Take control flow into account for checking fall-through switch branches

#KT-16133 Fixed

j2k/src/org/jetbrains/kotlin/j2k/SwitchConverter.kt

@@ -17,8 +17,13 @@
 package org.jetbrains.kotlin.j2k
 
 import com.intellij.psi.*
+import com.intellij.psi.controlFlow.ControlFlowFactory
+import com.intellij.psi.controlFlow.ControlFlowUtil
 import org.jetbrains.kotlin.j2k.ast.*
 import java.util.*
+import com.intellij.psi.controlFlow.LocalsOrMyInstanceFieldsControlFlowPolicy
+
+
 
 class SwitchConverter(private val codeConverter: CodeConverter) {
     fun convert(statement: PsiSwitchStatement): WhenStatement
@@ -95,7 +100,7 @@ class SwitchConverter(private val codeConverter: CodeConverter) {
         else {
             val block = case.statements.singleOrNull() as? PsiBlockStatement
             val statements = block?.codeBlock?.statements?.toList() ?: case.statements
-            !statements.any { it is PsiBreakStatement || it is PsiContinueStatement || it is PsiReturnStatement || it is PsiThrowStatement }
+            statements.fallsThrough()
         }
         return if (fallsThrough) // we fall through into the next case
             convertCaseStatements(case.statements, allowBlock = false) + convertCaseStatements(cases, caseIndex + 1, allowBlock = false)
@@ -112,4 +117,25 @@ class SwitchConverter(private val codeConverter: CodeConverter) {
     }
 
     private fun isSwitchBreak(statement: PsiStatement) = statement is PsiBreakStatement && statement.labelIdentifier == null
+
+    private fun List<PsiStatement>.fallsThrough(): Boolean {
+        for (statement in this) {
+            when (statement) {
+                is PsiBreakStatement -> return false
+                is PsiContinueStatement -> return false
+                is PsiReturnStatement -> return false
+                is PsiThrowStatement -> return false
+                is PsiSwitchStatement -> if (!statement.canCompleteNormally()) return false
+                is PsiIfStatement -> if (!statement.canCompleteNormally()) return false
+            }
+        }
+        return true
+    }
+
+    private fun PsiElement.canCompleteNormally(): Boolean {
+        val controlFlow = ControlFlowFactory.getInstance(project).getControlFlow(this, LocalsOrMyInstanceFieldsControlFlowPolicy.getInstance())
+        val startOffset = controlFlow.getStartOffset(this)
+        val endOffset = controlFlow.getEndOffset(this)
+        return startOffset == -1 || endOffset == -1 || ControlFlowUtil.canCompleteNormally(controlFlow, startOffset, endOffset)
+    }
 }

j2k/testData/fileOrElement/switch/nestedIf.java

@@ -0,0 +1,15 @@
+//method
+public String foo(int i, int j) {
+    switch (i) {
+        case 0:
+            if (j > 0) {
+                return "1"
+            } else{
+                return "2"
+            }
+        case 1:
+            return "3";
+        default:
+            return "4";
+    }
+}

j2k/testData/fileOrElement/switch/nestedIf.kt

@@ -0,0 +1,11 @@
+fun foo(i: Int, j: Int): String {
+    when (i) {
+        0 -> if (j > 0) {
+            return "1"
+        } else {
+            return "2"
+        }
+        1 -> return "3"
+        else -> return "4"
+    }
+}

j2k/testData/fileOrElement/switch/nestedIfFallback.java

@@ -0,0 +1,13 @@
+//method
+public String foo(int i, int j) {
+    switch (i) {
+        case 0:
+            if (j > 0) {
+                return "1"
+            }
+        case 1:
+            return "2";
+        default:
+            return "3";
+    }
+}

j2k/testData/fileOrElement/switch/nestedIfFallback.kt

@@ -0,0 +1,12 @@
+fun foo(i: Int, j: Int): String {
+    when (i) {
+        0 -> {
+            if (j > 0) {
+                return "1"
+            }
+            return "2"
+        }
+        1 -> return "2"
+        else -> return "3"
+    }
+}

j2k/testData/fileOrElement/switch/nestedSwitch.java

@@ -0,0 +1,16 @@
+//method
+public String foo(int i, int j) {
+    switch (i) {
+        case 0:
+            switch (j) {
+                case 1:
+                    return "0, 1";
+                default:
+                    return "0, x";
+            }
+        case 1:
+            return "1, x";
+        default:
+            return "x, x";
+    }
+}

j2k/testData/fileOrElement/switch/nestedSwitch.kt

@@ -0,0 +1,10 @@
+fun foo(i: Int, j: Int): String {
+    when (i) {
+        0 -> when (j) {
+            1 -> return "0, 1"
+            else -> return "0, x"
+        }
+        1 -> return "1, x"
+        else -> return "x, x"
+    }
+}

j2k/testData/fileOrElement/switch/nestedSwitchFallback.java

@@ -0,0 +1,15 @@
+//method
+public String foo(int i, int j) {
+    switch (i) {
+        case 0:
+            switch (j) {
+                case 1:
+                    return "0, 1";
+                case 2:
+                    return "0, 2";
+            }
+        case 1:
+            return "1, x";
+        default:
+            return "x, x";
+}

j2k/testData/fileOrElement/switch/nestedSwitchFallback.kt

@@ -0,0 +1,13 @@
+fun foo(i: Int, j: Int): String {
+    when (i) {
+        0 -> {
+            when (j) {
+                1 -> return "0, 1"
+                2 -> return "0, 2"
+            }
+            return "1, x"
+        }
+        1 -> return "1, x"
+        else -> return "x, x"
+    }
+}

j2k/tests/org/jetbrains/kotlin/j2k/JavaToKotlinConverterForWebDemoTestGenerated.java

@@ -4538,6 +4538,30 @@ public class JavaToKotlinConverterForWebDemoTestGenerated extends AbstractJavaTo
             doTest(fileName);
         }
 
+        @TestMetadata("nestedIf.java")
+        public void testNestedIf() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nestedIf.java");
+            doTest(fileName);
+        }
+
+        @TestMetadata("nestedIfFallback.java")
+        public void testNestedIfFallback() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nestedIfFallback.java");
+            doTest(fileName);
+        }
+
+        @TestMetadata("nestedSwitch.java")
+        public void testNestedSwitch() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nestedSwitch.java");
+            doTest(fileName);
+        }
+
+        @TestMetadata("nestedSwitchFallback.java")
+        public void testNestedSwitchFallback() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nestedSwitchFallback.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("nondefault.java")
         public void testNondefault() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nondefault.java");

j2k/tests/org/jetbrains/kotlin/j2k/JavaToKotlinConverterSingleFileTestGenerated.java

@@ -4538,6 +4538,30 @@ public class JavaToKotlinConverterSingleFileTestGenerated extends AbstractJavaTo
             doTest(fileName);
         }
 
+        @TestMetadata("nestedIf.java")
+        public void testNestedIf() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nestedIf.java");
+            doTest(fileName);
+        }
+
+        @TestMetadata("nestedIfFallback.java")
+        public void testNestedIfFallback() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nestedIfFallback.java");
+            doTest(fileName);
+        }
+
+        @TestMetadata("nestedSwitch.java")
+        public void testNestedSwitch() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nestedSwitch.java");
+            doTest(fileName);
+        }
+
+        @TestMetadata("nestedSwitchFallback.java")
+        public void testNestedSwitchFallback() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nestedSwitchFallback.java");
+            doTest(fileName);
+        }
+
         @TestMetadata("nondefault.java")
         public void testNondefault() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("j2k/testData/fileOrElement/switch/nondefault.java");