Back-end JVM: more accurate handling of when expressions with Unit result #KT-12192 Fixed

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

@@ -65,6 +65,7 @@ import org.jetbrains.kotlin.resolve.BindingContextUtils;
 import org.jetbrains.kotlin.resolve.DescriptorToSourceUtils;
 import org.jetbrains.kotlin.resolve.DescriptorUtils;
 import org.jetbrains.kotlin.resolve.annotations.AnnotationUtilKt;
+import org.jetbrains.kotlin.resolve.bindingContextUtil.BindingContextUtilsKt;
 import org.jetbrains.kotlin.resolve.calls.callResolverUtil.CallResolverUtilKt;
 import org.jetbrains.kotlin.resolve.calls.callUtil.CallUtilKt;
 import org.jetbrains.kotlin.resolve.calls.model.*;
@@ -4044,9 +4045,12 @@ The "returned" value of try expression with no finally is either the last expres
     }
 
     private boolean isExhaustive(@NotNull KtWhenExpression whenExpression, boolean isStatement) {
-        boolean exhaustive = Boolean.TRUE.equals(bindingContext.get(BindingContext.EXHAUSTIVE_WHEN, whenExpression));
-        return isStatement ? exhaustive || Boolean.TRUE.equals(bindingContext.get(BindingContext.IMPLICIT_EXHAUSTIVE_WHEN, whenExpression))
-                           : exhaustive;
+        if (isStatement && !BindingContextUtilsKt.isUsedAsExpression(whenExpression, bindingContext)) {
+            return Boolean.TRUE.equals(bindingContext.get(BindingContext.IMPLICIT_EXHAUSTIVE_WHEN, whenExpression));
+        }
+        else {
+            return Boolean.TRUE.equals(bindingContext.get(BindingContext.EXHAUSTIVE_WHEN, whenExpression));
+        }
     }
 
     public void putUnitInstanceOntoStackForNonExhaustiveWhen(

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

@@ -0,0 +1,18 @@
+enum class AccessMode { READ, WRITE, EXECUTE }
+
+fun whenExpr(access: AccessMode) {
+    when (access) {
+        AccessMode.READ -> {}
+        AccessMode.WRITE -> {}
+        AccessMode.EXECUTE -> {}
+    }
+}
+
+fun box(): String {
+    whenExpr(AccessMode.EXECUTE)
+    return "OK"
+}
+
+// 1 TABLESWITCH
+// 0 LOOKUPSWITCH
+// 0 ATHROW

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

@@ -1300,6 +1300,12 @@ public class BytecodeTextTestGenerated extends AbstractBytecodeTextTest {
             doTest(fileName);
         }
 
+        @TestMetadata("exhaustiveWhenUnitStatement.kt")
+        public void testExhaustiveWhenUnitStatement() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/when/exhaustiveWhenUnitStatement.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("integralWhenWithNoInlinedConstants.kt")
         public void testIntegralWhenWithNoInlinedConstants() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/codegen/bytecodeText/when/integralWhenWithNoInlinedConstants.kt");