Doc: fix mistaken reference to "PG_ARGNULL_xxx()" macro.

This should of course be just "PG_ARGISNULL()".

Also reorder a couple of paras to make the discussion of PG_ARGISNULL
less disjointed.

Back-patch to v10 where the error was introduced.

Laurenz Albe and Tom Lane, per an anonymous docs comment

Discussion: https://postgr.es/m/158399487096.5708.10696365251766477013@wrigleys.postgresql.org

diff --git a/doc/src/sgml/xfunc.sgml b/doc/src/sgml/xfunc.sgml
index d9afd3be4d038bb6ba6f3f4a2c5ba0b85079ecf5..b5d4b10c725d51c97e6f7ad689a48210ca35fab7 100644 (file)
--- a/doc/src/sgml/xfunc.sgml
+++ b/doc/src/sgml/xfunc.sgml
@@ -2239,9 +2239,9 @@ PG_FUNCTION_INFO_V1(funcname);
     
      In a version-1 function, each actual argument is fetched using a
      PG_GETARG_xxx()
-     macro that corresponds to the argument's data type.  In non-strict
+     macro that corresponds to the argument's data type.  (In non-strict
      functions there needs to be a previous check about argument null-ness
-     using PG_ARGNULL_xxx().
+     using PG_ARGISNULL(); see below.)
      The result is returned using a
      PG_RETURN_xxx()
      macro for the return type.
@@ -2403,14 +2403,6 @@ CREATE FUNCTION concat_text(text, text) RETURNS text
      explicitly, using PG_ARGISNULL().
     
 
-    
-     At first glance, the version-1 coding conventions might appear to be just
-     pointless obscurantism, over using plain C calling
-     conventions.  They do however allow to deal with NULLable
-     arguments/return values, and toasted (compressed or
-     out-of-line) values.
-    
-
     
      The macro PG_ARGISNULL(n)
      allows a function to test whether each input is null.  (Of course, doing
@@ -2425,6 +2417,14 @@ CREATE FUNCTION concat_text(text, text) RETURNS text
      this works in both strict and nonstrict functions.
     
 
+    
+     At first glance, the version-1 coding conventions might appear
+     to be just pointless obscurantism, compared to using
+     plain C calling conventions.  They do however allow
+     us to deal with NULLable arguments/return values,
+     and toasted (compressed or out-of-line) values.
+    
+
     
      Other options provided by the version-1 interface are two
      variants of the