[firebase_messaging] readme update per issue resolution flutter/flutter/issues/38459

[mictay]

Description

Using the latest firebase_messaging breaks gradle builds. Updating the documentation in the readme.md file aligns with the https://firebase.google.com/docs/cloud-messaging/android/client setup instructions that resolves the flutter gradle build issue.

Related Issues

flutter/flutter#38459

Checklist

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
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• I updated/added relevant documentation (doc comments with ///).
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• [ x] I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
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[collinjackson]

Thanks for the PR! Please sign the CLA, and update the pubspec.yaml and CHANGELOG.

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[collinjackson]

I took a closer look and I am unsure that this is the right approach.

Other Flutterfire plugins are specifying mostly just API dependencies; the implementation dependency is just 'com.google.firebase:firebase-common:16.1.0' and that seems to be enough for gradle to resolve the rest of the Firebase SDK.

The continuous integration is green and that means that the building the all_plugins test app is working. Something is different about what you're doing and what we're doing. I think the culprit is probably implementation 'com.google.firebase:firebase-core:17.0.0' in your app-level build.gradle... where did that come from? When I try combining that line with a dependency on firebase_messaging plugin I get similar build errors:

FAILURE: Build failed with an exception.                                
                                                                        
* What went wrong:                                                      
Could not determine the dependencies of task ':app:compileReleaseJavaWithJavac'.
> In project 'app' a resolved Google Play services library dependency depends on another at an exact version (e.g. "[18.0.
  0]", but isn't being resolved to that version. Behavior exhibited by the library will be unknown.
                                                                        
  Dependency failing: com.google.firebase:firebase-messaging:18.0.0 -> com.google.firebase:firebase-iid@[18.0.0], but fire
  base-iid version was 19.0.0.                                          
                                                                        
  The following dependencies are project dependencies that are direct or have transitive dependencies that lead to the art
  ifact with the issue.                                                 
  -- Project 'app' depends onto com.google.firebase:[email protected]
  -- Project 'app' depends on project 'firebase_messaging' which depends onto com.google.firebase:[email protected].
  0                                                                     
  -- Project 'app' depends onto com.google.firebase:[email protected]
  -- Project 'app' depends on project 'firebase_core' which depends onto com.google.firebase:[email protected]
  -- Project 'app' depends onto com.google.firebase:[email protected]
  -- Project 'app' depends onto com.google.android.gms:[email protected]
  -- Project 'app' depends onto com.google.firebase:[email protected] 
                                                                        
  For extended debugging info execute Gradle from the command line with ./gradlew --info :app:assembleDebug to see the dep
  endency paths to the artifact. This error message came from the google-services Gradle plugin, report issues at https://
  github.com/google/play-services-plugins and disable by adding "googleServices { disableVersionCheck = false }" to your b
  uild.gradle file.                                                     
                                                                        
* Try:                                                                  
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.
                                                                        
* Get more help at https://help.gradle.org                              
                                                                        
BUILD FAILED in 3s  

Perhaps we should be discouraging developers from specifying any implementation versions of Firebase libraries rather than adding more specific implementation dependencies as you're doing in this PR?

/cc @mklim @kroikie in case they have further thoughts

[kroikie]

@mictay Thank for the PR but the version of the native SDK should be determined by the plugin, if there is an issue the plugin should be updated to use the correct version of the SDK.