Improve error cursor positions for problems with partition bounds.

We failed to pass down the query string to check_new_partition_bound,
so that its attempts to provide error cursor positions were for naught;
one must have the query string to get parser_errposition to do anything.
Adjust its API to require a ParseState to be passed down.

Also, improve the logic inside check_new_partition_bound so that the
cursor points at the partition bound for the specific column causing
the issue, when one can be identified.

That part is also for naught if we can't determine the query position of
the column with the problem.  Improve transformPartitionBoundValue so
that it makes sure that const-simplified partition expressions will be
properly labeled with positions.  In passing, skip calling evaluate_expr
if the value is already a Const, which is surely the most common case.

Alexandra Wang, Ashwin Agrawal, Amit Langote; reviewed by Ashutosh Bapat

Discussion: https://postgr.es/m/CACiyaSopZoqssfMzgHk6fAkp01cL6vnqBdmTw2C5_KJaFR_aMg@mail.gmail.com
Discussion: https://postgr.es/m/CAJV4CdrZ5mKuaEsRSbLf2URQ3h6iMtKD=hik8MaF5WwdmC9uZw@mail.gmail.com

Author: tglsfdc

src/backend/commands/tablecmds.c

@@ -543,7 +543,8 @@ static void ComputePartitionAttrs(ParseState *pstate, Relation rel, List *partPa
 static void CreateInheritance(Relation child_rel, Relation parent_rel);
 static void RemoveInheritance(Relation child_rel, Relation parent_rel);
 static ObjectAddress ATExecAttachPartition(List **wqueue, Relation rel,
-										   PartitionCmd *cmd);
+										   PartitionCmd *cmd,
+										   AlterTableUtilityContext *context);
 static void AttachPartitionEnsureIndexes(Relation rel, Relation attachrel);
 static void QueuePartitionConstraintValidation(List **wqueue, Relation scanrel,
 											   List *partConstraint,
@@ -1007,7 +1008,7 @@ DefineRelation(CreateStmt *stmt, char relkind, Oid ownerId,
 		 * Check first that the new partition's bound is valid and does not
 		 * overlap with any of existing partitions of the parent.
 		 */
-		check_new_partition_bound(relname, parent, bound);
+		check_new_partition_bound(relname, parent, bound, pstate);
 
 		/*
 		 * If the default partition exists, its partition constraints will
@@ -4718,7 +4719,8 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
 									  cur_pass, context);
 			Assert(cmd != NULL);
 			if (rel->rd_rel->relkind == RELKIND_PARTITIONED_TABLE)
-				ATExecAttachPartition(wqueue, rel, (PartitionCmd *) cmd->def);
+				ATExecAttachPartition(wqueue, rel, (PartitionCmd *) cmd->def,
+									  context);
 			else
 				ATExecAttachPartitionIdx(wqueue, rel,
 										 ((PartitionCmd *) cmd->def)->name);
@@ -16280,7 +16282,8 @@ QueuePartitionConstraintValidation(List **wqueue, Relation scanrel,
  * Return the address of the newly attached partition.
  */
 static ObjectAddress
-ATExecAttachPartition(List **wqueue, Relation rel, PartitionCmd *cmd)
+ATExecAttachPartition(List **wqueue, Relation rel, PartitionCmd *cmd,
+					  AlterTableUtilityContext *context)
 {
 	Relation	attachrel,
 				catalog;
@@ -16295,6 +16298,9 @@ ATExecAttachPartition(List **wqueue, Relation rel, PartitionCmd *cmd)
 	const char *trigger_name;
 	Oid			defaultPartOid;
 	List	   *partBoundConstraint;
+	ParseState *pstate = make_parsestate(NULL);
+
+	pstate->p_sourcetext = context->queryString;
 
 	/*
 	 * We must lock the default partition if one exists, because attaching a
@@ -16460,7 +16466,7 @@ ATExecAttachPartition(List **wqueue, Relation rel, PartitionCmd *cmd)
 	 * error.
 	 */
 	check_new_partition_bound(RelationGetRelationName(attachrel), rel,
-							  cmd->bound);
+							  cmd->bound, pstate);
 
 	/* OK to create inheritance.  Rest of the checks performed there */
 	CreateInheritance(attachrel, rel);

src/backend/parser/parse_utilcmd.c

@@ -4164,7 +4164,7 @@ validateInfiniteBounds(ParseState *pstate, List *blist)
 }
 
 /*
- * Transform one constant in a partition bound spec
+ * Transform one entry in a partition bound spec, producing a constant.
  */
 static Const *
 transformPartitionBoundValue(ParseState *pstate, Node *val,
@@ -4176,6 +4176,13 @@ transformPartitionBoundValue(ParseState *pstate, Node *val,
 	/* Transform raw parsetree */
 	value = transformExpr(pstate, val, EXPR_KIND_PARTITION_BOUND);
 
+	/*
+	 * transformExpr() should have already rejected column references,
+	 * subqueries, aggregates, window functions, and SRFs, based on the
+	 * EXPR_KIND_ of a partition bound expression.
+	 */
+	Assert(!contain_var_clause(value));
+
 	/*
 	 * Check that the input expression's collation is compatible with one
 	 * specified for the parent's partition key (partcollation).  Don't throw
@@ -4220,7 +4227,11 @@ transformPartitionBoundValue(ParseState *pstate, Node *val,
 					 parser_errposition(pstate, exprLocation(value))));
 	}
 
-	/* Coerce to correct type */
+	/*
+	 * Coerce to the correct type.  This might cause an explicit coercion step
+	 * to be added on top of the expression, which must be evaluated before
+	 * returning the result to the caller.
+	 */
 	value = coerce_to_target_type(pstate,
 								  value, exprType(value),
 								  colType,
@@ -4236,25 +4247,35 @@ transformPartitionBoundValue(ParseState *pstate, Node *val,
 						format_type_be(colType), colName),
 				 parser_errposition(pstate, exprLocation(val))));
 
-	/* Simplify the expression, in case we had a coercion */
-	if (!IsA(value, Const))
-		value = (Node *) expression_planner((Expr *) value);
-
 	/*
-	 * transformExpr() should have already rejected column references,
-	 * subqueries, aggregates, window functions, and SRFs, based on the
-	 * EXPR_KIND_ for a default expression.
+	 * Evaluate the expression, if needed, assigning the partition key's data
+	 * type and collation to the resulting Const node.
 	 */
-	Assert(!contain_var_clause(value));
+	if (!IsA(value, Const))
+	{
+		value = (Node *) expression_planner((Expr *) value);
+		value = (Node *) evaluate_expr((Expr *) value, colType, colTypmod,
+									   partCollation);
+		if (!IsA(value, Const))
+			elog(ERROR, "could not evaluate partition bound expression");
+	}
+	else
+	{
+		/*
+		 * If the expression is already a Const, as is often the case, we can
+		 * skip the rather expensive steps above.  But we still have to insert
+		 * the right collation, since coerce_to_target_type doesn't handle
+		 * that.
+		 */
+		((Const *) value)->constcollid = partCollation;
+	}
 
 	/*
-	 * Evaluate the expression, assigning the partition key's collation to the
-	 * resulting Const expression.
+	 * Attach original expression's parse location to the Const, so that
+	 * that's what will be reported for any later errors related to this
+	 * partition bound.
 	 */
-	value = (Node *) evaluate_expr((Expr *) value, colType, colTypmod,
-								   partCollation);
-	if (!IsA(value, Const))
-		elog(ERROR, "could not evaluate partition bound expression");
+	((Const *) value)->location = exprLocation(val);
 
 	return (Const *) value;
 }