FIX: split/at when the delimiter is not found

resolves: Oldes/Rebol-issues#2490

Author: Oldes

src/mezz/mezz-series.reb

@@ -504,22 +504,21 @@ split: function [
 		return res
 	]
 	if at [
-		return reduce either integer? dlm [
-			[
-				copy/part series dlm
-				copy lib/at series dlm + 1
-			]
-		][
-			;-- Without adding a /tail refinement, we don't know if they want
-			;	to split at the head or tail of the delimiter, so we'll exclude
-			;	the delimiter from the result entirely. They know what the dlm
-			;	was that they passed in, so they can add it back to either side
-			;	of the result if they want to.
-			[
-				copy/part series find series :dlm
-				copy find/tail series :dlm
+		unless integer? :dlm [
+			return reduce either dlm: find series :dlm [
+				dlm: index? dlm
+				[
+					copy/part   series dlm - 1 ; excluding the delimiter
+					copy lib/at series dlm + 1
+				]
+			][
+				[copy series]
 			]
 		]
+		return reduce [
+			copy/part   series dlm
+			copy lib/at series dlm + 1
+		]
 	]
 	;print ['split 'parts? parts mold series mold dlm]
 	either all [block? dlm  parse dlm [some integer!]][

src/tests/units/series-test.r3

@@ -2004,6 +2004,19 @@ Rebol [
 	;@@ https://github.com/Oldes/Rebol-issues/issues/690
 	--assert (split "This! is a. test? to see " charset "!?.") = ["This" " is a" " test" " to see "]
 
+--test-- "split/at"
+	;@@ https://github.com/Oldes/Rebol-issues/issues/2490
+	--assert (split/at "a:b"   #":") = ["a" "b"]
+	--assert (split/at "a:b:c" #":") = ["a" "b:c"]
+	--assert (split/at "a"     #":") = ["a"]
+	--assert (split/at "a:"    #":") = ["a" ""]
+	--assert (split/at ":b"    #":") = ["" "b"]
+	--assert (split/at [1 a 2]     'a) = [[1] [2]]
+	--assert (split/at [1 a 2 3]   'a) = [[1] [2 3]]
+	--assert (split/at [1 a 2 a 3] 'a) = [[1] [2 a 3]]
+	--assert (split/at [1 2]       'a) = [[1 2]]
+
+
 ===end-group===