-
`DsM` was previously defined in `GHC.Tc.Types`, along with `TcM`. But `GHC.Tc.Types` is in the set of transitive dependencies of `GHC.Parser`, a set which we aim to minimise. Test case `CountParserDeps` checks for that. Having `DsM` in that set means the parser also depends on the innards of the pattern-match checker in `GHC.HsToCore.PmCheck.Types`, which is the reason we have that module in the first place. In the previous commit, we represented the `TyState` by an `InertSet`, but that pulls the constraint solver as well as 250 more modules into the set of dependencies, triggering failure of `CountParserDeps`. Clearly, we want to evolve the pattern-match checker (and the desugarer) without being concerned by this test, so this patch includes a small refactor that puts `DsM` into its own module.
a77e48d2