Thread

Commits

Fix accidentally cast away qualifiers
- 5ca5f12c2c62 19 (unreleased) landed

Fix accidentally cast away qualifiers

Peter Eisentraut <peter@eisentraut.org> — 2026-01-20T07:54:18Z

This patch fixes cases where a qualifier (const, in all cases here) was 
dropped by a cast, but the cast was otherwise necessary or desirable, so 
the straightforward fix is to add the qualifier into the cast.

This was checked with gcc -Wcast-qual, but it doesn't fix all such 
warnings, only the trivially fixable ones.

Re: Fix accidentally cast away qualifiers

Chao Li <li.evan.chao@gmail.com> — 2026-01-20T08:16:26Z


> On Jan 20, 2026, at 15:54, Peter Eisentraut <peter@eisentraut.org> wrote:
> 
> This patch fixes cases where a qualifier (const, in all cases here) was dropped by a cast, but the cast was otherwise necessary or desirable, so the straightforward fix is to add the qualifier into the cast.
> 
> This was checked with gcc -Wcast-qual, but it doesn't fix all such warnings, only the trivially fixable ones.<0001-Fix-accidentally-cast-away-qualifiers.patch>

Looks good to me. All changes are const-correctness fixes without semantic changes.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/

Re: Fix accidentally cast away qualifiers

Bertrand Drouvot <bertranddrouvot.pg@gmail.com> — 2026-01-20T12:10:57Z

Hi,

On Tue, Jan 20, 2026 at 08:54:18AM +0100, Peter Eisentraut wrote:
> This patch fixes cases where a qualifier (const, in all cases here) was
> dropped by a cast, but the cast was otherwise necessary or desirable, so the
> straightforward fix is to add the qualifier into the cast.
> 
> This was checked with gcc -Wcast-qual, but it doesn't fix all such warnings,
> only the trivially fixable ones.

diff --git a/src/include/varatt.h b/src/include/varatt.h
index eccd3ca04d6..03e9d1869aa 100644
--- a/src/include/varatt.h
+++ b/src/include/varatt.h

It looks like those changes produce:

../../../src/include/varatt.h: In function ‘VARDATA’:
../../../src/include/varatt.h:261:33: warning: return discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  261 | #define VARDATA_4B(PTR)         (((const varattrib_4b *) (PTR))->va_4byte.va_data)
      |                                 ^
../../../src/include/varatt.h:307:16: note: in expansion of macro ‘VARDATA_4B’
  307 |         return VARDATA_4B(PTR);
      |                ^~~~~~~~~~
../../../src/include/varatt.h: In function ‘VARDATA_SHORT’:
../../../src/include/varatt.h:263:33: warning: return discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  263 | #define VARDATA_1B(PTR)         (((const varattrib_1b *) (PTR))->va_data)
      |                                 ^
../../../src/include/varatt.h:321:16: note: in expansion of macro ‘VARDATA_1B’
  321 |         return VARDATA_1B(PTR);
      |                ^~~~~~~~~~
../../../src/include/varatt.h: In function ‘VARDATA_EXTERNAL’:
../../../src/include/varatt.h:264:33: warning: return discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  264 | #define VARDATA_1B_E(PTR)       (((const varattrib_1b_e *) (PTR))->va_data)
      |                                 ^
../../../src/include/varatt.h:342:16: note: in expansion of macro ‘VARDATA_1B_E’
  342 |         return VARDATA_1B_E(PTR);
      |                ^~~~~~~~~~~~
../../../src/include/varatt.h: In function ‘VARDATA_ANY’:
../../../src/include/varatt.h:488:52: warning: return discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
  488 |         return VARATT_IS_1B(PTR) ? VARDATA_1B(PTR) : VARDATA_4B(PTR);

as they are still used by functions that return non const:

"
static inline char *
VARDATA(const void *PTR)
{
    return VARDATA_4B(PTR);
}
"

> -	RangeType  *r1 = *(RangeType **) key1;
> -	RangeType  *r2 = *(RangeType **) key2;
> +	RangeType  *r1 = *(RangeType *const *) key1;
> +	RangeType  *r2 = *(RangeType *const *) key2;

That's correct. My improved cocci script [1] would incorrectly produce:

-       RangeType  *r1 = *(RangeType **) key1;
-       RangeType  *r2 = *(RangeType **) key2;
+       RangeType  *r1 = *(const RangeType **)key1;
+       RangeType  *r2 = *(const RangeType **)key2;

Same for:

> -	file_entry_t *fa = *((file_entry_t **) a);
> -	file_entry_t *fb = *((file_entry_t **) b);
> +	file_entry_t *fa = *((file_entry_t *const *) a);
> +	file_entry_t *fb = *((file_entry_t *const *) b);
>  
>  

Same for:

> -	Step	   *stepa = *((Step **) a);
> -	Step	   *stepb = *((Step **) b);
> +	Step	   *stepa = *((Step *const *) a);
> +	Step	   *stepb = *((Step *const *) b);
>  
> -	Step	   *step = *((Step **) b);
> +	Step	   *step = *((Step *const *) b);
>  
> diff --git a/src/test/modules/libpq_pipeline/libpq_pipeline.c b/src/test/modules/libpq_pipeline/libpq_pipeline.c
> index 03371721460..4a9bb65b9bb 100644
> --- a/src/test/modules/libpq_pipeline/libpq_pipeline.c
> +++ b/src/test/modules/libpq_pipeline/libpq_pipeline.c
> @@ -1576,7 +1576,7 @@ test_singlerowmode(PGconn *conn)
>  							  "SELECT generate_series(42, $1)",
>  							  1,
>  							  NULL,
> -							  (const char **) param,
> +							  (const char *const *) param,
>  							  NULL,
>  							  NULL,
>  							  0) != 1)

Correct, also according to:

"
int
PQsendQueryParams(PGconn *conn,
                  const char *command,
                  int nParams,
                  const Oid *paramTypes,
                  const char *const *paramValues,
                  const int *paramLengths,
                  const int *paramFormats,
                  int resultFormat)
{
"

Also [1], detected a few more trivially fixable ones (see attached).

[1]: https://github.com/bdrouvot/coccinelle_on_pg/blob/main/misc/search_const_away.cocci

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

Re: Fix accidentally cast away qualifiers

Peter Eisentraut <peter@eisentraut.org> — 2026-01-21T11:31:27Z

On 20.01.26 13:10, Bertrand Drouvot wrote:
> On Tue, Jan 20, 2026 at 08:54:18AM +0100, Peter Eisentraut wrote:
>> This patch fixes cases where a qualifier (const, in all cases here) was
>> dropped by a cast, but the cast was otherwise necessary or desirable, so the
>> straightforward fix is to add the qualifier into the cast.
>>
>> This was checked with gcc -Wcast-qual, but it doesn't fix all such warnings,
>> only the trivially fixable ones.
> 
> diff --git a/src/include/varatt.h b/src/include/varatt.h
> index eccd3ca04d6..03e9d1869aa 100644
> --- a/src/include/varatt.h
> +++ b/src/include/varatt.h
> 
> It looks like those changes produce:
> 
> ../../../src/include/varatt.h: In function ‘VARDATA’:
> ../../../src/include/varatt.h:261:33: warning: return discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
>    261 | #define VARDATA_4B(PTR)         (((const varattrib_4b *) (PTR))->va_4byte.va_data)

Strange, I don't see that.  What compiler is this, and do you use any 
special options?

> Also [1], detected a few more trivially fixable ones (see attached).

Yes, these should be included.

The one in spgquadtreeproc.c was #ifdef'ed out, so my testing didn't see 
it.  I suppose the other one is only compiled when you run the unicode 
tests.

Re: Fix accidentally cast away qualifiers

Bertrand Drouvot <bertranddrouvot.pg@gmail.com> — 2026-01-21T14:24:58Z

Hi,

On Wed, Jan 21, 2026 at 12:31:27PM +0100, Peter Eisentraut wrote:
> On 20.01.26 13:10, Bertrand Drouvot wrote:
> > On Tue, Jan 20, 2026 at 08:54:18AM +0100, Peter Eisentraut wrote:
> > > This patch fixes cases where a qualifier (const, in all cases here) was
> > > dropped by a cast, but the cast was otherwise necessary or desirable, so the
> > > straightforward fix is to add the qualifier into the cast.
> > > 
> > > This was checked with gcc -Wcast-qual, but it doesn't fix all such warnings,
> > > only the trivially fixable ones.
> > 
> > diff --git a/src/include/varatt.h b/src/include/varatt.h
> > index eccd3ca04d6..03e9d1869aa 100644
> > --- a/src/include/varatt.h
> > +++ b/src/include/varatt.h
> > 
> > It looks like those changes produce:
> > 
> > ../../../src/include/varatt.h: In function ‘VARDATA’:
> > ../../../src/include/varatt.h:261:33: warning: return discards ‘const’ qualifier from pointer target type [-Wdiscarded-qualifiers]
> >    261 | #define VARDATA_4B(PTR)         (((const varattrib_4b *) (PTR))->va_4byte.va_data)
> 
> Strange, I don't see that.  What compiler is this, and do you use any
> special options?

It's gcc 14.1.0 with "CFLAGS=-O0 -ggdb3 -fno-omit-frame-pointer -gdwarf-2 -g3
-Wdiscarded-qualifiers -Wunused-value -Werror=maybe-uninitialized
-Werror=format -Wreturn-type"

But I just tested with a simple test case, some compilers and some options and I've
always seen the warning (see [1]), so I'm not sure why you don't.

> 
> > Also [1], detected a few more trivially fixable ones (see attached).
> 
> Yes, these should be included.
> 
> The one in spgquadtreeproc.c was #ifdef'ed out, so my testing didn't see it.
> I suppose the other one is only compiled when you run the unicode tests.

Yeah, that could lead to the same "concern" that Tom had in [2] (and using 
a tool like Coccinelle could be an answer).

[1]: https://godbolt.org/z/T9hffKaPW
[2]: https://postgr.es/m/aVJCoNqO6ybov7eW%40ip-10-97-1-34.eu-west-3.compute.internal

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

Re: Fix accidentally cast away qualifiers

Bertrand Drouvot <bertranddrouvot.pg@gmail.com> — 2026-01-21T14:56:37Z

Hi,

On Wed, Jan 21, 2026 at 02:24:58PM +0000, Bertrand Drouvot wrote:
> Hi,
> 
> On Wed, Jan 21, 2026 at 12:31:27PM +0100, Peter Eisentraut wrote:
> > Strange, I don't see that.  What compiler is this, and do you use any
> > special options?
> 
> It's gcc 14.1.0 with "CFLAGS=-O0 -ggdb3 -fno-omit-frame-pointer -gdwarf-2 -g3
> -Wdiscarded-qualifiers -Wunused-value -Werror=maybe-uninitialized
> -Werror=format -Wreturn-type"
> 
> But I just tested with a simple test case, some compilers and some options and I've
> always seen the warning (see [1])

FWIW, and so does the CI: https://github.com/bdrouvot/postgres/runs/61028037498

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

Re: Fix accidentally cast away qualifiers

Chao Li <li.evan.chao@gmail.com> — 2026-01-22T08:22:24Z


> On Jan 21, 2026, at 22:56, Bertrand Drouvot <bertranddrouvot.pg@gmail.com> wrote:
> 
> Hi,
> 
> On Wed, Jan 21, 2026 at 02:24:58PM +0000, Bertrand Drouvot wrote:
>> Hi,
>> 
>> On Wed, Jan 21, 2026 at 12:31:27PM +0100, Peter Eisentraut wrote:
>>> Strange, I don't see that.  What compiler is this, and do you use any
>>> special options?
>> 
>> It's gcc 14.1.0 with "CFLAGS=-O0 -ggdb3 -fno-omit-frame-pointer -gdwarf-2 -g3
>> -Wdiscarded-qualifiers -Wunused-value -Werror=maybe-uninitialized
>> -Werror=format -Wreturn-type"
>> 
>> But I just tested with a simple test case, some compilers and some options and I've
>> always seen the warning (see [1])
> 
> FWIW, and so does the CI: https://github.com/bdrouvot/postgres/runs/61028037498
> 
> Regards,
> 
> -- 
> Bertrand Drouvot
> PostgreSQL Contributors Team
> RDS Open Source Databases
> Amazon Web Services: https://aws.amazon.com
> 

Yeah, I confirm I can see the same warnings:
```
In file included from xlogdesc.c:21:
In file included from ../../../src/include/utils/guc.h:17:
In file included from ../../../src/include/utils/array.h:65:
In file included from ../../../src/include/utils/expandeddatum.h:47:
../../../src/include/varatt.h:307:9: warning: returning 'const char[]' from a function with result type 'char *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
  307 |         return VARDATA_4B(PTR);
      |                ^~~~~~~~~~~~~~~
../../../src/include/varatt.h:261:26: note: expanded from macro 'VARDATA_4B'
  261 | #define VARDATA_4B(PTR)         (((const varattrib_4b *) (PTR))->va_4byte.va_data)
      |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../src/include/varatt.h:321:9: warning: returning 'const char[]' from a function with result type 'char *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
  321 |         return VARDATA_1B(PTR);
      |                ^~~~~~~~~~~~~~~
../../../src/include/varatt.h:263:26: note: expanded from macro 'VARDATA_1B'
  263 | #define VARDATA_1B(PTR)         (((const varattrib_1b *) (PTR))->va_data)
      |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../src/include/varatt.h:342:9: warning: returning 'const char[]' from a function with result type 'char *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
  342 |         return VARDATA_1B_E(PTR);
      |                ^~~~~~~~~~~~~~~~~
../../../src/include/varatt.h:264:27: note: expanded from macro 'VARDATA_1B_E'
  264 | #define VARDATA_1B_E(PTR)       (((const varattrib_1b_e *) (PTR))->va_data)
      |                                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../src/include/varatt.h:488:9: warning: returning 'const char *' from a function with result type 'char *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
  488 |         return VARATT_IS_1B(PTR) ? VARDATA_1B(PTR) : VARDATA_4B(PTR);
      |                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../src/include/varatt.h:235:2: note: expanded from macro 'VARATT_IS_1B'
  235 |         ((((const varattrib_1b *) (PTR))->va_header & 0x01) == 0x01)
      |         ^
4 warnings generated.
```

I didn’t use any special compiler option, just ran “make”.

My configure is:
```
./configure --enable-debug --enable-cassert --enable-tap-tests --enable-depend
```

Sorry, I didn’t notice the warnings in my first review. I guess I left my desktop while building at the time.

Best regards,
--
Chao Li (Evan)
HighGo Software Co., Ltd.
https://www.highgo.com/

Re: Fix accidentally cast away qualifiers

Peter Eisentraut <peter@eisentraut.org> — 2026-01-26T15:09:00Z

On 21.01.26 15:56, Bertrand Drouvot wrote:
> Hi,
> 
> On Wed, Jan 21, 2026 at 02:24:58PM +0000, Bertrand Drouvot wrote:
>> Hi,
>>
>> On Wed, Jan 21, 2026 at 12:31:27PM +0100, Peter Eisentraut wrote:
>>> Strange, I don't see that.  What compiler is this, and do you use any
>>> special options?
>>
>> It's gcc 14.1.0 with "CFLAGS=-O0 -ggdb3 -fno-omit-frame-pointer -gdwarf-2 -g3
>> -Wdiscarded-qualifiers -Wunused-value -Werror=maybe-uninitialized
>> -Werror=format -Wreturn-type"
>>
>> But I just tested with a simple test case, some compilers and some options and I've
>> always seen the warning (see [1])
> 
> FWIW, and so does the CI: https://github.com/bdrouvot/postgres/runs/61028037498

I must have done something wrong on my side.  I have committed it with 
your corrections.