[Wasm] Fix transforming setField in an inline class constructor body

IrSetField was transformed to its value to preserve side effects
This transformation produced invalid IR in cases where
IrSetField used in Unit-returning expression context.

This commit fixes it by producing Unit-typed expression

^KT-59084 Fixed

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/InlineClassDeclarationLowering.kt

@@ -9,6 +9,7 @@ import org.jetbrains.kotlin.backend.common.BodyLoweringPass
 import org.jetbrains.kotlin.backend.common.CommonBackendContext
 import org.jetbrains.kotlin.backend.common.DeclarationTransformer
 import org.jetbrains.kotlin.backend.common.getOrPut
+import org.jetbrains.kotlin.backend.common.ir.isPure
 import org.jetbrains.kotlin.ir.IrStatement
 import org.jetbrains.kotlin.ir.UNDEFINED_OFFSET
 import org.jetbrains.kotlin.ir.builders.*
@@ -105,7 +106,15 @@ class InlineClassLowering(val context: CommonBackendContext) {
                                     }
                                     expression.transformChildrenVoid()
                                     if (isMemberFieldSet) {
-                                        return expression.value
+                                        return builder.irBlock {
+                                            if (!expression.value.isPure(true)) {
+                                                // Preserving side effects
+                                                +expression.value
+                                                // Adding empty block to provide Unit value.
+                                                // This is useful when original IrSetField is the last statement in a Unit-returning block.
+                                                +builder.irBlock {}
+                                            }
+                                        }
                                     }
                                     return expression
                                 }

compiler/testData/codegen/boxWasmJsInterop/kt59084.kt

@@ -0,0 +1,18 @@
+// TARGET_BACKEND: WASM
+
+inline class JsDynamic(val value: JsAny?)
+
+val JsAny?.jsDyn: JsDynamic get() = JsDynamic(this)
+
+fun test(): Boolean {
+    val jsDynamic: JsAny? = 1.toJsNumber()
+    val jsDyn = jsDynamic.jsDyn
+    return jsDyn.value == jsDynamic
+}
+
+fun box(): String {
+    if (!test()) {
+        return "Fail"
+    }
+    return "OK"
+}

wasm/wasm.tests/tests-gen/org/jetbrains/kotlin/wasm/test/FirWasmCodegenWasmJsInteropTestGenerated.java

@@ -121,6 +121,12 @@ public class FirWasmCodegenWasmJsInteropTestGenerated extends AbstractFirWasmCod
         runTest("compiler/testData/codegen/boxWasmJsInterop/kt59082.kt");
     }
 
+    @Test
+    @TestMetadata("kt59084.kt")
+    public void testKt59084() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/kt59084.kt");
+    }
+
     @Test
     @TestMetadata("lambdaAdapterNameClash.kt")
     public void testLambdaAdapterNameClash() throws Exception {

wasm/wasm.tests/tests-gen/org/jetbrains/kotlin/wasm/test/K1WasmCodegenWasmJsInteropTestGenerated.java

@@ -121,6 +121,12 @@ public class K1WasmCodegenWasmJsInteropTestGenerated extends AbstractK1WasmCodeg
         runTest("compiler/testData/codegen/boxWasmJsInterop/kt59082.kt");
     }
 
+    @Test
+    @TestMetadata("kt59084.kt")
+    public void testKt59084() throws Exception {
+        runTest("compiler/testData/codegen/boxWasmJsInterop/kt59084.kt");
+    }
+
     @Test
     @TestMetadata("lambdaAdapterNameClash.kt")
     public void testLambdaAdapterNameClash() throws Exception {