Make eval_const_expressions() preserve typmod when simplifying something like

null::char(3) to a simple Const node.  (It already worked for non-null values,
but not when we skipped evaluation of a strict coercion function.)  This
prevents loss of typmod knowledge in situations such as exhibited in bug
#3598.  Unfortunately there seems no good way to fix that bug in 8.1 and 8.2,
because they simply don't carry a typmod for a plain Const node.

In passing I made all the other callers of makeNullConst supply "real" typmod
values too, though I think it probably doesn't matter anywhere else.

10 files changed, 21 insertions, 16 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 77e4b5e1cd..ede192298f 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -3179,12 +3179,15 @@ ATExecAddColumn(AlteredTableInfo *tab, Relation rel,
 
 	if (!defval && GetDomainConstraints(typeOid) != NIL)
 	{
-		Oid			basetype = getBaseType(typeOid);
+		Oid			baseTypeId;
+		int32		baseTypeMod;
 
-		defval = (Expr *) makeNullConst(basetype);
+		baseTypeMod = typmod;
+		baseTypeId = getBaseTypeAndTypmod(typeOid, &baseTypeMod);
+		defval = (Expr *) makeNullConst(baseTypeId, baseTypeMod);
 		defval = (Expr *) coerce_to_target_type(NULL,
 												(Node *) defval,
-												basetype,
+												baseTypeId,
 												typeOid,
 												typmod,
 												COERCION_ASSIGNMENT,
diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index 7acc7b255c..a6a970e759 100644
--- a/src/backend/executor/execQual.c
+++ b/src/backend/executor/execQual.c
@@ -4159,7 +4159,7 @@ ExecInitExpr(Expr *node, PlanState *parent)
 						 * don't really care what type of NULL it is, so
 						 * always make an int4 NULL.
 						 */
-						e = (Expr *) makeNullConst(INT4OID);
+						e = (Expr *) makeNullConst(INT4OID, -1);
 					}
 					estate = ExecInitExpr(e, parent);
 					outlist = lappend(outlist, estate);
diff --git a/src/backend/nodes/makefuncs.c b/src/backend/nodes/makefuncs.c
index 6aa17413a4..d83b5b95a5 100644
--- a/src/backend/nodes/makefuncs.c
+++ b/src/backend/nodes/makefuncs.c
@@ -174,19 +174,20 @@ makeConst(Oid consttype,
 
 /*
  * makeNullConst -
- *	  creates a Const node representing a NULL of the specified type
+ *	  creates a Const node representing a NULL of the specified type/typmod
  *
- * Note: for all current uses, OK to set typmod of the Const to -1.
+ * This is a convenience routine that just saves a lookup of the type's
+ * storage properties.
  */
 Const *
-makeNullConst(Oid consttype)
+makeNullConst(Oid consttype, int32 consttypmod)
 {
 	int16		typLen;
 	bool		typByVal;
 
 	get_typlenbyval(consttype, &typLen, &typByVal);
 	return makeConst(consttype,
-					 -1,
+					 consttypmod,
 					 (int) typLen,
 					 (Datum) 0,
 					 true,
diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c
index a7a2621ee1..afef1cfd47 100644
--- a/src/backend/optimizer/util/clauses.c
+++ b/src/backend/optimizer/util/clauses.c
@@ -2265,7 +2265,7 @@ eval_const_expressions_mutator(Node *node,
 
 		/* If all the arguments were constant null, the result is just null */
 		if (newargs == NIL)
-			return (Node *) makeNullConst(coalesceexpr->coalescetype);
+			return (Node *) makeNullConst(coalesceexpr->coalescetype, -1);
 
 		newcoalesce = makeNode(CoalesceExpr);
 		newcoalesce->coalescetype = coalesceexpr->coalescetype;
@@ -2833,7 +2833,7 @@ evaluate_function(Oid funcid, Oid result_type, int32 result_typmod, List *args,
 	 * function is not otherwise immutable.
 	 */
 	if (funcform->proisstrict && has_null_input)
-		return (Expr *) makeNullConst(result_type);
+		return (Expr *) makeNullConst(result_type, result_typmod);
 
 	/*
 	 * Otherwise, can simplify only if all inputs are constants. (For a
diff --git a/src/backend/parser/parse_coerce.c b/src/backend/parser/parse_coerce.c
index 7950d034bc..1459b98dbc 100644
--- a/src/backend/parser/parse_coerce.c
+++ b/src/backend/parser/parse_coerce.c
@@ -816,7 +816,7 @@ coerce_record_to_complex(ParseState *pstate, Node *node,
 			 * can't use atttypid here, but it doesn't really matter what type
 			 * the Const claims to be.
 			 */
-			newargs = lappend(newargs, makeNullConst(INT4OID));
+			newargs = lappend(newargs, makeNullConst(INT4OID, -1));
 			continue;
 		}
 
diff --git a/src/backend/parser/parse_relation.c b/src/backend/parser/parse_relation.c
index dd9499e417..f57e1a4348 100644
--- a/src/backend/parser/parse_relation.c
+++ b/src/backend/parser/parse_relation.c
@@ -1448,7 +1448,7 @@ expandTupleDesc(TupleDesc tupdesc, Alias *eref,
 					 * can't use atttypid here, but it doesn't really matter
 					 * what type the Const claims to be.
 					 */
-					*colvars = lappend(*colvars, makeNullConst(INT4OID));
+					*colvars = lappend(*colvars, makeNullConst(INT4OID, -1));
 				}
 			}
 			continue;
diff --git a/src/backend/parser/parse_target.c b/src/backend/parser/parse_target.c
index ef9bf189b5..e0c297e68e 100644
--- a/src/backend/parser/parse_target.c
+++ b/src/backend/parser/parse_target.c
@@ -393,7 +393,7 @@ transformAssignedExpr(ParseState *pstate,
 			 * is not really a source value to work with. Insert a NULL
 			 * constant as the source value.
 			 */
-			colVar = (Node *) makeNullConst(attrtype);
+			colVar = (Node *) makeNullConst(attrtype, attrtypmod);
 		}
 		else
 		{
diff --git a/src/backend/rewrite/rewriteHandler.c b/src/backend/rewrite/rewriteHandler.c
index e358d380d2..d83f21f256 100644
--- a/src/backend/rewrite/rewriteHandler.c
+++ b/src/backend/rewrite/rewriteHandler.c
@@ -193,7 +193,7 @@ AcquireRewriteLocks(Query *parsetree)
 							 * now-dropped type OID, but it doesn't really
 							 * matter what type the Const claims to be.
 							 */
-							aliasvar = (Var *) makeNullConst(INT4OID);
+							aliasvar = (Var *) makeNullConst(INT4OID, -1);
 						}
 					}
 					newaliasvars = lappend(newaliasvars, aliasvar);
diff --git a/src/backend/rewrite/rewriteManip.c b/src/backend/rewrite/rewriteManip.c
index f30e7796c9..fc8be972f7 100644
--- a/src/backend/rewrite/rewriteManip.c
+++ b/src/backend/rewrite/rewriteManip.c
@@ -896,7 +896,8 @@ resolve_one_var(Var *var, ResolveNew_context *context)
 		{
 			/* Otherwise replace unmatched var with a null */
 			/* need coerce_to_domain in case of NOT NULL domain constraint */
-			return coerce_to_domain((Node *) makeNullConst(var->vartype),
+			return coerce_to_domain((Node *) makeNullConst(var->vartype,
+														   var->vartypmod),
 									InvalidOid, -1,
 									var->vartype,
 									COERCE_IMPLICIT_CAST,
diff --git a/src/include/nodes/makefuncs.h b/src/include/nodes/makefuncs.h
index d8aa5f4fc3..6ae9e1b244 100644
--- a/src/include/nodes/makefuncs.h
+++ b/src/include/nodes/makefuncs.h
@@ -45,7 +45,7 @@ extern Const *makeConst(Oid consttype,
 		  bool constisnull,
 		  bool constbyval);
 
-extern Const *makeNullConst(Oid consttype);
+extern Const *makeNullConst(Oid consttype, int32 consttypmod);
 
 extern Node *makeBoolConst(bool value, bool isnull);