17550c27

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Refuse a second anonymous scalar in a positional constructor

A domain scalar is named by a record field or by a newtype of its own,
and the half of that already reachable was the synonym, which
HsNewtypeNotSynonym refuses. Nothing reached the commoner shape: a bare
Text, String or Int sitting in a positional constructor with no field
and no type naming it, which is exactly what the guide means by a scalar
that can be confused positionally.

The budget is one rather than zero because a constructor holding a
single primitive names it, which is how every error type in this
repository is written, and a relayed reason or a count that is a count
travels anonymously on purpose. A second primitive is named nowhere, so
a caller that has the two the other way round still typechecks.

Measured over 2330 modules of nix-ci, smos, sydtest, centjes, intray and
this repository: thirty-nine constructors over the budget, and none of
them here, so the rule ships with nothing to clean up.