starting to review the Extend NOT NULL representation to pg_constraint patch

Reference: https://commitfest.postgresql.org/action/patch_view?id=312

The patch from http://archives.postgresql.org/message-id/CA2E4C4762EAE28D68404E75@amenophis
does not apply cleanly to the current git master:

$ patch -p1 < extend_not_null.patch
patching file src/backend/catalog/heap.c
patching file q
Hunk #3 succeeded at 290 (offset 1 line).
Hunk #4 succeeded at 351 (offset 1 line).
Hunk #5 succeeded at 530 (offset 1 line).
Hunk #6 FAILED at 2709.
Hunk #7 succeeded at 2957 (offset 18 lines).
Hunk #8 succeeded at 4227 (offset 68 lines).
Hunk #9 succeeded at 4574 (offset 68 lines).
Hunk #10 succeeded at 4584 (offset 68 lines).
Hunk #11 succeeded at 4673 (offset 68 lines).
Hunk #12 succeeded at 6298 (offset 72 lines).
Hunk #13 succeeded at 6312 (offset 72 lines).
Hunk #14 succeeded at 6385 (offset 72 lines).
Hunk #15 succeeded at 7098 (offset 89 lines).
Hunk #16 succeeded at 7860 (offset 89 lines).
Hunk #17 succeeded at 7947 (offset 89 lines).
Hunk #18 succeeded at 8027 (offset 89 lines).
Hunk #19 succeeded at 8075 (offset 89 lines).
Hunk #20 succeeded at 8118 (offset 89 lines).
Hunk #21 succeeded at 8146 (offset 89 lines).
Hunk #22 succeeded at 8163 (offset 89 lines).
Hunk #23 succeeded at 8246 (offset 89 lines).
Hunk #24 succeeded at 8260 (offset 89 lines).
Hunk #25 succeeded at 8310 (offset 89 lines).
Hunk #26 succeeded at 8325 (offset 89 lines).
Hunk #27 succeeded at 8333 (offset 89 lines).
Hunk #28 succeeded at 8387 (offset 89 lines).
Hunk #29 succeeded at 8417 (offset 89 lines).
1 out of 29 hunks FAILED -- saving rejects to file
src/backend/commands/tablecmds.c.rej
patching file src/backend/parser/parse_utilcmd.c
patching file src/backend/port/pg_latch.c
patching file src/backend/utils/adt/ruleutils.c
patching file src/include/catalog/heap.h
patching file src/include/catalog/pg_constraint.h
patching file src/include/nodes/parsenodes.h
Hunk #1 succeeded at 1117 (offset 1 line).
patching file src/test/regress/expected/alter_table.out
patching file src/test/regress/expected/cluster.out

$ cat src/backend/commands/tablecmds.c.rej
*** src/backend/commands/tablecmds.c
--- src/backend/commands/tablecmds.c
*************** ATPrepCmd(List **wqueue, Relation rel, A
*** 2709,2715 ****
break;
case AT_DropNotNull: /* ALTER COLUMN DROP NOT NULL */
ATSimplePermissions(rel, false);
! ATSimpleRecursion(wqueue, rel, cmd, recurse, lockmode);
/* No command-specific prep needed */
pass = AT_PASS_DROP;
break;
--- 2752,2761 ----
break;
case AT_DropNotNull: /* ALTER COLUMN DROP NOT NULL */
ATSimplePermissions(rel, false);
!
! if (recurse)
! cmd->subtype = AT_DropNotNullRecurse;
!
/* No command-specific prep needed */
pass = AT_PASS_DROP;
break;