bootstrap: overhaul and improve

This fixes several weaknesses and buglets in the 'bootstrap' convenience
target offered in GNUmakefile (and its supporting code).  Refer to the
extensive code comments in there for more details.

* GNUmakefile: Almost completely rewritten.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>

1 files changed, 62 insertions, 43 deletions

diff --git a/GNUmakefile b/GNUmakefile
index 06766187d..20af004b9 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -15,54 +15,73 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+ifeq ($(filter bootstrap,$(MAKECMDGOALS)),)
+
 ifeq ($(wildcard Makefile),)
-  ifeq ($(filter bootstrap,$(MAKECMDGOALS)),bootstrap)
-    # Allow the user (or more likely the developer) to ask for a bootstrap
-    # of the package; of course, this can happen before configure is run,
-    # and in fact even before it is created.
-  else
-    # Else, If the user runs GNU make but has not yet run ./configure,
-    # give them an helpful diagnostic instead of a cryptic error.
-    $(warning There seems to be no Makefile in this directory.)
-    $(warning You must run ./configure before running 'make'.)
-    $(error Fatal Error)
-  endif
-else
-  include ./Makefile
-  include $(srcdir)/syntax-checks.mk
+  # Any target but 'bootstrap' specified in an unconfigured tree
+  # is an error, env when the user is running GNU make.
+  $(warning There seems to be no Makefile in this directory.)
+  $(warning You must run ./configure before running 'make'.)
+  $(error Fatal Error)
 endif
+include ./Makefile
+include $(srcdir)/syntax-checks.mk
+
+else # ! bootstrap in $(MAKECMDGOALS)
+
+other-targets := $(filter-out bootstrap,$(MAKECMDGOALS))
+config-status := $(wildcard ./config.status)
 
-# To allow bootstrapping also in an unconfigured tree.
-srcdir ?= .
-am__cd ?= CDPATH=. && unset CDPATH && cd
-AM_DEFAULT_VERBOSITY ?= 0
-V ?= $(AM_DEFAULT_VERBOSITY)
+BOOTSTRAP_SHELL ?= /bin/sh
+export BOOTSTRAP_SHELL
 
-ifeq ($(V),0)
-  AM_V_BOOTSTRAP = @echo "  BOOTSTRAP";
-  AM_V_CONFIGURE = @echo "  CONFIGURE";
-  AM_V_REMAKE    = @echo "  REMAKE";
-else
-  AM_V_BOOTSTRAP =
-  AM_V_CONFIGURE =
-  AM_V_REMAKE    =
+# Allow the user (or more likely the developer) to ask for a bootstrap
+# of the package.
+#
+# Two issues that must be kept in mind in the implementation below:
+#
+#  [1] "make bootstrap" can be invoked before 'configure' is run (and in
+#      fact, even before it is created, if we are bootstrapping from a
+#      freshly-cloned checkout).
+#
+#  [2] When re-bootstrapping an already configured tree, we must ensure
+#      that the automatic remake rules for Makefile and company do not
+#      kick in, because the tree might be in an inconsistent state (e.g.,
+#      we have just switched from 'maint' to 'master', and have the built
+#      'automake' script left from 'maint', but the files 'lib/am/*.am'
+#      are from 'master': if 'automake' gets run and used those files --
+#      boom!).
+
+ifdef config-status # Bootstrap from an already-configured tree.
+  # We need the definition of $(srcdir) in the 'bootstrap' rule
+  # below.
+  srcdir := $(shell echo @srcdir@ | $(config-status) --file=-)
+  ifndef srcdir
+    $(error Could not obtain $$(srcdir) from $(config-status))
+  endif
+  # Also, if we are re-bootstrapping an already-configured tree, we
+  # want to re-configure it with the same pre-existing configuration.
+  old-configure-flags := $(shell $(config-status) --config)
+else # Assume we are bootstrapping from an unconfigured srcdir.
+  srcdir := .
+  old-configure-flags :=
 endif
 
-# Must be phony, not to be confused with the 'bootstrap' script.
+configure-flags := $(old-configure-flags) $(BOOTSTRAP_CONFIGURE_FLAGS)
+
 .PHONY: bootstrap
 bootstrap:
-	$(AM_V_BOOTSTRAP)$(am__cd) $(srcdir) && ./bootstrap.sh
-	$(AM_V_CONFIGURE)set -e; \
-	am__bootstrap_configure () { \
-	  $(srcdir)/configure $${1+"$$@"} $(BOOTSTRAP_CONFIGURE_FLAGS); \
-	}; \
-	if test -f $(srcdir)/config.status; then \
-	  : config.status should return a string properly quoted for eval; \
-	  old_configure_flags=`$(srcdir)/config.status --config`; \
-	else \
-	  old_configure_flags=""; \
-	fi; \
-	eval am__bootstrap_configure "$$old_configure_flags"
-	# The "make check" below is to ensure all the testsuite-required
-	# files are rebuilt.
-	$(AM_V_REMAKE)$(MAKE) clean && $(MAKE) check TESTS=t/get-sysconf
+	cd $(srcdir) && $(SHELL) ./bootstrap.sh
+	$(srcdir)/configure $(configure-flags)
+	$(MAKE) clean
+	$(MAKE) check TESTS=t/get-sysconf
+
+# Ensure that all the specified targets but 'bootstrap' (if any) are
+# run with a properly re-bootstrapped tree.
+ifdef other-targets
+$(other-targets): restart
+.PHONY: $(other-targets) restart
+restart: bootstrap; $(MAKE) $(AM_MAKEFLAGS) $(other-targets)
+endif
+
+endif # ! bootstrap in $(MAKECMDGOALS)