[FYI] {maint} bootstrap: overhaul and improve

[Stefano Lattarini]

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 <address@hidden>
---
 GNUmakefile |  105 +++++++++++++++++++++++++++++++++++------------------------
 1 file changed, 62 insertions(+), 43 deletions(-)

diff --git a/GNUmakefile b/GNUmakefile
index 0676618..20af004 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)
-- 
1.7.9.5