Remove the hack in the grammar that "optimized away" DEFAULT NULL clauses.

Instead put in a test to drop a NULL default at the last moment before
storing the catalog entry.  This changes the behavior in a couple of ways:
* Specifying DEFAULT NULL when creating an inheritance child table will
  successfully suppress inheritance of any default expression from the
  parent's column, where formerly it failed to do so.
* Specifying DEFAULT NULL for a column of a domain type will correctly
  override any default belonging to the domain; likewise for a sub-domain.
The latter change happens because by the time the clause is checked,
it won't be a simple null Const but a CoerceToDomain expression.

Personally I think this should be back-patched, but there doesn't seem to
be consensus for that on pgsql-hackers, so refraining.

2 files changed, 16 insertions, 2 deletions

diff --git a/src/test/regress/expected/domain.out b/src/test/regress/expected/domain.out
index c7d5b50334..b951ce8caa 100644
--- a/src/test/regress/expected/domain.out
+++ b/src/test/regress/expected/domain.out
@@ -205,7 +205,15 @@ create table defaulttest
             , col8 ddef5
             );
 NOTICE:  CREATE TABLE / PRIMARY KEY will create implicit index "defaulttest_pkey" for table "defaulttest"
-insert into defaulttest default values;
+insert into defaulttest(col4) values(0); -- fails, col5 defaults to null
+ERROR:  null value in column "col5" violates not-null constraint
+alter table defaulttest alter column col5 drop default;
+insert into defaulttest default values; -- succeeds, inserts domain default
+-- We used to treat SET DEFAULT NULL as equivalent to DROP DEFAULT; wrong
+alter table defaulttest alter column col5 set default null;
+insert into defaulttest(col4) values(0); -- fails
+ERROR:  null value in column "col5" violates not-null constraint
+alter table defaulttest alter column col5 drop default;
 insert into defaulttest default values;
 insert into defaulttest default values;
 -- Test defaults with copy
diff --git a/src/test/regress/sql/domain.sql b/src/test/regress/sql/domain.sql
index 7da9971991..7a4ec383d2 100644
--- a/src/test/regress/sql/domain.sql
+++ b/src/test/regress/sql/domain.sql
@@ -168,7 +168,13 @@ create table defaulttest
             , col7 ddef4 DEFAULT 8000
             , col8 ddef5
             );
-insert into defaulttest default values;
+insert into defaulttest(col4) values(0); -- fails, col5 defaults to null
+alter table defaulttest alter column col5 drop default;
+insert into defaulttest default values; -- succeeds, inserts domain default
+-- We used to treat SET DEFAULT NULL as equivalent to DROP DEFAULT; wrong
+alter table defaulttest alter column col5 set default null;
+insert into defaulttest(col4) values(0); -- fails
+alter table defaulttest alter column col5 drop default;
 insert into defaulttest default values;
 insert into defaulttest default values;