[Bug c++/16029] New: incorrect "unused variable" message from -Wall

[Bug c++/16029] New: incorrect "unused variable" message from -Wall

[tromey at gcc dot gnu dot org]

Try this simple invalid program:

int main ()
{
  return whatever ();
}

I compile it with -Wall:

fleche. g++ -Wall -c main.cc
main.cc: In function `int main()':
main.cc:3: error: `whatever' was not declared in this scope
main.cc:3: warning: unused variable 'whatever'

The "unused variable" warning is odd, I think it should not
be emitted.


I'm using a recent cvs trunk:

Reading specs from
/home/tromey/gnu/Trunk/install/lib/gcc/i686-pc-linux-gnu/3.5.0/specs
Configured with: ../gcc/configure --prefix=/home/tromey/gnu/Trunk/install
--enable-languages=c++,java --enable-threads=posix --enable-checking=tree
--enable-java-awt=gtk,xlib --disable-static
Thread model: posix
gcc version 3.5.0 20040616 (experimental)

-- 
           Summary: incorrect "unused variable" message from -Wall
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tromey at gcc dot gnu dot org
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16029

[Bug c++/16029] incorrect "unused variable" message from -Wall

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-06-17 00:20 -------
Well, that's error recovery: the compiler has to assume something when 
encountering an error, before going on. In this case, it assumes that 
'whatever' is a variable, and seems to tentatively inject a declaration 
of it. Since the 'return' statement was in error, it is apparently not 
considered a 'use' of this variable.  
 
I am tempted to close this PR since it really is a case where one shouldn't 
place too much emphasis on follow-up errors, given that the first error 
is already pretty clear. However, it may also be easy enough to change the 
compiler to mark all tentative variable and function declarations in error 
recovery with __attribute__((used)) to avoid this kind of follow-up. 
 
W. 

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2004-06-17 00:20:08
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16029

[Bug c++/16029] incorrect "unused variable" message from -Wall

[bangerth at dealii dot org]

------- Additional Comments From bangerth at dealii dot org  2004-06-17 00:22 -------
It may or may not be worth stating that this warning was actually 
only introduced after the branch of 3.4, i.e. it is only present on 
mainline. Whether that qualifies this thing as a regression I consider 
doubtful nevertheless. 
 
W. 

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16029

[Bug c++/16029] [4.0 Regression] incorrect "unused variable" message from -Wall

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-09-16 07:21 -------
Related to bug 17393, this is a regression.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|enhancement                 |minor
           Keywords|                            |diagnostic
      Known to fail|                            |4.0.0
      Known to work|                            |3.4.0
            Summary|incorrect "unused variable" |[4.0 Regression] incorrect
                   |message from -Wall          |"unused variable" message
                   |                            |from -Wall
   Target Milestone|---                         |4.0.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16029

[Bug c++/16029] [4.0 Regression] incorrect "unused variable" message from -Wall

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2004-09-17 02:02 -------
Working on a fix.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|unassigned at gcc dot gnu   |mark at codesourcery dot com
                   |dot org                     |
             Status|NEW                         |ASSIGNED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16029

[Bug c++/16029] [4.0 Regression] incorrect "unused variable" message from -Wall

[cvs-commit at gcc dot gnu dot org]

------- Additional Comments From cvs-commit at gcc dot gnu dot org  2004-09-17 07:01 -------
Subject: Bug 16029

CVSROOT:	/cvs/gcc
Module name:	gcc
Changes by:	mmitchel@gcc.gnu.org	2004-09-17 07:01:11

Modified files:
	gcc/testsuite  : ChangeLog 
	gcc/cp         : ChangeLog lex.c parser.c 
Added files:
	gcc/testsuite/g++.dg/parse: error18.C 
	gcc/testsuite/g++.dg/warn: Wunused-8.C 

Log message:
	PR c++/16002
	* parser.c (cp_parser_simple_declaration): Commit to tentative
	parses after seeing a decl-specifier.
	(cp_parser_simple_declaration): Eliminate spurious message.
	(cp_parser_init_declarator): Adjust error message.
	
	PR c++/16029
	* lex.c (unqualified_name_lookup_error): Mark the dummy
	declaration as used.
	
	PR c++/16002
	* g++.dg/template/error18.C: New test.
	
	PR c++/16029
	* g++.dg/warn/Wunused-8.C: New test.

Patches:
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/ChangeLog.diff?cvsroot=gcc&r1=1.4303&r2=1.4304
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/ChangeLog.diff?cvsroot=gcc&r1=1.4360&r2=1.4361
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/lex.c.diff?cvsroot=gcc&r1=1.344&r2=1.345
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/cp/parser.c.diff?cvsroot=gcc&r1=1.248&r2=1.249
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/parse/error18.C.diff?cvsroot=gcc&r1=NONE&r2=1.1
http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/gcc/testsuite/g++.dg/warn/Wunused-8.C.diff?cvsroot=gcc&r1=NONE&r2=1.1



-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16029

[Bug c++/16029] [4.0 Regression] incorrect "unused variable" message from -Wall

[mmitchel at gcc dot gnu dot org]

------- Additional Comments From mmitchel at gcc dot gnu dot org  2004-09-17 07:12 -------
Fixed in GCC 4.0.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=16029