40032: consistency in handling of subscript slices outside the bounds of an array parameter

unposted: README: example describing 40032

ChangeLog

@@ -1,3 +1,10 @@
+2016-11-29  Barton E. Schaefer  <schaefer@brasslantern.com>
+
+	* unposted: README: example describing 40032
+
+	* 40032: Src/params.c: consistency in handling of subscript
+	slices outside the bounds of an array parameter
+
 2016-11-29  Peter Stephenson  <p.stephenson@samsung.com>
 
 	* 40037: Joshua Rubin: Unicode 9 character width support.

README

@@ -121,6 +121,45 @@ Previously, only "typeset" commands were output, never using "-g".
 <Tab> would be accepted to mean [Y].  Now <Space> and <Tab> are invalid
 choices: typing either of them remains at the prompt.
 
+9) The $ary[i,j] subscript syntax to take a slice of an array behaves
+differently when both i and j are larger than the number of elements in
+the array.  When i == j, such a slice always yields an empty array, and
+when i < j it always yields an array of one empty string element.  The
+following example illustrates how this differs from past versions.
+
+     nargs() { print $# }
+     a=(one two)
+     for i in 1 2 3 4; do
+      for j in 1 2 3 4 5; do
+       print -n "$i $j => "
+       nargs "${(@)a[i,j]}"
+      done
+     done
+     
+     5.2       |  5.3 **
+     ----------+----------
+     1 1 => 1  |  1 1 => 1
+     1 2 => 2  |  1 2 => 2
+     1 3 => 2  |  1 3 => 2
+     1 4 => 2  |  1 4 => 2
+     1 5 => 2  |  1 5 => 2
+     2 1 => 0  |  2 1 => 0
+     2 2 => 1  |  2 2 => 1
+     2 3 => 1  |  2 3 => 1
+     2 4 => 1  |  2 4 => 1
+     2 5 => 1  |  2 5 => 1
+     3 1 => 0  |  3 1 => 0
+     3 2 => 0  |  3 2 => 0
+     3 3 => 0  |  3 3 => 0
+     3 4 => 0  |  3 4 => 1   **
+     3 5 => 0  |  3 5 => 1   **
+     4 1 => 0  |  4 1 => 0
+     4 2 => 0  |  4 2 => 0
+     4 3 => 0  |  4 3 => 0
+     4 4 => 1  |  4 4 => 0   **
+     4 5 => 1  |  4 5 => 1
+
+
 Incompatibilities between 5.0.8 and 5.2
 ---------------------------------------
 

Src/params.c

@@ -2299,9 +2299,16 @@ getarrvalue(Value v)
     if (v->end <= v->start) {
 	s = arrdup_max(nular, 0);
     }
-    else if (arrlen_lt(s, v->start) || v->start < 0) {
+    else if (v->start < 0) {
 	s = arrdup_max(nular, 1);
-    } else {
+    }
+    else if (arrlen_le(s, v->start)) {
+	/* Handle $ary[i,i] consistently for any $i > $#ary
+	 * and $ary[i,j] consistently for any $j > $i > $#ary
+	 */
+	s = arrdup_max(nular, v->end - (v->start + 1));
+    }
+    else {
         /* Copy to a point before the end of the source array:
          * arrdup_max will copy at most v->end - v->start elements,
          * starting from v->start element. Original code said: