Warn about broken hypothetical BRIN indexes in some minor versions.

Hypothetical BRIN indexes are broken in some minor versions of pg10, pg11 and
pg12.  Detect those versions and warn users with a useful error message
recommending to update their minor versions of postgres.

Also add regression tests to make sure that support BRIN hypothetical indexes
doesn't get broken again.

Makefile

@@ -37,6 +37,9 @@ DATA = $(wildcard *--*.sql)
 PGXS := $(shell $(PG_CONFIG) --pgxs)
 include $(PGXS)
 
+ifneq ($(MAJORVERSION),$(filter $(MAJORVERSION), 9.2 9.3 9.4))
+	REGRESS += hypo_brin
+endif
 ifeq ($(MAJORVERSION),$(filter $(MAJORVERSION),9.2 9.3 9.4 9.5 9.6))
 	REGRESS += hypo_no_table
 else

expected/hypo_brin.out

@@ -0,0 +1,21 @@
+-- Hypothetical BRIN index tests
+CREATE TABLE hypo_brin (id integer);
+INSERT INTO hypo_brin SELECT generate_series(1, 10000);
+ANALYZE hypo_brin;
+SELECT COUNT(*) AS nb
+FROM public.hypopg_create_index('CREATE INDEX ON hypo_brin USING brin (id);');
+ nb 
+----
+  1
+(1 row)
+
+-- Should use hypothetical index
+SET enable_seqscan = 0;
+SELECT COUNT(*) FROM do_explain('SELECT * FROM hypo_brin WHERE id = 1') e
+WHERE e ~ 'Bitmap Index Scan on <\d+>brin_hypo_brin.*';
+ count 
+-------
+     1
+(1 row)
+
+DROP TABLE hypo_brin;

hypopg_index.c

@@ -339,6 +339,33 @@ hypo_index_store_parsetree(IndexStmt *node, const char *queryString)
 	ListCell   *lc;
 	int			attn;
 
+	/*
+	 * Support for hypothetical BRIN indexes is broken in some minor versions
+	 * of pg10, pg11 and pg12.  For simplicity, check PG_VERSION_NUM rather
+	 * than the real instance version, which should should be right most of the
+	 * time.  When it's not, the only effect is to have a less user-friendly
+	 * error message.
+	 */
+#if ((PG_VERSION_NUM >= 100000 && PG_VERSION_NUM < 100012) || \
+	(PG_VERSION_NUM >= 110000 && PG_VERSION_NUM < 110007) || \
+	(PG_VERSION_NUM >= 120000 && PG_VERSION_NUM < 120002))
+	if (get_am_oid(node->accessMethod, true) == BRIN_AM_OID)
+	{
+		elog(ERROR, "hypopg: BRIN hypothetical indexes are only supported"
+				" with PostgreSQL "
+#if PG_VERSION_NUM >= 120000
+				"12.2"
+#else
+#if PG_VERSION_NUM >= 110000
+				"11.7"
+#else
+				"10.12"
+#endif					/* pg 11 */
+#endif					/* pg 12 */
+				" and later.");
+	}
+#endif
+
 #if PG_VERSION_NUM < 100000
 	relid = RangeVarGetRelid(node->relation, AccessShareLock, false);
 #else

test/sql/hypo_brin.sql

@@ -0,0 +1,18 @@
+-- Hypothetical BRIN index tests
+
+CREATE TABLE hypo_brin (id integer);
+
+INSERT INTO hypo_brin SELECT generate_series(1, 10000);
+
+ANALYZE hypo_brin;
+
+SELECT COUNT(*) AS nb
+FROM public.hypopg_create_index('CREATE INDEX ON hypo_brin USING brin (id);');
+
+
+-- Should use hypothetical index
+SET enable_seqscan = 0;
+SELECT COUNT(*) FROM do_explain('SELECT * FROM hypo_brin WHERE id = 1') e
+WHERE e ~ 'Bitmap Index Scan on <\d+>brin_hypo_brin.*';
+
+DROP TABLE hypo_brin;