[gsi_web] Adds Sign In button.

[ditman]

• Adds web-only renderButton method.
• Implements new platform interface methods.
  • canAccessScopes method and userDataEvents stream.
• Adds button_tester example app.
• Adds a flex view that reflows flutter apps from its contents.

Breaking change: silentSignIn now returns a non-null user, after popular demand (and adding a method to check if a user canAccessScopes).

Issues

• Needs: [gsi_interface] Introduces canAccessScopes and userDataEvents. #3635
• Continues landing: [google_sign_in] Adds "Button" Sign In for Web. #3461
• Enables fixing: [google_sign_in_web] Display Sign In With Google button flutter#121781
  • Enables fixing: Build dashboard sign in silently is failing flutter#121275

Testing

• Button Test App deployed here: https://dit-gis-button-test.web.app

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[yjbanov]

[yjbanov]

FYI: using BoxConstraints from a LayoutBuilder may provide a better first guess than Size(1, 1).

[ditman]

For the best user experience in this usage, the initialSize should be guesstimated off of the button configuration.

The layout builder however tells me the constraints that flutter will apply to my widget, but it does not tell me what's the rendered size of the contents of the html element view, so I'm not sure that the estimation is going to be better (if I understand the layout builder correctly, in that case the widget will start large, and then likely shrink, and with Size(1,1) it'll start small and likely grow?)

[ditman]

Hey, @stuartmorgan just a quick heads-up that this is almost ready to land. Please do take a look!

I've updated the README with the latest changes; instructing users to canAccessScopes after sign in on the web, and removing the mentions that signInSilently always returns null (because it doesn't anymore).

(The latter change made me want to release this as a major version change, so people who have already migrated to 0.11 get these changes by accident)

I've also added a new test app (that only uses this plugin) to test what the button looks like with different configuration values (I've deployed the latest version to the URL I linked in the description).

Thanks! 🙏

[stuartmorgan-g]

The metadata LGTM with nits; I mostly didn't review the implementation part since that was already done.

[ditman]

Let's go with this! When programmers attempt to use signIn in the web, the plugin will warn them that there's better alternatives, and point them to the docs!