Bug 242742 - flex broken for %option noyywrap, yyclass, prefix
Summary: flex broken for %option noyywrap, yyclass, prefix
Alias: None
Product: Fedora
Classification: Fedora
Component: flex   
(Show other bugs)
Version: 7
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Petr Machata
QA Contact:
Keywords: Reopened
Depends On:
TreeView+ depends on / blocked
Reported: 2007-06-05 15:57 UTC by Jay Berkenbilt
Modified: 2015-05-05 01:33 UTC (History)
4 users (show)

Fixed In Version: 2.5.33-9.fc7
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of:
Last Closed: 2009-02-10 21:28:39 UTC
Type: ---
Regression: ---
Mount Type: ---
Documentation: ---
Verified Versions:
Category: ---
oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
tarfile containing example.fl and ExampleLexer.hh (10.00 KB, application/x-tar)
2007-06-05 15:57 UTC, Jay Berkenbilt
no flags Details
A modified flex-2.5.33-yy.patch which fixes this issue for me. (2.82 KB, patch)
2007-06-15 22:16 UTC, Srinivas Aji
no flags Details | Diff
Simple test file (1001 bytes, text/plain)
2009-02-09 14:59 UTC, Milos Jakubicek
no flags Details

Description Jay Berkenbilt 2007-06-05 15:57:22 UTC
Description of problem:

A certain combination of options causes flex to generate parsers that redefine
yywrap.  This problem does not happen with vanilla flex 2.5.33.  A perusal of
the changelog suggests that it may have been introduced in 2.5.33-5.

Version-Release number of selected component (if applicable):


I've removed the remaining boilerplate text and am providing examples of how to
reproduce the problem.

Extract the attached files: example.fl and ExampleLexer.hh.

Run the following:

  flex -+ -o FlexLexer.example.cc example.fl
  g++ -c -I. FlexLexer.example.cc

Actual output:

FlexLexer.example.cc:330:1: warning: "yywrap" redefined
FlexLexer.example.cc:23:1: warning: this is the location of the previous definition

Expected output:

There should be no warnings.

The problem is that the patch (flex-2.5.33-yy.patch) creates a definition for
yywrap unconditionally.  It should not do this if %option noyywrap is defined.


Comment 1 Jay Berkenbilt 2007-06-05 15:57:22 UTC
Created attachment 156239 [details]
tarfile containing example.fl and ExampleLexer.hh

Comment 2 Srinivas Aji 2007-06-15 21:50:38 UTC
I am seeing this issue too.
From the flex code and the patch, it looks like the problem is this.

All the symbols being #defined in flex-2.5.33-yy.patch are being modified with
specified prefix only in C mode, not in C++ mode. In C mode, with noyywrap, we
are okay since the output file later defines Prefix_wrap(n) rather than
redifining yywrap.
But in C++ mode, this leads to a redefinition of yywrap.

Solution would be to surround the lines introduced by this patch with
%if-c-only, %endif, (directly for flex.skl and strings of these for skel.c)
since they don't seem to be useful for C++ mode anyway.

I will attach a suitably modified 2.5.33-yy.patch after I test it.

Comment 3 Srinivas Aji 2007-06-15 22:16:42 UTC
Created attachment 157163 [details]
A modified flex-2.5.33-yy.patch which fixes this issue for me.

Diff from the earlier patch is:
$ diff flex-2.5.33-yy.patch flex-2.5.33-yy-fix.patch 
< @@ -54,6 +54,32 @@ m4_changequote([[, ]])
> @@ -54,6 +54,34 @@ m4_changequote([[, ]])
> +%if-c-only
> +%endif
< @@ -59,6 +59,32 @@ const char *skel[] = {
> @@ -59,6 +59,34 @@ const char *skel[] = {
> +  "%if-c-only",
> +  "%endif",

Comment 4 Petr Machata 2007-06-25 13:22:59 UTC
I applied fix and built new package. It should hit the repository in several
days. Thanks for patch!

Comment 5 Fedora Update System 2007-06-25 23:24:56 UTC
flex-2.5.33-9.fc7 has been pushed to the Fedora 7 stable repository.  If problems still persist, please make note of it in this bug report.

Comment 6 Milos Jakubicek 2009-02-08 02:11:07 UTC
Please could you reintroduce this patch (and try to move it upstream)? This problem still persists with flex in F10.

Comment 7 Petr Machata 2009-02-09 14:16:26 UTC
The patch was dropped because upstream contains the code.

And indeed, F-10 version seems to work for me:
$ ~/fedora/flex/F-10/flex-2.5.35/flex -+ -o FlexLexer.example.cc example.fl 
$ g++ -c -I. FlexLexer.example.cc

Comment 8 Milos Jakubicek 2009-02-09 14:59:55 UTC
Created attachment 331314 [details]
Simple test file

Hm, for the example.fl file it works, but look at the simple file I've attached (plain.l):

>flex -o plain.c plain.l
>gcc plain.c
plain.l:4:1: warning: "plainwrap" redefined
plain.c:354:1: warning: this is the location of the previous definition
[...the rest of output is not important]

Maybe it's because we build a C scanner, not C++?

Comment 9 Petr Machata 2009-02-10 00:32:27 UTC
Your file contains the "%option noyywrap" directive:

"""If you do not supply your own version of `yywrap()', then you must
either use `%option noyywrap' (in which case the scanner behaves as
though `yywrap()' returned 1), or you must link with `-lfl' to obtain
the default version of the routine, which always returns 1."""

So just either drop the directive, or your own "plainwrap" macro.

Comment 10 Milos Jakubicek 2009-02-10 21:28:39 UTC
You're right of course and I'm very sorry and thank you for clarification.

Unfortunately there is one more such a dumb warning, I'm afraid that this time it's not just my fault -- it is filed as bug 484961.

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