[econstr] Forbid calling `to_constr` in open terms.

We forbid calling `EConstr.to_constr` on terms that are not evar-free,
as to progress towards enforcing the invariant that `Constr.t` is
evar-free. [c.f. #6308]

Due to compatibility constraints we provide an optional parameter to
`to_constr`, `abort` which can be used to overcome this restriction
until we fix all parts of the code.

Now, grepping for `~abort:false` should return the questionable
parts of the system.

Not a lot of places had to be fixed, some comments:

- problems with the interface due to `Evd/Constr` [`Evd.define` being
  the prime example] do seem real!
- inductives also look bad with regards to `Constr/EConstr`.
- code in plugins needs work.

A notable user of this "feature" is `Obligations/Program` that seem to
like to generate kernel-level entries with free evars, then to scan
them and workaround this problem by generating constants.

1 files changed, 1 insertions, 1 deletions

diff --git a/plugins/cc/cctac.ml b/plugins/cc/cctac.ml
index d19817e74..c4db49cd3 100644
--- a/plugins/cc/cctac.ml
+++ b/plugins/cc/cctac.ml
@@ -90,7 +90,7 @@ let rec decompose_term env sigma t=
 	decompose_term env sigma c
     | _ ->
        let t = Termops.strip_outer_cast sigma t in
-       if closed0 sigma t then Symb (EConstr.to_constr sigma t) else raise Not_found
+       if closed0 sigma t then Symb (EConstr.to_constr ~abort_on_undefined_evars:false sigma t) else raise Not_found
 
 (* decompose equality in members and type *)
 open Termops