Disallow NULLS NOT DISTINCT indexes for primary keys

A unique index which is created with non-distinct NULLS cannot be
used for backing a primary key constraint.  Make sure to disallow
such table alterations and teach pg_dump to drop the non-distinct
NULLS clause on indexes where this has been set.

Bug: 17720
Reported-by: Reiner Peterke <zedaardv@drizzle.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/17720-dab8ee0fa85d316d@postgresql.org

src/backend/catalog/index.c

@@ -225,6 +225,19 @@ index_check_primary_key(Relation heapRel,
 						RelationGetRelationName(heapRel))));
 	}
 
+	/*
+	 * Indexes created with NULLS NOT DISTINCT cannot be used for primary key
+	 * constraints. While there is no direct syntax to reach here, it can be
+	 * done by creating a separate index and attaching it via ALTER TABLE ..
+	 * USING INDEX.
+	 */
+	if (indexInfo->ii_NullsNotDistinct)
+	{
+		ereport(ERROR,
+				(errcode(ERRCODE_INVALID_TABLE_DEFINITION),
+				 errmsg("primary keys cannot use NULLS NOT DISTINCT indexes")));
+	}
+
 	/*
 	 * Check that all of the attributes in a primary key are marked as not
 	 * null.  (We don't really expect to see that; it'd mean the parser messed

src/bin/pg_dump/pg_dump.c

@@ -16431,7 +16431,12 @@ dumpConstraint(Archive *fout, const ConstraintInfo *coninfo)
 		{
 			appendPQExpBufferStr(q,
 								 coninfo->contype == 'p' ? "PRIMARY KEY" : "UNIQUE");
-			if (indxinfo->indnullsnotdistinct)
+			/*
+			 * PRIMARY KEY constraints should not be using NULLS NOT DISTINCT
+			 * indexes. Being able to create this was fixed, but we need to
+			 * make the index distinct in order to be able to restore the dump.
+			 */
+			if (indxinfo->indnullsnotdistinct && coninfo->contype != 'p')
 				appendPQExpBufferStr(q, " NULLS NOT DISTINCT");
 			appendPQExpBufferStr(q, " (");
 			for (k = 0; k < indxinfo->indnkeyattrs; k++)

src/test/regress/expected/create_index.out

@@ -1595,6 +1595,12 @@ create unique index on cwi_test (a);
 alter table cwi_test add primary key using index cwi_test_a_idx ;
 ERROR:  ALTER TABLE / ADD CONSTRAINT USING INDEX is not supported on partitioned tables
 DROP TABLE cwi_test;
+-- PRIMARY KEY constraint cannot be backed by a NULLS NOT DISTINCT index
+CREATE TABLE cwi_test(a int, b int);
+CREATE UNIQUE INDEX cwi_a_nnd ON cwi_test (a) NULLS NOT DISTINCT;
+ALTER TABLE cwi_test ADD PRIMARY KEY USING INDEX cwi_a_nnd;
+ERROR:  primary keys cannot use NULLS NOT DISTINCT indexes
+DROP TABLE cwi_test;
 --
 -- Check handling of indexes on system columns
 --

src/test/regress/sql/create_index.sql

@@ -617,6 +617,12 @@ create unique index on cwi_test (a);
 alter table cwi_test add primary key using index cwi_test_a_idx ;
 DROP TABLE cwi_test;
 
+-- PRIMARY KEY constraint cannot be backed by a NULLS NOT DISTINCT index
+CREATE TABLE cwi_test(a int, b int);
+CREATE UNIQUE INDEX cwi_a_nnd ON cwi_test (a) NULLS NOT DISTINCT;
+ALTER TABLE cwi_test ADD PRIMARY KEY USING INDEX cwi_a_nnd;
+DROP TABLE cwi_test;
+
 --
 -- Check handling of indexes on system columns
 --