Re: Bison 3.5.91 with older Flex

[Akim Demaille]

Hi Bruno,

> Le 3 mai 2020 à 01:14, Bruno Haible <address@hidden> a écrit :
> 
> When a flex version < 2.6.4 is in $PATH, bison fails to build.
> [...]
> I don't know what the flex command is that the config.status attempts to
> execute (because you chose to hide it).

Passing V=1 to 'make' restores the initial verbosity.

> $ cd examples/c/reccalc/
> 
> $ grep -i flex Makefile local.mk 
> Makefile:FLEX = flex
> Makefile:       $(FLEX) $(FLEXFLAGS) -o$*.c --header-file=$*.h $<
> local.mk:if FLEX_WORKS
> local.mk:endif FLEX_WORKS
> 
> Apparently the --header-file option is not supported.
> 
> Indeed: https://github.com/westes/flex/blob/master/NEWS
> shows that the option --header was introduced in version 2.5.6.
> And 
> https://github.com/westes/flex/commit/56a530abf7e16ce35ea36748ff2e86f2f0022bc2
> shows that the option --header-file was introduced in version 2.6.4.

Thank you very much for the thorough investigation, and precise diagnostic!

I'll install this.  Cheers!

commit bc0511aa5f3dae16614c94b6ac9ed04c0202639d
Author: Akim Demaille <address@hidden>
Date:   Sun May 3 09:51:18 2020 +0200

    examples: beware of the portability of flex --header-file
    
    The option --header was introduced in version 2.5.6.
    The option --header-file was introduced in version 2.6.4.
    Reported by Bruno Haible.
    https://lists.gnu.org/r/bug-bison/2020-05/msg00013.html
    
    So use --header, and do bother with versions that don't support it.
    
    * m4/flex.m4: Check whether flex supports --header.
    * configure.ac (FLEX_WORKS, FLEX_CXX_WORKS): Set to false if it doesn't.
    * * examples/c/reccalc/local.mk, examples/c/reccalc/Makefile:
    Use --header rather than --header-file.

diff --git a/configure.ac b/configure.ac
index 68c54a12..c1b0c182 100644
--- a/configure.ac
+++ b/configure.ac
@@ -261,9 +261,8 @@ if ! "$LEX_IS_FLEX" || test "X$LEX" = X:; then
   AC_MSG_WARN([bypassing lex because flex is required])
   LEX=:
 fi
-AM_CONDITIONAL([FLEX_WORKS], [$LEX_IS_FLEX])
-AM_CONDITIONAL([FLEX_CXX_WORKS],
-  [$LEX_IS_FLEX && test $bison_cv_cxx_works = yes])
+AM_CONDITIONAL([FLEX_WORKS], [$LEX_IS_FLEX && $FLEX_SUPPORTS_HEADER_OPT])
+AM_CONDITIONAL([FLEX_CXX_WORKS], [$LEX_WORKS && test $bison_cv_cxx_works = 
yes])
 AC_PROG_YACC
 AC_PROG_RANLIB
 AC_PROG_GNU_M4
diff --git a/examples/c/reccalc/Makefile b/examples/c/reccalc/Makefile
index 84fbd3ee..a64ceedb 100644
--- a/examples/c/reccalc/Makefile
+++ b/examples/c/reccalc/Makefile
@@ -12,7 +12,7 @@ all: $(BASE)
        $(BISON) $(BISONFLAGS) --defines --xml --graph=$*.gv -o $*.c $<
 
 %.c %.h: %.l
-       $(FLEX) $(FLEXFLAGS) -o$*.c --header-file=$*.h $<
+       $(FLEX) $(FLEXFLAGS) -o$*.c --header=$*.h $<
 
 scan.o: parse.h
 parse.o: scan.h
diff --git a/examples/c/reccalc/local.mk b/examples/c/reccalc/local.mk
index de889789..0538f120 100644
--- a/examples/c/reccalc/local.mk
+++ b/examples/c/reccalc/local.mk
@@ -69,7 +69,9 @@ DASH = -
        $(AM_V_LEX)rm -f $@ $@.tmp
        $(AM_V_at)$(MKDIR_P) %D%
        $(AM_V_at)touch $@.tmp
-       $(AM_V_at)$(LEX) $(AM_LFLAGS) $(LFLAGS) -o%D%/scan.c 
--header-file=%D%/scan.h $(srcdir)/%D%/scan.l
+## --header introduced in 2.5.6, renamed as --header-file in 2.6.4.
+## Backward compatibility ensured since --header is an unambiguous prefix.
+       $(AM_V_at)$(LEX) $(AM_LFLAGS) $(LFLAGS) -o%D%/scan.c 
--header=%D%/scan.h $(srcdir)/%D%/scan.l
        $(AM_V_at)mv $@.tmp $@
 
 
diff --git a/m4/flex.m4 b/m4/flex.m4
index f17e7152..911a689e 100644
--- a/m4/flex.m4
+++ b/m4/flex.m4
@@ -41,6 +41,22 @@ else
 fi
 ])
 
+
+AC_CACHE_CHECK([whether flex supports --header=FILE],
+                [ac_cv_prog_lex_supports_header_opt],
+[if _AC_DO_VAR([LEX --header=conftest.h conftest.l]); then
+  ac_cv_prog_lex_supports_header_opt=yes
+else
+  ac_cv_prog_lex_supports_header_opt=no
+fi
+])
+if test "$ac_cv_prog_lex_supports_header_opt" = yes; then
+  FLEX_SUPPORTS_HEADER_OPT=true
+else
+  FLEX_SUPPORTS_HEADER_OPT=false
+fi
+
+
 cat >conftest.l <<_ACEOF[
 %%
 a { ECHO; }