"No trigger covering all quantified variables found" is still a warning with /warningsAsErrors

[mattmccutchen-amazon]

Dafny version

master (f6bd1b8)

Code to produce this issue

datatype MyResult = Ok | Err(error: set<string>)
function method warningTriggerTest(sr: seq<MyResult>): set<string> {
  set i, err | 0 <= i < |sr| && err in (if sr[i].Err? then sr[i].error else {}) :: err
}

Command to run and resulting output

% ./dafny /compile:0 /warningsAsErrors warning-trigger.dfy
.../warning-trigger.dfy(3,2): Warning: /!\ No trigger covering all quantified variables found.

Dafny program verifier finished with 1 verified, 0 errors

What happened?

I'd expect /warningsAsErrors to convert the warning to an error, or else the documentation should explain why it doesn't.

What type of operating system are you experiencing the problem on?

Linux