"This rule is never matched" warning is not shown if an active pattern is used in match expression

[vasily-kirichenko]

let _ =
    match obj() with
    | x -> ()
    | _ -> ()
    | _ -> ()

results with proper warnings:

However, if an active pattern is used in match expression, there are no warnings at all:

let (|AP|_|) x = Some()

let _ =
    match obj() with
    | AP -> ()
    | _ -> ()
    | _ -> ()

[auduchinok]

Seems to be a duplicate of #1281 (comment).
It looks like a thing worth fixing some day, though.

[dsyme]

For the above example I agree it would be good to fix.

That said, it will be a game of whack-a-mole - partial active patterns do impact on exhaustivity checking and always will, there will always be cases where the programmer feels that warnings should be given but the compiler doesn't give them.