Implemented autosave on a 5-second timer

[Levi-Lesches]

Fixes #2871 by saving the editor content to local storage under they key user_input every 5 seconds, and in dispose

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[Levi-Lesches]

@parlough I fixed the double quotes

[parlough]

Sweet! Thanks so much for implementing this again :D

[Levi-Lesches]

@parlough Any updates?

[Levi-Lesches]

Sorry for the annoying pings, just want to make sure this doesn't slip between the cracks

[parlough]

@Levi-Lesches Sorry for the delay, I've been away.

The change looks good to me, but before landing, we need to wait for others to determine DartPad's storage policies and how we will inform users of them.

I'll land this PR when able and ping you if any changes are needed.

Thanks again!

[Levi-Lesches]

Hi @parlough, any updates?

[johnpryan]

We added a cookie banner now (#3097), so we should be OK to use local storage.

[Levi-Lesches]

I'm trying to add an integration test that tests:

• entering text really does save content to the local storage
• loading the page results in the local storage text being displayed, unless
• if the page is loaded with a Gist, checks that the Gist is loaded instead of the local storage

This will complicate CI a bit, so I'm updating the README with instructions from the Flutter docs.

[Levi-Lesches]

I ended up going with unit tests instead as I couldn't get the integration tests to work: WidgetTester.enterText(String) calls WidgetTester.showKeyboard(), which requires an EditableText widget somewhere in the subtree, but the current setup with CodeMirror forwards keyboard input directly to the CodeMirror library without using Flutter's TextInput.

The test cases above are still tested, though, so I'm ready for another review.

EDIT ...okay, now I'm ready. I didn't add tests for:

• Fallback shows when a Gist has no main.dart file, because the flutterdevrelgists account has no such gist
• Flutter sample ID takes precedence, because I didn't want the tests to break when Flutter docs change

[Levi-Lesches]

Hey, bumping this again

[github-actions]

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[Levi-Lesches]

@johnpryan

Habits of writing cross-platform code, but of course this is a web-only project. Removed the conditional import and replaced it with the real web implementation.

Forgot -- the tests don't work with web-only imports. Try running the CI now