nit: @Hixie is trying to remove usages of ++ in our code, replacing them with += 1.

Fixed.

This is a personal preference, but I think it's easier to reason about code when there are fewer mutations. Here instead of mutating the errors list, and therefore making the logic sensitive to the order in which operations happen, we could instead create new lists of errors whose names describe what's in the list, e.g.:

bool isMissingDocError(AnalysisError error) => error.code == 'public_member_api_docs';

final List<AnalysisError> allErrors = ...;
final int membersMissingDocumentation = allErrors.where(isMissingDocError).length;
final int detailedErrors = allErrors.where((e) => !isMissingDocError(e)).toList()..sort();

I modified the code to create a separate detailedErrors list as you suggested.

Extraneous --watch

Removed.

nit: spaces around the named arguments

Fixed.

maybe instead of special-casing the flutter repo like this in the server, we should just give a "--dartdocs" option to the analyzer? Or a command-line option to enable/disable specific lints?

Several times Brian and I have discussed the best approach here. Our current top prospect is to add support for linter summaries in analysis_options.yaml, but that will take a while. This command line flag is intended to be very specific for your needs until the more general purpose mechanism is available.