buildsystem: sane warning if not using gmake

.gitignore

@@ -1,4 +1,4 @@
-/Makefile
+/GNUmakefile
 /aclocal.m4
 /autom4te.cache/
 /bin/

Makefile

@@ -0,0 +1,26 @@
+#
+# This Makefile serves two purposes:
+#
+# 1) If the user types "make" without having run "configure", we suggest
+#    running configure.
+#
+# 2) Our build system is written for GNU make, and makes liberal use of its
+#    features. We therefore put it into "GNUmakefile", which is picked up by
+#    GNU make, but ignored by other make versions, such as BSD make. Thus, if
+#    the user has BSD make, it will run this Makefile instead -- and we inform
+#    them that they need to use GNU make to compile Semigroups.
+#
+# To learn more about the GAP build system, see README.buildsys.md
+#
+.DEFAULT:
+	@if test -f GNUmakefile ; then \
+	    printf "Please use GNU make to build Semigroups (try 'gmake' or 'gnumake')\n" ; \
+	  else \
+		printf "You need to run "; \
+		if ! test -f configure ; then \
+			printf "./autogen.sh then "; \
+		fi; \
+		printf "./configure before make (please refer to README.md or Chapter 2 of the Semigroups package documentation for details)\n" ; \
+	  fi
+	@exit 1
+all: .DEFAULT

Makefile.gappkg

@@ -3,7 +3,7 @@
 # The build rules in this file are intended for use by GAP packages that
 # want to build a simple GAP kernel extensions. They are based on the
 # GAP build system, and require GNU make. To use this in your GAP
-# package, `include` this file from your primary Makefile. You must also
+# package, `include` this file from your primary GNUmakefile. You must also
 # set several variables beforehand:
 #
 # - GAPPATH must be set to the location of the GAP installation against
@@ -65,7 +65,7 @@ GAP_OBJEXT ?= lo
 # override KEXT_RECONF if your package needs a different invocation
 # for reconfiguring (e.g. `./config.status --recheck` for autoconf)
 ifdef KEXT_USE_AUTOCONF
-KEXT_RECONF ?= ./config.status Makefile
+KEXT_RECONF ?= ./config.status GNUmakefile
 else
 KEXT_RECONF ?= ./configure "$(GAPPATH)"
 endif
@@ -118,20 +118,20 @@ KEXT_DEPFILES = $(patsubst %.$(GAP_OBJEXT),%.d,$(KEXT_OBJS))
 KEXT_DEPFLAGS = -MQ "$@" -MMD -MP -MF $(@D)/$(*F).d
 
 # build rule for C code
-# The dependency on Makefile ensures that re-running configure recompiles everything
-gen/%.$(GAP_OBJEXT): %.c Makefile
+# The dependency on GNUmakefile ensures that re-running configure recompiles everything
+gen/%.$(GAP_OBJEXT): %.c GNUmakefile
 	@mkdir -p $(@D)
 	$(QUIET_GAC)$(GAC) -d -p "$(KEXT_DEPFLAGS)" -p "$(KEXT_CFLAGS)" -c $< -o $@
 
 # build rule for C++ code
-# The dependency on Makefile ensures that re-running configure recompiles everything
-gen/%.$(GAP_OBJEXT): %.cpp Makefile
+# The dependency on GNUmakefile ensures that re-running configure recompiles everything
+gen/%.$(GAP_OBJEXT): %.cpp GNUmakefile
 	@mkdir -p $(@D)
 	$(QUIET_GAC)$(GAC) -d -p "$(KEXT_DEPFLAGS)" -p "$(KEXT_CXXFLAGS)" -c $< -o $@
 
 # build rule for assembler code
-# The dependency on Makefile ensures that re-running configure recompiles everything
-gen/%.$(GAP_OBJEXT): %.s Makefile
+# The dependency on GNUmakefile ensures that re-running configure recompiles everything
+gen/%.$(GAP_OBJEXT): %.s GNUmakefile
 	@mkdir -p $(@D)
 	$(QUIET_GAC)$(GAC) -d -p "$(KEXT_DEPFLAGS)" -p "$(KEXT_CFLAGS)" -c $< -o $@
 
@@ -148,7 +148,7 @@ clean-kext:
 # hook into `make distclean`
 distclean: distclean-kext
 distclean-kext:
-	rm -rf bin gen Makefile
+	rm -rf bin gen GNUmakefile
 	rm -rf doc/_*.xml
 	rm -rf doc/*.aux doc/*.bbl doc/*.blg doc/*.brf doc/*.idx doc/*.idx
 	rm -rf doc/*.ilg doc/*.ind doc/*.log doc/*.out doc/*.pnr doc/*.toc
@@ -163,8 +163,8 @@ check: check-kext
 check-kext:
 	$(GAP) tst/testall.g
 
-# re-run configure if configure, Makefile.in or GAP itself changed
-Makefile: configure Makefile.in $(GAPPATH)/sysinfo.gap
+# re-run configure if configure, GNUmakefile.in or GAP itself changed
+GNUmakefile: configure GNUmakefile.in $(GAPPATH)/sysinfo.gap
 	$(KEXT_RECONF)
 
 ifdef KEXT_USE_AUTOCONF
@@ -182,12 +182,12 @@ configure: $(configure_deps)
 	 fi
 endif # MAINTAINER_MODE
 
-# re-run configure if configure, Makefile.in or GAP itself changed
+# re-run configure if configure, GNUmakefile.in or GAP itself changed
 config.status: configure $(GAPPATH)/sysinfo.gap
 	./config.status --recheck
 
-# update Makefile if config.status changed
-Makefile: config.status
+# update GNUmakefile if config.status changed
+GNUmakefile: config.status
 
 gen/pkgconfig.h: gen/pkgconfig.h.stamp
 	@if test ! -f $@; then rm -f $<; else :; fi
@@ -218,7 +218,7 @@ endif # KEXT_USE_AUTOCONF
 .PHONY: check-kext clean-kext distclean-kext doc-kext
 
 ########################################################################
-# Makefile debugging trick:
+# GNUmakefile debugging trick:
 # call print-VARIABLE to see the runtime value of any variable
 ########################################################################
 print-%:

configure.ac

@@ -17,7 +17,7 @@ AC_CONFIG_MACRO_DIR([m4])
 AX_PREFIX_CONFIG_H([src/semigroups-config.hpp],[semigroups],[gen/pkgconfig.h])
 
 dnl ## abs_top_builddir seems to hold the top build dir for the subpackage
-dnl ## libsemigroups which is why this contains ../ 
+dnl ## libsemigroups which is why this contains ../
 AC_PREFIX_DEFAULT('${abs_top_builddir}/../bin/')
 
 dnl ##
@@ -67,5 +67,5 @@ AX_CHECK_HPCOMBI
 dnl ##
 dnl ## Output everything
 dnl ##
-AC_CONFIG_FILES([Makefile])
+AC_CONFIG_FILES([GNUmakefile])
 AC_OUTPUT