Fail fast in Regex.findAll on an invalid startIndex #KT-28356

libraries/stdlib/js/src/kotlin/text/regex.kt

@@ -77,11 +77,17 @@ public actual class Regex actual constructor(pattern: String, options: Set<Regex
     /**
      * Returns a sequence of all occurrences of a regular expression within the [input] string, beginning at the specified [startIndex].
      *
+     * @throws IndexOutOfBoundsException if [startIndex] is less than zero or greater than the length of the [input] char sequence.
+     *
      * @sample samples.text.Regexps.findAll
      */
     @Suppress("ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS")
-    public actual fun findAll(input: CharSequence, startIndex: Int = 0): Sequence<MatchResult> =
-        generateSequence({ find(input, startIndex) }, { match -> match.next() })
+    public actual fun findAll(input: CharSequence, startIndex: Int = 0): Sequence<MatchResult> {
+        if (startIndex < 0 || startIndex > input.length) {
+            throw IndexOutOfBoundsException("Start index out of bounds: $startIndex, input length: ${input.length}")
+        }
+        return generateSequence({ find(input, startIndex) }, { match -> match.next() })
+    }
 
     /**
      * Attempts to match the entire [input] CharSequence against the pattern.

libraries/stdlib/jvm/src/kotlin/text/regex/Regex.kt

@@ -122,11 +122,17 @@ internal constructor(private val nativePattern: Pattern) : Serializable {
     /**
      * Returns a sequence of all occurrences of a regular expression within the [input] string, beginning at the specified [startIndex].
      *
+     * @throws IndexOutOfBoundsException if [startIndex] is less than zero or greater than the length of the [input] char sequence.
+     *
      * @sample samples.text.Regexps.findAll
      */
     @Suppress("ACTUAL_FUNCTION_WITH_DEFAULT_ARGUMENTS")
-    public actual fun findAll(input: CharSequence, startIndex: Int = 0): Sequence<MatchResult> =
-        generateSequence({ find(input, startIndex) }, MatchResult::next)
+    public actual fun findAll(input: CharSequence, startIndex: Int = 0): Sequence<MatchResult> {
+        if (startIndex < 0 || startIndex > input.length) {
+            throw IndexOutOfBoundsException("Start index out of bounds: $startIndex, input length: ${input.length}")
+        }
+        return generateSequence({ find(input, startIndex) }, MatchResult::next)
+    }
 
     /**
      * Attempts to match the entire [input] CharSequence against the pattern.

libraries/stdlib/test/text/RegexTest.kt

@@ -67,6 +67,10 @@ class RegexTest {
         assertEquals(expected.drop(1), pattern.findAll(input, startIndex = 3).map { it.value }.toList())
 
         assertEquals(listOf(0..2, 4..6, 8..10), matches.map { it.range }.toList())
+
+        assertFailsWith<IndexOutOfBoundsException> { pattern.findAll(input, -1) }
+        assertFailsWith<IndexOutOfBoundsException> { pattern.findAll(input, input.length + 1) }
+        assertEquals(emptyList(), pattern.findAll(input, input.length).toList())
     }
 
     @Test fun matchAllSequence() {
@@ -76,6 +80,8 @@ class RegexTest {
         assertEquals(input, matches[0].value)
         assertEquals(input, matches.joinToString("") { it.value })
         assertEquals(2, matches.size)
+
+        assertEquals("", pattern.findAll(input, input.length).single().value)
     }
 
     @Test fun matchGroups() {