Fix assertion after aborting internal subtransaction at transaction end

Previously, aborting an internal subtransaction during COMMIT or
PREPARE TRANSACTION could cause the following assertion failure.
This could happen, for example, when a deferred constraint trigger fired
at COMMIT and its PL/pgSQL exception block caught an error raised
while executing the trigger function.

    TRAP: failed Assert("s->blockState == TBLOCK_SUBINPROGRESS || s->blockState
    == TBLOCK_INPROGRESS || s->blockState == TBLOCK_IMPLICIT_INPROGRESS ||
    s->blockState == TBLOCK_PARALLEL_INPROGRESS || s->blockState ==
    TBLOCK_STARTED"), File: "xact.c", Line: 4851, PID: 73455

An internal subtransaction should be able to be aborted while the parent
transaction is in the COMMIT or PREPARE TRANSACTION phase. However,
RollbackAndReleaseCurrentSubTransaction()'s assertion check previously
did not allow TBLOCK_END and TBLOCK_PREPARE as parent transaction
states, causing the assertion failure.

This commit fixes the assertion check by allowing those two parent
transaction states.

Backpatch to all supported versions.

Reported-by: Fabrízio de Royes Mello <fabrizio@planetscale.com>
Author: Patrick Reynolds <piki@planetscale.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Fabrízio de Royes Mello <fabrizio@planetscale.com>
Discussion: https://postgr.es/m/CABo-N97AeMbWuYTWg-3%3D2DkTR3EkvS%2BFt%3DyEaWB181STsR1mBg%40mail.gmail.com
Backpatch-through: 14

src/backend/access/transam/xact.c

@@ -4624,6 +4624,8 @@ RollbackAndReleaseCurrentSubTransaction(void)
 	AssertState(s->blockState == TBLOCK_SUBINPROGRESS ||
 				s->blockState == TBLOCK_INPROGRESS ||
 				s->blockState == TBLOCK_IMPLICIT_INPROGRESS ||
+				s->blockState == TBLOCK_END ||
+				s->blockState == TBLOCK_PREPARE ||
 				s->blockState == TBLOCK_STARTED);
 }
 

src/test/regress/expected/triggers.out

@@ -2467,6 +2467,34 @@ select * from parted;
 
 drop table parted;
 drop function parted_trigfunc();
+-- Test exception handling in a deferred constraint trigger at COMMIT.
+create table deferred_trigger_test (a int);
+create function deferred_trigger_func() returns trigger
+  language plpgsql as $$
+begin
+  perform 1 / 0;
+  return new;
+exception when division_by_zero then
+  raise notice 'caught division_by_zero';
+  return new;
+end;
+$$;
+create constraint trigger deferred_trigger
+  after insert on deferred_trigger_test
+  deferrable initially deferred
+  for each row execute function deferred_trigger_func();
+begin;
+insert into deferred_trigger_test values (1);
+commit;
+NOTICE:  caught division_by_zero
+select * from deferred_trigger_test;
+ a 
+---
+ 1
+(1 row)
+
+drop table deferred_trigger_test;
+drop function deferred_trigger_func();
 --
 -- Constraint triggers and partitioned tables
 create table parted_constr_ancestor (a int, b text)

src/test/regress/sql/triggers.sql

@@ -1691,6 +1691,31 @@ select * from parted;
 drop table parted;
 drop function parted_trigfunc();
 
+-- Test exception handling in a deferred constraint trigger at COMMIT.
+create table deferred_trigger_test (a int);
+create function deferred_trigger_func() returns trigger
+  language plpgsql as $$
+begin
+  perform 1 / 0;
+  return new;
+exception when division_by_zero then
+  raise notice 'caught division_by_zero';
+  return new;
+end;
+$$;
+create constraint trigger deferred_trigger
+  after insert on deferred_trigger_test
+  deferrable initially deferred
+  for each row execute function deferred_trigger_func();
+
+begin;
+insert into deferred_trigger_test values (1);
+commit;
+select * from deferred_trigger_test;
+
+drop table deferred_trigger_test;
+drop function deferred_trigger_func();
+
 --
 -- Constraint triggers and partitioned tables
 create table parted_constr_ancestor (a int, b text)