CFLAGS="-Wall -Werror" breaks AC_C_CONST (autoconf 2.59)

[Chris Frost]

When I run
        $ CFLAGS="-W -Wall -Werror" ./configure
against a configure.in that uses AC_C_CONST, const support is incorrectly
detected as absent because the const test has unused variables.

This is using autoconf 2.59 and gcc/g++ 3.3.5.

I was not able to find anything through a quick google or mailing search.
Is this a known bug? (Or is this the intended behavior?)


The const config.log snippet:

configure:3986: checking for an ANSI C-conforming const
configure:4053: gcc -c -W -Wall -Werror  conftest.c >&5
conftest.c: In function `main':
conftest.c:42: warning: unused variable `s'
conftest.c:62: warning: unused variable `foo'
conftest.c:23: warning: unused variable `x'
conftest.c:29: warning: unused variable `zero'
configure:4059: $? = 1
configure: failed program was:
| /* confdefs.h.  */
| 
| #define PACKAGE_NAME "mswatch"
| #define PACKAGE_TARNAME "mswatch"
| #define PACKAGE_VERSION "1.0"
| #define PACKAGE_STRING "mswatch 1.0"
| #define PACKAGE_BUGREPORT ""
| #define PACKAGE "mswatch"
| #define VERSION "1.0"
| #define _GNU_SOURCE 1
| #ifdef __cplusplus
| extern "C" void std::exit (int) throw (); using std::exit;
| #endif
| /* end confdefs.h.  */
| 
| int
| main ()
| {
| /* FIXME: Include the comments suggested by Paul. */
| #ifndef __cplusplus
|   /* Ultrix mips cc rejects this.  */
|   typedef int charset[2];
|   const charset x;
|   /* SunOS 4.1.1 cc rejects this.  */
|   char const *const *ccp;
|   char **p;
|   /* NEC SVR4.0.2 mips cc rejects this.  */
|   struct point {int x, y;};
|   static struct point const zero = {0,0};
|   /* AIX XL C 1.02.0.0 rejects this.
|      It does not let you subtract one const X* pointer from another in
|      an arm of an if-expression whose if-part is not a constant
|      expression */
|   const char *g = "string";
|   ccp = &g + (g ? g-g : 0);
|   /* HPUX 7.0 cc rejects these. */
|   ++ccp;
|   p = (char**) ccp;
|   ccp = (char const *const *) p;
|   { /* SCO 3.2v4 cc rejects this.  */
|     char *t;
|     char const *s = 0 ? (char *) 0 : (char const *) 0;
| 
|     *t++ = 0;
|   }
|   { /* Someone thinks the Sun supposedly-ANSI compiler will reject this.  */
|     int x[] = {25, 17};
|     const int *foo = &x[0];
|     ++foo;
|   }
|   { /* Sun SC1.0 ANSI compiler rejects this -- but not the above. */
|     typedef const int *iptr;
|     iptr p = 0;
|     ++p;
|   }
|   { /* AIX XL C 1.02.0.0 rejects this saying
|        "k.c", line 2.27: 1506-025 (S) Operand must be a modifiable lvalue. */
|     struct s { int j; const int *ap[3]; };
|     struct s *b; b->j = 5;
|   }
|   { /* ULTRIX-32 V3.1 (Rev 9) vcc rejects this */
|     const int foo = 10;
|   }
| #endif
| 
|   ;
|   return 0;
| }
configure:4082: result: no


-- 
Chris Frost  |  <http://www.frostnet.net/chris/>
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