Allow referring to functions without arguments when unique

In DDL commands referring to an existing function, allow omitting the
argument list if the function name is unique in its schema, per SQL
standard.

This uses the same logic that the regproc type uses for finding
functions by name only.

Reviewed-by: Michael Paquier <[email protected]>

17 files changed, 143 insertions, 28 deletions

diff --git a/doc/src/sgml/ref/alter_extension.sgml b/doc/src/sgml/ref/alter_extension.sgml
index de6d6dca16..a7c0927d1c 100644
--- a/doc/src/sgml/ref/alter_extension.sgml
+++ b/doc/src/sgml/ref/alter_extension.sgml
@@ -39,7 +39,7 @@ ALTER EXTENSION <replaceable class="PARAMETER">name</replaceable> DROP <replacea
   EVENT TRIGGER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN DATA WRAPPER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN TABLE <replaceable class="PARAMETER">object_name</replaceable> |
-  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) |
+  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ] |
   MATERIALIZED VIEW <replaceable class="PARAMETER">object_name</replaceable> |
   OPERATOR <replaceable class="PARAMETER">operator_name</replaceable> (<replaceable class="PARAMETER">left_type</replaceable>, <replaceable class="PARAMETER">right_type</replaceable>) |
   OPERATOR CLASS <replaceable class="PARAMETER">object_name</replaceable> USING <replaceable class="parameter">index_method</replaceable> |
diff --git a/doc/src/sgml/ref/alter_function.sgml b/doc/src/sgml/ref/alter_function.sgml
index 0388d06b95..168eeb7c52 100644
--- a/doc/src/sgml/ref/alter_function.sgml
+++ b/doc/src/sgml/ref/alter_function.sgml
@@ -21,15 +21,15 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     <replaceable class="PARAMETER">action</replaceable> [ ... ] [ RESTRICT ]
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     RENAME TO <replaceable>new_name</replaceable>
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     OWNER TO { <replaceable>new_owner</replaceable> | CURRENT_USER | SESSION_USER }
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     SET SCHEMA <replaceable>new_schema</replaceable>
-ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] )
+ALTER FUNCTION <replaceable>name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ]
     DEPENDS ON EXTENSION <replaceable>extension_name</replaceable>
 
 <phrase>where <replaceable class="PARAMETER">action</replaceable> is one of:</phrase>
@@ -75,7 +75,8 @@ ALTER FUNCTION <replaceable>name</replaceable> ( [ [ <replaceable class="paramet
     <term><replaceable class="parameter">name</replaceable></term>
     <listitem>
      <para>
-      The name (optionally schema-qualified) of an existing function.
+      The name (optionally schema-qualified) of an existing function.  If no
+      argument list is specified, the name must be unique in its schema.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/alter_opfamily.sgml b/doc/src/sgml/ref/alter_opfamily.sgml
index 4511c7f7b2..0bafe5b8f8 100644
--- a/doc/src/sgml/ref/alter_opfamily.sgml
+++ b/doc/src/sgml/ref/alter_opfamily.sgml
@@ -25,7 +25,7 @@ ALTER OPERATOR FAMILY <replaceable>name</replaceable> USING <replaceable class="
   {  OPERATOR <replaceable class="parameter">strategy_number</replaceable> <replaceable class="parameter">operator_name</replaceable> ( <replaceable class="parameter">op_type</replaceable>, <replaceable class="parameter">op_type</replaceable> )
               [ FOR SEARCH | FOR ORDER BY <replaceable class="parameter">sort_family_name</replaceable> ]
    | FUNCTION <replaceable class="parameter">support_number</replaceable> [ ( <replaceable class="parameter">op_type</replaceable> [ , <replaceable class="parameter">op_type</replaceable> ] ) ]
-              <replaceable class="parameter">function_name</replaceable> ( <replaceable class="parameter">argument_type</replaceable> [, ...] )
+              <replaceable class="parameter">function_name</replaceable> [ ( <replaceable class="parameter">argument_type</replaceable> [, ...] ) ]
   } [, ... ]
 
 ALTER OPERATOR FAMILY <replaceable>name</replaceable> USING <replaceable class="parameter">index_method</replaceable> DROP
@@ -195,8 +195,9 @@ ALTER OPERATOR FAMILY <replaceable>name</replaceable> USING <replaceable class="
     <term><replaceable class="parameter">function_name</replaceable></term>
     <listitem>
      <para>
-      The name (optionally schema-qualified) of a function that is an
-      index method support procedure for the operator family.
+      The name (optionally schema-qualified) of a function that is an index
+      method support procedure for the operator family.  If no argument list
+      is specified, the name must be unique in its schema.
      </para>
     </listitem>
    </varlistentry>
diff --git a/doc/src/sgml/ref/comment.sgml b/doc/src/sgml/ref/comment.sgml
index c1cf587cb2..7483c8c03f 100644
--- a/doc/src/sgml/ref/comment.sgml
+++ b/doc/src/sgml/ref/comment.sgml
@@ -37,7 +37,7 @@ COMMENT ON
   EVENT TRIGGER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN DATA WRAPPER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN TABLE <replaceable class="PARAMETER">object_name</replaceable> |
-  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) |
+  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ] |
   INDEX <replaceable class="PARAMETER">object_name</replaceable> |
   LARGE OBJECT <replaceable class="PARAMETER">large_object_oid</replaceable> |
   MATERIALIZED VIEW <replaceable class="PARAMETER">object_name</replaceable> |
diff --git a/doc/src/sgml/ref/create_cast.sgml b/doc/src/sgml/ref/create_cast.sgml
index 11266755e5..a7d13edc22 100644
--- a/doc/src/sgml/ref/create_cast.sgml
+++ b/doc/src/sgml/ref/create_cast.sgml
@@ -19,7 +19,7 @@
  <refsynopsisdiv>
 <synopsis>
 CREATE CAST (<replaceable>source_type</replaceable> AS <replaceable>target_type</replaceable>)
-    WITH FUNCTION <replaceable>function_name</replaceable> (<replaceable>argument_type</replaceable> [, ...])
+    WITH FUNCTION <replaceable>function_name</replaceable> [ (<replaceable>argument_type</replaceable> [, ...]) ]
     [ AS ASSIGNMENT | AS IMPLICIT ]
 
 CREATE CAST (<replaceable>source_type</replaceable> AS <replaceable>target_type</replaceable>)
@@ -192,7 +192,7 @@ SELECT CAST ( 2 AS numeric ) + 4.0;
     </varlistentry>
 
     <varlistentry>
-     <term><replaceable>function_name</replaceable>(<replaceable>argument_type</replaceable> [, ...])</term>
+     <term><literal><replaceable>function_name</replaceable>[(<replaceable>argument_type</replaceable> [, ...])]</literal></term>
 
      <listitem>
       <para>
@@ -200,6 +200,8 @@ SELECT CAST ( 2 AS numeric ) + 4.0;
        be schema-qualified.  If it is not, the function will be looked
        up in the schema search path.  The function's result data type must
        match the target type of the cast.   Its arguments are discussed below.
+       If no argument list is specified, the function name must be unique in
+       its schema.
       </para>
      </listitem>
     </varlistentry>
diff --git a/doc/src/sgml/ref/create_transform.sgml b/doc/src/sgml/ref/create_transform.sgml
index f44ee89d33..647c3b9f05 100644
--- a/doc/src/sgml/ref/create_transform.sgml
+++ b/doc/src/sgml/ref/create_transform.sgml
@@ -19,8 +19,8 @@
  <refsynopsisdiv>
 <synopsis>
 CREATE [ OR REPLACE ] TRANSFORM FOR <replaceable>type_name</replaceable> LANGUAGE <replaceable>lang_name</replaceable> (
-    FROM SQL WITH FUNCTION <replaceable>from_sql_function_name</replaceable> (<replaceable>argument_type</replaceable> [, ...]),
-    TO SQL WITH FUNCTION <replaceable>to_sql_function_name</replaceable> (<replaceable>argument_type</replaceable> [, ...])
+    FROM SQL WITH FUNCTION <replaceable>from_sql_function_name</replaceable> [ (<replaceable>argument_type</replaceable> [, ...]) ],
+    TO SQL WITH FUNCTION <replaceable>to_sql_function_name</replaceable> [ (<replaceable>argument_type</replaceable> [, ...]) ]
 );
 </synopsis>
  </refsynopsisdiv>
@@ -104,7 +104,7 @@ CREATE [ OR REPLACE ] TRANSFORM FOR <replaceable>type_name</replaceable> LANGUAG
     </varlistentry>
 
     <varlistentry>
-     <term><replaceable>from_sql_function_name</replaceable>(<replaceable>argument_type</replaceable> [, ...])</term>
+     <term><literal><replaceable>from_sql_function_name</replaceable>[(<replaceable>argument_type</replaceable> [, ...])]</literal></term>
 
      <listitem>
       <para>
@@ -116,12 +116,14 @@ CREATE [ OR REPLACE ] TRANSFORM FOR <replaceable>type_name</replaceable> LANGUAG
        SQL-level function returning <type>internal</type> without at
        least one argument of type <type>internal</type>.)  The actual return
        value will be something specific to the language implementation.
+       If no argument list is specified, the function name must be unique in
+       its schema.
       </para>
      </listitem>
     </varlistentry>
 
     <varlistentry>
-     <term><replaceable>to_sql_function_name</replaceable>(<replaceable>argument_type</replaceable> [, ...])</term>
+     <term><literal><replaceable>to_sql_function_name</replaceable>[(<replaceable>argument_type</replaceable> [, ...])]</literal></term>
 
      <listitem>
       <para>
@@ -130,6 +132,8 @@ CREATE [ OR REPLACE ] TRANSFORM FOR <replaceable>type_name</replaceable> LANGUAG
        <type>internal</type> and return the type that is the type for the
        transform.  The actual argument value will be something specific to the
        language implementation.
+       If no argument list is specified, the function name must be unique in
+       its schema.
       </para>
      </listitem>
     </varlistentry>
diff --git a/doc/src/sgml/ref/drop_function.sgml b/doc/src/sgml/ref/drop_function.sgml
index 5969b084b4..0aa984528d 100644
--- a/doc/src/sgml/ref/drop_function.sgml
+++ b/doc/src/sgml/ref/drop_function.sgml
@@ -21,7 +21,7 @@ PostgreSQL documentation
 
  <refsynopsisdiv>
 <synopsis>
-DROP FUNCTION [ IF EXISTS ] <replaceable class="parameter">name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) [, ...]
+DROP FUNCTION [ IF EXISTS ] <replaceable class="parameter">name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ] [, ...]
     [ CASCADE | RESTRICT ]
 </synopsis>
  </refsynopsisdiv>
@@ -56,7 +56,8 @@ DROP FUNCTION [ IF EXISTS ] <replaceable class="parameter">name</replaceable> (
     <term><replaceable class="parameter">name</replaceable></term>
     <listitem>
      <para>
-      The name (optionally schema-qualified) of an existing function.
+      The name (optionally schema-qualified) of an existing function.  If no
+      argument list is specified, the name must be unique in its schema.
      </para>
     </listitem>
    </varlistentry>
@@ -141,14 +142,40 @@ DROP FUNCTION sqrt(integer);
 <programlisting>
 DROP FUNCTION sqrt(integer), sqrt(bigint);
 </programlisting></para>
+
+  <para>
+   If the function name is unique in its schema, it can be referred to without
+   an argument list:
+<programlisting>
+DROP FUNCTION update_employee_salaries;
+</programlisting>
+   Note that this is different from
+<programlisting>
+DROP FUNCTION update_employee_salaries();
+</programlisting>
+   which refers to a function with zero arguments, whereas the first variant
+   can refer to a function with any number of arguments, including zero, as
+   long as the name is unique.
+  </para>
  </refsect1>
 
  <refsect1 id="SQL-DROPFUNCTION-compatibility">
   <title>Compatibility</title>
 
   <para>
-   A <command>DROP FUNCTION</command> statement is defined in the SQL
-   standard, but it is not compatible with this command.
+   This command conforms to the SQL standard, with
+   these <productname>PostgreSQL</productname> extensions:
+   <itemizedlist>
+    <listitem>
+     <para>The standard only allows one function to be dropped per command.</para>
+    </listitem>
+    <listitem>
+     <para>The <literal>IF EXISTS</literal> option</para>
+    </listitem>
+    <listitem>
+     <para>The ability to specify argument modes and names</para>
+    </listitem>
+   </itemizedlist>
   </para>
  </refsect1>
 
diff --git a/doc/src/sgml/ref/grant.sgml b/doc/src/sgml/ref/grant.sgml
index d8ca39f869..9fb4c2fd7e 100644
--- a/doc/src/sgml/ref/grant.sgml
+++ b/doc/src/sgml/ref/grant.sgml
@@ -55,7 +55,7 @@ GRANT { USAGE | ALL [ PRIVILEGES ] }
     TO <replaceable class="PARAMETER">role_specification</replaceable> [, ...] [ WITH GRANT OPTION ]
 
 GRANT { EXECUTE | ALL [ PRIVILEGES ] }
-    ON { FUNCTION <replaceable>function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_type</replaceable> [, ...] ] ) [, ...]
+    ON { FUNCTION <replaceable>function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_type</replaceable> [, ...] ] ) ] [, ...]
          | ALL FUNCTIONS IN SCHEMA <replaceable class="PARAMETER">schema_name</replaceable> [, ...] }
     TO <replaceable class="PARAMETER">role_specification</replaceable> [, ...] [ WITH GRANT OPTION ]
 
diff --git a/doc/src/sgml/ref/revoke.sgml b/doc/src/sgml/ref/revoke.sgml
index fc00129620..ce532543f0 100644
--- a/doc/src/sgml/ref/revoke.sgml
+++ b/doc/src/sgml/ref/revoke.sgml
@@ -70,7 +70,7 @@ REVOKE [ GRANT OPTION FOR ]
 
 REVOKE [ GRANT OPTION FOR ]
     { EXECUTE | ALL [ PRIVILEGES ] }
-    ON { FUNCTION <replaceable>function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_type</replaceable> [, ...] ] ) [, ...]
+    ON { FUNCTION <replaceable>function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">arg_name</replaceable> ] <replaceable class="parameter">arg_type</replaceable> [, ...] ] ) ] [, ...]
          | ALL FUNCTIONS IN SCHEMA <replaceable>schema_name</replaceable> [, ...] }
     FROM { [ GROUP ] <replaceable class="PARAMETER">role_name</replaceable> | PUBLIC } [, ...]
     [ CASCADE | RESTRICT ]
diff --git a/doc/src/sgml/ref/security_label.sgml b/doc/src/sgml/ref/security_label.sgml
index 998fe3b7c0..afd86aff3a 100644
--- a/doc/src/sgml/ref/security_label.sgml
+++ b/doc/src/sgml/ref/security_label.sgml
@@ -30,7 +30,7 @@ SECURITY LABEL [ FOR <replaceable class="PARAMETER">provider</replaceable> ] ON
   DOMAIN <replaceable class="PARAMETER">object_name</replaceable> |
   EVENT TRIGGER <replaceable class="PARAMETER">object_name</replaceable> |
   FOREIGN TABLE <replaceable class="PARAMETER">object_name</replaceable>
-  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) |
+  FUNCTION <replaceable class="PARAMETER">function_name</replaceable> [ ( [ [ <replaceable class="parameter">argmode</replaceable> ] [ <replaceable class="parameter">argname</replaceable> ] <replaceable class="parameter">argtype</replaceable> [, ...] ] ) ] |
   LARGE OBJECT <replaceable class="PARAMETER">large_object_oid</replaceable> |
   MATERIALIZED VIEW <replaceable class="PARAMETER">object_name</replaceable> |
   [ PROCEDURAL ] LANGUAGE <replaceable class="PARAMETER">object_name</replaceable> |
diff --git a/src/backend/nodes/copyfuncs.c b/src/backend/nodes/copyfuncs.c
index bfc2ac1716..25fd051d6e 100644
--- a/src/backend/nodes/copyfuncs.c
+++ b/src/backend/nodes/copyfuncs.c
@@ -3067,6 +3067,7 @@ _copyObjectWithArgs(const ObjectWithArgs *from)
 
 	COPY_NODE_FIELD(objname);
 	COPY_NODE_FIELD(objargs);
+	COPY_SCALAR_FIELD(args_unspecified);
 
 	return newnode;
 }
diff --git a/src/backend/nodes/equalfuncs.c b/src/backend/nodes/equalfuncs.c
index 54e9c983a0..67529e3f86 100644
--- a/src/backend/nodes/equalfuncs.c
+++ b/src/backend/nodes/equalfuncs.c
@@ -1119,6 +1119,7 @@ _equalObjectWithArgs(const ObjectWithArgs *a, const ObjectWithArgs *b)
 {
 	COMPARE_NODE_FIELD(objname);
 	COMPARE_NODE_FIELD(objargs);
+	COMPARE_SCALAR_FIELD(args_unspecified);
 
 	return true;
 }
diff --git a/src/backend/parser/gram.y b/src/backend/parser/gram.y
index e7acc2d9a2..6316688a88 100644
--- a/src/backend/parser/gram.y
+++ b/src/backend/parser/gram.y
@@ -7202,6 +7202,33 @@ function_with_argtypes:
 					n->objargs = extractArgTypes($2);
 					$$ = n;
 				}
+			/*
+			 * Because of reduce/reduce conflicts, we can't use func_name
+			 * below, but we can write it out the long way, which actually
+			 * allows more cases.
+			 */
+			| type_func_name_keyword
+				{
+					ObjectWithArgs *n = makeNode(ObjectWithArgs);
+					n->objname = list_make1(makeString(pstrdup($1)));
+					n->args_unspecified = true;
+					$$ = n;
+				}
+			| ColId
+				{
+					ObjectWithArgs *n = makeNode(ObjectWithArgs);
+					n->objname = list_make1(makeString($1));
+					n->args_unspecified = true;
+					$$ = n;
+				}
+			| ColId indirection
+				{
+					ObjectWithArgs *n = makeNode(ObjectWithArgs);
+					n->objname = check_func_name(lcons(makeString($1), $2),
+												  yyscanner);
+					n->args_unspecified = true;
+					$$ = n;
+				}
 		;
 
 /*
diff --git a/src/backend/parser/parse_func.c b/src/backend/parser/parse_func.c
index dd9749f205..55853c20bb 100644
--- a/src/backend/parser/parse_func.c
+++ b/src/backend/parser/parse_func.c
@@ -1895,8 +1895,10 @@ func_signature_string(List *funcname, int nargs,
 
 /*
  * LookupFuncName
- *		Given a possibly-qualified function name and a set of argument types,
- *		look up the function.
+ *
+ * Given a possibly-qualified function name and optionally a set of argument
+ * types, look up the function.  Pass nargs == -1 to indicate that no argument
+ * types are specified.
  *
  * If the function name is not schema-qualified, it is sought in the current
  * namespace search path.
@@ -1914,6 +1916,35 @@ LookupFuncName(List *funcname, int nargs, const Oid *argtypes, bool noError)
 
 	clist = FuncnameGetCandidates(funcname, nargs, NIL, false, false, noError);
 
+	/*
+	 * If no arguments were specified, the name must yield a unique candidate.
+	 */
+	if (nargs == -1)
+	{
+		if (clist)
+		{
+			if (clist->next)
+			{
+				if (!noError)
+					ereport(ERROR,
+							(errcode(ERRCODE_AMBIGUOUS_FUNCTION),
+							 errmsg("function name \"%s\" is not unique",
+									NameListToString(funcname)),
+							 errhint("Specify the argument list to select the function unambiguously.")));
+			}
+			else
+				return clist->oid;
+		}
+		else
+		{
+			if (!noError)
+				ereport(ERROR,
+						(errcode(ERRCODE_UNDEFINED_FUNCTION),
+						 errmsg("could not find a function named \"%s\"",
+								NameListToString(funcname))));
+		}
+	}
+
 	while (clist)
 	{
 		if (memcmp(argtypes, clist->args, nargs * sizeof(Oid)) == 0)
@@ -1962,7 +1993,7 @@ LookupFuncWithArgs(ObjectWithArgs *func, bool noError)
 		args_item = lnext(args_item);
 	}
 
-	return LookupFuncName(func->objname, argcount, argoids, noError);
+	return LookupFuncName(func->objname, func->args_unspecified ? -1 : argcount, argoids, noError);
 }
 
 /*
diff --git a/src/include/nodes/parsenodes.h b/src/include/nodes/parsenodes.h
index a44d2178e1..d576523f6a 100644
--- a/src/include/nodes/parsenodes.h
+++ b/src/include/nodes/parsenodes.h
@@ -1811,6 +1811,9 @@ typedef struct ObjectWithArgs
 	NodeTag		type;
 	List	   *objname;		/* qualified name of function/operator */
 	List	   *objargs;		/* list of Typename nodes */
+	bool		args_unspecified; /* argument list was omitted, so name must
+								   * be unique (note that objargs == NIL means
+								   * zero args) */
 } ObjectWithArgs;
 
 /*
diff --git a/src/test/regress/expected/create_function_3.out b/src/test/regress/expected/create_function_3.out
index cc4e98a1d4..b5e19485e5 100644
--- a/src/test/regress/expected/create_function_3.out
+++ b/src/test/regress/expected/create_function_3.out
@@ -218,13 +218,21 @@ SELECT routine_name, ordinal_position, parameter_name, parameter_default
 (7 rows)
 
 DROP FUNCTION functest_IS_1(int, int, text), functest_IS_2(int), functest_IS_3(int);
+-- overload
+CREATE FUNCTION functest_B_2(bigint) RETURNS bool LANGUAGE 'sql'
+       IMMUTABLE AS 'SELECT $1 > 0';
+DROP FUNCTION functest_b_1;
+DROP FUNCTION functest_b_1;  -- error, not found
+ERROR:  could not find a function named "functest_b_1"
+DROP FUNCTION functest_b_2;  -- error, ambiguous
+ERROR:  function name "functest_b_2" is not unique
+HINT:  Specify the argument list to select the function unambiguously.
 -- Cleanups
 DROP SCHEMA temp_func_test CASCADE;
 NOTICE:  drop cascades to 16 other objects
 DETAIL:  drop cascades to function functest_a_1(text,date)
 drop cascades to function functest_a_2(text[])
 drop cascades to function functest_a_3()
-drop cascades to function functest_b_1(integer)
 drop cascades to function functest_b_2(integer)
 drop cascades to function functest_b_3(integer)
 drop cascades to function functest_b_4(integer)
@@ -237,5 +245,6 @@ drop cascades to function functext_f_1(integer)
 drop cascades to function functext_f_2(integer)
 drop cascades to function functext_f_3(integer)
 drop cascades to function functext_f_4(integer)
+drop cascades to function functest_b_2(bigint)
 DROP USER regress_unpriv_user;
 RESET search_path;
diff --git a/src/test/regress/sql/create_function_3.sql b/src/test/regress/sql/create_function_3.sql
index 66a463b089..0a0e407aab 100644
--- a/src/test/regress/sql/create_function_3.sql
+++ b/src/test/regress/sql/create_function_3.sql
@@ -158,6 +158,14 @@ SELECT routine_name, ordinal_position, parameter_name, parameter_default
 
 DROP FUNCTION functest_IS_1(int, int, text), functest_IS_2(int), functest_IS_3(int);
 
+-- overload
+CREATE FUNCTION functest_B_2(bigint) RETURNS bool LANGUAGE 'sql'
+       IMMUTABLE AS 'SELECT $1 > 0';
+
+DROP FUNCTION functest_b_1;
+DROP FUNCTION functest_b_1;  -- error, not found
+DROP FUNCTION functest_b_2;  -- error, ambiguous
+
 
 -- Cleanups
 DROP SCHEMA temp_func_test CASCADE;