Harden tableam against nonexistant / wrong kind of AMs.

Previously it was allowed to set default_table_access_method to an
empty string. That makes sense for default_tablespace, where that was
copied from, as it signals falling back to the database's default
tablespace. As there is no equivalent for table AMs, forbid that.

Also make sure to throw a usable error when creating a table using an
index AM, by using get_am_type_oid() to implement get_table_am_oid()
instead of a separate copy. Previously we'd error out only later, in
GetTableAmRoutine().

Thirdly remove GetTableAmRoutineByAmId() - it was only used in an
earlier version of 8586bf7ed8.

Add tests for the above (some for index AMs as well).

src/test/regress/expected/create_am.out

@@ -3,6 +3,11 @@
 --
 -- Make gist2 over gisthandler. In fact, it would be a synonym to gist.
 CREATE ACCESS METHOD gist2 TYPE INDEX HANDLER gisthandler;
+-- Verify return type checks for handlers
+CREATE ACCESS METHOD bogus TYPE INDEX HANDLER int4in;
+ERROR:  function int4in(internal) does not exist
+CREATE ACCESS METHOD bogus TYPE INDEX HANDLER heap_tableam_handler;
+ERROR:  function heap_tableam_handler must return type index_am_handler
 -- Try to create gist2 index on fast_emp4000: fail because opclass doesn't exist
 CREATE INDEX grect2ind2 ON fast_emp4000 USING gist2 (home_base);
 ERROR:  data type box has no default operator class for access method "gist2"
@@ -102,8 +107,24 @@ NOTICE:  drop cascades to index grect2ind2
 --
 -- Test table access methods
 --
+-- prevent empty values
+SET default_table_access_method = '';
+ERROR:  invalid value for parameter "default_table_access_method": ""
+DETAIL:  default_table_access_method may not be empty.
+-- prevent nonexistant values
+SET default_table_access_method = 'I do not exist AM';
+ERROR:  invalid value for parameter "default_table_access_method": "I do not exist AM"
+DETAIL:  Table access method "I do not exist AM" does not exist.
+-- prevent setting it to an index AM
+SET default_table_access_method = 'btree';
+ERROR:  access method "btree" is not of type TABLE
 -- Create a heap2 table am handler with heapam handler
 CREATE ACCESS METHOD heap2 TYPE TABLE HANDLER heap_tableam_handler;
+-- Verify return type checks for handlers
+CREATE ACCESS METHOD bogus TYPE TABLE HANDLER int4in;
+ERROR:  function int4in(internal) does not exist
+CREATE ACCESS METHOD bogus TYPE TABLE HANDLER bthandler;
+ERROR:  function bthandler must return type table_am_handler
 SELECT amname, amhandler, amtype FROM pg_am where amtype = 't' ORDER BY 1, 2;
  amname |      amhandler       | amtype 
 --------+----------------------+--------
@@ -253,6 +274,18 @@ ORDER BY 3, 1, 2;
 
 -- don't want to keep those tables, nor the default
 ROLLBACK;
+-- Third, check that we can neither create a table using a nonexistant
+-- AM, nor using an index AM
+CREATE TABLE i_am_a_failure() USING "";
+ERROR:  zero-length delimited identifier at or near """"
+LINE 1: CREATE TABLE i_am_a_failure() USING "";
+                                            ^
+CREATE TABLE i_am_a_failure() USING i_do_not_exist_am;
+ERROR:  access method "i_do_not_exist_am" does not exist
+CREATE TABLE i_am_a_failure() USING "I do not exist AM";
+ERROR:  access method "I do not exist AM" does not exist
+CREATE TABLE i_am_a_failure() USING "btree";
+ERROR:  access method "btree" is not of type TABLE
 -- Drop table access method, which fails as objects depends on it
 DROP ACCESS METHOD heap2;
 ERROR:  cannot drop access method heap2 because other objects depend on it

src/test/regress/expected/type_sanity.out

@@ -520,6 +520,24 @@ WHERE p1.relkind IN ('S', 'v', 'f', 'c') and
 -----+---------
 (0 rows)
 
+-- Indexes should have AMs of type 'i'
+SELECT pc.oid, pc.relname, pa.amname, pa.amtype
+FROM pg_class as pc JOIN pg_am AS pa ON (pc.relam = pa.oid)
+WHERE pc.relkind IN ('i') and
+    pa.amtype != 'i';
+ oid | relname | amname | amtype 
+-----+---------+--------+--------
+(0 rows)
+
+-- Tables, matviews etc should have AMs of type 't'
+SELECT pc.oid, pc.relname, pa.amname, pa.amtype
+FROM pg_class as pc JOIN pg_am AS pa ON (pc.relam = pa.oid)
+WHERE pc.relkind IN ('r', 't', 'm') and
+    pa.amtype != 't';
+ oid | relname | amname | amtype 
+-----+---------+--------+--------
+(0 rows)
+
 -- **************** pg_attribute ****************
 -- Look for illegal values in pg_attribute fields
 SELECT p1.attrelid, p1.attname

src/test/regress/sql/create_am.sql

@@ -5,6 +5,11 @@
 -- Make gist2 over gisthandler. In fact, it would be a synonym to gist.
 CREATE ACCESS METHOD gist2 TYPE INDEX HANDLER gisthandler;
 
+-- Verify return type checks for handlers
+CREATE ACCESS METHOD bogus TYPE INDEX HANDLER int4in;
+CREATE ACCESS METHOD bogus TYPE INDEX HANDLER heap_tableam_handler;
+
+
 -- Try to create gist2 index on fast_emp4000: fail because opclass doesn't exist
 CREATE INDEX grect2ind2 ON fast_emp4000 USING gist2 (home_base);
 
@@ -72,11 +77,26 @@ DROP ACCESS METHOD gist2 CASCADE;
 -- Test table access methods
 --
 
+-- prevent empty values
+SET default_table_access_method = '';
+
+-- prevent nonexistant values
+SET default_table_access_method = 'I do not exist AM';
+
+-- prevent setting it to an index AM
+SET default_table_access_method = 'btree';
+
+
 -- Create a heap2 table am handler with heapam handler
 CREATE ACCESS METHOD heap2 TYPE TABLE HANDLER heap_tableam_handler;
 
+-- Verify return type checks for handlers
+CREATE ACCESS METHOD bogus TYPE TABLE HANDLER int4in;
+CREATE ACCESS METHOD bogus TYPE TABLE HANDLER bthandler;
+
 SELECT amname, amhandler, amtype FROM pg_am where amtype = 't' ORDER BY 1, 2;
 
+
 -- First create tables employing the new AM using USING
 
 -- plain CREATE TABLE
@@ -178,6 +198,13 @@ ORDER BY 3, 1, 2;
 -- don't want to keep those tables, nor the default
 ROLLBACK;
 
+-- Third, check that we can neither create a table using a nonexistant
+-- AM, nor using an index AM
+CREATE TABLE i_am_a_failure() USING "";
+CREATE TABLE i_am_a_failure() USING i_do_not_exist_am;
+CREATE TABLE i_am_a_failure() USING "I do not exist AM";
+CREATE TABLE i_am_a_failure() USING "btree";
+
 -- Drop table access method, which fails as objects depends on it
 DROP ACCESS METHOD heap2;
 

src/test/regress/sql/type_sanity.sql

@@ -379,6 +379,18 @@ FROM pg_class as p1
 WHERE p1.relkind IN ('S', 'v', 'f', 'c') and
     p1.relam != 0;
 
+-- Indexes should have AMs of type 'i'
+SELECT pc.oid, pc.relname, pa.amname, pa.amtype
+FROM pg_class as pc JOIN pg_am AS pa ON (pc.relam = pa.oid)
+WHERE pc.relkind IN ('i') and
+    pa.amtype != 'i';
+
+-- Tables, matviews etc should have AMs of type 't'
+SELECT pc.oid, pc.relname, pa.amname, pa.amtype
+FROM pg_class as pc JOIN pg_am AS pa ON (pc.relam = pa.oid)
+WHERE pc.relkind IN ('r', 't', 'm') and
+    pa.amtype != 't';
+
 -- **************** pg_attribute ****************
 
 -- Look for illegal values in pg_attribute fields