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.

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.231 2007/08/21 01:11:14 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/tablecmds.c,v 1.232 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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,

src/backend/executor/execQual.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.221 2007/08/31 18:33:40 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.222 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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);

src/backend/nodes/makefuncs.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/nodes/makefuncs.c,v 1.56 2007/06/23 22:12:50 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/nodes/makefuncs.c,v 1.57 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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,

src/backend/optimizer/util/clauses.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.248 2007/09/03 00:39:15 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/clauses.c,v 1.249 2007/09/06 17:31:58 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -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

src/backend/parser/parse_coerce.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_coerce.c,v 2.156 2007/08/21 01:11:15 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_coerce.c,v 2.157 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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;
 		}
 

src/backend/parser/parse_relation.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_relation.c,v 1.127 2007/01/05 22:19:34 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_relation.c,v 1.128 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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;

src/backend/parser/parse_target.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_target.c,v 1.154 2007/02/03 14:06:54 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_target.c,v 1.155 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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
 		{

src/backend/rewrite/rewriteHandler.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/rewrite/rewriteHandler.c,v 1.173 2007/03/19 23:38:29 wieck Exp $
+ *	  $PostgreSQL: pgsql/src/backend/rewrite/rewriteHandler.c,v 1.174 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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);

src/backend/rewrite/rewriteManip.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/rewrite/rewriteManip.c,v 1.104 2007/06/11 01:16:25 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/rewrite/rewriteManip.c,v 1.105 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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,

src/include/nodes/makefuncs.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/nodes/makefuncs.h,v 1.59 2007/06/23 22:12:52 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/nodes/makefuncs.h,v 1.60 2007/09/06 17:31:58 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -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);