Fix accidentally cast away qualifiers

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/

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

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.

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]https://godbolt.org/z/T9hffKaPW), 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]/messages/by-id/aVJCoNqO6ybov7eW@ip-10-97-1-34.eu-west-3.compute.internal (and using
a tool like Coccinelle could be an answer).

[1]: https://godbolt.org/z/T9hffKaPW
[2]: /messages/by-id/aVJCoNqO6ybov7eW@ip-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

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

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/

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.