Allow aggregate functions to be VARIADIC.

There's no inherent reason why an aggregate function can't be variadic
(even VARIADIC ANY) if its transition function can handle the case.
Indeed, this patch to add the feature touches none of the planner or
executor, and little of the parser; the main missing stuff was DDL and
pg_dump support.

It is true that variadic aggregates can create the same sort of ambiguity
about parameters versus ORDER BY keys that was complained of when we
(briefly) had both one- and two-argument forms of string_agg().  However,
the policy formed in response to that discussion only said that we'd not
create any built-in aggregates with varying numbers of arguments, not that
we shouldn't allow users to do it.  So the logical extension of that is
we can allow users to make variadic aggregates as long as we're wary about
shipping any such in core.

In passing, this patch allows aggregate function arguments to be named, to
the extent of remembering the names in pg_proc and dumping them in pg_dump.
You can't yet call an aggregate using named-parameter notation.  That seems
like a likely future extension, but it'll take some work, and it's not what
this patch is really about.  Likewise, there's still some work needed to
make window functions handle VARIADIC fully, but I left that for another
day.

initdb forced because of new aggvariadic field in Aggref parse nodes.

8 files changed, 145 insertions, 25 deletions

diff --git a/doc/src/sgml/ref/alter_aggregate.sgml b/doc/src/sgml/ref/alter_aggregate.sgml
index 571a50a502e..aab5b2b695e 100644
--- a/doc/src/sgml/ref/alter_aggregate.sgml
+++ b/doc/src/sgml/ref/alter_aggregate.sgml
@@ -21,9 +21,12 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-ALTER AGGREGATE <replaceable>name</replaceable> ( <replaceable>argtype</replaceable> [ , ... ] ) RENAME TO <replaceable>new_name</replaceable>
-ALTER AGGREGATE <replaceable>name</replaceable> ( <replaceable>argtype</replaceable> [ , ... ] ) OWNER TO <replaceable>new_owner</replaceable>
-ALTER AGGREGATE <replaceable>name</replaceable> ( <replaceable>argtype</replaceable> [ , ... ] ) SET SCHEMA <replaceable>new_schema</replaceable>
+ALTER AGGREGATE <replaceable>name</replaceable> ( [ <replaceable>argmode</replaceable> ] [ <replaceable>arg_name</replaceable> ] <replaceable>arg_data_type</replaceable> [ , ... ] )
+  RENAME TO <replaceable>new_name</replaceable>
+ALTER AGGREGATE <replaceable>name</replaceable> ( [ <replaceable>argmode</replaceable> ] [ <replaceable>arg_name</replaceable> ] <replaceable>arg_data_type</replaceable> [ , ... ] )
+  OWNER TO <replaceable>new_owner</replaceable>
+ALTER AGGREGATE <replaceable>name</replaceable> ( [ <replaceable>argmode</replaceable> ] [ <replaceable>arg_name</replaceable> ] <replaceable>arg_data_type</replaceable> [ , ... ] )
+  SET SCHEMA <replaceable>new_schema</replaceable>
 </synopsis>
  </refsynopsisdiv>
 
@@ -62,12 +65,36 @@ ALTER AGGREGATE <replaceable>name</replaceable> ( <replaceable>argtype</replacea
    </varlistentry>
 
    <varlistentry>
-    <term><replaceable class="parameter">argtype</replaceable></term>
+    <term><replaceable class="parameter">argmode</replaceable></term>
+
+    <listitem>
+     <para>
+      The mode of an argument: <literal>IN</> or <literal>VARIADIC</>.
+      If omitted, the default is <literal>IN</>.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">arg_name</replaceable></term>
+
+    <listitem>
+     <para>
+      The name of an argument.
+      Note that <command>ALTER AGGREGATE</command> does not actually pay
+      any attention to argument names, since only the argument data
+      types are needed to determine the aggregate function's identity.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">arg_data_type</replaceable></term>
     <listitem>
      <para>
       An input data type on which the aggregate function operates.
       To reference a zero-argument aggregate function, write <literal>*</>
-      in place of the list of input data types.
+      in place of the list of argument specifications.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/alter_extension.sgml b/doc/src/sgml/ref/alter_extension.sgml
index 2dbba0c0bbb..a14fcb48683 100644
--- a/doc/src/sgml/ref/alter_extension.sgml
+++ b/doc/src/sgml/ref/alter_extension.sgml
@@ -30,7 +30,7 @@ ALTER EXTENSION <replaceable class="PARAMETER">name</replaceable> DROP <replacea
 
 <phrase>where <replaceable class="PARAMETER">member_object</replaceable> is:</phrase>
 
-  AGGREGATE <replaceable class="PARAMETER">agg_name</replaceable> (<replaceable class="PARAMETER">agg_type</replaceable> [, ...] ) |
+  AGGREGATE <replaceable class="PARAMETER">agg_name</replaceable> ( [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">agg_type</replaceable> [, ...] ) |
   CAST (<replaceable>source_type</replaceable> AS <replaceable>target_type</replaceable>) |
   COLLATION <replaceable class="PARAMETER">object_name</replaceable> |
   CONVERSION <replaceable class="PARAMETER">object_name</replaceable> |
@@ -179,7 +179,7 @@ ALTER EXTENSION <replaceable class="PARAMETER">name</replaceable> DROP <replacea
       <para>
        An input data type on which the aggregate function operates.
        To reference a zero-argument aggregate function, write <literal>*</>
-       in place of the list of input data types.
+       in place of the list of argument specifications.
       </para>
      </listitem>
     </varlistentry>
diff --git a/doc/src/sgml/ref/comment.sgml b/doc/src/sgml/ref/comment.sgml
index e94dd4b8ded..e55050042a8 100644
--- a/doc/src/sgml/ref/comment.sgml
+++ b/doc/src/sgml/ref/comment.sgml
@@ -23,7 +23,7 @@ PostgreSQL documentation
 <synopsis>
 COMMENT ON
 {
-  AGGREGATE <replaceable class="PARAMETER">agg_name</replaceable> (<replaceable class="PARAMETER">agg_type</replaceable> [, ...] ) |
+  AGGREGATE <replaceable class="PARAMETER">agg_name</replaceable> ( [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">agg_type</replaceable> [, ...] ) |
   CAST (<replaceable>source_type</replaceable> AS <replaceable>target_type</replaceable>) |
   COLLATION <replaceable class="PARAMETER">object_name</replaceable> |
   COLUMN <replaceable class="PARAMETER">relation_name</replaceable>.<replaceable class="PARAMETER">column_name</replaceable> |
@@ -126,7 +126,7 @@ COMMENT ON
      <para>
       An input data type on which the aggregate function operates.
       To reference a zero-argument aggregate function, write <literal>*</>
-      in place of the list of input data types.
+      in place of the list of argument specifications.
      </para>
     </listitem>
    </varlistentry>
@@ -156,7 +156,7 @@ COMMENT ON
       The mode of a function argument: <literal>IN</>, <literal>OUT</>,
       <literal>INOUT</>, or <literal>VARIADIC</>.
       If omitted, the default is <literal>IN</>.
-      Note that <command>COMMENT ON FUNCTION</command> does not actually pay
+      Note that <command>COMMENT</command> does not actually pay
       any attention to <literal>OUT</> arguments, since only the input
       arguments are needed to determine the function's identity.
       So it is sufficient to list the <literal>IN</>, <literal>INOUT</>,
@@ -170,7 +170,7 @@ COMMENT ON
     <listitem>
      <para>
       The name of a function argument.
-      Note that <command>COMMENT ON FUNCTION</command> does not actually pay
+      Note that <command>COMMENT</command> does not actually pay
       any attention to argument names, since only the argument data
       types are needed to determine the function's identity.
      </para>
diff --git a/doc/src/sgml/ref/create_aggregate.sgml b/doc/src/sgml/ref/create_aggregate.sgml
index d5e4e272fce..2b35fa4d522 100644
--- a/doc/src/sgml/ref/create_aggregate.sgml
+++ b/doc/src/sgml/ref/create_aggregate.sgml
@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> ( <replaceable class="PARAMETER">input_data_type</replaceable> [ , ... ] ) (
+CREATE AGGREGATE <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_data_type</replaceable> [ , ... ] ) (
     SFUNC = <replaceable class="PARAMETER">sfunc</replaceable>,
     STYPE = <replaceable class="PARAMETER">state_data_type</replaceable>
     [ , FINALFUNC = <replaceable class="PARAMETER">ffunc</replaceable> ]
@@ -118,7 +118,7 @@ CREATE AGGREGATE <replaceable class="PARAMETER">name</replaceable> (
    Note that this behavior is only available when
    <replaceable class="PARAMETER">state_data_type</replaceable>
    is the same as the first
-   <replaceable class="PARAMETER">input_data_type</replaceable>.
+   <replaceable class="PARAMETER">arg_data_type</replaceable>.
    When these types are different, you must supply a nonnull initial
    condition or use a nonstrict transition function.
   </para>
@@ -187,12 +187,36 @@ SELECT col FROM tab ORDER BY col USING sortop LIMIT 1;
    </varlistentry>
 
    <varlistentry>
-    <term><replaceable class="PARAMETER">input_data_type</replaceable></term>
+    <term><replaceable class="parameter">argmode</replaceable></term>
+
+    <listitem>
+     <para>
+      The mode of an argument: <literal>IN</> or <literal>VARIADIC</>.
+      (Aggregate functions do not support <literal>OUT</> arguments.)
+      If omitted, the default is <literal>IN</>.  Only the last argument
+      can be marked <literal>VARIADIC</>.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">arg_name</replaceable></term>
+
+    <listitem>
+     <para>
+      The name of an argument.  This is currently only useful for
+      documentation purposes.  If omitted, the argument has no name.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="PARAMETER">arg_data_type</replaceable></term>
     <listitem>
      <para>
       An input data type on which this aggregate function operates.
       To create a zero-argument aggregate function, write <literal>*</>
-      in place of the list of input data types.  (An example of such an
+      in place of the list of argument specifications.  (An example of such an
       aggregate is <function>count(*)</function>.)
      </para>
     </listitem>
@@ -205,8 +229,8 @@ SELECT col FROM tab ORDER BY col USING sortop LIMIT 1;
       In the old syntax for <command>CREATE AGGREGATE</>, the input data type
       is specified by a <literal>basetype</> parameter rather than being
       written next to the aggregate name.  Note that this syntax allows
-      only one input parameter.  To define a zero-argument aggregate function,
-      specify the <literal>basetype</> as
+      only one input parameter.  To define a zero-argument aggregate function
+      with this syntax, specify the <literal>basetype</> as
       <literal>"ANY"</> (not <literal>*</>).
      </para>
     </listitem>
diff --git a/doc/src/sgml/ref/drop_aggregate.sgml b/doc/src/sgml/ref/drop_aggregate.sgml
index 1ed152f6a05..06060fb4f7b 100644
--- a/doc/src/sgml/ref/drop_aggregate.sgml
+++ b/doc/src/sgml/ref/drop_aggregate.sgml
@@ -21,7 +21,9 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-DROP AGGREGATE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> ( <replaceable class="PARAMETER">argtype</replaceable> [ , ... ] ) [ CASCADE | RESTRICT ]
+DROP AGGREGATE [ IF EXISTS ]
+  <replaceable class="parameter">name</replaceable> ( [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_data_type</replaceable> [ , ... ] )
+  [ CASCADE | RESTRICT ]
 </synopsis>
  </refsynopsisdiv>
 
@@ -60,12 +62,36 @@ DROP AGGREGATE [ IF EXISTS ] <replaceable class="PARAMETER">name</replaceable> (
    </varlistentry>
 
    <varlistentry>
-    <term><replaceable class="parameter">argtype</replaceable></term>
+    <term><replaceable class="parameter">argmode</replaceable></term>
+
+    <listitem>
+     <para>
+      The mode of an argument: <literal>IN</> or <literal>VARIADIC</>.
+      If omitted, the default is <literal>IN</>.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">arg_name</replaceable></term>
+
+    <listitem>
+     <para>
+      The name of an argument.
+      Note that <command>DROP AGGREGATE</command> does not actually pay
+      any attention to argument names, since only the argument data
+      types are needed to determine the aggregate function's identity.
+     </para>
+    </listitem>
+   </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">arg_data_type</replaceable></term>
     <listitem>
      <para>
       An input data type on which the aggregate function operates.
       To reference a zero-argument aggregate function, write <literal>*</>
-      in place of the list of input data types.
+      in place of the list of argument specifications.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/security_label.sgml b/doc/src/sgml/ref/security_label.sgml
index 52cb1d16f4c..76c131f94ee 100644
--- a/doc/src/sgml/ref/security_label.sgml
+++ b/doc/src/sgml/ref/security_label.sgml
@@ -25,7 +25,7 @@ SECURITY LABEL [ FOR <replaceable class="PARAMETER">provider</replaceable> ] ON
 {
   TABLE <replaceable class="PARAMETER">object_name</replaceable> |
   COLUMN <replaceable class="PARAMETER">table_name</replaceable>.<replaceable class="PARAMETER">column_name</replaceable> |
-  AGGREGATE <replaceable class="PARAMETER">agg_name</replaceable> (<replaceable class="PARAMETER">agg_type</replaceable> [, ...] ) |
+  AGGREGATE <replaceable class="PARAMETER">agg_name</replaceable> ( [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">agg_type</replaceable> [, ...] ) |
   DATABASE <replaceable class="PARAMETER">object_name</replaceable> |
   DOMAIN <replaceable class="PARAMETER">object_name</replaceable> |
   EVENT TRIGGER <replaceable class="PARAMETER">object_name</replaceable> |
@@ -107,12 +107,12 @@ SECURITY LABEL [ FOR <replaceable class="PARAMETER">provider</replaceable> ] ON
    </varlistentry>
 
    <varlistentry>
-    <term><replaceable class="parameter">arg_type</replaceable></term>
+    <term><replaceable class="parameter">agg_type</replaceable></term>
     <listitem>
      <para>
       An input data type on which the aggregate function operates.
       To reference a zero-argument aggregate function, write <literal>*</>
-      in place of the list of input data types.
+      in place of the list of argument specifications.
      </para>
     </listitem>
    </varlistentry>
@@ -125,7 +125,7 @@ SECURITY LABEL [ FOR <replaceable class="PARAMETER">provider</replaceable> ] ON
       The mode of a function argument: <literal>IN</>, <literal>OUT</>,
       <literal>INOUT</>, or <literal>VARIADIC</>.
       If omitted, the default is <literal>IN</>.
-      Note that <command>SECURITY LABEL ON FUNCTION</command> does not actually
+      Note that <command>SECURITY LABEL</command> does not actually
       pay any attention to <literal>OUT</> arguments, since only the input
       arguments are needed to determine the function's identity.
       So it is sufficient to list the <literal>IN</>, <literal>INOUT</>,
@@ -140,7 +140,7 @@ SECURITY LABEL [ FOR <replaceable class="PARAMETER">provider</replaceable> ] ON
     <listitem>
      <para>
       The name of a function argument.
-      Note that <command>SECURITY LABEL ON FUNCTION</command> does not actually
+      Note that <command>SECURITY LABEL</command> does not actually
       pay any attention to argument names, since only the argument data
       types are needed to determine the function's identity.
      </para>
diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index 803ed855c82..e3dbc4b5ea5 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -2524,6 +2524,13 @@ SELECT concat_lower_or_upper('Hello', 'World', uppercase := true);
     having numerous parameters that have default values, named or mixed
     notation can save a great deal of writing and reduce chances for error.
    </para>
+
+   <note>
+    <para>
+     Named and mixed call notations can currently be used only with regular
+     functions, not with aggregate functions or window functions.
+    </para>
+   </note>
   </sect2>
  </sect1>
 
diff --git a/doc/src/sgml/xaggr.sgml b/doc/src/sgml/xaggr.sgml
index 1822f6d4abd..9ed7d99f7c0 100644
--- a/doc/src/sgml/xaggr.sgml
+++ b/doc/src/sgml/xaggr.sgml
@@ -170,6 +170,42 @@ SELECT attrelid::regclass, array_accum(atttypid::regtype)
   </para>
 
   <para>
+   An aggregate function can be made to accept a varying number of arguments
+   by declaring its last argument as a <literal>VARIADIC</> array, in much
+   the same fashion as for regular functions; see
+   <xref linkend="xfunc-sql-variadic-functions">.  The aggregate's transition
+   function must have the same array type as its last argument.  The
+   transition function typically would also be marked <literal>VARIADIC</>,
+   but this is not strictly required.
+  </para>
+
+  <note>
+   <para>
+    Variadic aggregates are easily misused in connection with
+    the <literal>ORDER BY</> option (see <xref linkend="syntax-aggregates">),
+    since the parser cannot tell whether the wrong number of actual arguments
+    have been given in such a combination.  Keep in mind that everything to
+    the right of <literal>ORDER BY</> is a sort key, not an argument to the
+    aggregate.  For example, in
+<programlisting>
+SELECT myaggregate(a ORDER BY a, b, c) FROM ...
+</programlisting>
+    the parser will see this as a single aggregate function argument and
+    three sort keys.  However, the user might have intended
+<programlisting>
+SELECT myaggregate(a, b, c ORDER BY a) FROM ...
+</programlisting>
+    If <literal>myaggregate</> is variadic, both these calls could be
+    perfectly valid.
+   </para>
+
+   <para>
+    For the same reason, it's wise to think twice before creating aggregate
+    functions with the same names and different numbers of regular arguments.
+   </para>
+  </note>
+
+  <para>
    A function written in C can detect that it is being called as an
    aggregate transition or final function by calling
    <function>AggCheckCallContext</>, for example: