A warning for partial field accesses

This was originally proposed by @rae, but I couldn't find a ticket for it:

data R = MkR1 { foo :: Int } | MkR2 Bool

bar :: R -> Int
bar r = foo r + 1

This generates no warnings but is dangerously partial.

The warning would be similar to -Wpartial-fields (#7169 (closed)) which warns about partial field definitions as in the first line of the example.

The warning proposed here would warn about the usage of such a partial field as in the last line of the example.

The warning could be called -Wincomplete-record-accesses in analogy to -Wincomplete-record-updates.

Initially the warning should not be included in -Wall – instead it should see some testing in practice before potentially being added to -Wall.

The linked thread on the original proposal already contains some discussion on the warning proposed here.