doc: clarify how dropping of extensions affects dependent objs.

Clarify that functions/procedures are dropped when any extension that
depends on them is dropped.

Reported-by: David G. Johnston

Discussion: https://postgr.es/m/CAKFQuwbPSHMDGkisRUmewopweC1bFvytVqB=a=X4GFg=4ZWxPA@mail.gmail.com

Backpatch-through: 13

doc/src/sgml/ref/alter_function.sgml

@@ -160,8 +160,10 @@ ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="param
      <para>
       This form marks the function as dependent on the extension, or no longer
       dependent on that extension if <literal>NO</literal> is specified.
-      A function that's marked as dependent on an extension is automatically
-      dropped when the extension is dropped.
+      A function that's marked as dependent on an extension is dropped when the
+      extension is dropped, even if <literal>CASCADE</literal> is not specified.
+      A function can depend upon multiple extensions, and will be dropped when
+      any one of those extensions is dropped.
      </para>
     </listitem>
    </varlistentry>

doc/src/sgml/ref/alter_procedure.sgml

@@ -147,7 +147,12 @@ ALTER PROCEDURE <replaceable>name</replaceable> [ ( [ [ <replaceable class="para
     <term><replaceable class="parameter">extension_name</replaceable></term>
     <listitem>
      <para>
-      The name of the extension that the procedure is to depend on.
+      This form marks the procedure as dependent on the extension, or no longer
+      dependent on the extension if <literal>NO</literal> is specified.
+      A procedure that's marked as dependent on an extension is dropped when the
+      extension is dropped, even if cascade is not specified.
+      A procedure can depend upon multiple extensions, and will be dropped when
+      any one of those extensions is dropped.
      </para>
     </listitem>
    </varlistentry>

doc/src/sgml/ref/drop_extension.sgml

@@ -30,7 +30,9 @@ DROP EXTENSION [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [
 
   <para>
    <command>DROP EXTENSION</command> removes extensions from the database.
-   Dropping an extension causes its component objects to be dropped as well.
+   Dropping an extension causes its component objects, and other explicitly
+   dependent routines (see <xref linkend="sql-alterroutine"/>,
+   the depends on extension action), to be dropped as well.
   </para>
 
   <para>
@@ -77,9 +79,9 @@ DROP EXTENSION [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [
     <term><literal>RESTRICT</literal></term>
     <listitem>
      <para>
-      Refuse to drop the extension if any objects depend on it (other than
-      its own member objects and other extensions listed in the same
-      <command>DROP</command> command).  This is the default.
+      This option prevents the specified extensions from being dropped
+      if there exists non-extension-member objects that depends on any
+      the extensions.  This is the default.
      </para>
     </listitem>
    </varlistentry>