Fix tests of pg_upgrade across different major versions

This fixes a set of issues that cause different breakages or annoyances
when using pg_upgrade's test.sh to do upgrades across different major
versions:
- test.sh is completely broken when using v14 as new version because of
the removal of testtablespace/ as Makefile rule.  Older versions of
pg_regress don't support --make-tablespacedir, blocking the creation of
the tablespace.  In order to fix that, it is simple enough to create
those directories in the script itself, but only do that when an old
version is involved.  This fix is needed on HEAD and REL_14_STABLE.
- The script would fail when using PG <= v11 as old version because of
WITH OIDS relations not supported in v12.  In order to fix this, this
steals a method from the buildfarm that uses a DO block to change all
the relations marked as WITH OIDS, allowing pg_upgrade to pass.  This is
more portable than using ALTER TABLE queries on the relations causing
issues.  This is fixed down to v12, and authored originally by Andrew
Dunstan.
- Not using --extra-float-digits=0 with v11 as old version causes
a lot of diffs in the dumps, making the whole unreadable.  This gets
only done when using v11 as old version.  This is fixed down to v12.
The buildfarm code uses that already.

Note that the addition of --wal-segsize and --allow-group-access breaks
the script when using v10 or older at initdb time as these got added in
11.  10 would be EOL'd next year and nobody has complained about those
problems yet, so nothing is done about that.  This means that this
commit fixes upgrade tests using test.sh with v11 as minimum older
version, up to HEAD, and that it is enough to apply this change down to
12.  The old and new dumps still generate diffs, still require manual
checks, and more could be done to reduce the noise, but this allows the
tests to run with a rather minimal amount of them.

I have tested this commit and test.sh with v11 as minimum across all the
branches where this is applied.  Note that this commit has no impact on
the normal pg_upgrade test run with a simple "make check".

Author:  Justin Pryzby, Andrew Dunstan, Michael Paquier
Discussion: https://postgr.es/m/20201206180248.GI24052@telsasoft.com
Backpatch-through: 12

src/bin/pg_upgrade/test.sh

@@ -23,7 +23,8 @@ standard_initdb() {
 	# To increase coverage of non-standard segment size and group access
 	# without increasing test runtime, run these tests with a custom setting.
 	# Also, specify "-A trust" explicitly to suppress initdb's warning.
-	"$1" -N --wal-segsize 1 -g -A trust
+	# --allow-group-access and --wal-segsize have been added in v11.
+	"$1" -N --wal-segsize 1 --allow-group-access -A trust
 	if [ -n "$TEMP_CONFIG" -a -r "$TEMP_CONFIG" ]
 	then
 		cat "$TEMP_CONFIG" >> "$PGDATA/postgresql.conf"
@@ -165,24 +166,62 @@ createdb "regression$dbname1" || createdb_status=$?
 createdb "regression$dbname2" || createdb_status=$?
 createdb "regression$dbname3" || createdb_status=$?
 
+# Extra options to apply to the dump.  This may be changed later.
+extra_dump_options=""
+
 if "$MAKE" -C "$oldsrc" installcheck-parallel; then
 	oldpgversion=`psql -X -A -t -d regression -c "SHOW server_version_num"`
 
-	# before dumping, get rid of objects not feasible in later versions
+	# Before dumping, tweak the database of the old instance depending
+	# on its version.
 	if [ "$newsrc" != "$oldsrc" ]; then
 		fix_sql=""
+		# Get rid of objects not feasible in later versions
 		case $oldpgversion in
 			804??)
 				fix_sql="DROP FUNCTION public.myfunc(integer);"
 				;;
 		esac
-		fix_sql="$fix_sql
-				 DROP FUNCTION IF EXISTS
-					public.oldstyle_length(integer, text);	-- last in 9.6";
+
+		# Last appeared in v9.6
+		if [ $oldpgversion -lt 100000 ]; then
+			fix_sql="$fix_sql
+					 DROP FUNCTION IF EXISTS
+						public.oldstyle_length(integer, text);"
+		fi
 		psql -X -d regression -c "$fix_sql;" || psql_fix_sql_status=$?
+
+		# WITH OIDS is not supported anymore in v12, so remove support
+		# for any relations marked as such.
+		if [ $oldpgversion -lt 120000 ]; then
+			fix_sql="DO \$stmt\$
+				DECLARE
+					rec text;
+				BEGIN
+				FOR rec in
+					SELECT oid::regclass::text
+					FROM pg_class
+					WHERE relname !~ '^pg_'
+						AND relhasoids
+						AND relkind in ('r','m')
+					ORDER BY 1
+				LOOP
+					execute 'ALTER TABLE ' || rec || ' SET WITHOUT OIDS';
+				END LOOP;
+				END; \$stmt\$;"
+			psql -X -d regression -c "$fix_sql;" || psql_fix_sql_status=$?
+		fi
+
+		# Handling of --extra-float-digits gets messy after v12.
+		# Note that this changes the dumps from the old and new
+		# instances if involving an old cluster of v11 or older.
+		if [ $oldpgversion -lt 120000 ]; then
+			extra_dump_options="--extra-float-digits=0"
+		fi
 	fi
 
-	pg_dumpall --no-sync -f "$temp_root"/dump1.sql || pg_dumpall1_status=$?
+	pg_dumpall $extra_dump_options --no-sync \
+		-f "$temp_root"/dump1.sql || pg_dumpall1_status=$?
 
 	if [ "$newsrc" != "$oldsrc" ]; then
 		# update references to old source tree's regress.so etc
@@ -252,7 +291,8 @@ case $testhost in
 	*)		sh ./analyze_new_cluster.sh ;;
 esac
 
-pg_dumpall --no-sync -f "$temp_root"/dump2.sql || pg_dumpall2_status=$?
+pg_dumpall $extra_dump_options --no-sync \
+	-f "$temp_root"/dump2.sql || pg_dumpall2_status=$?
 pg_ctl -m fast stop
 
 if [ -n "$pg_dumpall2_status" ]; then