Date: Thu, 18 Dec 2025 13:55:23 +0000
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: pgsql-hackers@lists.postgresql.org
Subject: Don't cast away const where possible
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Hi hackers,

Some functions are casting away the const qualifiers from their signatures in
local variables.

These 3 patches add const to read only local variables, preserving the const
qualifiers from the function signatures.

0001: those are simple changes in 6 files (16 changes in total)

0002: Add const to read only TableInfo pointers in pg_dump

Functions that dump table data receive their parameters through const void *
but were casting away const. Add const qualifiers to functions that only read
the table information.

Also change getRootTableInfo to return const TableInfo *, since it only traverses
the parent chain without modifying any TableInfo structures. This allows the dump
functions to maintain const correctness when calling it.

0003: Separate read and write pointers in pg_saslprep

Use separate pointers for reading const input ('p') and writing
to mutable output ('outp'), avoiding the need to cast away const on the input
parameter.

It has been done with the help of [1], but not all the changes proposed by it have
been implemented. Indeed, I did some filtering and decided not to change the ones
that:

- are just thin wrappers
- would require public API changes
- rely on external functions (such as LZ4F_compressUpdate())
- would require changes beyond the scope of this cleanup

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

Thoughts?

Regards,

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

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	filename="v1-0001-Don-t-cast-away-const-where-possible.patch"

From f65cb5dfdf8208282ae3a924f33a9df7677ba8ca Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Thu, 18 Dec 2025 09:51:01 +0000
Subject: [PATCH v1 1/3] Don't cast away const where possible

Add const to read only local variables, preserving the const qualifiers from the
function signatures.

This does not change all such instances, but only those hand-picked by the author.

The ones that are not changed:

- are just thin wrappers
- would require public API changes
- rely on external functions (such as LZ4F_compressUpdate())
- would require complex subsystem changes
---
 src/backend/access/brin/brin_minmax_multi.c          | 4 ++--
 src/backend/access/heap/pruneheap.c                  | 4 ++--
 src/backend/access/spgist/spgkdtreeproc.c            | 8 ++++----
 src/backend/statistics/mcv.c                         | 4 ++--
 src/backend/tsearch/spell.c                          | 4 ++--
 src/test/modules/injection_points/injection_points.c | 8 ++++----
 6 files changed, 16 insertions(+), 16 deletions(-)
  10.8% src/backend/access/brin/
  12.8% src/backend/access/heap/
  19.8% src/backend/access/spgist/
   8.8% src/backend/statistics/
  11.2% src/backend/tsearch/
  36.2% src/test/modules/injection_points/

diff --git a/src/backend/access/brin/brin_minmax_multi.c b/src/backend/access/brin/brin_minmax_multi.c
index 0298a9da8ba..a2d72aa1791 100644
--- a/src/backend/access/brin/brin_minmax_multi.c
+++ b/src/backend/access/brin/brin_minmax_multi.c
@@ -1304,8 +1304,8 @@ merge_overlapping_ranges(FmgrInfo *cmp, Oid colloid,
 static int
 compare_distances(const void *a, const void *b)
 {
-	DistanceValue *da = (DistanceValue *) a;
-	DistanceValue *db = (DistanceValue *) b;
+	const DistanceValue *da = (const DistanceValue *) a;
+	const DistanceValue *db = (const DistanceValue *) b;
 
 	if (da->value < db->value)
 		return 1;
diff --git a/src/backend/access/heap/pruneheap.c b/src/backend/access/heap/pruneheap.c
index 07aa08cfe14..dbb417217f1 100644
--- a/src/backend/access/heap/pruneheap.c
+++ b/src/backend/access/heap/pruneheap.c
@@ -2021,8 +2021,8 @@ heap_log_freeze_eq(xlhp_freeze_plan *plan, HeapTupleFreeze *frz)
 static int
 heap_log_freeze_cmp(const void *arg1, const void *arg2)
 {
-	HeapTupleFreeze *frz1 = (HeapTupleFreeze *) arg1;
-	HeapTupleFreeze *frz2 = (HeapTupleFreeze *) arg2;
+	const HeapTupleFreeze *frz1 = (const HeapTupleFreeze *) arg1;
+	const HeapTupleFreeze *frz2 = (const HeapTupleFreeze *) arg2;
 
 	if (frz1->xmax < frz2->xmax)
 		return -1;
diff --git a/src/backend/access/spgist/spgkdtreeproc.c b/src/backend/access/spgist/spgkdtreeproc.c
index f0167d6ffa6..dc29d6898c5 100644
--- a/src/backend/access/spgist/spgkdtreeproc.c
+++ b/src/backend/access/spgist/spgkdtreeproc.c
@@ -84,8 +84,8 @@ typedef struct SortedPoint
 static int
 x_cmp(const void *a, const void *b)
 {
-	SortedPoint *pa = (SortedPoint *) a;
-	SortedPoint *pb = (SortedPoint *) b;
+	const SortedPoint *pa = (const SortedPoint *) a;
+	const SortedPoint *pb = (const SortedPoint *) b;
 
 	if (pa->p->x == pb->p->x)
 		return 0;
@@ -95,8 +95,8 @@ x_cmp(const void *a, const void *b)
 static int
 y_cmp(const void *a, const void *b)
 {
-	SortedPoint *pa = (SortedPoint *) a;
-	SortedPoint *pb = (SortedPoint *) b;
+	const SortedPoint *pa = (const SortedPoint *) a;
+	const SortedPoint *pb = (const SortedPoint *) b;
 
 	if (pa->p->y == pb->p->y)
 		return 0;
diff --git a/src/backend/statistics/mcv.c b/src/backend/statistics/mcv.c
index ec650ba029f..1d210cdba3c 100644
--- a/src/backend/statistics/mcv.c
+++ b/src/backend/statistics/mcv.c
@@ -402,8 +402,8 @@ count_distinct_groups(int numrows, SortItem *items, MultiSortSupport mss)
 static int
 compare_sort_item_count(const void *a, const void *b, void *arg)
 {
-	SortItem   *ia = (SortItem *) a;
-	SortItem   *ib = (SortItem *) b;
+	const SortItem *ia = (const SortItem *) a;
+	const SortItem *ib = (const SortItem *) b;
 
 	if (ia->count == ib->count)
 		return 0;
diff --git a/src/backend/tsearch/spell.c b/src/backend/tsearch/spell.c
index e5badb6b43f..1af6b212245 100644
--- a/src/backend/tsearch/spell.c
+++ b/src/backend/tsearch/spell.c
@@ -210,8 +210,8 @@ cmpspellaffix(const void *s1, const void *s2)
 static int
 cmpcmdflag(const void *f1, const void *f2)
 {
-	CompoundAffixFlag *fv1 = (CompoundAffixFlag *) f1,
-			   *fv2 = (CompoundAffixFlag *) f2;
+	const CompoundAffixFlag *fv1 = (const CompoundAffixFlag *) f1,
+			   *fv2 = (const CompoundAffixFlag *) f2;
 
 	Assert(fv1->flagMode == fv2->flagMode);
 
diff --git a/src/test/modules/injection_points/injection_points.c b/src/test/modules/injection_points/injection_points.c
index 25340e8d81b..df8f4cf1717 100644
--- a/src/test/modules/injection_points/injection_points.c
+++ b/src/test/modules/injection_points/injection_points.c
@@ -189,7 +189,7 @@ injection_init_shmem(void)
  * otherwise.
  */
 static bool
-injection_point_allowed(InjectionPointCondition *condition)
+injection_point_allowed(const InjectionPointCondition *condition)
 {
 	bool		result = true;
 
@@ -232,7 +232,7 @@ injection_points_cleanup(int code, Datum arg)
 void
 injection_error(const char *name, const void *private_data, void *arg)
 {
-	InjectionPointCondition *condition = (InjectionPointCondition *) private_data;
+	const InjectionPointCondition *condition = (const InjectionPointCondition *) private_data;
 	char	   *argstr = (char *) arg;
 
 	if (!injection_point_allowed(condition))
@@ -248,7 +248,7 @@ injection_error(const char *name, const void *private_data, void *arg)
 void
 injection_notice(const char *name, const void *private_data, void *arg)
 {
-	InjectionPointCondition *condition = (InjectionPointCondition *) private_data;
+	const InjectionPointCondition *condition = (const InjectionPointCondition *) private_data;
 	char	   *argstr = (char *) arg;
 
 	if (!injection_point_allowed(condition))
@@ -268,7 +268,7 @@ injection_wait(const char *name, const void *private_data, void *arg)
 	uint32		old_wait_counts = 0;
 	int			index = -1;
 	uint32		injection_wait_event = 0;
-	InjectionPointCondition *condition = (InjectionPointCondition *) private_data;
+	const InjectionPointCondition *condition = (const InjectionPointCondition *) private_data;
 
 	if (inj_state == NULL)
 		injection_init_shmem();
-- 
2.34.1


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	filename="v1-0002-Add-const-to-read-only-TableInfo-pointers-in-pg_d.patch"

From a3d493f1f8430949a1bae1d5718baae9caea61cb Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Thu, 18 Dec 2025 12:47:07 +0000
Subject: [PATCH v1 2/3] Add const to read only TableInfo pointers in pg_dump

Functions that dump table data receive their parameters through const void *
but were casting away const. Add const qualifiers to functions that only read
the table information.

Also change getRootTableInfo to return const TableInfo *, since it only traverses
the parent chain without modifying any TableInfo structures. This allows the dump
functions to maintain const correctness when calling it.
---
 src/bin/pg_dump/pg_dump.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)
 100.0% src/bin/pg_dump/

diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index 24ad201af2f..6aecc8b32fd 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -412,7 +412,7 @@ static void appendReloptionsArrayAH(PQExpBuffer buffer, const char *reloptions,
 static char *get_synchronized_snapshot(Archive *fout);
 static void set_restrict_relation_kind(Archive *AH, const char *value);
 static void setupDumpWorker(Archive *AH);
-static TableInfo *getRootTableInfo(const TableInfo *tbinfo);
+static const TableInfo *getRootTableInfo(const TableInfo *tbinfo);
 static bool forcePartitionRootLoad(const TableInfo *tbinfo);
 static void read_dump_filters(const char *filename, DumpOptions *dopt);
 
@@ -2379,8 +2379,8 @@ selectDumpableObject(DumpableObject *dobj, Archive *fout)
 static int
 dumpTableData_copy(Archive *fout, const void *dcontext)
 {
-	TableDataInfo *tdinfo = (TableDataInfo *) dcontext;
-	TableInfo  *tbinfo = tdinfo->tdtable;
+	const TableDataInfo *tdinfo = (const TableDataInfo *) dcontext;
+	const TableInfo *tbinfo = tdinfo->tdtable;
 	const char *classname = tbinfo->dobj.name;
 	PQExpBuffer q = createPQExpBuffer();
 
@@ -2547,8 +2547,8 @@ dumpTableData_copy(Archive *fout, const void *dcontext)
 static int
 dumpTableData_insert(Archive *fout, const void *dcontext)
 {
-	TableDataInfo *tdinfo = (TableDataInfo *) dcontext;
-	TableInfo  *tbinfo = tdinfo->tdtable;
+	const TableDataInfo *tdinfo = (const TableDataInfo *) dcontext;
+	const TableInfo *tbinfo = tdinfo->tdtable;
 	DumpOptions *dopt = fout->dopt;
 	PQExpBuffer q = createPQExpBuffer();
 	PQExpBuffer insertStmt = NULL;
@@ -2618,7 +2618,7 @@ dumpTableData_insert(Archive *fout, const void *dcontext)
 		 */
 		if (insertStmt == NULL)
 		{
-			TableInfo  *targettab;
+			const TableInfo *targettab;
 
 			insertStmt = createPQExpBuffer();
 
@@ -2813,10 +2813,10 @@ dumpTableData_insert(Archive *fout, const void *dcontext)
  * getRootTableInfo:
  *     get the root TableInfo for the given partition table.
  */
-static TableInfo *
+static const TableInfo *
 getRootTableInfo(const TableInfo *tbinfo)
 {
-	TableInfo  *parentTbinfo;
+	const TableInfo *parentTbinfo;
 
 	Assert(tbinfo->ispartition);
 	Assert(tbinfo->numParents == 1);
@@ -2870,7 +2870,7 @@ static void
 dumpTableData(Archive *fout, const TableDataInfo *tdinfo)
 {
 	DumpOptions *dopt = fout->dopt;
-	TableInfo  *tbinfo = tdinfo->tdtable;
+	const TableInfo *tbinfo = tdinfo->tdtable;
 	PQExpBuffer copyBuf = createPQExpBuffer();
 	PQExpBuffer clistBuf = createPQExpBuffer();
 	DataDumperPtr dumpFn;
@@ -2891,7 +2891,7 @@ dumpTableData(Archive *fout, const TableDataInfo *tdinfo)
 		(dopt->load_via_partition_root ||
 		 forcePartitionRootLoad(tbinfo)))
 	{
-		TableInfo  *parentTbinfo;
+		const TableInfo *parentTbinfo;
 		char	   *sanitized;
 
 		parentTbinfo = getRootTableInfo(tbinfo);
-- 
2.34.1


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	filename="v1-0003-Separate-read-and-write-pointers-in-pg_saslprep.patch"

From f32dd7b645090b85e1297f312c73353d93c83383 Mon Sep 17 00:00:00 2001
From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
Date: Thu, 18 Dec 2025 12:17:21 +0000
Subject: [PATCH v1 3/3] Separate read and write pointers in pg_saslprep

Use separate pointers for reading const input ('p') and writing
to mutable output ('outp'), avoiding the need to cast away const
on the input parameter.
---
 src/common/saslprep.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)
 100.0% src/common/

diff --git a/src/common/saslprep.c b/src/common/saslprep.c
index 101e8d65a4d..b215ab0bf8e 100644
--- a/src/common/saslprep.c
+++ b/src/common/saslprep.c
@@ -1054,7 +1054,8 @@ pg_saslprep(const char *input, char **output)
 	int			count;
 	int			i;
 	bool		contains_RandALCat;
-	unsigned char *p;
+	const unsigned char *p;
+	unsigned char *outp;
 	char32_t   *wp;
 
 	/* Ensure we return *output as NULL on failure */
@@ -1087,7 +1088,7 @@ pg_saslprep(const char *input, char **output)
 	if (!input_chars)
 		goto oom;
 
-	p = (unsigned char *) input;
+	p = (const unsigned char *) input;
 	for (i = 0; i < input_size; i++)
 	{
 		input_chars[i] = utf8_to_unicode(p);
@@ -1217,14 +1218,14 @@ pg_saslprep(const char *input, char **output)
 	 * There are no error exits below here, so the error exit paths don't need
 	 * to worry about possibly freeing "result".
 	 */
-	p = (unsigned char *) result;
+	outp = (unsigned char *) result;
 	for (wp = output_chars; *wp; wp++)
 	{
-		unicode_to_utf8(*wp, p);
-		p += pg_utf_mblen(p);
+		unicode_to_utf8(*wp, outp);
+		outp += pg_utf_mblen(outp);
 	}
-	Assert((char *) p == result + result_size);
-	*p = '\0';
+	Assert((char *) outp == result + result_size);
+	*outp = '\0';
 
 	FREE(input_chars);
 	FREE(output_chars);
-- 
2.34.1


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