Convert to expression body: take nested whens into account

idea/testData/intentions/convertToExpressionBody/elvisWhenUnitNonExhaustive.kt

@@ -0,0 +1,9 @@
+// IS_APPLICABLE: false
+enum class AccessMode { READ, WRITE, RW }
+fun whenExpr(access: AccessMode) {
+    <caret>println("result") ?: when (access) {
+        AccessMode.READ -> println("read")
+        AccessMode.WRITE -> println("write")
+    }
+}
+fun println(s: String) {}

idea/testData/intentions/convertToExpressionBody/ifWhenUnitExhaustive.kt

@@ -0,0 +1,19 @@
+// IS_APPLICABLE: true
+enum class AccessMode { READ, WRITE, RW }
+fun whenExpr(mode: Boolean, access: AccessMode) {
+    <caret>if (mode) {
+        when (access) {
+            AccessMode.READ -> println("read")
+            AccessMode.WRITE -> println("write")
+            AccessMode.RW -> println("both")
+        }
+    }
+    else {
+        when (access) {
+            AccessMode.READ -> println("noread")
+            AccessMode.WRITE -> println("nowrite")
+            AccessMode.RW -> println("no both")
+        }
+    }
+}
+fun println(s: String) {}

idea/testData/intentions/convertToExpressionBody/ifWhenUnitExhaustive.kt.after

@@ -0,0 +1,17 @@
+// IS_APPLICABLE: true
+enum class AccessMode { READ, WRITE, RW }
+fun whenExpr(mode: Boolean, access: AccessMode) = if (mode) {
+    when (access) {
+        AccessMode.READ -> println("read")
+        AccessMode.WRITE -> println("write")
+        AccessMode.RW -> println("both")
+    }
+}
+else {
+    when (access) {
+        AccessMode.READ -> println("noread")
+        AccessMode.WRITE -> println("nowrite")
+        AccessMode.RW -> println("no both")
+    }
+}
+fun println(s: String) {}

idea/testData/intentions/convertToExpressionBody/ifWhenUnitNonExhaustive.kt

@@ -0,0 +1,18 @@
+// IS_APPLICABLE: false
+enum class AccessMode { READ, WRITE, RW }
+fun whenExpr(mode: Boolean, access: AccessMode) {
+    <caret>if (mode) {
+        when (access) {
+            AccessMode.READ -> println("read")
+            AccessMode.WRITE -> println("write")
+        }
+    }
+    else {
+        when (access) {
+            AccessMode.READ -> println("noread")
+            AccessMode.WRITE -> println("nowrite")
+            AccessMode.RW -> println("no both")
+        }
+    }
+}
+fun println(s: String) {}

idea/testData/intentions/convertToExpressionBody/lambdaWhenUnitNonExhaustive.kt

@@ -0,0 +1,13 @@
+// IS_APPLICABLE: true
+enum class AccessMode { READ, WRITE, RW }
+fun <T> run(f: () -> T) = f()
+fun whenExpr(access: AccessMode) {
+    <caret>run {
+        println("run")
+        when (access) {
+            AccessMode.READ -> println("read")
+            AccessMode.WRITE -> println("write")
+        }
+    }
+}
+fun println(s: String) {}

idea/testData/intentions/convertToExpressionBody/lambdaWhenUnitNonExhaustive.kt.after

@@ -0,0 +1,11 @@
+// IS_APPLICABLE: true
+enum class AccessMode { READ, WRITE, RW }
+fun <T> run(f: () -> T) = f()
+fun whenExpr(access: AccessMode) = run {
+    println("run")
+    when (access) {
+        AccessMode.READ -> println("read")
+        AccessMode.WRITE -> println("write")
+    }
+}
+fun println(s: String) {}