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Subject: bug#68832: Testing: POSIX yacc and C++ linkage
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Hi,

I ran tests for automake 1.16.5 on OpenIndiana and following 4 tests
failed:

FAIL: t/yacc-cxx.sh
FAIL: t/yacc-clean-cxx.sh
FAIL: t/yacc-d-cxx.sh
FAIL: t/yacc-mix-c-cxx.sh


The cause for the failure is this:

parse1.yy:30:7: error: conflicting declaration of 'void yyerror(const char*)' with 'C' linkage
parse1.yy:7:6: note: previous declaration with 'C++' linkage
    7 | void yyerror (const char *s) {}
      |      ^~~~~~~
parse1.yy:34:6: error: conflicting declaration of 'int yylex()' with 'C' linkage
parse1.yy:6:5: note: previous declaration with 'C++' linkage
    6 | int yylex (void) { return std::getchar (); }
      |     ^~~~~


For testing there is the default system yacc used.  It is the illumos
yacc as inherited from Solaris with some changes[1].  The generated code
that causes the failure is this:

 24 #if defined(__cplusplus) || defined(__STDC__)
 25 
 26 #if defined(__cplusplus)
 27 extern "C" {
 28 #endif
 29 #ifndef yyerror
 30 #if defined(__cplusplus)
 31         void yyerror(YYCONST char *);
 32 #endif
 33 #endif
 34 #ifndef yylex
 35         int yylex(void);
 36 #endif
 37         int yyparse(void);
 38 #if defined(__cplusplus)
 39 }
 40 #endif
 41 
 42 #endif

The issue is apparent.  The yacc generated code create both yyerror()
and yylex() with the C linkage, but testing expects C++ linkage.  This
is exactly what the compiler error says.

All of this is obvious.  So where is the bug and what should be fixed?
There are few possible views:

1. yacc is buggy and should not force C linkage for C++ source.  This is
grey area because POSIX says nothing about linkage or C++[2].

2. The tests' expectations about yacc behavior re C++ are too strong.
This seems to be true for illumos yacc.  Other yacc implementations, for
example GNU bison, does better job and do not force C linkage for
affected functions.

My proposal to solve the issue is to change affected tests to require
bison instead of yacc.  Please see attachment.


Thank you.


[1] for example this: https://www.illumos.org/issues/16136
[2] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/yacc.html

-- 
+-------------------------------------------+
| Marcel Telka   e-mail:   marcel@HIDDEN  |
|                homepage: http://telka.sk/ |
+-------------------------------------------+

--Yf0zFUp9B7SJlIQ6
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	filename="automake-1.16.5-test-yacc-cxx-bison.patch"

--- automake-1.16.5/t/yacc-cxx.sh.orig
+++ automake-1.16.5/t/yacc-cxx.sh
@@ -18,7 +18,7 @@
 # headers are not involved).
 # Keep in sync with sister test 'yacc-basic.sh'.
 
-required='c++ yacc'
+required='c++ bison'
 . test-init.sh
 
 cat >> configure.ac << 'END'
--- automake-1.16.5/t/yacc-clean-cxx.sh.orig
+++ automake-1.16.5/t/yacc-clean-cxx.sh
@@ -20,7 +20,7 @@
 # "make maintainer-clean".
 # See also sister test 'yacc-clean.sh'.
 
-required='c++ yacc'
+required='c++ bison'
 . test-init.sh
 
 cat >> configure.ac << 'END'
--- automake-1.16.5/t/yacc-d-cxx.sh.orig
+++ automake-1.16.5/t/yacc-d-cxx.sh
@@ -18,7 +18,7 @@
 # (i.e., '-d' in *YFLAGS).
 # Keep in sync with sister test 'yacc-d-basic.sh'.
 
-required='c++ yacc'
+required='c++ bison'
 . test-init.sh
 
 write_parse ()
--- automake-1.16.5/t/yacc-mix-c-cxx.sh.orig
+++ automake-1.16.5/t/yacc-mix-c-cxx.sh
@@ -17,7 +17,7 @@
 # Check that many different Yacc parsers (both C and C++) can co-exists
 # in the same directory.
 
-required='cc c++ yacc'
+required='cc c++ bison'
 . test-init.sh
 
 cat >> configure.ac << 'END'

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From: help-debbugs@HIDDEN (GNU bug Tracking System)
To: Marcel Telka <marcel@HIDDEN>
Subject: bug#68832: Acknowledgement (Testing: POSIX yacc and C++ linkage)
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References: <ZbldnY-_UKmOctnv@telcontar>
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Date: Tue, 30 Jan 2024 23:59:02 +0000

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Subject: bug#68832: Testing: POSIX yacc and C++ linkage
References: <ZbldnY-_UKmOctnv@telcontar>
Resent-From: Karl Berry <karl@HIDDEN>
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Date: Wed, 31 Jan 2024 15:47:09 -0700
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    parse1.yy:30:7: error: conflicting declaration of 'void yyerror(const char*)' with 'C' linkage
    parse1.yy:7:6: note: previous declaration with 'C++' linkage

Thanks much for the careful and complete report.

I think this is another manifestation of what Bogdan fixed in other
cases in https://debbugs.gnu.org/cgi/bugreport.cgi?bug=62886. His idea
there was to essentially add an extern "C" only on Solaris, via
sufficient #ifdef's.

In these new cases, I guess braces would be required, so the test code
would end up looking like:

#if (defined __cplusplus) && ((!defined __sun) || (defined __EXTERN_C__))
extern "C" {
#endif
int yylex (void) { return std::getchar (); }
void yyerror (const char *s) {}
#if (defined __cplusplus) && ((!defined __sun) || (defined __EXTERN_C__))
}
#endif

Although I could try to do this, I can't easily test the result, and I'd
probably mess up the editing. I'm also far from sure that this will
actually solve the problem without introducing new ones.

So maybe you could edit one of the test *.sh files and rerun the test
and see what happens? In case you don't know, you can run a single test
with, e.g.,
  make check TESTS='t/yacc-cxx.sh' keep_testdirs=yes
(the keep_testdirs keeps the <testdir>.dir/ around so it can be
inspected afterward.)

    My proposal to solve the issue is to change affected tests to
    require bison instead of yacc.  

A lot of work has gone into making the tests work with Solaris tools
(despite the current failures), so I'm reluctant to throw that
possibility away.

Also, there have been similar bug reports with older versions of bison.
There is no panacea :( ...  --thanks, karl.

Last modified: Wed, 31 Jan 2024 23:00:01 UTC

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