LiveData.switchMap should allow to return `null` instead LiveData [132923666]

Fixed

Feature Request

Status Update

No update yet.

Description

ma...@gmail.com

created issue #1

May 17, 2019 10:59AM

Component used: androidx.lifecycle:lifecycle-livedata-ktx
Version used: 2.2.0-alpha01

LiveData.switchMap breaks the nullability contracts of the corresponding Java Transformations.switchMap.
Transformations.switchMap allows returning null, while the Kotlin extension function does not.
I can write

Transformations.switchMap(fooLiveData) { it?.barLiveData }

but I can't write

fooLiveData.switchMap { it?.barLiveData }

since I'm expected to return a non-nullable LiveData<Y>.
To make it compile, I would need to write an ugly

fooLiveData.switchMap { it?.barLiveData ?: MutableLiveData<Bar>(null) }

The null return value is safely handled in the Java implementation, so I believe there should be no reason to force a non-null return type.

Please consider changing the switchMap function signature from
inline fun <X, Y> LiveData<X>.switchMap(crossinline transform: (X) -> LiveData<Y>): LiveData<Y>
to
inline fun <X, Y> LiveData<X>.switchMap(crossinline transform: (X) -> LiveData<Y>?): LiveData<Y>

Comments

pe...@gmail.com <pe...@gmail.com> #2Nov 21, 2019 02:39PM

This is likely due to an incorrect service loader specified somewhere.

If you are unable to fix the server loader spec, you can add a -dontwarn rule for the class to silence the error using:

-dontwarn com.google.protobuf.java_com_google_android_gmscore_sdk_target_granule__proguard_group_gtm_N1281923064GeneratedExtensionRegistryLite$Loader

A discussion of a similar situation can be found in b/279996549

pe...@gmail.com <pe...@gmail.com> #3Nov 21, 2019 03:24PM

Could you see which service file the class is declared in? You will need to look for the class referenced META-INF/services/<somefile>.

Alternatively you can create a compiler input dump and attach in public here or privately with zerny@google.com and/or mkroghj@google.com and we can find the service info in that.

[Deleted User] <[Deleted User]> #4Nov 29, 2019 02:45AM

Unexpected reference to missing service implementation class in META-INF/services/com.google.protobuf.GeneratedExtensionRegistryLoader: com.google.protobuf.java_com_google_android_gmscore_sdk_target_granule__proguard_group_gtm_N1281923064GeneratedExtensionRegistryLite$Loader.

Unexpected reference to missing service class: META-INF/services/com.google.protobuf.GeneratedExtensionRegistryLoader.

Unexpected reference to missing service class: META-INF/services/org.jetbrains.kotlin.compiler.plugin.CommandLineProcessor.

Unexpected reference to missing service class: META-INF/services/org.jetbrains.kotlin.compiler.plugin.ComponentRegistrar.

Unexpected reference to missing service class: META-INF/services/org.jetbrains.kotlin.diagnostics.rendering.DefaultErrorMessages$Extension.

Caused by: [CIRCULAR REFERENCE: com.android.tools.r8.utils.b: Missing class com.google.protobuf.java_com_google_android_gmscore_sdk_target_granule__proguard_group_gtm_N1281923064GeneratedExtensionRegistryLite$Loader (referenced from: java.util.List kotlinx.coroutines.internal.FastServiceLoader.load(java.lang.Class, java.lang.ClassLoader))]

pe...@gmail.com <pe...@gmail.com> #5May 28, 2020 08:51AM

The app doesn't work with

-dontwarn com.google.protobuf.java_com_google_android_gmscore_sdk_target_granule__proguard_group_gtm_N1281923064GeneratedExtensionRegistryLite$Loader

la...@gtempaccount.com <la...@gtempaccount.com> #6Oct 19, 2020 08:22PM

You will need a -dontwarn for each type that is missing.

il...@google.com <il...@google.com> Nov 18, 2021 10:12PM

Status: New

il...@google.com <il...@google.com> Feb 1, 2022 09:34PM

Assigned to jb...@google.com.

ap...@google.com <ap...@google.com> #7Feb 2, 2022 11:27PM

But "missing_rules.txt" has only -dontwarn com.google.protobuf.java_com_google_android_gmscore_sdk_target_granule__proguard_group_gtm_N1281923064GeneratedExtensionRegistryLite$Loader

After adding this to pro-guard, app stops working as intended.

jb...@google.com <jb...@google.com> #8Feb 2, 2022 11:30PM

Marked as fixed.

I get the error:

java.lang.ClassCastException: java.lang.Class cannot be cast to java.lang.reflect.ParameterizedType