[NI] Fix coercion to Unit for lambdas with empty labeled return

compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionToUnitForIfAsLastExpressionInLambda.kt

@@ -0,0 +1,42 @@
+// !LANGUAGE: +NewInference
+
+class Obj
+
+fun foo(): String? {
+    run {
+        if (true) return@run
+
+        if (true) Obj()
+    }
+
+    run {
+        if (true) return@run
+
+        if (true) return <!TYPE_MISMATCH, TYPE_MISMATCH!>Obj()<!> // correct error, type check against return type of function "foo"
+    }
+
+    run {
+        if (true)
+            return@run
+        else
+            if (true) <!UNUSED_EXPRESSION!>42<!>
+    }
+
+    run {
+        if (true)
+            42
+        else
+            <!INVALID_IF_AS_EXPRESSION!>if<!> (true) 42
+    }
+
+    run {
+        if (true) return@run
+
+        if (true) {
+            Obj()
+        } else
+            if (true) return null
+    }
+
+    return ""
+}

compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionToUnitForIfAsLastExpressionInLambda.txt

@@ -0,0 +1,10 @@
+package
+
+public fun foo(): kotlin.String?
+
+public final class Obj {
+    public constructor Obj()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}

compiler/testData/diagnostics/tests/inference/coercionToUnit/nonPropagationOfCoercionToUnitInsideNestedLambda.kt

@@ -0,0 +1,52 @@
+// !LANGUAGE: +NewInference
+
+class Obj
+
+fun foo(): String? {
+    run {
+        if (true) return@run
+
+        run {
+            if (true) {
+                Obj()
+            } else
+                <!INVALID_IF_AS_EXPRESSION!>if<!> (true) return null // Error, coercion to Unit doesn't propagate inside nested lambdas
+        }
+
+        if (true) {
+            Obj()
+        } else
+            if (true) return null // OK, no error
+    }
+
+    run {
+        if (true) return@run
+
+        run {
+            if (true) {
+                Obj()
+            } else
+            <!INVALID_IF_AS_EXPRESSION!>if<!> (true) return null // Error, coercion to Unit doesn't propagate inside nested lambdas
+        }
+    }
+
+    run {
+        if (true) return@run
+
+        run nestedRun@{
+            if (true) return@nestedRun
+
+            if (true) {
+                Obj()
+            } else
+                if (true) return null // OK, additional empty labeled return helps
+        }
+
+        if (true) {
+            Obj()
+        } else
+            if (true) return null // OK, no error
+    }
+
+    return ""
+}

compiler/testData/diagnostics/tests/inference/coercionToUnit/nonPropagationOfCoercionToUnitInsideNestedLambda.txt

@@ -0,0 +1,10 @@
+package
+
+public fun foo(): kotlin.String?
+
+public final class Obj {
+    public constructor Obj()
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}