Before this change, we had an enforcement that either 'get lintCode' or
'get lintCodes' is implemented, but it was a runtime enforcement. And it
was a little roundabout.
The new system is simpler and more typical:
* `AbstractLintRule` is the parent type, and it's sealed. It provides
`get lintCodes` as an interface. Code outside of the lint rules
requires this getter, in registering codes, etc.
* `LintRule` is the new subclass which is the "90% case." It declares
a `get lintRule`, and offers simpler reporting methods for reporting
a single code everywhere.
* `MultiLintRule` is the new subclass which represents that last
"10% case." It only declares the reporting methods which all require
a LintCode parameter, since there is no concept of a "default lint
code among all my lint codes."
Work towards https://github.com/dart-lang/sdk/issues/50986
Change-Id: I63cbbfc1d936bb4428aa0b8f5fb0638c9b61b3dc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/426284
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Sam Rawlins
abd4e7754c