Fix ALTER TABLE code to update domain constraints when needed.

It's possible for dropping a column, or altering its type, to require
changes in domain CHECK constraint expressions; but the code was
previously only expecting to find dependent table CHECK constraints.
Make the necessary adjustments.

This is a fairly old oversight, but it's a lot easier to encounter
the problem in the context of domains over composite types than it
was before.  Given the lack of field complaints, I'm not going to
bother with a back-patch, though I'd be willing to reconsider that
decision if someone does complain.

Patch by me, reviewed by Michael Paquier

Discussion: https://postgr.es/m/30656.1509128130@sss.pgh.pa.us

src/backend/commands/tablecmds.c

@@ -425,7 +425,8 @@ static void ATPostAlterTypeParse(Oid oldId, Oid oldRelId, Oid refRelId,
 					 char *cmd, List **wqueue, LOCKMODE lockmode,
 					 bool rewrite);
 static void RebuildConstraintComment(AlteredTableInfo *tab, int pass,
-						 Oid objid, Relation rel, char *conname);
+						 Oid objid, Relation rel, List *domname,
+						 char *conname);
 static void TryReuseIndex(Oid oldId, IndexStmt *stmt);
 static void TryReuseForeignKey(Oid oldId, Constraint *con);
 static void change_owner_fix_column_acls(Oid relationOid,
@@ -3319,6 +3320,7 @@ AlterTableGetLockLevel(List *cmds)
 			case AT_ProcessedConstraint:	/* becomes AT_AddConstraint */
 			case AT_AddConstraintRecurse:	/* becomes AT_AddConstraint */
 			case AT_ReAddConstraint:	/* becomes AT_AddConstraint */
+			case AT_ReAddDomainConstraint:	/* becomes AT_AddConstraint */
 				if (IsA(cmd->def, Constraint))
 				{
 					Constraint *con = (Constraint *) cmd->def;
@@ -3819,7 +3821,9 @@ ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode)
 			rel = relation_open(tab->relid, NoLock);
 
 			foreach(lcmd, subcmds)
-				ATExecCmd(wqueue, tab, rel, (AlterTableCmd *) lfirst(lcmd), lockmode);
+				ATExecCmd(wqueue, tab, rel,
+						  castNode(AlterTableCmd, lfirst(lcmd)),
+						  lockmode);
 
 			/*
 			 * After the ALTER TYPE pass, do cleanup work (this is not done in
@@ -3936,6 +3940,13 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
 				ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
 									true, true, lockmode);
 			break;
+		case AT_ReAddDomainConstraint:	/* Re-add pre-existing domain check
+										 * constraint */
+			address =
+				AlterDomainAddConstraint(((AlterDomainStmt *) cmd->def)->typeName,
+										 ((AlterDomainStmt *) cmd->def)->def,
+										 NULL);
+			break;
 		case AT_ReAddComment:	/* Re-add existing comment */
 			address = CommentObject((CommentStmt *) cmd->def);
 			break;
@@ -9616,7 +9627,15 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
 		if (!HeapTupleIsValid(tup)) /* should not happen */
 			elog(ERROR, "cache lookup failed for constraint %u", oldId);
 		con = (Form_pg_constraint) GETSTRUCT(tup);
+		if (OidIsValid(con->conrelid))
 			relid = con->conrelid;
+		else
+		{
+			/* must be a domain constraint */
+			relid = get_typ_typrelid(getBaseType(con->contypid));
+			if (!OidIsValid(relid))
+				elog(ERROR, "could not identify relation associated with constraint %u", oldId);
+		}
 		confrelid = con->confrelid;
 		conislocal = con->conislocal;
 		ReleaseSysCache(tup);
@@ -9753,7 +9772,7 @@ ATPostAlterTypeParse(Oid oldId, Oid oldRelId, Oid refRelId, char *cmd,
 
 			foreach(lcmd, stmt->cmds)
 			{
-				AlterTableCmd *cmd = (AlterTableCmd *) lfirst(lcmd);
+				AlterTableCmd *cmd = castNode(AlterTableCmd, lfirst(lcmd));
 
 				if (cmd->subtype == AT_AddIndex)
 				{
@@ -9777,13 +9796,14 @@ ATPostAlterTypeParse(Oid oldId, Oid oldRelId, Oid refRelId, char *cmd,
 					RebuildConstraintComment(tab,
 											 AT_PASS_OLD_INDEX,
 											 oldId,
-											 rel, indstmt->idxname);
+											 rel,
+											 NIL,
+											 indstmt->idxname);
 				}
 				else if (cmd->subtype == AT_AddConstraint)
 				{
-					Constraint *con;
+					Constraint *con = castNode(Constraint, cmd->def);
 
-					con = castNode(Constraint, cmd->def);
 					con->old_pktable_oid = refRelId;
 					/* rewriting neither side of a FK */
 					if (con->contype == CONSTR_FOREIGN &&
@@ -9797,13 +9817,41 @@ ATPostAlterTypeParse(Oid oldId, Oid oldRelId, Oid refRelId, char *cmd,
 					RebuildConstraintComment(tab,
 											 AT_PASS_OLD_CONSTR,
 											 oldId,
-											 rel, con->conname);
+											 rel,
+											 NIL,
+											 con->conname);
 				}
 				else
 					elog(ERROR, "unexpected statement subtype: %d",
 						 (int) cmd->subtype);
 			}
 		}
+		else if (IsA(stm, AlterDomainStmt))
+		{
+			AlterDomainStmt *stmt = (AlterDomainStmt *) stm;
+
+			if (stmt->subtype == 'C')	/* ADD CONSTRAINT */
+			{
+				Constraint *con = castNode(Constraint, stmt->def);
+				AlterTableCmd *cmd = makeNode(AlterTableCmd);
+
+				cmd->subtype = AT_ReAddDomainConstraint;
+				cmd->def = (Node *) stmt;
+				tab->subcmds[AT_PASS_OLD_CONSTR] =
+					lappend(tab->subcmds[AT_PASS_OLD_CONSTR], cmd);
+
+				/* recreate any comment on the constraint */
+				RebuildConstraintComment(tab,
+										 AT_PASS_OLD_CONSTR,
+										 oldId,
+										 NULL,
+										 stmt->typeName,
+										 con->conname);
+			}
+			else
+				elog(ERROR, "unexpected statement subtype: %d",
+					 (int) stmt->subtype);
+		}
 		else
 			elog(ERROR, "unexpected statement type: %d",
 				 (int) nodeTag(stm));
@@ -9813,12 +9861,19 @@ ATPostAlterTypeParse(Oid oldId, Oid oldRelId, Oid refRelId, char *cmd,
 }
 
 /*
- * Subroutine for ATPostAlterTypeParse() to recreate a comment entry for
- * a constraint that is being re-added.
+ * Subroutine for ATPostAlterTypeParse() to recreate any existing comment
+ * for a table or domain constraint that is being rebuilt.
+ *
+ * objid is the OID of the constraint.
+ * Pass "rel" for a table constraint, or "domname" (domain's qualified name
+ * as a string list) for a domain constraint.
+ * (We could dig that info, as well as the conname, out of the pg_constraint
+ * entry; but callers already have them so might as well pass them.)
  */
 static void
 RebuildConstraintComment(AlteredTableInfo *tab, int pass, Oid objid,
-						 Relation rel, char *conname)
+						 Relation rel, List *domname,
+						 char *conname)
 {
 	CommentStmt *cmd;
 	char	   *comment_str;
@@ -9829,12 +9884,23 @@ RebuildConstraintComment(AlteredTableInfo *tab, int pass, Oid objid,
 	if (comment_str == NULL)
 		return;
 
-	/* Build node CommentStmt */
+	/* Build CommentStmt node, copying all input data for safety */
 	cmd = makeNode(CommentStmt);
+	if (rel)
+	{
 		cmd->objtype = OBJECT_TABCONSTRAINT;
-	cmd->object = (Node *) list_make3(makeString(get_namespace_name(RelationGetNamespace(rel))),
+		cmd->object = (Node *)
+			list_make3(makeString(get_namespace_name(RelationGetNamespace(rel))),
 					   makeString(pstrdup(RelationGetRelationName(rel))),
 					   makeString(pstrdup(conname)));
+	}
+	else
+	{
+		cmd->objtype = OBJECT_DOMCONSTRAINT;
+		cmd->object = (Node *)
+			list_make2(makeTypeNameFromNameList(copyObject(domname)),
+					   makeString(pstrdup(conname)));
+	}
 	cmd->comment = comment_str;
 
 	/* Append it to list of commands */

src/backend/utils/adt/ruleutils.c

@@ -460,6 +460,7 @@ static char *generate_function_name(Oid funcid, int nargs,
 					   bool has_variadic, bool *use_variadic_p,
 					   ParseExprKind special_exprkind);
 static char *generate_operator_name(Oid operid, Oid arg1, Oid arg2);
+static char *generate_qualified_type_name(Oid typid);
 static text *string_to_text(char *str);
 static char *flatten_reloptions(Oid relid);
 
@@ -1866,17 +1867,29 @@ pg_get_constraintdef_worker(Oid constraintId, bool fullCommand,
 	initStringInfo(&buf);
 
 	if (fullCommand)
+	{
+		if (OidIsValid(conForm->conrelid))
 		{
 			/*
 			 * Currently, callers want ALTER TABLE (without ONLY) for CHECK
-		 * constraints, and other types of constraints don't inherit anyway so
-		 * it doesn't matter whether we say ONLY or not.  Someday we might
-		 * need to let callers specify whether to put ONLY in the command.
+			 * constraints, and other types of constraints don't inherit
+			 * anyway so it doesn't matter whether we say ONLY or not. Someday
+			 * we might need to let callers specify whether to put ONLY in the
+			 * command.
 			 */
 			appendStringInfo(&buf, "ALTER TABLE %s ADD CONSTRAINT %s ",
 							 generate_qualified_relation_name(conForm->conrelid),
 							 quote_identifier(NameStr(conForm->conname)));
 		}
+		else
+		{
+			/* Must be a domain constraint */
+			Assert(OidIsValid(conForm->contypid));
+			appendStringInfo(&buf, "ALTER DOMAIN %s ADD CONSTRAINT %s ",
+							 generate_qualified_type_name(conForm->contypid),
+							 quote_identifier(NameStr(conForm->conname)));
+		}
+	}
 
 	switch (conForm->contype)
 	{
@@ -10778,6 +10791,42 @@ generate_operator_name(Oid operid, Oid arg1, Oid arg2)
 	return buf.data;
 }
 
+/*
+ * generate_qualified_type_name
+ *		Compute the name to display for a type specified by OID
+ *
+ * This is different from format_type_be() in that we unconditionally
+ * schema-qualify the name.  That also means no special syntax for
+ * SQL-standard type names ... although in current usage, this should
+ * only get used for domains, so such cases wouldn't occur anyway.
+ */
+static char *
+generate_qualified_type_name(Oid typid)
+{
+	HeapTuple	tp;
+	Form_pg_type typtup;
+	char	   *typname;
+	char	   *nspname;
+	char	   *result;
+
+	tp = SearchSysCache1(TYPEOID, ObjectIdGetDatum(typid));
+	if (!HeapTupleIsValid(tp))
+		elog(ERROR, "cache lookup failed for type %u", typid);
+	typtup = (Form_pg_type) GETSTRUCT(tp);
+	typname = NameStr(typtup->typname);
+
+	nspname = get_namespace_name(typtup->typnamespace);
+	if (!nspname)
+		elog(ERROR, "cache lookup failed for namespace %u",
+			 typtup->typnamespace);
+
+	result = quote_qualified_identifier(nspname, typname);
+
+	ReleaseSysCache(tp);
+
+	return result;
+}
+
 /*
  * generate_collation_name
  *		Compute the name to display for a collation specified by OID

src/include/nodes/parsenodes.h

@@ -1713,6 +1713,7 @@ typedef enum AlterTableType
 	AT_AddConstraint,			/* add constraint */
 	AT_AddConstraintRecurse,	/* internal to commands/tablecmds.c */
 	AT_ReAddConstraint,			/* internal to commands/tablecmds.c */
+	AT_ReAddDomainConstraint,	/* internal to commands/tablecmds.c */
 	AT_AlterConstraint,			/* alter constraint */
 	AT_ValidateConstraint,		/* validate constraint */
 	AT_ValidateConstraintRecurse,	/* internal to commands/tablecmds.c */

src/test/regress/expected/domain.out

@@ -284,6 +284,31 @@ Rules:
   WHERE (dcomptable.d1).i > 0::double precision
 
 drop table dcomptable;
+drop type comptype cascade;
+NOTICE:  drop cascades to type dcomptype
+-- check altering and dropping columns used by domain constraints
+create type comptype as (r float8, i float8);
+create domain dcomptype as comptype;
+alter domain dcomptype add constraint c1 check ((value).r > 0);
+comment on constraint c1 on domain dcomptype is 'random commentary';
+select row(0,1)::dcomptype;  -- fail
+ERROR:  value for domain dcomptype violates check constraint "c1"
+alter type comptype alter attribute r type varchar;  -- fail
+ERROR:  operator does not exist: character varying > double precision
+HINT:  No operator matches the given name and argument types. You might need to add explicit type casts.
+alter type comptype alter attribute r type bigint;
+alter type comptype drop attribute r;  -- fail
+ERROR:  cannot drop composite type comptype column r because other objects depend on it
+DETAIL:  constraint c1 depends on composite type comptype column r
+HINT:  Use DROP ... CASCADE to drop the dependent objects too.
+alter type comptype drop attribute i;
+select conname, obj_description(oid, 'pg_constraint') from pg_constraint
+  where contypid = 'dcomptype'::regtype;  -- check comment is still there
+ conname |  obj_description  
+---------+-------------------
+ c1      | random commentary
+(1 row)
+
 drop type comptype cascade;
 NOTICE:  drop cascades to type dcomptype
 -- Test domains over arrays of composite

src/test/regress/sql/domain.sql

@@ -159,6 +159,26 @@ drop table dcomptable;
 drop type comptype cascade;
 
 
+-- check altering and dropping columns used by domain constraints
+create type comptype as (r float8, i float8);
+create domain dcomptype as comptype;
+alter domain dcomptype add constraint c1 check ((value).r > 0);
+comment on constraint c1 on domain dcomptype is 'random commentary';
+
+select row(0,1)::dcomptype;  -- fail
+
+alter type comptype alter attribute r type varchar;  -- fail
+alter type comptype alter attribute r type bigint;
+
+alter type comptype drop attribute r;  -- fail
+alter type comptype drop attribute i;
+
+select conname, obj_description(oid, 'pg_constraint') from pg_constraint
+  where contypid = 'dcomptype'::regtype;  -- check comment is still there
+
+drop type comptype cascade;
+
+
 -- Test domains over arrays of composite
 
 create type comptype as (r float8, i float8);