Debugger: Fix missing NOP in empty 'when' header (KT-29189)

compiler/backend/src/org/jetbrains/kotlin/codegen/ExpressionCodegen.java

@@ -4856,6 +4856,10 @@ The "returned" value of try expression with no finally is either the last expres
             KtProperty subjectVariable = expression.getSubjectVariable();
             KtExpression subjectExpression = expression.getSubjectExpression();
 
+            if (subjectVariable == null && subjectExpression == null) {
+                v.nop();
+            }
+
             SwitchCodegen switchCodegen = switchCodegenProvider.buildAppropriateSwitchCodegenIfPossible(
                     expression, isStatement, CodegenUtil.isExhaustive(bindingContext, expression, isStatement)
             );

compiler/testData/lineNumber/custom/when.kt

@@ -12,4 +12,4 @@ fun foo(x: Int) {
     }
 }
 
-// 2 +3 4 5 6 +8 +9 10 11 8 13
+// 2 3 4 5 6 +8 9 10 11 8 13

idea/testData/debugger/tinyApp/src/stepping/stepOver/stepOverWhenWithInline.kt

@@ -86,4 +86,4 @@ inline fun foo(f: () -> Int): Int {
 
 fun test(i: Int) = i
 
-// STEP_OVER: 30
+// STEP_OVER: 32

idea/testData/debugger/tinyApp/src/stepping/stepOver/stepOverWhenWithInline.out

@@ -2,13 +2,16 @@ LineBreakpoint created at stepOverWhenWithInline.kt:5
 Run Java
 Connected to the target VM
 stepOverWhenWithInline.kt:5
+stepOverWhenWithInline.kt:7
 stepOverWhenWithInline.kt:8
 stepOverWhenWithInline.kt:9
 stepOverWhenWithInline.kt:7
+stepOverWhenWithInline.kt:13
 stepOverWhenWithInline.kt:14
 stepOverWhenWithInline.kt:17
 stepOverWhenWithInline.kt:18
 stepOverWhenWithInline.kt:13
+stepOverWhenWithInline.kt:25
 stepOverWhenWithInline.kt:26
 stepOverWhenWithInline.kt:27
 stepOverWhenWithInline.kt:25
@@ -21,14 +24,16 @@ stepOverWhenWithInline.kt:38
 stepOverWhenWithInline.kt:51
 stepOverWhenWithInline.kt:52
 stepOverWhenWithInline.kt:51
+stepOverWhenWithInline.kt:57
 stepOverWhenWithInline.kt:58
 stepOverWhenWithInline.kt:57
+stepOverWhenWithInline.kt:63
 stepOverWhenWithInline.kt:64
 stepOverWhenWithInline.kt:65
 stepOverWhenWithInline.kt:63
+stepOverWhenWithInline.kt:75
 stepOverWhenWithInline.kt:76
 stepOverWhenWithInline.kt:75
-stepOverWhenWithInline.kt:80
 Disconnected from the target VM
 
 Process finished with exit code 0

idea/testData/debugger/tinyApp/src/stepping/stepOver/whenWithoutExpression.kt

@@ -0,0 +1,19 @@
+package whenWithoutExpression
+
+fun test(a: String): String {
+    val b = a.toLowerCase()
+    //Breakpoint!
+    return when {
+        b.startsWith("a") -> "A"
+        b.startsWith("b") -> "B"
+        b.startsWith("c") -> "C"
+        else -> "other"
+    }
+}
+
+fun main() {
+    test("abcd")
+}
+
+// STEP_OVER: 4
+// PRINT_FRAME

idea/testData/debugger/tinyApp/src/stepping/stepOver/whenWithoutExpression.out

@@ -0,0 +1,11 @@
+LineBreakpoint created at whenWithoutExpression.kt:6
+Run Java
+Connected to the target VM
+whenWithoutExpression.kt:6
+whenWithoutExpression.kt:7
+whenWithoutExpression.kt:6
+whenWithoutExpression.kt:15
+whenWithoutExpression.kt:16
+Disconnected from the target VM
+
+Process finished with exit code 0

idea/tests/org/jetbrains/kotlin/idea/debugger/KotlinSteppingTestGenerated.java

@@ -922,6 +922,11 @@ public class KotlinSteppingTestGenerated extends AbstractKotlinSteppingTest {
         public void testStopInlineCallInLocalFunInSecondaryConstructor() throws Exception {
             runTest("idea/testData/debugger/tinyApp/src/stepping/stepOver/stopInlineCallInLocalFunInSecondaryConstructor.kt");
         }
+
+        @TestMetadata("whenWithoutExpression.kt")
+        public void testWhenWithoutExpression() throws Exception {
+            runTest("idea/testData/debugger/tinyApp/src/stepping/stepOver/whenWithoutExpression.kt");
+        }
     }
 
     @TestMetadata("idea/testData/debugger/tinyApp/src/stepping/stepOverForce")