From 6642083a190f791656cc06b2c1b7959fba5b2c12 Mon Sep 17 00:00:00 2001
From: Patrick Reynolds <patrick@piki.org>
Date: Thu, 13 Aug 2026 12:45:32 -0400
Subject: [PATCH v1] Fix failing assert in deferred constraint trigger

This SQL crashes assert-enabled builds:

    CREATE TABLE t(a int);
    CREATE FUNCTION f() RETURNS trigger LANGUAGE plpgsql AS $$
    BEGIN
        BEGIN
            PERFORM 1 / 0;
        EXCEPTION WHEN division_by_zero THEN
            NULL;
        END;
        RETURN NEW;
    END
    $$;
    CREATE CONSTRAINT TRIGGER trg
    AFTER INSERT ON t
    DEFERRABLE INITIALLY DEFERRED
    FOR EACH ROW EXECUTE FUNCTION f();
    BEGIN;
    INSERT INTO t VALUES (1);
    COMMIT;  -- backend aborts here on assert builds

The failure in the logs is:

    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
    0   postgres                 0x0000000104e6b330 ExceptionalCondition + 108
    1   postgres                 0x0000000104a33620 AbortSubTransaction + 0
    2   plpgsql.dylib            0x00000001056b14b8 exec_stmt_block + 640
    3   plpgsql.dylib            0x00000001056b1d00 exec_stmts + 188

`PREPARE TRANSACTION 'tx'` in place of the final `COMMIT` crashes in the
same way.

fa0e318f947 updated BeginInternalSubTransaction to allow creating a
subtransaction with a parent of TBLOCK_END and TBLOCK_PREPARE but didn't
add those states to the assert in RollbackAndReleaseCurrentSubTransaction.

The `division_by_zero` exception in the example forces a subtransaction to
abort in the context of the final `COMMIT`, so
RollbackAndReleaseCurrentSubTransaction needs to allow TBLOCK_PREPARE and
TBLOCK_END.

Now it does.

This problem only affects assert-enabled builds, possibly as far back as
8.2.  I've personally confirmed the problem on 18.4 and 17.10.  The assert
is the only thing wrong here; adding the two additional parent states to
it doesn't allow through any behavior that we didn't intend.
---
 src/backend/access/transam/xact.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index aca92507ebd..ebb010853cf 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -4901,6 +4901,8 @@ RollbackAndReleaseCurrentSubTransaction(void)
 		   s->blockState == TBLOCK_INPROGRESS ||
 		   s->blockState == TBLOCK_IMPLICIT_INPROGRESS ||
 		   s->blockState == TBLOCK_PARALLEL_INPROGRESS ||
+		   s->blockState == TBLOCK_END ||
+		   s->blockState == TBLOCK_PREPARE ||
 		   s->blockState == TBLOCK_STARTED);
 }
 
-- 
2.55.0