pgsql: Reject enforcing a parent CHECK constraint over a NOT VALID chil

Reject enforcing a parent CHECK constraint over a NOT VALID child

ALTER TABLE ... ALTER CONSTRAINT ... ENFORCED on a parent's NOT ENFORCED
CHECK constraint marked the parent's constraint validated, but when it
recursed to a child whose matching constraint was already ENFORCED and
NOT VALID, it left that child alone, since its enforceability was
unchanged. The child's existing rows were therefore never checked, and
the parent ended up validated with a child that was not. Constraint
exclusion could then skip the child when querying the parent, and so
miss rows that violate the constraint.

Fix by raising the same error that ALTER TABLE ... INHERIT already
raises when a child has a NOT VALID copy of a parent's constraint, with
a hint to validate the child's constraint first. Validating the child
implicitly instead was considered, but ALTER CONSTRAINT ... ENFORCED
does not validate an ENFORCED NOT VALID constraint when run directly
against the table that has it, so doing so only when reached through a
parent would be inconsistent.

Add regression tests for both regular inheritance and partitioning.

Bug introduced in 342051d73b3.

Reported-by: Shihao Zhong <zhong950419(at)gmail(dot)com>
Author: Shihao Zhong <zhong950419(at)gmail(dot)com>
Author: Jian He <jian(dot)universality(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Andrew Dunstan <andrew(at)dunslane(dot)net>
Discussion: https://postgr.es/m/CAGRkXqSGE=fQrjCoNQsyiCZRKfQ4SrB015CAR=3pXYB5tB=ieg@mail.gmail.com
Backpatch-through: 19

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0b12a5a7435a3b50cccea85347d9e3cf8128d88a

Modified Files
--------------
src/backend/commands/tablecmds.c | 15 +++++++++++++++
src/test/regress/expected/constraints.out | 11 +++++++++++
src/test/regress/expected/inherit.out | 22 ++++++++++++++++++++++
src/test/regress/sql/constraints.sql | 11 +++++++++++
src/test/regress/sql/inherit.sql | 14 ++++++++++++++
5 files changed, 73 insertions(+)