if ${findstring gnatmake, \
+                               ${notdir ${call mung_string,${GNAT_BUILDER}}}}, \
+                  ${GNAT_BUILDER_FLAGS} \
+                     -cargs ${ADAFLAGS} \
+                     -bargs ${GNATBINDFLAGS} \
+                     -largs ${GNATLINKFLAGS} ${LDFLAGS}, \
+                  ${GNAT_BUILDER_FLAGS} \
+                     -cargs:Ada ${ADAFLAGS} \
+                     -cargs:C ${CPPFLAGS} ${CFLAGS} \
+                     -cargs:C++ ${CPPFLAGS} ${CXXFLAGS} \
+                     -cargs:Fortran ${FFLAGS} \
+                     -bargs ${GNATBINDFLAGS} \
+                     -largs ${LDFLAGS}}
 
 # (DESTDIR is also supported.)
 
+# Containing makefiles may assign default values to the options variables
+# GNAT_BUILDER_FLAGS, ADAFLAGS, CPPFLAGS, CFLAGS, CXXFLAGS, FFLAGS,
+# GNATBINDFLAGS, GNATLINKFLAGS and LDFLAGS if they are undefined in the
+# environment, but should expect that users and distributions may override
+# those defaults.
+
 
 #
 # These variables should be overridden on the command line as needed, but will
@@ -57,72 +73,138 @@ endif
 #
 
 dirgpr =
-# dirgpr should be the filename of the directory project if there is one. It
-# becomes the Gnatprep symbols Directory_GPR and Directory_Project.
+# dirgpr should be the filename of the target system's directories project if
+# there is one. The Gnatprep symbols Directories_GPR and Directories_Project
+# will be derived from dirgpr, and project files will be configured to use the
+# directories project.
+
+relocatable_package = false
+# If relocatable_package is true, then directory variables in project files
+# will be configured with relative pathnames so that the installed directory
+# tree as a whole can be moved to another location in the filesystem without
+# breaking the project files.
+# dirgpr takes precedence over relocatable_package.
 
 prefix        = /usr/local
 exec_prefix   = ${prefix}
-bindir        = ${exec_prefix}/bin
-libexecdir    = ${exec_prefix}/libexec
 datarootdir   = ${prefix}/share
-datadir       = ${datarootdir}
-sysconfdir    = ${prefix}/etc
 localstatedir = ${prefix}/var
-includedir    = ${prefix}/include
-libdir        = ${exec_prefix}/lib
-gprdir        = ${datarootdir}/gpr
-localedir     = ${datarootdir}/locale
-mandir        = ${datarootdir}/man
-infodir       = ${datarootdir}/info
-# These are the directories where different kinds of files will be installed on
-# the target system. Some of these directory variables aren't used in this file
-# but may be needed in containing makefiles.
-
-builddir = build
+# These variables are used in constructing the default values of the directory
+# variables below.
+
+bindir     = ${exec_prefix}/bin
+libexecdir = ${exec_prefix}/libexec
+datadir    = ${datarootdir}
+sysconfdir = ${prefix}/etc
+statedir   = ${localstatedir}/lib
+cachedir   = ${localstatedir}/cache
+logdir     = ${localstatedir}/log
+includedir = ${prefix}/include
+libdir     = ${exec_prefix}/lib
+gprdir     = ${datarootdir}/gpr
+localedir  = ${datarootdir}/locale
+mandir     = ${datarootdir}/man
+infodir    = ${datarootdir}/info
+miscdocdir = ${datarootdir}/doc
+runtimedir = /run
+lockdir    = ${runtimedir}/lock
+# These are the directories where different kinds of files will be located on
+# the target system.
+
+builddir = ${CURDIR}
 objdir   = ${builddir}/obj
 stagedir = ${builddir}/stage
+# builddir is the build directory, which may be separate from the source tree.
 # Intermediate files produced during the build are kept in objdir. Files to be
-# installed are written to stagedir, and then copied to their destination in
+# installed are written under stagedir, and then copied to their destination in
 # the installation step.
 
-ifeq (${DESTDIR},)
-   install_cp_flags =
-else   
-   install_cp_flags = --preserve=timestamps
-endif
-# Timestamps are preserved when installation is done to a staging directory. 
+# Containing makefiles should avoid modifying the directory variables. Users
+# should be able to rely on these defaults.
+
+install_cp_flags = ${if ${DESTDIR},--preserve=timestamps}
+# Timestamps are preserved when installation is done to a staging directory.
 # This matters for files that aren't generated during the build but copied from
 # the source tree. Timestamps are not preserved when installation is done
-# directly to the target system, because that would change the timestamps of 
+# directly to the target system, because that would change the timestamps of
 # existing directories.
 
 
 #
-# Containing makefiles should assign or append to these variables as needed:
+# Containing makefiles may use these variables in their rules, but nothing
+# should modify them:
 #
 
-ifneq (${origin configured_files},file)
-   configured_files := ${basename ${wildcard *.in}}
-endif
-# configured_files is a list of files to be produced in the preprocessing step
-# at the beginning of the build. Containing makefiles may override it or append
-# additional filenames to it.
+srcdir := ${abspath ${dir ${lastword ${MAKEFILE_LIST}}}}
+# srcdir is the root of the source tree, computed as the directory part of the
+# last pathname in MAKEFILE_LIST – which is this file since there is no include
+# directive above this point.
+
+stage_bindir     = ${stagedir}${bindir}
+stage_libexecdir = ${stagedir}${libexecdir}
+stage_datadir    = ${stagedir}${datadir}
+stage_sysconfdir = ${stagedir}${sysconfdir}
+stage_statedir   = ${stagedir}${statedir}
+stage_cachedir   = ${stagedir}${cachedir}
+stage_logdir     = ${stagedir}${logdir}
+stage_includedir = ${stagedir}${includedir}
+stage_libdir     = ${stagedir}${libdir}
+stage_gprdir     = ${stagedir}${gprdir}
+stage_localedir  = ${stagedir}${localedir}
+stage_mandir     = ${stagedir}${mandir}
+stage_infodir    = ${stagedir}${infodir}
+stage_miscdocdir = ${stagedir}${miscdocdir}
+# These are the directories where different kinds of files to be installed are
+# written during the build.
+
+preprocess_file = "${GNATPREP}" ${firstword ${filter %.gp,$^}} $@ \
+                  ${options_preprocessing} ${Gnatprep_arguments} \
+                  ${if ${filter ${notdir $@},${notdir ${usage_GPRs}}}, \
+                       ${usage_directories}, \
+                       '-DSrcdir="${srcdir}"'}
+# preprocess_file is a command for use in recipes. It runs the first .gp file
+# among the rule's prerequisites through Gnatprep to produce the target. If the
+# target is a usage project, then the usage-relevant directory variables are
+# conveyed to it as Gnatprep symbols. Otherwise srcdir is conveyed.
+
+build_GPR = "${GNAT_BUILDER}" -P ${firstword ${filter %.gpr,$^}} \
+            -aP${srcdir} -aP${builddir} -p \
+            ${options_building} ${builder_arguments} ${GNATFLAGS}
+# build_GPR is a command for use in recipes. It performs a build controlled by
+# the first project file among the rule's prerequisites.
+
+
+#
+# Containing makefiles should assign or append to these variables as needed:
+#
 
 ifneq (${origin build_GPRs},file)
-   build_GPRs :=
+   build_GPRs =
 endif
 # build_GPRs shall name one or more project files for building the software.
 # These project files will be used when "make" or "make build" is invoked.
 
 ifneq (${origin usage_GPRs},file)
-   usage_GPRs :=
+   usage_GPRs =
 endif
 # If the build produces libraries, then usage_GPRs shall name the project files
 # that other projects should import to link to the libraries. These project
 # files will be installed to the target system.
 
+ifneq (${origin preprocessed_files},file)
+   preprocessed_files = \
+      ${filter-out ${notdir ${usage_GPRs}}, \
+                   ${basename ${notdir ${wildcard ${srcdir}/*.gp}}}}
+endif
+# preprocessed_files is a list of files to be produced in the preprocessing
+# step at the beginning of the build. Containing makefiles may override it or
+# append additional filenames to it.
+# The files are assumed to be needed during the build. The default list is all
+# the .gp files in srcdir except for usage projects, minus the .gp suffix. This
+# includes comfignat.gpr.
+
 ifneq (${origin options},file)
-   options :=
+   options =
 endif
 # options may be assigned a list of variable names. Those variables may be
 # overridden on the command line, and will be defined as Gnatprep symbols.
@@ -130,65 +212,255 @@ endif
 # The containing makefile should assign a default value to each variable unless
 # it shall be mandatory to always set the option on the command line.
 
-ifneq (${origin Gnatprep_definitions},file)
-   Gnatprep_definitions :=
+ifneq (${origin Gnatprep_arguments},file)
+   Gnatprep_arguments =
 endif
-# Any text assigned to Gnatprep_definitions will be included in the Gnatprep
+# Any text assigned to Gnatprep_arguments will be included in the Gnatprep
 # command line. It may be used for additional symbol definitions.
 
+ifneq (${origin builder_arguments},file)
+   builder_arguments =
+endif
+# Any text assigned to builder_arguments will be included in the GPRbuild or
+# Gnatmake command line. It may be used for external variables for project
+# files or other arguments that are essential for the build to work. Global
+# default values for optional arguments should be set in the options variables
+# instead.
+
+VPATH += ${srcdir} ${builddir}
+# VPATH is a list of directories that Make should search for prerequisites.
+
+configuration_variables += \
+   GNATPREP GNAT_BUILDER \
+   GNAT_BUILDER_FLAGS ADAFLAGS CPPFLAGS CFLAGS CXXFLAGS FFLAGS GNATBINDFLAGS \
+   GNATLINKFLAGS LDFLAGS GNATFLAGS \
+   DESTDIR \
+   dirgpr relocatable_package \
+   prefix exec_prefix datarootdir localstatedir \
+   bindir libexecdir datadir sysconfdir statedir cachedir logdir includedir \
+   libdir gprdir localedir mandir infodir miscdocdir runtimedir lockdir \
+   objdir stagedir \
+   install_cp_flags \
+   ${options}
+# configuration_variables is a list of variables that can be saved in the
+# persistent configuration with "make configure". Containing makefiles may
+# append additional variable names.
+
+
+#
+# Read the configuration file if there is one:
+#
+
+configuration = ${builddir}/comfignat_configuration.mk
+
+-include ${configuration}
+
 
 #
-# Compute the symbol definitions for Gnatprep, and some other data that the
-# rules need:
+# Ensure that builddir, objdir and stagedir are absolute pathnames:
 #
 
-# Convey objdir and stagedir to Gnatprep.
-definitions = '-DObjdir="${objdir}"' '-DStagedir="${stagedir}"'
+ifeq (${origin builddir},command line)
+   override builddir := ${abspath ${builddir}}
+endif
+ifeq (${origin objdir},command line)
+   override objdir := ${abspath ${objdir}}
+   objdir_is_configured = true
+endif
+ifeq (${origin stagedir},command line)
+   override stagedir := ${abspath ${stagedir}}
+   stagedir_is_configured = true
+endif
+# These pathnames need to be absolute in project files, because a pathname
+# relative to a project file can be wrong when a separate build directory is
+# used and project files are both in srcdir and in builddir. objdir and
+# stagedir also need to be absolute in the configuration file because the
+# working directory might change between Make invocations.
+# Once modified the variables are no longer of command line origin, so they are
+# marked as configured so that "make configure" will save them.
+
 
-# Convey the prefix variables too, although they're supposed to be unused when
-# the preprocessing is done with Make.
-definitions += '-DPrefix="${prefix}"' '-DExec_Prefix="${exec_prefix}"'
+#
+# Compute symbol definitions for Gnatprep and external variable assignments for
+# build projects:
+#
+
+nil =
+inert_space = _Comfignat_magic_protective_space_character_substitute_
+inert_percent = _Comfignat_magic_protective_percent_character_substitute_
+mung_string = ${subst %,${inert_percent},${subst ${nil} ,${inert_space},${1}}}
+unmung_string = ${subst ${inert_percent},%,${subst ${inert_space}, ,${1}}}
+# mung_string and unmung_string are used to prevent Make from interpreting
+# space and percent characters in strings.
+
+relativize = ${if ${filter ${2}%,${1}}, \
+                  ${3}${1:${2}%=%}, \
+                  ${call relativize,${1},${dir ${2:%/=%}},${3}../}}
+# relativize is the recursive algorithm that converts an absolute pathname into
+# a relative one.
+# Parameters:
+#    1: an absolute pathname to convert to relative
+#    2: the absolute base pathname, being shortened until it's a prefix of 1
+#    3: a growing series of "../" to lead the relative pathname with
+# If 2 is a prefix of 1, then return 3 concatenated with the part of 1 that
+# differs from 2. Otherwise delete the last element of 2, add one level of
+# "../" to 3, and repeat.
+# Within relativize all pathnames have one trailing slash so that only whole
+# directory names will match. Otherwise "/usr/lib" could match "/usr/lib64" for
+# example.
+
+prepare_pathname = ${subst //,/,${abspath ${call mung_string,${1}}}/}
+# prepare_pathname prepares a pathname for use as a parameter to relativize.
+#    · Protect space and percent characters from interpretation by Make.
+#    · Normalize the pathname, eliminating ".", ".." and "//".
+#    · Append a slash.
+#    · If the input was "/", then it is now "//". Change that back to "/".
+
+relative_to = \
+   ${or ${call unmung_string \
+              ,${patsubst %/,%,${call relativize \
+                                     ,${call prepare_pathname,${1}} \
+                                     ,${call prepare_pathname,${2}},}}},.}
+# relative_to converts an absolute pathname into a relative one. What it
+# actually does is to prepare the input to relativize and fix up its output.
+# Parameters:
+#    1: an absolute pathname to convert to relative
+#    2: the absolute base pathname that 1 shall be made relative to
+# Processing:
+#    · Prepare the two input pathnames with prepare_pathname.
+#    · Call relativize with the prepared pathnames for parameters 1 and 2, and
+#      an empty string for 3.
+#    · Strip the result of surrounding spaces and the trailing slash.
+#    · Reverse the protection of space and percent characters.
+#    · If the result is an empty string, then return "." instead.
+
+maybe_relative_to = \
+   ${if ${or ${filter-out 1,${words ${relocatable_package}}}, \
+             ${filter-out true false,${relocatable_package}}}, \
+        ${error relocatable_package must be "true" or "false"} \
+       ,${if ${filter true,${relocatable_package}} \
+            ,${call relative_to,${1},${2}},${1}}}
+# maybe_relative_to converts an absolute pathname into a relative one if a
+# relocatable package is desired.
+# Parameters:
+#    1: an absolute pathname to convert to relative
+#    2: the absolute base pathname that 1 may be made relative to
+# First check that the value of relocatable_package is a single word and that
+# that word is either "true" or "false". Complain and stop if that isn't so.
+# Then, if relocatable_package is "true", let relative_to convert the pathname,
+# otherwise return parameter 1 unchanged.
+
+embed_pathname = ${call maybe_relative_to,${1},${bindir}}
+# embed_pathname converts an absolute pathname into the right form for
+# inclusion in a program, which means that it is made relative to bindir if a
+# relocatable package is desired.
+
+usage_pathname = ${call maybe_relative_to,${1},${gprdir}}
+# usage_pathname converts an absolute pathname into the right form for
+# inclusion in a usage project, which means that it is made relative to gprdir
+# if a relocatable package is desired.
+
+# Convey builddir, objdir and stagedir to comfignat.gpr.
+all_directories = '-DBuilddir="${builddir}"' '-DObjdir="${objdir}"' \
+                  '-DStagedir="${stagedir}"'
+
+# Convey the builder-irrelevant directory variables, making them available to
+# build projects for inclusion in binaries. Make most of the pathnames relative
+# if a relocatable package is desired.
+all_directories += '-DDatadir="${call embed_pathname,${datadir}}"'
+all_directories += '-DSysconfdir="${call embed_pathname,${sysconfdir}}"'
+all_directories += '-DStatedir="${call embed_pathname,${statedir}}"'
+all_directories += '-DCachedir="${call embed_pathname,${cachedir}}"'
+all_directories += '-DLogdir="${call embed_pathname,${logdir}}"'
+all_directories += '-DGPRdir="${call embed_pathname,${gprdir}}"'
+all_directories += '-DLocaledir="${call embed_pathname,${localedir}}"'
+all_directories += '-DMandir="${call embed_pathname,${mandir}}"'
+all_directories += '-DInfodir="${call embed_pathname,${infodir}}"'
+all_directories += '-DMiscdocdir="${call embed_pathname,${miscdocdir}}"'
+all_directories += '-DRuntimedir="${runtimedir}"'
+all_directories += '-DLockdir="${lockdir}"'
+# runtimedir and lockdir belong to the operating system and are used for
+# communication between subsystems. It wouldn't make sense for an application
+# to have its own runtimedir. Therefore these variables are always absolute
+# pathnames.
 
-# If a directory project is used, then make project files take the directory
-# variables from there. Otherwise convey the ones defined above.
 ifeq (${dirgpr},)
-   definitions += '-DBindir="${bindir}"' '-DLibexecdir="${libexecdir}"'
-   definitions += '-DIncludedir="${includedir}"' '-DLibdir="${libdir}"'
+
+   # No directories project was provided, so convey even the builder-relevant
+   # directory variables to comfignat.gpr, and convey the usage-relevant ones
+   # to usage projects in the form that usage projects need.
+
+   all_directories += '-DBindir="${call embed_pathname,${bindir}}"'
+   all_directories += '-DLibexecdir="${call embed_pathname,${libexecdir}}"'
+   all_directories += '-DIncludedir="${call embed_pathname,${includedir}}"'
+   all_directories += '-DLibdir="${call embed_pathname,${libdir}}"'
+
+   all_directories += '-DStage_Bindir="${stage_bindir}"'
+   all_directories += '-DStage_Libexecdir="${stage_libexecdir}"'
+   all_directories += '-DStage_Includedir="${stage_includedir}"'
+   all_directories += '-DStage_Libdir="${stage_libdir}"'
+
+   usage_directories = '-DIncludedir="${call usage_pathname,${includedir}}"' \
+                       '-DLibdir="${call usage_pathname,${libdir}}"'
+
 else
-   directory_project := ${basename ${notdir ${dirgpr}}}
-   definitions += '-DDirectory_GPR="${dirgpr}"'
-   definitions += '-DDirectory_Project=${directory_project}'
-   definitions += '-DBindir=${directory_project}.Bindir'
-   definitions += '-DLibexecdir=${directory_project}.Libexecdir'
-   definitions += '-DIncludedir=${directory_project}.Includedir'
-   definitions += '-DLibdir=${directory_project}.Libdir'
+
+   # A directories project is used, so make project files take the builder-
+   # relevant directory variables from there.
+
+   directories_project := ${basename ${notdir ${call mung_string,${dirgpr}}}}
+
+   all_directories += '-DDirectories_GPR="${dirgpr}"'
+   all_directories += '-DDirectories_Project=${directories_project}'
+   all_directories += '-DBindir=${directories_project}.Bindir'
+   all_directories += '-DLibexecdir=${directories_project}.Libexecdir'
+   all_directories += '-DIncludedir=${directories_project}.Includedir'
+   all_directories += '-DLibdir=${directories_project}.Libdir'
+
+   usage_directories = '-DDirectories_GPR="${dirgpr}"' \
+                       '-DIncludedir=${directories_project}.Includedir' \
+                       '-DLibdir=${directories_project}.Libdir'
+
 endif
 
-# Convey boolean options to Gnatprep.
-definitions += \
-   ${foreach option,${options},\
-             ${if ${and ${filter-out environment,${origin ${option}}},\
-                        ${filter 1,${words ${${option}}}},\
-                        ${filter true false,${${option}}}},\
-                  -D${option}=${${option}},\
-                  ${error ${option} must be "true" or "false".}}}
+option_values = \
+   ${foreach option,${options}, \
+             ${if ${and ${filter-out environment,${origin ${option}}}, \
+                        ${filter 1,${words ${${option}}}}, \
+                        ${filter true false,${${option}}}}, \
+                  ${option}=${${option}}, \
+                  ${error ${option} must be "true" or "false"}}}
 # For each variable listed in options, check that it didn't come from the
 # environment (to prevent accidents), that its value is a single word, and that
-# that word is either "true" or "false". If so, append a symbol definition;
+# that word is either "true" or "false". If so, output a name/value pair;
 # otherwise complain and stop.
 
-# Convey any additional symbols that the containing makefile has defined.
-definitions += ${Gnatprep_definitions}
+# Convey boolean options to Gnatprep.
+options_preprocessing = ${addprefix -D,${option_values}}
 
-build_targets = ${addsuffix .phony_target,${build_GPRs}}
+# Convey boolean options to build projects.
+options_building = ${addprefix -X,${option_values}}
+
+
+#
+# Some other data that the rules below need:
+#
+
+delegation_command := @$${MAKE} --file=${abspath ${firstword ${MAKEFILE_LIST}}}\
+                     --include-dir=${srcdir} --no-print-directory
+# delegation_command is the Make command line that delegating makefiles in
+# separate build directories use to delegate commands to the main makefile. The
+# first pathname in MAKEFILE_LIST is the main makefile.
 
-stage_any_GPRs = ${if ${usage_GPRs},stage_GPRs}
+build_targets = ${addsuffix .phony_target,${build_GPRs}}
+# A phony target is defined for each build project, and the job of determining
+# whether the project needs rebuilding is delegated to the builder.
 
-build_GPR = "${GNAT_BUILDER}" -P ${firstword ${filter %.gpr,$^}} -p \
-            ${GNATFLAGS} -margs
-# build_GPR is a command for use in recipies. It performs a build controlled by
-# the first project file among the rule's prerequisites. Arguments for the
-# builder may be appended.
+staged_usage_GPRs = ${addprefix ${stage_gprdir}/,${usage_GPRs}}
+preprocessed_files_in_builddir = ${addprefix ${builddir}/,${preprocessed_files}}
+# When usage projects are preprocessed they are written to stage_gprdir. Other
+# preprocessed files are assumed to be needed during the build and are written
+# to builddir.
 
 
 #
@@ -197,24 +469,76 @@ build_GPR = "${GNAT_BUILDER}" -P ${firstword ${filter %.gpr,$^}} -p \
 
 .SECONDEXPANSION:
 
-all: build
-
-%.gpr: %.gpr.in
-	"${GNATPREP}" $< $@ ${definitions}
-
-configure: $${configured_files}
-
-%.gpr.phony_target: %.gpr configure
+Comfignat_default_goal: build
+
+# How to make directories:
+${builddir} ${stage_gprdir}:
+	mkdir -p $@
+
+# How to initialize a build directory with a delegating makefile:
+${builddir}/Makefile: | ${builddir}
+	@echo 'Writing $@.'
+	@( echo 'Comfignat_default_goal: force ; ${delegation_command}'; \
+	   echo '%: force ; ${delegation_command} $$@'; \
+	   echo 'force: ;'; \
+	   echo 'Makefile: ;' \
+	 ) > $@
+# This rule generates a delegating makefile in a separate build directory. The
+# generated makefile delegates all commands to the main makefile. The default
+# rule invokes the main makefile without a specified goal, triggering the main
+# makefile's default goal. A match-anything rule forwards any specified goals
+# to the main makefile. An empty recipe for "Makefile" prevents Make from using
+# the match-anything rule to update the makefile.
+
+# How to save configured variables:
+configure:: ${builddir}/Makefile
+	@echo "Writing ${configuration}."
+	@( ${foreach variable,${configuration_variables}, \
+	             ${if ${or ${findstring command line, \
+	                                    ${origin ${variable}}}, \
+	                       ${filter true,${${variable}_is_configured}}}, \
+	                  echo 'ifneq "$${origin ${variable}}" "command line"';\
+	                  echo 'override ${variable} = ${value ${variable}}'; \
+	                  echo 'endif'; \
+	                  echo '${variable}_is_configured = true';}} \
+	   true \
+	 ) > "${configuration}"
+# Out of the variables listed in configuration_variables, all that were
+# overridden on the command line, and all that were previously configured, are
+# written to the configuration file. Configured values override defaults
+# defined later in the containing makefile, but can be overridden on the
+# command line. A variable is considered previously configured if there is
+# another variable with "_is_configured" appended to its name and a value of
+# "true". Such a variable is also written for each configured variable. As a
+# side effect of this it is possible to delete a variable V from the
+# configuration by running "make configure V_is_configured=false".
+
+# How to preprocess the project Comfignat:
+${builddir}/comfignat.gpr: comfignat.gpr.gp | ${builddir}
+	"${GNATPREP}" $< $@ -DInvoked_By_Makefile ${all_directories}
+
+# How to preprocess files that are needed during the build:
+${builddir}/%: %.gp | ${builddir}
+	${preprocess_file}
+
+# How to preprocess usage projects:
+${stage_gprdir}/%: %.gp | ${stage_gprdir}
+	${preprocess_file}
+
+# How to stage usage projects that don't need preprocessing:
+${stage_gprdir}/%: % | ${stage_gprdir}
+	cp -p $< $@
+
+preprocess: $${preprocessed_files_in_builddir}
+
+# How to build a project:
+%.gpr.phony_target: %.gpr preprocess
 	${build_GPR}
 # Instead of tracking dependencies between project files, this rule simply
-# requires that all preprocessing is done before any project is built.
+# requires that all preprocessing of files that are needed during the build is
+# done before any project is built.
 
-stage_GPRs: $${usage_GPRs}
-	mkdir -p "${stagedir}${gprdir}"
-	cp -p ${usage_GPRs} "${stagedir}${gprdir}"
-.PHONY: stage_GPRs
-
-build: $${build_targets} $${stage_any_GPRs}
+build: $${build_targets} $${staged_usage_GPRs}
 
 ${stagedir}:
 	@${MAKE} build --no-print-directory
@@ -222,10 +546,16 @@ ${stagedir}:
 # something has been built then "make install" doesn't rebuild anything, just
 # copies the built files to their destination.
 
+# How to install what has been built and staged:
 install: ${stagedir}
 	mkdir -p "${DESTDIR}/"
 	cp -RPf ${install_cp_flags} "${stagedir}"/* "${DESTDIR}/"
 .PHONY: install
 
 clean::
-	rm -Rf ${builddir} ${configured_files}
+	rm -Rf "${objdir}" "${stagedir}" ${preprocessed_files_in_builddir}
+
+unconfigure::
+	rm -f "${configuration}"
+
+distclean: clean unconfigure