[econstr] Continue consolidation of EConstr API under `interp`.

This commit was motivated by true spurious conversions arising in my
`to_constr` debug branch.

The changes here need careful review as the tradeoffs are subtle and
still a lot of clean up remains to be done in `vernac/*`.

We have opted for penalize [minimally] the few users coming from true
`Constr`-land, but I am sure we can tweak code in a much better way.

In particular, it is not clear if internalization should take an
`evar_map` even in the cases where it is not triggered, see the
changes under `plugins` for a good example.

Also, the new return type of `Pretyping.understand` should undergo
careful review.

We don't touch `Impargs` as it is not clear how to proceed, however,
the current type of `compute_implicits_gen` looks very suspicious as
it is called often with free evars.

Some TODOs are:

- impargs was calling whd_all, the Econstr equivalent can be either
  + Reductionops.whd_all [which does refolding and no sharing]
  + Reductionops.clos_whd_flags with all as a flag.

1 files changed, 2 insertions, 2 deletions

diff --git a/vernac/comProgramFixpoint.ml b/vernac/comProgramFixpoint.ml
index af34f8b29..bd7ee0978 100644
--- a/vernac/comProgramFixpoint.ml
+++ b/vernac/comProgramFixpoint.ml
@@ -171,8 +171,8 @@ let build_wellfounded (recname,pl,n,bl,arityc,body) poly r measure notation =
   let sigma, intern_body =
     let ctx = LocalAssum (Name recname, get_type curry_fun) :: binders_rel in
     let (r, l, impls, scopes) =
-      Constrintern.compute_internalization_data env
-        Constrintern.Recursive (EConstr.Unsafe.to_constr full_arity) impls
+      Constrintern.compute_internalization_data env sigma
+        Constrintern.Recursive full_arity impls
     in
     let newimpls = Id.Map.singleton recname
         (r, l, impls @ [(Some (Id.of_string "recproof", Impargs.Manual, (true, false)))],