Fix failure for generated column with a not-null domain constraint.

If a GENERATED column is declared to have a domain data type where
the domain's constraints disallow null values, INSERT commands failed
because we built a targetlist that included coercing a null constant
to the domain's type.  The failure occurred even when the generated
value would have been perfectly OK.  This is adjacent to the issues
fixed in 0da39aa76, but we didn't notice for lack of testing a domain
with such a constraint.

We aren't going to use the result of the targetlist entry for the
generated column --- ExecComputeStoredGenerated will overwrite it.
So it's not really necessary that it have the exact datatype of
the generated column.  This patch fixes the problem by changing
the targetlist entry to be a null Const of the domain's base type,
which should be sufficiently legal.  (We do have to tweak
ExecCheckPlanOutput to accept the situation, though.)

This has been broken since we implemented generated columns.
However, this patch only applies easily as far back as v14, partly
because I (tgl) only carried 0da39aa76 back that far, but mostly
because v14 significantly refactored the handling of INSERT/UPDATE
targetlists.  Given the lack of field complaints and the short
remaining support lifetime of v13, I judge the cost-benefit ratio
not good for devising a version that would work in v13.

Reported-by: jian he <jian.universality@gmail.com>
Author: jian he <jian.universality@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/CACJufxG59tip2+9h=rEv-ykOFjt0cbsPVchhi0RTij8bABBA0Q@mail.gmail.com
Backpatch-through: 14

1 files changed, 38 insertions, 15 deletions

diff --git a/src/backend/optimizer/prep/preptlist.c b/src/backend/optimizer/prep/preptlist.c
index c2a77503d4b..ffc9d6c3f30 100644
--- a/src/backend/optimizer/prep/preptlist.c
+++ b/src/backend/optimizer/prep/preptlist.c
@@ -44,6 +44,7 @@
 #include "optimizer/tlist.h"
 #include "parser/parse_coerce.h"
 #include "parser/parsetree.h"
+#include "utils/lsyscache.h"
 #include "utils/rel.h"
 
 static List *expand_insert_targetlist(PlannerInfo *root, List *tlist,
@@ -419,9 +420,8 @@ expand_insert_targetlist(PlannerInfo *root, List *tlist, Relation rel)
 			 *
 			 * INSERTs should insert NULL in this case.  (We assume the
 			 * rewriter would have inserted any available non-NULL default
-			 * value.)  Also, if the column isn't dropped, apply any domain
-			 * constraints that might exist --- this is to catch domain NOT
-			 * NULL.
+			 * value.)  Also, normally we must apply any domain constraints
+			 * that might exist --- this is to catch domain NOT NULL.
 			 *
 			 * When generating a NULL constant for a dropped column, we label
 			 * it INT4 (any other guaranteed-to-exist datatype would do as
@@ -431,21 +431,17 @@ expand_insert_targetlist(PlannerInfo *root, List *tlist, Relation rel)
 			 * representation is datatype-independent.  This could perhaps
 			 * confuse code comparing the finished plan to the target
 			 * relation, however.
+			 *
+			 * Another exception is that if the column is generated, the value
+			 * we produce here will be ignored, and we don't want to risk
+			 * throwing an error.  So in that case we *don't* want to apply
+			 * domain constraints, so we must produce a NULL of the base type.
+			 * Again, code comparing the finished plan to the target relation
+			 * must account for this.
 			 */
 			Node	   *new_expr;
 
-			if (!att_tup->attisdropped)
-			{
-				new_expr = coerce_null_to_domain(att_tup->atttypid,
-												 att_tup->atttypmod,
-												 att_tup->attcollation,
-												 att_tup->attlen,
-												 att_tup->attbyval);
-				/* Must run expression preprocessing on any non-const nodes */
-				if (!IsA(new_expr, Const))
-					new_expr = eval_const_expressions(root, new_expr);
-			}
-			else
+			if (att_tup->attisdropped)
 			{
 				/* Insert NULL for dropped column */
 				new_expr = (Node *) makeConst(INT4OID,
@@ -456,6 +452,33 @@ expand_insert_targetlist(PlannerInfo *root, List *tlist, Relation rel)
 											  true, /* isnull */
 											  true /* byval */ );
 			}
+			else if (att_tup->attgenerated)
+			{
+				/* Generated column, insert a NULL of the base type */
+				Oid			baseTypeId = att_tup->atttypid;
+				int32		baseTypeMod = att_tup->atttypmod;
+
+				baseTypeId = getBaseTypeAndTypmod(baseTypeId, &baseTypeMod);
+				new_expr = (Node *) makeConst(baseTypeId,
+											  baseTypeMod,
+											  att_tup->attcollation,
+											  att_tup->attlen,
+											  (Datum) 0,
+											  true, /* isnull */
+											  att_tup->attbyval);
+			}
+			else
+			{
+				/* Normal column, insert a NULL of the column datatype */
+				new_expr = coerce_null_to_domain(att_tup->atttypid,
+												 att_tup->atttypmod,
+												 att_tup->attcollation,
+												 att_tup->attlen,
+												 att_tup->attbyval);
+				/* Must run expression preprocessing on any non-const nodes */
+				if (!IsA(new_expr, Const))
+					new_expr = eval_const_expressions(root, new_expr);
+			}
 
 			new_tle = makeTargetEntry((Expr *) new_expr,
 									  attrno,