Re: [PATCH] parse-datetime: avoid "%pure-parser" deprecation warning from Bison 3.4

[Bruno Haible]

Hi Bernhard,

> +     parse-datetime: avoid "%pure-parser" deprecation warning from Bison 3.4

I've pushed your change.

However, I think it would be good for "make" to behave reasonably when bison
is not found or too old.

Here's a proposed patch (untested so far):


2019-07-19  Bruno Haible  <br...@clisp.org>

        parse-datetime: Require Bison 2.7 or newer.
        * m4/parse-datetime.m4 (gl_PARSE_DATETIME): Set PARSE_DATETIME_BISON.
        Code taken from gettext's intl.m4.
        * modules/parse-datetime (Makefile.am): Use PARSE_DATETIME_BISON instead
        of YACC.

diff --git a/m4/parse-datetime.m4 b/m4/parse-datetime.m4
index 597a44c..dd5e643 100644
--- a/m4/parse-datetime.m4
+++ b/m4/parse-datetime.m4
@@ -1,4 +1,4 @@
-# parse-datetime.m4 serial 22
+# parse-datetime.m4 serial 23
 dnl Copyright (C) 2002-2006, 2008-2019 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -26,6 +26,37 @@ AC_DEFUN([gl_C_COMPOUND_LITERALS],
 
 AC_DEFUN([gl_PARSE_DATETIME],
 [
+  dnl parse-datetime.c is generated from parse-datetime.y. It requires bison,
+  dnl because parse-datetime.y uses bison specific features. It requires at
+  dnl least bison-2.7 for %define api.pure.
+  dnl bison is only needed for the maintainer (who touches parse-datetime.y).
+  dnl But in order to avoid separate Makefiles or --enable-maintainer-mode,
+  dnl we put the rule in general Makefile. Now, some people carelessly touch
+  dnl the files or have a broken "make" program, hence the parse-datetime.c
+  dnl rule will sometimes fire. To avoid an error, defines PARSE_DATETIME_BISON
+  dnl to ":" if it is not present or too old.
+  AC_CHECK_PROGS([PARSE_DATETIME_BISON], [bison])
+  if test -z "$PARSE_DATETIME_BISON"; then
+    ac_verc_fail=yes
+  else
+    dnl Found it, now check the version.
+    AC_MSG_CHECKING([version of bison])
+changequote(<<,>>)dnl
+    ac_prog_version=`$PARSE_DATETIME_BISON --version 2>&1 | sed -n 's/^.*GNU 
Bison.* \([0-9]*\.[0-9.]*\).*$/\1/p'`
+    case $ac_prog_version in
+      '') ac_prog_version="v. ?.??, bad"; ac_verc_fail=yes;;
+      2.[7-9]* | [3-9].*)
+changequote([,])dnl
+         ac_prog_version="$ac_prog_version, ok"; ac_verc_fail=no;;
+      *) ac_prog_version="$ac_prog_version, bad"; ac_verc_fail=yes;;
+    esac
+    AC_MSG_RESULT([$ac_prog_version])
+  fi
+  if test $ac_verc_fail = yes; then
+    PARSE_DATETIME_BISON=:
+  fi
+  AC_SUBST([PARSE_DATETIME_BISON])
+
   dnl Prerequisites of lib/parse-datetime.h.
   AC_REQUIRE([AM_STDBOOL_H])
   AC_REQUIRE([gl_TIMESPEC])
diff --git a/modules/parse-datetime b/modules/parse-datetime
index 692da25..d54dafd 100644
--- a/modules/parse-datetime
+++ b/modules/parse-datetime
@@ -38,7 +38,7 @@ parse-datetime.c: parse-datetime.y
                                      y.tab.c parse-datetime.c \
                                      y.tab.h parse-datetime.h \
                                      y.output parse-datetime.output \
-                                     -- $(YACC) $(YFLAGS) $(AM_YFLAGS) && \
+                                     -- $(PARSE_DATETIME_BISON) -y -d 
$(YFLAGS) $(AM_YFLAGS) && \
        sed -e 's|".*/parse-datetime.y"|"parse-datetime.y"|' \
         < parse-datetime.c > parse-datetime.c-t && \
        rm -f parse-datetime.c && \