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.)

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/src/sgml/syntax.sgml b/doc/src/sgml/syntax.sgml
index 8d8a1e91fc3..bf740e05205 100644
--- a/doc/src/sgml/syntax.sgml
+++ b/doc/src/sgml/syntax.sgml
@@ -2464,6 +2464,14 @@ 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 currently cannot be used when calling an
+     aggregate function (but they do work when an aggregate function is used
+     as a window function).
+    </para>
+   </note>
   </sect2>
  </sect1>