Dfyjkt

There is recently a @Nullable change to GMS tasks library. The first few lines of decompiled .class looks like

public abstract class Task<TResult> {
 public Task() 
 

 public abstract boolean isComplete();

 public abstract boolean isSuccessful();

 public abstract boolean isCanceled();

 @Nullable
 public abstract TResult getResult();

Previously my Kotlin code compiled:

 if (task.isSuccessful) {
 task.result.user?.getIdToken(false)?.addOnCompleteListener taskk ->
 this.emailIdTokenCompleteListener()(taskk)
 

After updating some gms play-services-zzz dependencies the code now has compile error:

LoginActivity.kt: (148, 28): Only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type AuthResult?

The question is, does isSuccessful() == true imply that getResult != null? Or would it just be better to change the if test to if (task.result != null)?

What you are seeing is the Kotlin compiler failing to smart-cast the result to a NonNull type based on the result of isSuccessful, this can happen when interacting with both Java and Kotlin code.

In Kotlin 1.3 an implementation of "Contracts" was added to the language to allow developers to add meta data about a method in a format that the IDE can use to statically analyze and infer type (smart-cast).

See Section 1.2 "Returns and Implies" https://proandroiddev.com/kotlin-contracts-make-great-deals-with-the-compiler-f524e57f11c

So with contracts it would correctly smart-cast if the implementation looked like this:

open class Task<T> 
 var result: T? = null
 private set

 fun isSuccessful(): Boolean 
 contract 
 returns(true) implies (result != null)
 
 return result != null
 

In your case however you probably want to throw on another safe call operator ? and call your !task.isSuccessful code with the Elvis operator ?: like this:

if (task.isSuccessful) 
 task.result?.user?.getIdToken(false)?.addOnCompleteListener taskk ->
 this.emailIdTokenCompleteListener()(taskk)
 ?: handleFailure() // Defensively call just in case
 else 
 handleFailure()