Support default arguments and named-argument notation for window functions.

These things didn't work because the planner omitted to do the necessary
preprocessing of a WindowFunc's argument list.  Add the few dozen lines
of code needed to handle that.

Although this sounds like a feature addition, it's really a bug fix because
the default-argument case was likely to crash previously, due to lack of
checking of the number of supplied arguments in the built-in window
functions.  It's not a security issue because there's no way for a
non-superuser to create a window function definition with defaults that
refers to a built-in C function, but nonetheless people might be annoyed
that it crashes rather than producing a useful error message.  So
back-patch as far as the patch applies easily, which turns out to be 9.2.
I'll put a band-aid in earlier versions as a separate patch.

(Note that these features still don't work for aggregates, and fixing that
case will be harder since we represent aggregate arg lists as target lists
not bare expression lists.  There's no crash risk though because CREATE
AGGREGATE doesn't accept defaults, and we reject named-argument notation
when parsing an aggregate call.)

2 files changed, 45 insertions, 0 deletions

diff --git a/src/test/regress/expected/window.out b/src/test/regress/expected/window.out
index 752c7b42ff..200f1d2468 100644
--- a/src/test/regress/expected/window.out
+++ b/src/test/regress/expected/window.out
@@ -1022,3 +1022,38 @@ SELECT nth_value(four, 0) OVER (ORDER BY ten), ten, four FROM tenk1;
 ERROR:  argument of nth_value must be greater than zero
 -- cleanup
 DROP TABLE empsalary;
+-- test user-defined window function with named args and default args
+CREATE FUNCTION nth_value_def(val anyelement, n integer = 1) RETURNS anyelement
+  LANGUAGE internal WINDOW IMMUTABLE STRICT AS 'window_nth_value';
+SELECT nth_value_def(n := 2, val := ten) OVER (PARTITION BY four), ten, four
+  FROM (SELECT * FROM tenk1 WHERE unique2 < 10 ORDER BY four, ten) s;
+ nth_value_def | ten | four 
+---------------+-----+------
+             0 |   0 |    0
+             0 |   0 |    0
+             0 |   4 |    0
+             1 |   1 |    1
+             1 |   1 |    1
+             1 |   7 |    1
+             1 |   9 |    1
+               |   0 |    2
+             3 |   1 |    3
+             3 |   3 |    3
+(10 rows)
+
+SELECT nth_value_def(ten) OVER (PARTITION BY four), ten, four
+  FROM (SELECT * FROM tenk1 WHERE unique2 < 10 ORDER BY four, ten) s;
+ nth_value_def | ten | four 
+---------------+-----+------
+             0 |   0 |    0
+             0 |   0 |    0
+             0 |   4 |    0
+             1 |   1 |    1
+             1 |   1 |    1
+             1 |   7 |    1
+             1 |   9 |    1
+             0 |   0 |    2
+             1 |   1 |    3
+             1 |   3 |    3
+(10 rows)
+
diff --git a/src/test/regress/sql/window.sql b/src/test/regress/sql/window.sql
index 769be0fdc6..a97a04c4c2 100644
--- a/src/test/regress/sql/window.sql
+++ b/src/test/regress/sql/window.sql
@@ -266,3 +266,13 @@ SELECT nth_value(four, 0) OVER (ORDER BY ten), ten, four FROM tenk1;
 
 -- cleanup
 DROP TABLE empsalary;
+
+-- test user-defined window function with named args and default args
+CREATE FUNCTION nth_value_def(val anyelement, n integer = 1) RETURNS anyelement
+  LANGUAGE internal WINDOW IMMUTABLE STRICT AS 'window_nth_value';
+
+SELECT nth_value_def(n := 2, val := ten) OVER (PARTITION BY four), ten, four
+  FROM (SELECT * FROM tenk1 WHERE unique2 < 10 ORDER BY four, ten) s;
+
+SELECT nth_value_def(ten) OVER (PARTITION BY four), ten, four
+  FROM (SELECT * FROM tenk1 WHERE unique2 < 10 ORDER BY four, ten) s;