Fix handling of inherited check constraints in ALTER COLUMN TYPE (again).

The previous way of reconstructing check constraints was to do a separate
"ALTER TABLE ONLY tab ADD CONSTRAINT" for each table in an inheritance
hierarchy.  However, that way has no hope of reconstructing the check
constraints' own inheritance properties correctly, as pointed out in
bug #13779 from Jan Dirk Zijlstra.  What we should do instead is to do
a regular "ALTER TABLE", allowing recursion, at the topmost table that
has a particular constraint, and then suppress the work queue entries
for inherited instances of the constraint.

Annoyingly, we'd tried to fix this behavior before, in commit 5ed6546cf,
but we failed to notice that it wasn't reconstructing the pg_constraint
field values correctly.

As long as I'm touching pg_get_constraintdef_worker anyway, tweak it to
always schema-qualify the target table name; this seems like useful backup
to the protections installed by commit 5f173040.

In HEAD/9.5, get rid of get_constraint_relation_oids, which is now unused.
(I could alternatively have modified it to also return conislocal, but that
seemed like a pretty single-purpose API, so let's not pretend it has some
other use.)  It's unused in the back branches as well, but I left it in
place just in case some third-party code has decided to use it.

In HEAD/9.5, also rename pg_get_constraintdef_string to
pg_get_constraintdef_command, as the previous name did nothing to explain
what that entry point did differently from others (and its comment was
equally useless).  Again, that change doesn't seem like material for
back-patching.

I did a bit of re-pgindenting in tablecmds.c in HEAD/9.5, as well.

Otherwise, back-patch to all supported branches.

1 files changed, 24 insertions, 13 deletions

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 75bdf7ba0c4..a7497e5c2a5 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -3390,7 +3390,7 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
 		case AT_ReAddConstraint:		/* Re-add pre-existing check
 										 * constraint */
 			ATExecAddConstraint(wqueue, tab, rel, (Constraint *) cmd->def,
-								false, true, lockmode);
+								true, true, lockmode);
 			break;
 		case AT_AddIndexConstraint:		/* ADD CONSTRAINT USING INDEX */
 			ATExecAddIndexConstraint(tab, rel, (IndexStmt *) cmd->def, lockmode);
@@ -5764,13 +5764,6 @@ ATExecAddConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
  * AddRelationNewConstraints would normally assign different names to the
  * child constraints.  To fix that, we must capture the name assigned at
  * the parent table and pass that down.
- *
- * When re-adding a previously existing constraint (during ALTER COLUMN TYPE),
- * we don't need to recurse here, because recursion will be carried out at a
- * higher level; the constraint name issue doesn't apply because the names
- * have already been assigned and are just being re-used.  We need a separate
- * "is_readd" flag for that; just setting recurse=false would result in an
- * error if there are child tables.
  */
 static void
 ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
@@ -5798,7 +5791,7 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 	 */
 	newcons = AddRelationNewConstraints(rel, NIL,
 										list_make1(copyObject(constr)),
-										recursing,		/* allow_merge */
+										recursing | is_readd,	/* allow_merge */
 										!recursing,		/* is_local */
 										is_readd);		/* is_internal */
 
@@ -5842,10 +5835,8 @@ ATAddCheckConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel,
 
 	/*
 	 * If adding a NO INHERIT constraint, no need to find our children.
-	 * Likewise, in a re-add operation, we don't need to recurse (that will be
-	 * handled at higher levels).
 	 */
-	if (constr->is_no_inherit || is_readd)
+	if (constr->is_no_inherit)
 		return;
 
 	/*
@@ -8204,10 +8195,30 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
 			def_item, tab->changedConstraintDefs)
 	{
 		Oid			oldId = lfirst_oid(oid_item);
+		HeapTuple	tup;
+		Form_pg_constraint con;
 		Oid			relid;
 		Oid			confrelid;
+		bool		conislocal;
+
+		tup = SearchSysCache1(CONSTROID, ObjectIdGetDatum(oldId));
+		if (!HeapTupleIsValid(tup))		/* should not happen */
+			elog(ERROR, "cache lookup failed for constraint %u", oldId);
+		con = (Form_pg_constraint) GETSTRUCT(tup);
+		relid = con->conrelid;
+		confrelid = con->confrelid;
+		conislocal = con->conislocal;
+		ReleaseSysCache(tup);
+
+		/*
+		 * If the constraint is inherited (only), we don't want to inject a
+		 * new definition here; it'll get recreated when ATAddCheckConstraint
+		 * recurses from adding the parent table's constraint.  But we had to
+		 * carry the info this far so that we can drop the constraint below.
+		 */
+		if (!conislocal)
+			continue;
 
-		get_constraint_relation_oids(oldId, &relid, &confrelid);
 		ATPostAlterTypeParse(oldId, relid, confrelid,
 							 (char *) lfirst(def_item),
 							 wqueue, lockmode, tab->rewrite);