[webview_flutter] Migrate to null-safety

[mehmetf]

Description

Migrating webview-flutter to null-safety.

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[amirh]

Looks like some tests are failing and we have analysis errors

[mehmetf]

I have no idea why. I am possibly setting the dependency versions wrong. Could you (or someone else) help check?

[amirh]

The analysis unnecessary_null_comparison warnings seems legit.

The Gradle build errors on master channel are a framework regression, @blasten is handling that in flutter/flutter#71964.

The stable channel errors are because the plugin cannot work on stable after this change, as this is the first plugin we migrate on flutter/plugins master that's the first time we need to solve this. The easy fix would be to disable stable channel checks for the entire repository though I'm a little hesitant to do that, I'd prefer to only skip it for pre-release version that can't resolve on stable though I may be over-naive in how simple it is to do that. @blasten any thoughts on that? I can take a look at the CI change.

Side note - I basically have zero non-meeting time today so I only expect to get to it tomorrow.

[mehmetf]

Analysis errors are expected. They are coming from asserts. Is that lint turned off for package:flutter ?

[amirh]

Is the practice to keep assert(foo != null) for non nullable foo?

[mehmetf]

Yeah. That's what package:flutter has been following since these asserts have value for mixed mode code.

[amirh]

AFAICT unnecessary_null_comparison is not turned off in flutter/flutter (I'm not an expert of the analysis rules configuration for flutter/flutter though I believe https://github.com/flutter/flutter/blob/master/analysis_options.yaml is the source of truth)

[mehmetf]

Weird. How is code like:

https://github.com/flutter/flutter/blob/f55117840818eae1b3972a6abe9d2784fc8fb9b4/packages/flutter/lib/src/material/color_scheme.dart#L21-L47

passing analysis checks?

[amirh]

AFAICT unnecessary_null_comparison is not turned off in flutter/flutter (I'm not an expert of the analysis rules configuration for flutter/flutter though I believe https://github.com/flutter/flutter/blob/master/analysis_options.yaml is the source of truth)

Actually that's not true, it's turned off here: https://github.com/flutter/flutter/blob/52ea6c2a318537eb4d2ab260143bccaf6ec2151a/packages/flutter/analysis_options.yaml#L8

I guess we should do the same then.

[mehmetf]

Cool.

[blasten]

@mehmetf #3318 should help get the checks green on stable as it skips this plugin.

[mehmetf]

I am going to close this PR and open a new one.