Generate debug information for 'when' subject variable

NB debugger tests currently don't support language version or individual
language feature settings.

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

@@ -4513,11 +4513,12 @@ The "returned" value of try expression with no finally is either the last expres
 
             int subjectLocal;
             Type subjectType;
+            VariableDescriptor subjectVariableDescriptor = null;
             if (subjectVariable != null) {
-                VariableDescriptor variableDescriptor = bindingContext.get(BindingContext.VARIABLE, subjectVariable);
-                assert variableDescriptor != null : "Unresolved subject variable: " + subjectVariable.getName();
-                subjectType = asmType(variableDescriptor.getType());
-                subjectLocal = myFrameMap.enter(variableDescriptor, subjectType);
+                subjectVariableDescriptor = bindingContext.get(BindingContext.VARIABLE, subjectVariable);
+                assert subjectVariableDescriptor != null : "Unresolved subject variable: " + subjectVariable.getName();
+                subjectType = asmType(subjectVariableDescriptor.getType());
+                subjectLocal = myFrameMap.enter(subjectVariableDescriptor, subjectType);
                 visitProperty(subjectVariable, null);
                 tempVariables.put(subjectExpression, StackValue.local(subjectLocal, subjectType));
             }
@@ -4533,6 +4534,9 @@ The "returned" value of try expression with no finally is either the last expres
                 subjectType = Type.VOID_TYPE;
             }
 
+            Label begin = new Label();
+            v.mark(begin);
+
             Label end = new Label();
             boolean hasElse = KtPsiUtil.checkWhenExpressionHasSingleElse(expression);
 
@@ -4572,7 +4576,16 @@ The "returned" value of try expression with no finally is either the last expres
             markLineNumber(expression, isStatement);
             v.mark(end);
 
-            myFrameMap.leaveTemp(subjectType);
+            if (subjectVariableDescriptor != null) {
+                myFrameMap.leave(subjectVariableDescriptor);
+                v.visitLocalVariable(
+                        subjectVariableDescriptor.getName().asString(), subjectType.getDescriptor(), null,
+                        begin, end, subjectLocal
+                );
+            }
+            else {
+                myFrameMap.leaveTemp(subjectType);
+            }
             tempVariables.remove(subjectExpression);
             return null;
         });

compiler/backend/src/org/jetbrains/kotlin/codegen/when/SwitchCodegen.kt

@@ -8,6 +8,7 @@ package org.jetbrains.kotlin.codegen.`when`
 import org.jetbrains.kotlin.cfg.WhenChecker
 import org.jetbrains.kotlin.codegen.ExpressionCodegen
 import org.jetbrains.kotlin.codegen.StackValue
+import org.jetbrains.kotlin.descriptors.VariableDescriptor
 import org.jetbrains.kotlin.psi.KtWhenExpression
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.constants.ConstantValue
@@ -69,6 +70,9 @@ abstract class SwitchCodegen(
         generateSubjectValue()
         generateSubjectValueToIndex()
 
+        val beginLabel = Label()
+        v.mark(beginLabel)
+
         generateSwitchInstructionByTransitionsTable()
 
         generateEntries()
@@ -81,6 +85,13 @@ abstract class SwitchCodegen(
 
         codegen.markLineNumber(expression, isStatement)
         v.mark(endLabel)
+
+        subjectVariableDescriptor?.let {
+            v.visitLocalVariable(
+                it.name.asString(), subjectType.descriptor, null,
+                beginLabel, endLabel, subjectLocal
+            )
+        }
     }
 
     /**
@@ -115,19 +126,23 @@ abstract class SwitchCodegen(
         }
     }
 
+    private var subjectVariableDescriptor: VariableDescriptor? = null
+
     /**
      * Generates subject value on top of the stack.
      * If the subject is a variable, it's stored and loaded.
      */
     private fun generateSubjectValue() {
         if (subjectVariable != null) {
-            val variableDescriptor = bindingContext[BindingContext.VARIABLE, subjectVariable]
+            val mySubjectVariable = bindingContext[BindingContext.VARIABLE, subjectVariable]
                     ?: throw AssertionError("Unresolved subject variable: $expression")
-            subjectLocal = codegen.frameMap.enter(variableDescriptor, subjectType)
+            subjectLocal = codegen.frameMap.enter(mySubjectVariable, subjectType)
             codegen.visitProperty(subjectVariable, null)
             StackValue.local(subjectLocal, subjectType).put(subjectType, codegen.v)
+            subjectVariableDescriptor = mySubjectVariable
         } else {
             codegen.gen(subjectExpression, subjectType)
+            subjectVariableDescriptor = null
         }
     }
 

compiler/testData/codegen/bytecodeText/when/subjectValHasLocalVariableSlot.kt

@@ -0,0 +1,10 @@
+// !LANGUAGE: +VariableDeclarationInWhenSubject
+
+fun test(a: Any) =
+    when (val subject = a) {
+        is Int -> "Int $subject"
+        is String -> "String ${subject.length}"
+        else -> "other"
+    }
+
+// 1 LOCALVARIABLE subject Ljava/lang/Object;

compiler/testData/codegen/bytecodeText/when/subjectValInEnumWhenHasLocalVariableSlot.kt

@@ -0,0 +1,12 @@
+// !LANGUAGE: +VariableDeclarationInWhenSubject
+
+enum class X { A, B, C }
+
+fun test(a: X) =
+    when (val subject = a) {
+        X.A -> 0
+        X.B -> 1
+        X.C -> 2
+    }
+
+// 1 LOCALVARIABLE subject

compiler/testData/codegen/bytecodeText/when/subjectValInIntWhenHasLocalVariableSlot.kt

@@ -0,0 +1,11 @@
+// !LANGUAGE: +VariableDeclarationInWhenSubject
+
+fun test(a: Int) =
+    when (val subject = a) {
+        1 -> 0
+        2 -> 1
+        3 -> 2
+        else -> -1
+    }
+
+// 1 LOCALVARIABLE subject

compiler/testData/codegen/bytecodeText/when/subjectValInStringWhenHasLocalVariableSlot.kt

@@ -0,0 +1,10 @@
+// !LANGUAGE: +VariableDeclarationInWhenSubject
+
+fun test(a: String) =
+    when (val subject = a) {
+        "" -> 0
+        "a" -> 1
+        else -> -1
+    }
+
+// 1 LOCALVARIABLE subject

compiler/tests/org/jetbrains/kotlin/codegen/BytecodeTextTestGenerated.java

@@ -2811,6 +2811,26 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             runTest("compiler/testData/codegen/bytecodeText/when/simpleConstValsInsideWhen.kt");
         }
 
+        @TestMetadata("subjectValHasLocalVariableSlot.kt")
+        public void testSubjectValHasLocalVariableSlot() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/when/subjectValHasLocalVariableSlot.kt");
+        }
+
+        @TestMetadata("subjectValInEnumWhenHasLocalVariableSlot.kt")
+        public void testSubjectValInEnumWhenHasLocalVariableSlot() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/when/subjectValInEnumWhenHasLocalVariableSlot.kt");
+        }
+
+        @TestMetadata("subjectValInIntWhenHasLocalVariableSlot.kt")
+        public void testSubjectValInIntWhenHasLocalVariableSlot() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/when/subjectValInIntWhenHasLocalVariableSlot.kt");
+        }
+
+        @TestMetadata("subjectValInStringWhenHasLocalVariableSlot.kt")
+        public void testSubjectValInStringWhenHasLocalVariableSlot() throws Exception {
+            runTest("compiler/testData/codegen/bytecodeText/when/subjectValInStringWhenHasLocalVariableSlot.kt");
+        }
+
         @TestMetadata("whenNull.kt")
         public void testWhenNull() throws Exception {
             runTest("compiler/testData/codegen/bytecodeText/when/whenNull.kt");