KT-16661 Simplify Strings#split

Do not search for next occurrence if limit is reached.

libraries/stdlib/src/kotlin/text/Strings.kt

@@ -1167,7 +1167,7 @@ public fun CharSequence.split(vararg delimiters: String, ignoreCase: Boolean = f
     if (delimiters.size == 1) {
         val delimiter = delimiters[0]
         if (!delimiter.isEmpty()) {
-            return split(delimiters[0], ignoreCase, limit)
+            return split(delimiter, ignoreCase, limit)
         }
     }
 
@@ -1212,33 +1212,20 @@ private fun CharSequence.split(delimiter: String, ignoreCase: Boolean, limit: In
 
     var currentOffset = 0
     var nextIndex = indexOf(delimiter, currentOffset, ignoreCase)
-    val isLimited = limit > 0
-    // This condition cannot be moved inside of ctor call because it will kill laziness of internal array allocation
-    val result = if (isLimited) ArrayList<String>(limit.coerceAtMost(10)) else ArrayList<String>()
-
-    while (nextIndex != -1) {
-        if (!isLimited || result.size < limit - 1) {
-            result.add(substring(currentOffset, nextIndex))
-            currentOffset = nextIndex + delimiter.length
-            nextIndex = indexOf(delimiter, currentOffset, ignoreCase)
-        } else {
-            result.add(substring(currentOffset, length))
-            currentOffset = length
-            break
-        }
-    }
-
-    if (currentOffset == 0) {
-        // If no matches found return single element list
-        // instead of triggering allocation of underlying array in 'result'
-        // Speedup is ~15% for small string
+    if (nextIndex == -1) {
         return listOf(this.toString())
     }
 
-    if (!isLimited || result.size < limit) {
-        result.add(substring(currentOffset, length))
+    val isLimited = limit > 0
+    val result = ArrayList<String>(if (isLimited) limit.coerceAtMost(10) else 10)
+    while (nextIndex != -1 && (!isLimited || result.size < limit - 1)) {
+        result.add(substring(currentOffset, nextIndex))
+        currentOffset = nextIndex + delimiter.length
+        // Do not search for next occurrence if we're reaching limit
+        nextIndex = if (result.size == limit - 1) break else indexOf(delimiter, currentOffset, ignoreCase)
     }
 
+    result.add(substring(currentOffset, length))
     return result
 }
 

libraries/stdlib/test/text/StringTest.kt

@@ -527,12 +527,16 @@ class StringTest {
         assertEquals(listOf("test"), (+"test").split(*arrayOf<String>()), "empty list of delimiters, none matched -> entire string returned")
 
         assertEquals(listOf("abc", "def", "123;456"), (+"abc;def,123;456").split(';', ',', limit = 3))
+        assertEquals(listOf("abc;def,123;456"), (+"abc;def,123;456").split(';', ',', limit = 1))
 
         assertEquals(listOf("abc", "def", "123", "456"), (+"abc=-def==123=456").split("==", "=-", "="))
 
         assertEquals(listOf("", "a", "b", "c", ""), (+"abc").split(""))
         assertEquals(listOf("", "a", "b", "b", "a", ""), (+"abba").split("", "a"))
         assertEquals(listOf("", "", "b", "b", "", ""), (+"abba").split("a", ""))
+        assertEquals(listOf("", "bb", ""), (+"abba").split("a", "c"))
+        assertEquals(listOf("", "bb", ""), (+"abba").split('a', 'c'))
+
     }
 
     @Test fun splitSingleDelimiter() = withOneCharSequenceArg { arg1 ->
@@ -543,10 +547,21 @@ class StringTest {
         assertEquals(listOf("abc", "def", "123,456"), (+"abc,def,123,456").split(',', limit = 3))
         assertEquals(listOf("abc", "def", "123,456"), (+"abc,def,123,456").split(",", limit = 3))
 
+        assertEquals(listOf("abc", "def", "123,456,789"), (+"abc,def,123,456,789").split(',', limit = 3))
+        assertEquals(listOf("abc", "def", "123,456,789"), (+"abc,def,123,456,789").split(",", limit = 3))
+
+        assertEquals(listOf("abc", "def", "123,456,789,"), (+"abc,def,123,456,789,").split(',', limit = 3))
+        assertEquals(listOf("abc", "def", "123,456,789,"), (+"abc,def,123,456,789,").split(",", limit = 3))
+
+        assertEquals(listOf("abc,def,123,456,789,"), (+"abc,def,123,456,789,").split(',', limit = 1))
+        assertEquals(listOf("abc,def,123,456,789,"), (+"abc,def,123,456,789,").split(",", limit = 1))
+
         assertEquals(listOf("abc", "def", "123", "456"), (+"abc<BR>def<br>123<bR>456").split("<BR>", ignoreCase = true))
         assertEquals(listOf("abc", "def<br>123<bR>456"), (+"abc<BR>def<br>123<bR>456").split("<BR>", ignoreCase = false))
 
         assertEquals(listOf("a", "b", "c"), (+"a*b*c").split("*"))
+        assertEquals(listOf("", "bb", ""), (+"abba").split("a"))
+        assertEquals(listOf("", "bb", ""), (+"abba").split('a'))
     }
 
     @Test fun splitToLines() = withOneCharSequenceArg { arg1 ->