[flutter_plugin_tools] Test and comment Dart analysis

[stuartmorgan-g]

Adds a unit test and comments intended to avoid accidental breakage of
the Dart repo's run of analysis against this repository.

Addresses #4183 (comment)

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. (Note that unlike the flutter/flutter repo, the flutter/plugins repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the plugin 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.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test exempt.
• All existing and new tests are passing.

[stuartmorgan-g]

@devoncarew How does this look?

[devoncarew]

This looks good - I'm guessing that this will help in terms of reducing upstream breakages (or letting people know when we'll need to update things upstream).

I wonder if a good end state would be to allow a bare run of dart plugin_tools analyze to just work on the flutter/plugins (and flutter/packages) repos? We wouldn't have to know about specific analyze scripts in the repos, or, specific values of flags to pass in.

[stuartmorgan-g]

I wonder if a good end state would be to allow a bare run of dart plugin_tools analyze to just work on the flutter/plugins (and flutter/packages) repos?

What is dart plugin_tools?

[gaaclarke]

Wouldn't it make more sense to have this warning in the cirrus file next to the invocation there?

[stuartmorgan-g]

Good thought, that's more likely to be noticed in review. I left this longer explanation here, and added a shorter warning to .cirrus.yml that references it.

[gaaclarke]

LGTM. This is definitely an improvement. I would have rather seen the cirrus script and the dart script share invocations so they can both be updated from this repo. Hopefully it wont be necessary after all this cleanup though.

[devoncarew]

What is dart plugin_tools?

Ah, sorry, I'd meant flutter_plugin_tools, the tool in script/tool (I'd seen 'plugin_tool' from https://github.com/flutter/plugins/blob/master/script/common.sh#L11 but forget it was a bash function).

[stuartmorgan-g]

The long term goal is not too have anything on custom analysis files, as previously discussed. I'm not sure how a totally bare invocation would work though; you added the SDK flag specifically for this use (IIRC because you preferred that to adjusting PATH, which would be the other way to run it).