new warnings with clang-21 / how const is Datum

From cb71953c5e4ce5203bb4867711e68ff2891ad3b8 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 8 Sep 2025 12:38:06 +0200
Subject: [PATCH 1/2] Silence compiler warning on clang 21

Clang 21 shows some new compiler warnings, for example:

warning: variable 'dstsize' is uninitialized when passed as a const pointer argument here [-Wuninitialized-const-pointer]

The fix is to initialize the variables when they are defined.  This is
similar to, for example, the existing situation in gistKeyIsEQ().

Discussion: https://www.postgresql.org/message-id/flat/6604ad6e-5934-43ac-8590-15113d6ae4b1%40eisentraut.org
---
 src/backend/access/common/toast_internals.c | 2 +-
 src/backend/access/gist/gistutil.c          | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/backend/access/common/toast_internals.c b/src/backend/access/common/toast_internals.c
index a1d0eed8953..75e908c2e80 100644
--- a/src/backend/access/common/toast_internals.c
+++ b/src/backend/access/common/toast_internals.c
@@ -135,7 +135,7 @@ toast_save_datum(Relation rel, Datum value,
 		char		data[TOAST_MAX_CHUNK_SIZE + VARHDRSZ];
 		/* ensure union is aligned well enough: */
 		int32		align_it;
-	}			chunk_data;
+	}			chunk_data = {0};	/* silence compiler warning */
 	int32		chunk_size;
 	int32		chunk_seq = 0;
 	char	   *data_p;
diff --git a/src/backend/access/gist/gistutil.c b/src/backend/access/gist/gistutil.c
index c0aa7d0222f..cdc4ab3151b 100644
--- a/src/backend/access/gist/gistutil.c
+++ b/src/backend/access/gist/gistutil.c
@@ -157,7 +157,7 @@ gistMakeUnionItVec(GISTSTATE *giststate, IndexTuple *itvec, int len,
 {
 	int			i;
 	GistEntryVector *evec;
-	int			attrsize;
+	int			attrsize = 0;	/* silence compiler warning */
 
 	evec = (GistEntryVector *) palloc((len + 2) * sizeof(GISTENTRY) + GEVHDRSZ);
 
@@ -242,7 +242,7 @@ gistMakeUnionKey(GISTSTATE *giststate, int attno,
 		char		padding[2 * sizeof(GISTENTRY) + GEVHDRSZ];
 	}			storage;
 	GistEntryVector *evec = &storage.gev;
-	int			dstsize;
+	int			dstsize = 0;	/* silence compiler warning */
 
 	evec->n = 2;
 

base-commit: 8191e0c16a0373f851a9f5a8112e3aec105b5276
-- 
2.51.0

From a4e9c43d5fa9642adcd2efa0f7db8efa45328236 Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <peter@eisentraut.org>
Date: Mon, 8 Sep 2025 13:24:29 +0200
Subject: [PATCH 2/2] Some stylistic improvements in toast_save_datum()

Move some variables to a smaller scope.  Initialize chunk_data before
storing a pointer to it; this avoids compiler warnings on clang21, or
respectively us having to work around it by initializing it to zero
before the variable is used.

Discussion: https://www.postgresql.org/message-id/flat/6604ad6e-5934-43ac-8590-15113d6ae4b1%40eisentraut.org
---
 src/backend/access/common/toast_internals.c | 39 +++++++++------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/src/backend/access/common/toast_internals.c b/src/backend/access/common/toast_internals.c
index 75e908c2e80..81dbd67c725 100644
--- a/src/backend/access/common/toast_internals.c
+++ b/src/backend/access/common/toast_internals.c
@@ -121,22 +121,10 @@ toast_save_datum(Relation rel, Datum value,
 {
 	Relation	toastrel;
 	Relation   *toastidxs;
-	HeapTuple	toasttup;
 	TupleDesc	toasttupDesc;
-	Datum		t_values[3];
-	bool		t_isnull[3];
 	CommandId	mycid = GetCurrentCommandId(true);
 	struct varlena *result;
 	struct varatt_external toast_pointer;
-	union
-	{
-		struct varlena hdr;
-		/* this is to make the union big enough for a chunk: */
-		char		data[TOAST_MAX_CHUNK_SIZE + VARHDRSZ];
-		/* ensure union is aligned well enough: */
-		int32		align_it;
-	}			chunk_data = {0};	/* silence compiler warning */
-	int32		chunk_size;
 	int32		chunk_seq = 0;
 	char	   *data_p;
 	int32		data_todo;
@@ -289,21 +277,23 @@ toast_save_datum(Relation rel, Datum value,
 		}
 	}
 
-	/*
-	 * Initialize constant parts of the tuple data
-	 */
-	t_values[0] = ObjectIdGetDatum(toast_pointer.va_valueid);
-	t_values[2] = PointerGetDatum(&chunk_data);
-	t_isnull[0] = false;
-	t_isnull[1] = false;
-	t_isnull[2] = false;
-
 	/*
 	 * Split up the item into chunks
 	 */
 	while (data_todo > 0)
 	{
-		int			i;
+		HeapTuple	toasttup;
+		Datum		t_values[3];
+		bool		t_isnull[3] = {0};
+		union
+		{
+			struct varlena hdr;
+			/* this is to make the union big enough for a chunk: */
+			char		data[TOAST_MAX_CHUNK_SIZE + VARHDRSZ];
+			/* ensure union is aligned well enough: */
+			int32		align_it;
+		}			chunk_data;
+		int32		chunk_size;
 
 		CHECK_FOR_INTERRUPTS();
 
@@ -315,9 +305,12 @@ toast_save_datum(Relation rel, Datum value,
 		/*
 		 * Build a tuple and store it
 		 */
+		t_values[0] = ObjectIdGetDatum(toast_pointer.va_valueid);
 		t_values[1] = Int32GetDatum(chunk_seq++);
 		SET_VARSIZE(&chunk_data, chunk_size + VARHDRSZ);
 		memcpy(VARDATA(&chunk_data), data_p, chunk_size);
+		t_values[2] = PointerGetDatum(&chunk_data);
+
 		toasttup = heap_form_tuple(toasttupDesc, t_values, t_isnull);
 
 		heap_insert(toastrel, toasttup, mycid, options, NULL);
@@ -333,7 +326,7 @@ toast_save_datum(Relation rel, Datum value,
 		 * Note also that there had better not be any user-created index on
 		 * the TOAST table, since we don't bother to update anything else.
 		 */
-		for (i = 0; i < num_indexes; i++)
+		for (int i = 0; i < num_indexes; i++)
 		{
 			/* Only index relations marked as ready can be updated */
 			if (toastidxs[i]->rd_index->indisready)
-- 
2.51.0