testing: add an integration test for yaml-test-suite

[tanriol]

The official YAML test suite (https://github.com/yaml/yaml-test-suite).
Requires the submodule to be checked out.

This is a draft PR because there's quite a number of failures. At the moment I'm seeing 62 unexpected errors (and 19 more errors where yaml-rust Event / Parser / EventReceiver API does not provide enough information about the document). I can mark the other errors as expected errors for now, but want to look at them first to check whether they're yaml-rust errors or some mistakes in this test harness.

[perlpunk]

I would like to mention that I added yaml-rust to the test matrix: https://matrix.yaml.info/ with the help of @tanriol

[tanriol]

@chyh1990 / @dtolnay
Sorry for pinging directly, but I've seen no reaction to this PR yet. Should I continue trying to contribute to this repository, or should I instead fork the crate completely and work on improving it in my own fork?

[neithernut]

Well, according to @chyh1990's profile, their last activity was on June 3, 2020. But even before that, the activity was rather sparse. PRs and issues just kept accumulating without any meaningful progress for years now.

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Maybe there are more active forks already?

[dtolnay]

I am not involved in this crate, since it is no longer used by serde_yaml.

[tanriol]

I am not involved in this crate, since it is no longer used by serde_yaml.

Sounds reasonable given the maintenance state of this crate. I'm leaving this PR open just in case, but don't really care about its fate in this case.

[davvid]

FWIW I have a fork I'm maintaining since I need this to keep working for the long-haul: https://github.com/davvid/yaml-rust/

I'd be happy to take PRs related to this topic there.