[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/ssr/ssrview.ml b/plugins/ssr/ssrview.ml
index aa614fbc1..afe03533d 100644
--- a/plugins/ssr/ssrview.ml
+++ b/plugins/ssr/ssrview.ml
@@ -254,7 +254,7 @@ let finalize_view s0 ?(simple_types=true) p =
 Goal.enter_one ~__LOC__ begin fun g ->
   let env = Goal.env g in
   let sigma = Goal.sigma g in
-  let evars_of_p = Evd.evars_of_term (EConstr.to_constr sigma p) in
+  let evars_of_p = Evd.evars_of_term (EConstr.to_constr ~abort_on_undefined_evars:false sigma p) in
   let filter x _ = Evar.Set.mem x evars_of_p in
   let sigma = Typeclasses.resolve_typeclasses ~fail:false ~filter env sigma in
   let p = Reductionops.nf_evar sigma p in