Re: AC_PROG_LEX behavior

[Eric Blake]

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[moving to autoconf-patches]

According to Ralf Wildenhues on 6/4/2009 3:05 PM:
> Hi Patrick,

Hi Ralf, Patrick,

>>>
>>> Is this intentional ? Is it documented somewhere ? In other words, is it
>>> ok for me to check for "test $LEX != ':'" to discover success ?
> 
> Hmm.  I'd probably say that would be ok.  Not because I think it is a
> good idea to document that LEX is set to ':' when not found, but because
> I think we cannot change that anyway because software relies on it.
> 
> So, if Eric wants to adjust the documentation to reflect the ':' value
> of LEX here, I'd be fine with that.

Sounds good.  I'm applying the patch below.

> then but of course the user could still fool you by adding a wrapper
> script for a non-flex lex or some other program.  Thus I think the
> configure.ac test should just try to execute `$LEX --version' or look
> for some needed option in the --help output or so.

I think I covered this issue, too.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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>From bef5cc354c3d837446ebb730426e7f9ab32622ec Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Sat, 6 Jun 2009 10:38:23 -0600
Subject: [PATCH] Document fallback behavior of AC_PROG_LEX.

* doc/autoconf.texi (Particular Programs) <AC_PROG_LEX>: Mention
why fallback is :, and that a --version check must be used to
determine whether flex was found.
Reported by Patrick Welche.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog         |    8 ++++++++
 doc/autoconf.texi |   11 ++++++++++-
 2 files changed, 18 insertions(+), 1 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 8a994a9..45cc4b4 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2009-06-06  Eric Blake  <address@hidden>
+
+       Document fallback behavior of AC_PROG_LEX.
+       * doc/autoconf.texi (Particular Programs) <AC_PROG_LEX>: Mention
+       why fallback is :, and that a --version check must be used to
+       determine whether flex was found.
+       Reported by Patrick Welche.
+
 2009-05-28  Jim Meyering  <address@hidden>

        Fix syntax errors in autoconf.texi.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 5eb8964..215c864 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -3922,7 +3922,11 @@ Particular Programs
 If @code{flex} is found, set output variable @code{LEX} to @samp{flex}
 and @code{LEXLIB} to @option{-lfl}, if that library is in a standard
 place.  Otherwise set @code{LEX} to @samp{lex} and @code{LEXLIB} to
address@hidden
address@hidden, if found.  If neither variant is available, set @code{LEX}
+to @samp{:}; for packages that ship the generated @file{file.yy.c}
+alongside the source @file{file.l}, this default allows users without a
+lexer generator to still build the package even if the timestamp for
address@hidden is inadvertantly changed.

 Define @code{YYTEXT_POINTER} if @code{yytext} defaults to @samp{char *} instead
 of to @samp{char []}.  Also set output variable @code{LEX_OUTPUT_ROOT} to
@@ -3952,6 +3956,11 @@ Particular Programs
 The shell script @command{missing} can be found in the Automake
 distribution.

+Remember that the user may have supplied an alternate location in
address@hidden, so if Flex is required, it is better to check that the user
+provided something sufficient by parsing the output of @samp{$LEX
+--version} than by simply relying on @code{test "x$LEX" = xflex}.
+
 To ensure backward compatibility, Automake's @code{AM_PROG_LEX} invokes
 (indirectly) this macro twice, which causes an annoying but benign
 address@hidden invoked multiple times'' warning.  Future versions
-- 
1.6.3.rc3.2.g4b51