This commit introduces changes in induction and destruct.

The main change is that selection of subterm is made similar whether
the given term is fully applied or not.
- The selection of subterm now works as follows depending on whether
  the "at" is given, of whether the subterm is fully applied or not,
  and whether there are incompatible subterms matching the pattern. In
  particular, we have:
  "at" given
  | subterm fully applied
  | | incompatible subterms
  | | |
  Y Y - it works like in 8.4
  Y N - this was broken in 8.4 ("at" was ineffective and it was finding
        all subterms syntactically equal to the first one which matches)
  N Y Y it now finds all subterms like the first one which matches
        while in 8.4 it used to fail (I hope it is not a too risky in-draft
        for a semantics we would regret...) (e.g. "destruct (S _)" on
        goal "S x = S y + S x" now selects the two occurrences of "S x"
        while it was failing before)
  N Y N it works like in 8.4
  N N - it works like in 8.4, selecting all subterms like the
        first one which matches
- Note that the "historical" semantics, when looking for a subterm, to
  select all subterms that syntactically match the first subterm to
  match the pattern (looking from left to right) is now internally called
  "like first".
- Selection of subterms can now find the type by pattern-matching (useful e.g.
  for "induction (nat_rect _ _ _ _)")
- A version of Unification.w_unify w/o any conversion is used for
  finding the subterm: it could be easily replaced by an other
  matching algorithm.

In particular, "destruct H" now works on a goal such as "H:True -> x<=y |- P y".

Secondary change is in the interpretation of terms with existential
variables:
- When several arguments are given, interpretation is delayed at the
  time of execution
- Because we aim at eventually accepting "edestruct c" with unresolved
  holes in c, we need the sigma obtained from c to be an extension of
  the sigma of the tactics, while before, we just type-checked c
  independently of the sigma of the tactic
- Finishing the resolution of evars (using type classes, candidates,
  pending conversion problems) is made slightly cleaner: it now takes
  three states: a term is evaluated in state sigma, leading to state
  sigma' >= sigma, with evars finally solved in state sigma'' >=
  sigma'; we solve evars in the diff of sigma' and sigma and report
  the solution in sigma''
- We however renounce to give now a success semantics to "edestruct c"
  when "c" has unresolved holes, waiting instead for a decision on
  what to do in the case of a similar eapply (see mail to coqdev).

An auxiliary change is that an "in" clause can be attached to each component
of a "destruct t, u, v", etc.

Incidentally, make_abstraction does not do evar resolution itself any longer.

1 files changed, 10 insertions, 5 deletions

diff --git a/pretyping/unification.mli b/pretyping/unification.mli
index bedd6bf16..3b4998129 100644
--- a/pretyping/unification.mli
+++ b/pretyping/unification.mli
@@ -45,7 +45,7 @@ val elim_no_delta_flags : unit -> unify_flags
 val w_unify :
   env -> evar_map -> conv_pb -> ?flags:unify_flags -> constr -> constr -> evar_map
 
-(** [w_unify_to_subterm env (c,t) m] performs unification of [c] with a
+(** [w_unify_to_subterm env m (c,t)] performs unification of [c] with a
    subterm of [t]. Constraints are added to [m] and the matched
    subterm of [t] is also returned. *)
 val w_unify_to_subterm :
@@ -63,20 +63,25 @@ val w_coerce_to_type : env -> evar_map -> constr -> types -> types ->
 
 (* Looking for subterms in contexts at some occurrences, possibly with pattern*)
 
+exception PatternNotFound
+
 type abstraction_request =
-| AbstractPattern of Names.Name.t * (evar_map * constr) * Locus.clause * bool * Pretyping.inference_flags
+| AbstractPattern of bool * Names.Name.t * pending_constr * Locus.clause Locus.or_like_first * bool
 | AbstractExact of Names.Name.t * constr * types option * Locus.clause * bool
 
 val finish_evar_resolution : ?flags:Pretyping.inference_flags ->
-  env -> Evd.evar_map -> open_constr -> Evd.evar_universe_context * constr
+  env -> Evd.evar_map -> pending_constr -> Evd.evar_map * constr
 
 type abstraction_result =
-  Names.Id.t * Context.named_declaration list * Names.Id.t option *
-    constr * (Evd.evar_universe_context * constr)
+  Names.Id.t * named_context_val *
+    Context.named_declaration list * Names.Id.t option *
+    types * (Evd.evar_map * constr) option
 
 val make_abstraction : env -> Evd.evar_map -> constr ->
   abstraction_request -> abstraction_result
 
+val pose_all_metas_as_evars : env -> evar_map -> constr -> evar_map * constr
+
 (*i This should be in another module i*)
 
 (** [abstract_list_all env evd t c l]