[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, 6 insertions, 3 deletions

diff --git a/printing/ppconstr.ml b/printing/ppconstr.ml
index 3c7095505..dedad1990 100644
--- a/printing/ppconstr.ml
+++ b/printing/ppconstr.ml
@@ -701,13 +701,16 @@ let tag_var = tag Tag.variable
     | { CAst.v = CAppExpl ((None,f,us),[]) } -> str "@" ++ pr_cref f us
     | c -> pr prec c
 
-  let transf env c =
+  let transf env sigma c =
     if !Flags.beautify_file then
-      let r = Constrintern.for_grammar (Constrintern.intern_constr env) c in
+      let r = Constrintern.for_grammar (Constrintern.intern_constr env sigma) c in
       Constrextern.extern_glob_constr (Termops.vars_of_env env) r
     else c
 
-  let pr_expr prec c = pr prec (transf (Global.env()) c)
+  let pr_expr prec c =
+    let env = Global.env () in
+    let sigma = Evd.from_env env in
+    pr prec (transf env sigma c)
 
   let pr_simpleconstr = pr_expr lsimpleconstr