[JVM] Improve debug step behavior around lambdas.

- Add tests to clarify problematic behavior
- Avoid line numbers on return instructions of lambdas without explicit returns

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

@@ -1759,8 +1759,7 @@ public class ExpressionCodegen extends KtVisitor<StackValue, StackValue> impleme
         if (!endsWithReturn(expr)) {
             if (isLambdaVoidBody(expr, typeForExpression)) {
                 markLineNumber((KtFunctionLiteral) expr.getParent(), true);
-            }
+            } else if (!isLambdaBody(expr)){
-            else {
                 markLineNumber(expr, true);
             }
 
@@ -1782,13 +1781,14 @@ public class ExpressionCodegen extends KtVisitor<StackValue, StackValue> impleme
     }
 
     private static boolean isLambdaVoidBody(@NotNull KtElement bodyExpression, @NotNull Type returnType) {
+        return isLambdaBody(bodyExpression) && Type.VOID_TYPE.equals(returnType);
+    }
+
+    private static boolean isLambdaBody(@NotNull KtElement bodyExpression) {
         if (bodyExpression instanceof KtBlockExpression) {
             PsiElement parent = bodyExpression.getParent();
-            if (parent instanceof KtFunctionLiteral) {
+            return parent instanceof KtFunctionLiteral;
-                return Type.VOID_TYPE.equals(returnType);
-            }
         }
-
         return false;
     }
 

compiler/testData/codegen/boxInline/smap/defaultLambda/inlinInDefault2.kt

@@ -133,7 +133,6 @@ test/_1Kt$lParams$1
 71#2,2:12
 30#2:15
 51#3:14
-69#3:16
 *E
 *S KotlinDebug
 *F
@@ -144,5 +143,4 @@ _2Kt
 6#1,2:12
 6#1:15
 6#1:14
-6#1:16
 *E

compiler/testData/debug/stepping/lambdaStepInline.kt

@@ -0,0 +1,23 @@
+
+// FILE: test.kt
+inline fun foo(stringMaker: () -> String): String {
+    return stringMaker()
+}
+
+fun box(): String {
+    foo { "OK "}
+    foo {
+        "OK"
+        // Comment
+    }
+    return "OK"
+}
+
+// LINENUMBERS
+// test.kt:8
+// test.kt:4
+// test.kt:8
+// test.kt:9
+// test.kt:4
+// test.kt:10
+// test.kt:13

compiler/testData/debug/stepping/lambdaStepInlineWithDefaults.kt

@@ -0,0 +1,42 @@
+// IGNORE_BACKEND: JVM_IR
+// FILE: test.kt
+inline fun foo(stringMaker: () -> String = { "OK" }): String {
+    return stringMaker()
+}
+
+inline fun foo2(stringMaker: () -> String = {
+    "OK"
+    // Comment
+}): String {
+    return stringMaker()
+}
+
+fun box(): String {
+    foo()
+    foo2()
+    return "OK"
+}
+
+// The IR Backend does the following:
+// test.kt:15
+// test.kt:3
+// test.kt:4
+// test.kt:3
+// test.kt:3 <---
+// test.kt:16
+// test.kt:7
+// test.kt:11
+// test.kt:8
+// test.kt:7 <---
+// test.kt:17
+
+// LINENUMBERS
+// test.kt:15
+// test.kt:3
+// test.kt:4
+// test.kt:3
+// test.kt:16
+// test.kt:7
+// test.kt:11
+// test.kt:8
+// test.kt:17

compiler/testData/debug/stepping/voidLambdaStepInline.kt

@@ -0,0 +1,16 @@
+
+// FILE: test.kt
+fun box(): String {
+    run { "O" + "K" }
+    run {
+        "O" + "K"
+    }
+    return "OK"
+}
+
+// LINENUMBERS
+// test.kt:4
+// test.kt:5
+// test.kt:6
+// test.kt:5
+// test.kt:8

compiler/tests/org/jetbrains/kotlin/codegen/debugInformation/IrSteppingTestGenerated.java

@@ -91,6 +91,18 @@ public class IrSteppingTestGenerated extends AbstractIrSteppingTest {
         runTest("compiler/testData/debug/stepping/inlineNamedCallableReference.kt");
     }
 
+    @Test
+    @TestMetadata("lambdaStepInline.kt")
+    public void testLambdaStepInline() throws Exception {
+        runTest("compiler/testData/debug/stepping/lambdaStepInline.kt");
+    }
+
+    @Test
+    @TestMetadata("lambdaStepInlineWithDefaults.kt")
+    public void testLambdaStepInlineWithDefaults() throws Exception {
+        runTest("compiler/testData/debug/stepping/lambdaStepInlineWithDefaults.kt");
+    }
+
     @Test
     @TestMetadata("namedCallableReference.kt")
     public void testNamedCallableReference() throws Exception {
@@ -132,4 +144,10 @@ public class IrSteppingTestGenerated extends AbstractIrSteppingTest {
     public void testThrowException() throws Exception {
         runTest("compiler/testData/debug/stepping/throwException.kt");
     }
+
+    @Test
+    @TestMetadata("voidLambdaStepInline.kt")
+    public void testVoidLambdaStepInline() throws Exception {
+        runTest("compiler/testData/debug/stepping/voidLambdaStepInline.kt");
+    }
 }

compiler/tests/org/jetbrains/kotlin/codegen/debugInformation/SteppingTestGenerated.java

@@ -91,6 +91,18 @@ public class SteppingTestGenerated extends AbstractSteppingTest {
         runTest("compiler/testData/debug/stepping/inlineNamedCallableReference.kt");
     }
 
+    @Test
+    @TestMetadata("lambdaStepInline.kt")
+    public void testLambdaStepInline() throws Exception {
+        runTest("compiler/testData/debug/stepping/lambdaStepInline.kt");
+    }
+
+    @Test
+    @TestMetadata("lambdaStepInlineWithDefaults.kt")
+    public void testLambdaStepInlineWithDefaults() throws Exception {
+        runTest("compiler/testData/debug/stepping/lambdaStepInlineWithDefaults.kt");
+    }
+
     @Test
     @TestMetadata("namedCallableReference.kt")
     public void testNamedCallableReference() throws Exception {
@@ -132,4 +144,10 @@ public class SteppingTestGenerated extends AbstractSteppingTest {
     public void testThrowException() throws Exception {
         runTest("compiler/testData/debug/stepping/throwException.kt");
     }
+
+    @Test
+    @TestMetadata("voidLambdaStepInline.kt")
+    public void testVoidLambdaStepInline() throws Exception {
+        runTest("compiler/testData/debug/stepping/voidLambdaStepInline.kt");
+    }
 }