Add CASCADE support for CREATE EXTENSION.

Without CASCADE, if an extension has an unfullfilled dependency on
another extension, CREATE EXTENSION ERRORs out with "required extension
... is not installed". That is annoying, especially when that dependency
is an implementation detail of the extension, rather than something the
extension's user can make sense of.

In addition to CASCADE this also includes a small set of regression
tests around CREATE EXTENSION.

Author: Petr Jelinek, editorialized by Michael Paquier, Andres Freund
Reviewed-By: Michael Paquier, Andres Freund, Jeff Janes
Discussion: 557E0520.3040800@2ndquadrant.com

contrib/hstore_plperl/expected/hstore_plperl.out

-CREATE EXTENSION hstore;
-CREATE EXTENSION plperl;
-CREATE EXTENSION hstore_plperl;
+CREATE EXTENSION hstore_plperl CASCADE;
+NOTICE:  installing required extension "hstore"
+NOTICE:  installing required extension "plperl"
 SELECT transforms.udt_schema, transforms.udt_name,
        routine_schema, routine_name,
        group_name, transform_type

contrib/hstore_plperl/expected/hstore_plperlu.out

-CREATE EXTENSION hstore;
-CREATE EXTENSION plperlu;
-CREATE EXTENSION hstore_plperlu;
+CREATE EXTENSION hstore_plperlu CASCADE;
+NOTICE:  installing required extension "hstore"
+NOTICE:  installing required extension "plperlu"
 SELECT transforms.udt_schema, transforms.udt_name,
        routine_schema, routine_name,
        group_name, transform_type

contrib/hstore_plperl/sql/hstore_plperl.sql

-CREATE EXTENSION hstore;
-CREATE EXTENSION plperl;
-CREATE EXTENSION hstore_plperl;
+CREATE EXTENSION hstore_plperl CASCADE;
 
 SELECT transforms.udt_schema, transforms.udt_name,
        routine_schema, routine_name,

contrib/hstore_plperl/sql/hstore_plperlu.sql

-CREATE EXTENSION hstore;
-CREATE EXTENSION plperlu;
-CREATE EXTENSION hstore_plperlu;
+CREATE EXTENSION hstore_plperlu CASCADE;
 
 SELECT transforms.udt_schema, transforms.udt_name,
        routine_schema, routine_name,

contrib/hstore_plpython/expected/hstore_plpython.out

-CREATE EXTENSION plpython2u;
-CREATE EXTENSION hstore_plpython2u;
+CREATE EXTENSION hstore_plpython2u CASCADE;
+NOTICE:  installing required extension "plpython2u"
 -- test hstore -> python
 CREATE FUNCTION test1(val hstore) RETURNS int
 LANGUAGE plpythonu

contrib/hstore_plpython/sql/hstore_plpython.sql

-CREATE EXTENSION plpython2u;
-CREATE EXTENSION hstore_plpython2u;
+CREATE EXTENSION hstore_plpython2u CASCADE;
 
 
 -- test hstore -> python

contrib/ltree_plpython/expected/ltree_plpython.out

-CREATE EXTENSION plpython2u;
-CREATE EXTENSION ltree_plpython2u;
+CREATE EXTENSION ltree_plpython2u CASCADE;
+NOTICE:  installing required extension "plpython2u"
 CREATE FUNCTION test1(val ltree) RETURNS int
 LANGUAGE plpythonu
 TRANSFORM FOR TYPE ltree

contrib/ltree_plpython/sql/ltree_plpython.sql

-CREATE EXTENSION plpython2u;
-CREATE EXTENSION ltree_plpython2u;
+CREATE EXTENSION ltree_plpython2u CASCADE;
 
 
 CREATE FUNCTION test1(val ltree) RETURNS int

doc/src/sgml/ref/create_extension.sgml

@@ -25,6 +25,7 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
     [ WITH ] [ SCHEMA <replaceable class="parameter">schema_name</replaceable> ]
              [ VERSION <replaceable class="parameter">version</replaceable> ]
              [ FROM <replaceable class="parameter">old_version</replaceable> ]
+             [ CASCADE ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -94,6 +95,35 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
         If not specified, and the extension's control file does not specify a
         schema either, the current default object creation schema is used.
        </para>
+       <para>
+        If the extension specifies <literal>schema</> in its control file,
+        the schema cannot be overriden with <literal>SCHEMA</> clause.
+        The <literal>SCHEMA</> clause in this case works as follows:
+        <itemizedlist>
+         <listitem>
+          <para>
+           If <replaceable class="parameter">schema_name</replaceable> matches
+           the schema in control file, it will be used normally as there is no
+           conflict.
+          </para>
+         </listitem>
+         <listitem>
+          <para>
+           If the <literal>CASCADE</> clause is given, the
+           <replaceable class="parameter">schema_name</replaceable> will only
+           be used for the missing required extensions which do not specify
+           <literal>schema</> in their control files.
+          </para>
+         </listitem>
+         <listitem>
+          <para>
+           If <replaceable class="parameter">schema_name</replaceable> is not
+           the same as the one in extension's control file and the
+           <literal>CASCADE</> clause is not given, error will be thrown.
+          </para>
+         </listitem>
+        </itemizedlist>
+       </para>
        <para>
         Remember that the extension itself is not considered to be within any
         schema: extensions have unqualified names that must be unique
@@ -139,6 +169,18 @@ CREATE EXTENSION [ IF NOT EXISTS ] <replaceable class="parameter">extension_name
        </para>
       </listitem>
      </varlistentry>
+
+     <varlistentry>
+      <term><literal>CASCADE</></term>
+      <listitem>
+       <para>
+        Try to install extension including the required dependencies
+        recursively. The <literal>SCHEMA</> option will be propagated
+        to the required extensions.  Other options are not recursively
+        applied when using this clause.
+       </para>
+      </listitem>
+     </varlistentry>
   </variablelist>
  </refsect1>
 

src/backend/commands/extension.c

@@ -43,11 +43,13 @@
 #include "catalog/pg_type.h"
 #include "commands/alter.h"
 #include "commands/comment.h"
+#include "commands/defrem.h"
 #include "commands/extension.h"
 #include "commands/schemacmds.h"
 #include "funcapi.h"
 #include "mb/pg_wchar.h"
 #include "miscadmin.h"
+#include "nodes/makefuncs.h"
 #include "storage/fd.h"
 #include "tcop/utility.h"
 #include "utils/builtins.h"
@@ -1165,18 +1167,25 @@ find_update_path(List *evi_list,
 }
 
 /*
- * CREATE EXTENSION
+ * CREATE EXTENSION worker
+ *
+ * When CASCADE is specified CreateExtensionInternal() recurses if required
+ * extensions need to be installed. To sanely handle cyclic dependencies
+ * cascade_parent contains the dependency chain leading to the current
+ * invocation; thus allowing to error out if there's a cyclic dependency.
  */
-ObjectAddress
-CreateExtension(CreateExtensionStmt *stmt)
+static ObjectAddress
+CreateExtensionInternal(CreateExtensionStmt *stmt, List *parents)
 {
 	DefElem    *d_schema = NULL;
 	DefElem    *d_new_version = NULL;
 	DefElem    *d_old_version = NULL;
-	char	   *schemaName;
-	Oid			schemaOid;
+	DefElem    *d_cascade = NULL;
+	char	   *schemaName = NULL;
+	Oid			schemaOid = InvalidOid;
 	char	   *versionName;
 	char	   *oldVersionName;
+	bool		cascade = false;
 	Oid			extowner = GetUserId();
 	ExtensionControlFile *pcontrol;
 	ExtensionControlFile *control;
@@ -1187,41 +1196,6 @@ CreateExtension(CreateExtensionStmt *stmt)
 	ListCell   *lc;
 	ObjectAddress address;
 
-	/* Check extension name validity before any filesystem access */
-	check_valid_extension_name(stmt->extname);
-
-	/*
-	 * Check for duplicate extension name.  The unique index on
-	 * pg_extension.extname would catch this anyway, and serves as a backstop
-	 * in case of race conditions; but this is a friendlier error message, and
-	 * besides we need a check to support IF NOT EXISTS.
-	 */
-	if (get_extension_oid(stmt->extname, true) != InvalidOid)
-	{
-		if (stmt->if_not_exists)
-		{
-			ereport(NOTICE,
-					(errcode(ERRCODE_DUPLICATE_OBJECT),
-					 errmsg("extension \"%s\" already exists, skipping",
-							stmt->extname)));
-			return InvalidObjectAddress;
-		}
-		else
-			ereport(ERROR,
-					(errcode(ERRCODE_DUPLICATE_OBJECT),
-					 errmsg("extension \"%s\" already exists",
-							stmt->extname)));
-	}
-
-	/*
-	 * We use global variables to track the extension being created, so we can
-	 * create only one extension at the same time.
-	 */
-	if (creating_extension)
-		ereport(ERROR,
-				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				 errmsg("nested CREATE EXTENSION is not supported")));
-
 	/*
 	 * Read the primary control file.  Note we assume that it does not contain
 	 * any non-ASCII data, so there is no need to worry about encoding at this
@@ -1260,6 +1234,15 @@ CreateExtension(CreateExtensionStmt *stmt)
 						 errmsg("conflicting or redundant options")));
 			d_old_version = defel;
 		}
+		else if (strcmp(defel->defname, "cascade") == 0)
+		{
+			if (d_cascade)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("conflicting or redundant options")));
+			d_cascade = defel;
+			cascade = defGetBoolean(d_cascade);
+		}
 		else
 			elog(ERROR, "unrecognized option: %s", defel->defname);
 	}
@@ -1337,33 +1320,37 @@ CreateExtension(CreateExtensionStmt *stmt)
 	{
 		/*
 		 * User given schema, CREATE EXTENSION ... WITH SCHEMA ...
-		 *
-		 * It's an error to give a schema different from control->schema if
-		 * control->schema is specified.
 		 */
 		schemaName = strVal(d_schema->arg);
 
-		if (control->schema != NULL &&
-			strcmp(control->schema, schemaName) != 0)
-			ereport(ERROR,
-					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
-				errmsg("extension \"%s\" must be installed in schema \"%s\"",
-					   control->name,
-					   control->schema)));
-
-		/* If the user is giving us the schema name, it must exist already */
+		/* If the user is giving us the schema name, it must exist already. */
 		schemaOid = get_namespace_oid(schemaName, false);
 	}
-	else if (control->schema != NULL)
+
+	if (control->schema != NULL)
 	{
 		/*
 		 * The extension is not relocatable and the author gave us a schema
-		 * for it.  We create the schema here if it does not already exist.
+		 * for it.
+		 *
+		 * Unless CASCADE parameter was given, it's an error to give a schema
+		 * different from control->schema if control->schema is specified.
 		 */
+		if (schemaName && strcmp(control->schema, schemaName) != 0 &&
+			!cascade)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				errmsg("extension \"%s\" must be installed in schema \"%s\"",
+					   control->name,
+					   control->schema)));
+
+		/* Always use the schema from control file for current extension. */
 		schemaName = control->schema;
+
+		/* Find or create the schema in case it does not exist. */
 		schemaOid = get_namespace_oid(schemaName, true);
 
-		if (schemaOid == InvalidOid)
+		if (!OidIsValid(schemaOid))
 		{
 			CreateSchemaStmt *csstmt = makeNode(CreateSchemaStmt);
 
@@ -1375,16 +1362,17 @@ CreateExtension(CreateExtensionStmt *stmt)
 
 			/*
 			 * CreateSchemaCommand includes CommandCounterIncrement, so new
-			 * schema is now visible
+			 * schema is now visible.
 			 */
 			schemaOid = get_namespace_oid(schemaName, false);
 		}
 	}
-	else
+	else if (!OidIsValid(schemaOid))
 	{
 		/*
-		 * Else, use the current default creation namespace, which is the
-		 * first explicit entry in the search_path.
+		 * Neither user nor author of the extension specified schema, use the
+		 * current default creation namespace, which is the first explicit
+		 * entry in the search_path.
 		 */
 		List	   *search_path = fetch_search_path(false);
 
@@ -1423,16 +1411,65 @@ CreateExtension(CreateExtensionStmt *stmt)
 		Oid			reqext;
 		Oid			reqschema;
 
-		/*
-		 * We intentionally don't use get_extension_oid's default error
-		 * message here, because it would be confusing in this context.
-		 */
 		reqext = get_extension_oid(curreq, true);
 		if (!OidIsValid(reqext))
-			ereport(ERROR,
-					(errcode(ERRCODE_UNDEFINED_OBJECT),
-					 errmsg("required extension \"%s\" is not installed",
-							curreq)));
+		{
+			if (cascade)
+			{
+				CreateExtensionStmt *ces;
+				ListCell   *lc;
+				ObjectAddress addr;
+				List *cascade_parents;
+
+				/* Check extension name validity before trying to cascade */
+				check_valid_extension_name(curreq);
+
+				/* Check for cyclic dependency between extensions. */
+				foreach(lc, parents)
+				{
+					char	   *pname = (char *) lfirst(lc);
+
+					if (strcmp(pname, curreq) == 0)
+						ereport(ERROR,
+								(errcode(ERRCODE_INVALID_RECURSION),
+								 errmsg("cyclic dependency detected between extensions \"%s\" and \"%s\"",
+										curreq, stmt->extname)));
+				}
+
+				ereport(NOTICE,
+						(errmsg("installing required extension \"%s\"",
+								curreq)));
+
+				/* Create and execute new CREATE EXTENSION statement. */
+				ces = makeNode(CreateExtensionStmt);
+				ces->extname = curreq;
+
+				/* Propagate the CASCADE option */
+				ces->options = list_make1(d_cascade);
+
+				/* Propagate the SCHEMA option if given. */
+				if (d_schema && d_schema->arg)
+					ces->options = lappend(ces->options, d_schema);
+
+				/*
+				 * Pass the current list of parents + the current extension to
+				 * the "child" CreateExtensionInternal().
+				 */
+				cascade_parents =
+					lappend(list_copy(parents), stmt->extname);
+
+				/* Create the required extension. */
+				addr = CreateExtensionInternal(ces, cascade_parents);
+				reqext = addr.objectId;
+			}
+			else
+				ereport(ERROR,
+						(errcode(ERRCODE_UNDEFINED_OBJECT),
+						 errmsg("required extension \"%s\" is not installed",
+								curreq),
+						 errhint("Use CREATE EXTENSION CASCADE to install required extensions too.")));
+		}
+
 		reqschema = get_extension_schema(reqext);
 		requiredExtensions = lappend_oid(requiredExtensions, reqext);
 		requiredSchemas = lappend_oid(requiredSchemas, reqschema);
@@ -1473,6 +1510,52 @@ CreateExtension(CreateExtensionStmt *stmt)
 	return address;
 }
 
+/*
+ * CREATE EXTENSION
+ */
+ObjectAddress
+CreateExtension(CreateExtensionStmt *stmt)
+{
+	/* Check extension name validity before any filesystem access */
+	check_valid_extension_name(stmt->extname);
+
+	/*
+	 * Check for duplicate extension name.  The unique index on
+	 * pg_extension.extname would catch this anyway, and serves as a backstop
+	 * in case of race conditions; but this is a friendlier error message, and
+	 * besides we need a check to support IF NOT EXISTS.
+	 */
+	if (get_extension_oid(stmt->extname, true) != InvalidOid)
+	{
+		if (stmt->if_not_exists)
+		{
+			ereport(NOTICE,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("extension \"%s\" already exists, skipping",
+							stmt->extname)));
+			return InvalidObjectAddress;
+		}
+		else
+			ereport(ERROR,
+					(errcode(ERRCODE_DUPLICATE_OBJECT),
+					 errmsg("extension \"%s\" already exists",
+							stmt->extname)));
+	}
+
+	/*
+	 * We use global variables to track the extension being created, so we can
+	 * create only one extension at the same time.
+	 */
+	if (creating_extension)
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+				 errmsg("nested CREATE EXTENSION is not supported")));
+
+
+	/* Finally create the extension. */
+	return CreateExtensionInternal(stmt, NIL);
+}
+
 /*
  * InsertExtensionTuple
  *

src/backend/parser/gram.y

@@ -3876,6 +3876,10 @@ create_extension_opt_item:
 				{
 					$$ = makeDefElem("old_version", (Node *)makeString($2));
 				}
+			| CASCADE
+				{
+					$$ = makeDefElem("cascade", (Node *)makeInteger(TRUE));
+				}
 		;
 
 /*****************************************************************************

src/bin/psql/tab-complete.c

@@ -2264,7 +2264,12 @@ psql_completion(const char *text, int start, int end)
 	/* CREATE EXTENSION <name> */
 	else if (pg_strcasecmp(prev3_wd, "CREATE") == 0 &&
 			 pg_strcasecmp(prev2_wd, "EXTENSION") == 0)
-		COMPLETE_WITH_CONST("WITH SCHEMA");
+	{
+		static const char *const list_CREATE_EXTENSION[] =
+		{"WITH SCHEMA", "CASCADE", NULL};
+
+		COMPLETE_WITH_LIST(list_CREATE_EXTENSION);
+	}
 
 	/* CREATE FOREIGN */
 	else if (pg_strcasecmp(prev2_wd, "CREATE") == 0 &&

src/test/modules/Makefile

@@ -9,6 +9,7 @@ SUBDIRS = \
 		  commit_ts \
 		  dummy_seclabel \
 		  test_ddl_deparse \
+		  test_extensions \
 		  test_parser \
 		  test_rls_hooks \
 		  test_shm_mq \

src/test/modules/test_extensions/.gitignore

+# Generated subdirectories
+/log/
+/results/
+/tmp_check/

src/test/modules/test_extensions/Makefile

+# src/test/modules/test_extensions/Makefile
+
+MODULE = test_extensions
+PGFILEDESC = "test_extensions - regression testing for EXTENSION support"
+
+EXTENSION = test_ext1 test_ext2 test_ext3 test_ext4 test_ext5 \
+			test_ext_cyclic1 test_ext_cyclic2
+DATA = test_ext1--1.0.sql test_ext2--1.0.sql test_ext3--1.0.sql \
+	   test_ext4--1.0.sql test_ext5--1.0.sql test_ext_cyclic1--1.0.sql \
+	   test_ext_cyclic2--1.0.sql
+
+REGRESS = test_extensions
+
+ifdef USE_PGXS
+PG_CONFIG = pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = src/test/modules/test_extensions
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif

src/test/modules/test_extensions/expected/test_extensions.out

+-- test some errors
+CREATE EXTENSION test_ext1;
+ERROR:  required extension "test_ext2" is not installed
+HINT:  Use CREATE EXTENSION CASCADE to install required extensions too.
+CREATE EXTENSION test_ext1 SCHEMA test_ext1;
+ERROR:  schema "test_ext1" does not exist
+CREATE EXTENSION test_ext1 SCHEMA test_ext;
+ERROR:  schema "test_ext" does not exist
+CREATE SCHEMA test_ext;
+CREATE EXTENSION test_ext1 SCHEMA test_ext;
+ERROR:  extension "test_ext1" must be installed in schema "test_ext1"
+-- finally success
+CREATE EXTENSION test_ext1 SCHEMA test_ext CASCADE;
+NOTICE:  installing required extension "test_ext2"
+NOTICE:  installing required extension "test_ext3"
+NOTICE:  installing required extension "test_ext5"
+NOTICE:  installing required extension "test_ext4"
+SELECT extname, nspname, extversion, extrelocatable FROM pg_extension e, pg_namespace n WHERE extname LIKE 'test_ext%' AND e.extnamespace = n.oid ORDER BY 1;
+  extname  |  nspname  | extversion | extrelocatable 
+-----------+-----------+------------+----------------
+ test_ext1 | test_ext1 | 1.0        | f
+ test_ext2 | test_ext  | 1.0        | t
+ test_ext3 | test_ext  | 1.0        | t
+ test_ext4 | test_ext  | 1.0        | t
+ test_ext5 | test_ext  | 1.0        | t
+(5 rows)
+
+CREATE EXTENSION test_ext_cyclic1 CASCADE;
+NOTICE:  installing required extension "test_ext_cyclic2"
+ERROR:  cyclic dependency detected between extensions "test_ext_cyclic1" and "test_ext_cyclic2"
+DROP SCHEMA test_ext CASCADE;
+NOTICE:  drop cascades to 5 other objects
+DETAIL:  drop cascades to extension test_ext3
+drop cascades to extension test_ext5
+drop cascades to extension test_ext2
+drop cascades to extension test_ext4
+drop cascades to extension test_ext1

src/test/modules/test_extensions/sql/test_extensions.sql

+-- test some errors
+CREATE EXTENSION test_ext1;
+CREATE EXTENSION test_ext1 SCHEMA test_ext1;
+CREATE EXTENSION test_ext1 SCHEMA test_ext;
+CREATE SCHEMA test_ext;
+CREATE EXTENSION test_ext1 SCHEMA test_ext;
+
+-- finally success
+CREATE EXTENSION test_ext1 SCHEMA test_ext CASCADE;
+
+SELECT extname, nspname, extversion, extrelocatable FROM pg_extension e, pg_namespace n WHERE extname LIKE 'test_ext%' AND e.extnamespace = n.oid ORDER BY 1;
+
+CREATE EXTENSION test_ext_cyclic1 CASCADE;
+
+DROP SCHEMA test_ext CASCADE;

src/test/modules/test_extensions/test_ext1--1.0.sql

+/* src/test/modules/test_extensions/test_ext1--1.0.sql */
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_ext1" to load this file. \quit

src/test/modules/test_extensions/test_ext1.control

+comment = 'Test extension 1'
+default_version = '1.0'
+schema = 'test_ext1'
+relocatable = false
+requires = 'test_ext2,test_ext4'

src/test/modules/test_extensions/test_ext2--1.0.sql

+/* src/test/modules/test_extensions/test_ext2--1.0.sql */
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_ext2" to load this file. \quit

src/test/modules/test_extensions/test_ext2.control

+comment = 'Test extension 2'
+default_version = '1.0'
+relocatable = true
+requires = 'test_ext3,test_ext5'

src/test/modules/test_extensions/test_ext3--1.0.sql

+/* src/test/modules/test_extensions/test_ext3--1.0.sql */
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_ext3" to load this file. \quit

src/test/modules/test_extensions/test_ext3.control

+comment = 'Test extension 3'
+default_version = '1.0'
+relocatable = true

src/test/modules/test_extensions/test_ext4--1.0.sql

+/* src/test/modules/test_extensions/test_ext4--1.0.sql */
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_ext4" to load this file. \quit

src/test/modules/test_extensions/test_ext4.control

+comment = 'Test extension 4'
+default_version = '1.0'
+relocatable = true
+requires = 'test_ext5'

src/test/modules/test_extensions/test_ext5--1.0.sql

+/* src/test/modules/test_extensions/test_ext5--1.0.sql */
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_ext5" to load this file. \quit

src/test/modules/test_extensions/test_ext5.control

+comment = 'Test extension 5'
+default_version = '1.0'
+relocatable = true

src/test/modules/test_extensions/test_ext_cyclic1--1.0.sql

+/* src/test/modules/test_extensions/test_ext_cyclic1--1.0.sql */
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_ext_cyclic1" to load this file. \quit

src/test/modules/test_extensions/test_ext_cyclic1.control

+comment = 'Test extension cyclic 1'
+default_version = '1.0'
+relocatable = true
+requires = 'test_ext_cyclic2'

src/test/modules/test_extensions/test_ext_cyclic2--1.0.sql

+/* src/test/modules/test_extensions/test_ext_cyclic2--1.0.sql */
+-- complain if script is sourced in psql, rather than via CREATE EXTENSION
+\echo Use "CREATE EXTENSION test_ext_cyclic2" to load this file. \quit

src/test/modules/test_extensions/test_ext_cyclic2.control

+comment = 'Test extension cyclic 2'
+default_version = '1.0'
+relocatable = true
+requires = 'test_ext_cyclic1'

src/tools/msvc/Mkvcbuild.pm

@@ -41,7 +41,8 @@ my $contrib_extrasource = {
 	'seg'  => [ 'contrib/seg/segscan.l',   'contrib/seg/segparse.y' ], };
 my @contrib_excludes = (
 	'commit_ts',      'hstore_plperl', 'hstore_plpython', 'intagg',
-	'ltree_plpython', 'pgcrypto',      'sepgsql',         'brin');
+	'ltree_plpython', 'pgcrypto',      'sepgsql',         'brin',
+	'test_extensions');
 
 # Set of variables for frontend modules
 my $frontend_defines = { 'initdb' => 'FRONTEND' };