refactor(build): Portable bootstrap in makefiles

Avoid "target-specific variable values" (that looks like
"target: variable=value") that works with GNU make only when building
'stage1flex'. A portable alternative is starting a sub-instance of
'make' with overridden variables (CC="$CC_FOR_BUILD" etc.). Make the
bootstrap work even when EXEEXT and BUILD_EXEEXT might differ. The
makefiles are designed that only the main instance of 'make' would
handle the 'stage1bin/flex$(BUILD_EXEEXT)' so that no data contention
can potentially occur.

.gitignore

@@ -31,6 +31,7 @@ Makefile
 /flex
 /flex.exe
 /libfl.la
+/stage1bin/
 /stage1flex
 /stage1flex.exe
 *.lo

configure.ac

@@ -127,6 +127,10 @@ AC_PATH_PROG([HELP2MAN], help2man, [\${top_srcdir}/build-aux/missing help2man])
     AC_MSG_WARN(help2man: program not found: building man page will not work)
   )
 
+AM_CONDITIONAL([AUTO_BUILD_MAN_PAGE],
+  [test "$HELP2MAN" != "\${top_srcdir}/build-aux/missing help2man" &&
+    { test "x$enable_bootstrap" = xyes || test "$cross_compiling" = no; }])
+
 AC_PATH_PROGS([TEXI2DVI], [gtexi2dvi texi2dvi], [\${top_srcdir}/build-aux/missing texi2dvi])
   AS_IF([test "$TEXI2DVI" = "\${top_srcdir}/build-aux/missing texi2dvi"],
     AC_MSG_WARN(texi2dvi: program not found: building pdf version of manual will not work)

doc/.gitignore

@@ -25,6 +25,3 @@ flex.ps
 version.texi
 flex.html
 flex.t2p
-
-flex
-flex.exe

doc/local.mk

@@ -1,7 +1,7 @@
 if CROSS
-FLEX_FOR_DOC = stage1flex
+FLEX_FOR_DOC = stage1bin/flex
 else
-FLEX_FOR_DOC = flex$(EXEEXT)
+FLEX_FOR_DOC = flex
 endif
 
 TEXI2DVI = @TEXI2DVI@ -I $(srcdir)/examples/manual/
@@ -33,16 +33,44 @@ CLEANFILES += \
 	doc/flex
 
 # Use a fixed program name, without extension (such as ".exe"), for man
-# page generation. 'help2man' strips directory prefix ("./") from the
-# usage string, but not file extensions.
+# page generation. 'help2man' strips directory prefix from the usage
+# string, but not file extensions.
+#
+# Note: Do NOT run the '$(FLEX_FOR_DOC)$(BUILD_EXEEXT)' target in
+# another instance of 'make'! The scanner code also depends on the
+# target and two 'make' instances may contest building the same file.
 
-doc/flex.1: $(srcdir)/configure.ac $(srcdir)/src/cpp-flex.skl $(srcdir)/src/options.c $(srcdir)/src/options.h
-	$(MAKE) $(AM_MAKEFLAGS) $(FLEX_FOR_DOC)
-	$(INSTALL) -m 700 $(FLEX_FOR_DOC) doc/flex$(EXEEXT)
+if AUTO_BUILD_MAN_PAGE
+doc/flex.1: $(FLEX_FOR_DOC)$(BUILD_EXEEXT)
+	$(MKDIR_P) doc
 	$(HELP2MAN) \
 	--name='$(PACKAGE_NAME)' \
 	--section=1 \
 	--source='The Flex Project' \
 	--manual='Programming' \
 	--output=$@ \
-	doc/flex
+	./$(FLEX_FOR_DOC)
+else
+doc/flex.1: $(srcdir)/configure.ac $(srcdir)/src/cpp-flex.skl $(srcdir)/src/options.c $(srcdir)/src/options.h
+	@option_text=''; \
+	{ test '$(FLEX_FOR_DOC)' = flex || \
+	  : $${option_text=" with --enable-bootstrap'"}; }; \
+	echo "error: flex man page outdated; please install help2man and rerun 'configure'$${option_text}" 1>&2;
+	@false
+endif
+
+distclean-local: distclean-local-doc
+
+# Clean the man page in the build directory only if it is not the
+# source directory.
+
+distclean-local-doc:
+	test '$(srcdir)' = . || { \
+	  if mv -f $(srcdir)/doc/flex.1 $(srcdir)/doc/flex.1.tmp; then \
+	  s=0; else s=$$? || :; fi; \
+	  rm -f doc/flex.1 || :; \
+	  test "$$s" -ne 0 || \
+	    mv -f $(srcdir)/doc/flex.1.tmp $(srcdir)/doc/flex.1; \
+	}
+
+.PHONY: distclean-local-doc

src/local.mk

@@ -31,24 +31,67 @@ nodist_stage1flex_SOURCES = \
 	$(SKELINCLUDES)
 
 if CROSS
-stage1flex_LDADD =
+
 stage1flex_SOURCES += \
 	lib/malloc.c \
 	lib/realloc.c
-stage1flex_LINK = $(LIBTOOL) --tag=CC --mode=link $(CC_FOR_BUILD) \
-		  $(CFLAGS_FOR_BUILD) $(LDFLAGS_FOR_BUILD) -o $@
-
-$(stage1flex_OBJECTS): CC=$(CC_FOR_BUILD)
-$(stage1flex_OBJECTS): CFLAGS=$(CFLAGS_FOR_BUILD) -DUSE_CONFIG_FOR_BUILD
-$(stage1flex_OBJECTS): CPP=$(CPP_FOR_BUILD)
-$(stage1flex_OBJECTS): CPPFLAGS=$(CPPFLAGS_FOR_BUILD)
-$(stage1flex_OBJECTS): LDFLAGS=$(LDFLAGS_FOR_BUILD)
+
+stage1flex_CPPFLAGS = -DUSE_CONFIG_FOR_BUILD $(AM_CPPFLAGS)
+
+# This also overrides AM_LIBTOOLFLAGS and AM_LDFLAGS
+stage1flex_LINK = $(LIBTOOL) $(AM_V_lt) --tag=CC $(LIBTOOLFLAGS) \
+	--mode=link $(CC_FOR_BUILD) $(CFLAGS_FOR_BUILD) \
+	$(LDFLAGS_FOR_BUILD) -o $@
+
+stage1flex_LDADD =
+
 else
+
+stage1flex_CPPFLAGS = $(AM_CPPFLAGS)
+
+stage1flex_LINK = $(LIBTOOL) $(AM_V_lt) --tag=CC $(LIBTOOLFLAGS) \
+	--mode=link $(CCLD) $(CFLAGS) $(LDFLAGS) -o $@
+
 stage1flex_LDADD = $(LDADD)
-stage1flex_LINK = $(LINK)
-stage1flex_CFLAGS = $(AM_CFLAGS)
+
 endif
 
+# Suppress build warnings when compiling and linking stage1flex.
+stage1flex_CFLAGS =
+
+# Override the 'stage1flex$(EXEEXT)' target automake would generate.
+# If the compiler is not $(CC_FOR_BUILD) when this target is invoked,
+# delete the object files that would be linked to 'stage1flex' to force
+# rebuild all of them.
+
+stage1flex$(EXEEXT): $(stage1flex_OBJECTS) $(stage1flex_DEPENDENCIES) $(EXTRA_stage1flex_DEPENDENCIES)
+	@rm -f stage1flex$(EXEEXT)
+	@{ test 'x$(CC)' = 'x$(CC_FOR_BUILD)' && test 'x$(CPP)' = 'x$(CPP_FOR_BUILD)'; } || { \
+	  rm -f src/stage1flex-*.$(OBJEXT); \
+	  echo 'error: stage1flex must be built with a native compiler' 1>&2; \
+	  false; \
+	}
+	$(AM_V_CCLD)$(stage1flex_LINK) $(stage1flex_OBJECTS) $(stage1flex_LDADD) $(LIBS)
+
+# The 'stage1bin/flex$(BUILD_EXEEXT)' target is not managed by
+# automake. We use a different file name from the automake-managed
+# 'stage1flex$(EXEEXT)' target to avoid clashing.
+
+stage1bin/flex$(BUILD_EXEEXT):
+	@if test 'x$(EXEEXT)' != 'x$(BUILD_EXEEXT)'; then rm -f stage1flex$(EXEEXT); else :; fi
+	@if test 'x$(OBJEXT)' != 'x$(BUILD_OBJEXT)'; then rm -f src/stage1flex-*.$(OBJEXT); else :; fi
+	$(MAKE) $(AM_MAKEFLAGS) \
+	  CC='$(CC_FOR_BUILD)' \
+	  CPP='$(CPP_FOR_BUILD)' \
+	  CFLAGS='$(CFLAGS_FOR_BUILD)' \
+	  CPPFLAGS='$(CPPFLAGS_FOR_BUILD)' \
+	  LDFLAGS='$(LDFLAGS_FOR_BUILD)' \
+	  EXEEXT='$(BUILD_EXEEXT)' \
+	  OBJEXT='$(BUILD_OBJEXT)' \
+	  stage1flex$(BUILD_EXEEXT)
+	$(MKDIR_P) stage1bin
+	$(INSTALL) -m 700 stage1flex$(BUILD_EXEEXT) $@
+
 flex_SOURCES = \
 	$(COMMON_SOURCES)
 
@@ -108,11 +151,15 @@ EXTRA_DIST += \
 
 MOSTLYCLEANFILES += \
 	$(SKELINCLUDES) \
+	src/stage1flex-*.$(BUILD_OBJEXT) \
 	src/stage1scan.c \
 	src/stage2scan.c \
 	src/stage2compare
 
-CLEANFILES += stage1flex$(EXEEXT)
+CLEANFILES += \
+	stage1bin/flex$(BUILD_EXEEXT) \
+	stage1flex$(BUILD_EXEEXT) \
+	stage1flex$(EXEEXT)
 
 SKELINCLUDES = \
 	src/cpp-flex.h \
@@ -137,8 +184,8 @@ src/go-flex.h: src/go-flex.skl src/mkskel.sh
 # The input and output file names are fixed for deterministic scanner
 # generation. If scan.l is not modified by builders, stage1scan.c should
 # be bit-identical to the scan.c pregenerated on release.
-src/stage1scan.c: src/scan.l stage1flex$(EXEEXT)
-	( cd $(srcdir)/src && $(abs_builddir)/stage1flex$(EXEEXT) \
+src/stage1scan.c: src/scan.l stage1bin/flex$(BUILD_EXEEXT)
+	( cd $(srcdir)/src && $(abs_builddir)/stage1bin/flex$(BUILD_EXEEXT) \
 	  $(AM_LFLAGS) $(LFLAGS) -o scan.c -t scan.l ) >$@ || \
 	{ s=$$?; rm -f $@; exit $$s; }