Add-comments-on-MinimalTupleSlots-usage.patch

From d3614733cf7904edc3040c6fe140ea1e75544529 Mon Sep 17 00:00:00 2001
From: Pavel Borisov <pashkin.elfe@gmail.com>
Date: Fri, 22 Mar 2024 08:41:20 +0400
Subject: [PATCH] Add comments on MinimalTupleSlots usage.

Also refine error message introduced in 0997e0af273d80add
---
 src/backend/executor/execTuples.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/backend/executor/execTuples.c b/src/backend/executor/execTuples.c
index 7a7c786041..0ae240ced4 100644
--- a/src/backend/executor/execTuples.c
+++ b/src/backend/executor/execTuples.c
@@ -549,6 +549,10 @@ tts_minimal_getsomeattrs(TupleTableSlot *slot, int natts)
 	slot_deform_heap_tuple(slot, mslot->tuple, &mslot->off, natts);
 }
 
+/*
+ * MinimalTupleTableSlots never provide system attributes. We generally
+ * shouldn't get here, but provide a user-friendly message if we do.
+ */
 static Datum
 tts_minimal_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
 {
@@ -561,6 +565,11 @@ tts_minimal_getsysattr(TupleTableSlot *slot, int attnum, bool *isnull)
 	return 0;					/* silence compiler warnings */
 }
 
+/*
+ * Within MinimalTuple abstraction transaction information is unavailable.
+ * We generally shouldn't get here, but provide a user-friendly message if
+ * we do.
+ */
 static bool
 tts_minimal_is_current_xact_tuple(TupleTableSlot *slot)
 {
@@ -568,7 +577,7 @@ tts_minimal_is_current_xact_tuple(TupleTableSlot *slot)
 
 	ereport(ERROR,
 			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-			 errmsg("don't have a storage tuple in this context")));
+			 errmsg("don't have transaction information for this type of tuple")));
 
 	return false;				/* silence compiler warnings */
 }
-- 
2.39.2 (Apple Git-143)