Support arrays of composite types, including the rowtypes of regular tables

and views (but not system catalogs, nor sequences or toast tables).  Get rid
of the hardwired convention that a type's array type is named exactly "_type",
instead using a new column pg_type.typarray to provide the linkage.  (It still
will be named "_type", though, except in odd corner cases such as
maximum-length type names.)

Along the way, make tracking of owner and schema dependencies for types more
uniform: a type directly created by the user has these dependencies, while a
table rowtype or auto-generated array type does not have them, but depends on
its parent object instead.

David Fetter, Andrew Dunstan, Tom Lane

doc/src/sgml/ref/create_type.sgml

@@ -1,5 +1,5 @@
 <!--
-$PostgreSQL: pgsql/doc/src/sgml/ref/create_type.sgml,v 1.69 2007/04/02 03:49:37 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/ref/create_type.sgml,v 1.70 2007/05/11 17:57:11 tgl Exp $
 PostgreSQL documentation
 -->
 
@@ -312,15 +312,17 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
    <title>Array Types</title>
 
    <para>
-    Whenever a user-defined base or enum data type is created,
+    Whenever a user-defined type is created,
     <productname>PostgreSQL</productname> automatically creates an
     associated array type, whose name consists of the base type's
-    name prepended with an underscore.  The parser understands this
-    naming convention, and translates requests for columns of type
-    <literal>foo[]</> into requests for type <literal>_foo</>.
-    The implicitly-created array type is variable length and uses the
+    name prepended with an underscore, and truncated if necessary to keep
+    it less than <symbol>NAMEDATALEN</symbol> bytes long.  (If the name
+    so generated collides with an existing type name, the process is
+    repeated until a non-colliding name is found.)
+    This implicitly-created array type is variable length and uses the
     built-in input and output functions <literal>array_in</> and
-    <literal>array_out</>.
+    <literal>array_out</>.  The array type tracks any changes in its
+    element type's owner or schema, and is dropped if the element type is.
    </para>
 
    <para>
@@ -330,10 +332,9 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
     making a fixed-length type that happens to be internally an array of a number of
     identical things, and you want to allow these things to be accessed
     directly by subscripting, in addition to whatever operations you plan
-    to provide for the type as a whole.  For example, type <type>name</>
-    allows its constituent <type>char</> elements to be accessed this way.
-    A 2-D <type>point</> type could allow its two component numbers to be
-    accessed like <literal>point[0]</> and <literal>point[1]</>.
+    to provide for the type as a whole.  For example, type <type>point</>
+    is represented as just two floating-point numbers, which it allows to be
+    accessed as <literal>point[0]</> and <literal>point[1]</>.
     Note that
     this facility only works for fixed-length types whose internal form
     is exactly a sequence of identical fixed-length fields.  A subscriptable
@@ -529,12 +530,15 @@ CREATE TYPE <replaceable class="parameter">name</replaceable>
   <title>Notes</title>
 
   <para>
-   User-defined type names should not begin with the underscore character
-   (<literal>_</literal>) and should only be 62 characters
-   long (or in general <symbol>NAMEDATALEN</symbol> - 2, rather than
-   the <symbol>NAMEDATALEN</symbol> - 1 characters allowed for other
-   names).  Type names beginning with underscore are reserved for
-   internally-created array type names.
+   It is best to avoid using type names that begin with the underscore
+   character (<literal>_</literal>).  <productname>PostgreSQL</productname>
+   forms the name of an array type by prepending one or more underscores
+   to the element type's name, and these names may collide with user-defined
+   type names that begin with underscore.  While the system will modify
+   generated array type names to avoid collisions, this does not help if the
+   conflicting array type already exists when you try to create your type.
+   Also, various old client software may assume that names beginning with
+   underscores always represent arrays.
   </para>
 
   <para>