UnreachableCode.getUnreachableTextRanges always returns at least one range #KT-14158 Fixed

compiler/frontend/src/org/jetbrains/kotlin/cfg/UnreachableCode.kt

@@ -42,7 +42,12 @@ class UnreachableCodeImpl(
 
     override fun getUnreachableTextRanges(element: KtElement): List<TextRange> {
         return if (element.hasChildrenInSet(reachableElements)) {
-            element.getLeavesOrReachableChildren().removeReachableElementsWithMeaninglessSiblings().mergeAdjacentTextRanges()
+            with (element.getLeavesOrReachableChildren().removeReachableElementsWithMeaninglessSiblings().mergeAdjacentTextRanges()) {
+                if (isNotEmpty()) this
+                // Specific case like condition in when:
+                // element is dead but its only child is alive and has the same text range
+                else listOf(element.textRange.endOffset.let { TextRange(it, it) })
+            }
         }
         else {
             listOf(element.textRange!!)

compiler/testData/cli/jvm/returnAsWhenKey.args

@@ -0,0 +1,3 @@
+$TESTDATA_DIR$/returnAsWhenKey.kt
+-d
+$TEMP_DIR$

compiler/testData/cli/jvm/returnAsWhenKey.kt

@@ -0,0 +1,7 @@
+// KT-14158: NoSuchElementException while compiling...
+
+fun foo(): Int {
+    when (true) {
+        return 0 -> return 1
+    }
+}

compiler/testData/cli/jvm/returnAsWhenKey.out

@@ -0,0 +1,7 @@
+compiler/testData/cli/jvm/returnAsWhenKey.kt:5:17: warning: unreachable code
+        return 0 -> return 1
+                ^
+compiler/testData/cli/jvm/returnAsWhenKey.kt:5:21: warning: unreachable code
+        return 0 -> return 1
+                    ^
+OK

compiler/testData/diagnostics/tests/controlStructures/kt786.kt

@@ -16,7 +16,7 @@ fun fff(): Int {
     var d = 3
     when(d) {
         4 -> <!UNUSED_EXPRESSION!>21<!>
-        return 2 -> <!UNREACHABLE_CODE!>return 47<!>
+        return 2<!UNREACHABLE_CODE!><!> -> <!UNREACHABLE_CODE!>return 47<!>
         <!UNREACHABLE_CODE!>bar() -> 45<!>
         <!UNREACHABLE_CODE!>444 -> true<!>
     }

compiler/tests/org/jetbrains/kotlin/cli/CliTestGenerated.java

@@ -253,6 +253,12 @@ public class CliTestGenerated extends AbstractCliTest {
             doJvmTest(fileName);
         }
 
+        @TestMetadata("returnAsWhenKey.args")
+        public void testReturnAsWhenKey() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/cli/jvm/returnAsWhenKey.args");
+            doJvmTest(fileName);
+        }
+
         @TestMetadata("sanitized-name.clash.args")
         public void testSanitized_name_clash() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/cli/jvm/sanitized-name.clash.args");