Be aggressive about checking state consistency

src/base/run_state.ml

@@ -31,9 +31,12 @@ module Vector = struct
   let emplace_back (type x) (T ((module T), _, t) : x t) x = T.emplace_back t x
 end
 
+let id = ref 0
+
 (** The internal state used to run a checked computation. *)
 type 'field t =
-  { system : 'field Constraint_system.t option
+  { id : int
+  ; system : 'field Constraint_system.t option
   ; input : 'field Vector.t
   ; aux : 'field Vector.t
   ; eval_constraints : bool
@@ -57,7 +60,10 @@ let make ~num_inputs ~input ~next_auxiliary ~aux ?system ~eval_constraints
   next_auxiliary := num_inputs ;
   (* We can't evaluate the constraints if we are not computing over a value. *)
   let eval_constraints = eval_constraints && with_witness in
-  { system
+  let my_id = !id in
+  incr id ;
+  { id = my_id
+  ; system
   ; input
   ; aux
   ; eval_constraints
@@ -90,6 +96,8 @@ let alloc_var { next_auxiliary; _ } () =
   let v = !next_auxiliary in
   incr next_auxiliary ; Cvar.Unsafe.of_index v
 
+let id { id; _ } = id
+
 let has_witness { has_witness; _ } = has_witness
 
 let as_prover { as_prover; _ } = !as_prover

src/base/run_state.mli

@@ -44,6 +44,8 @@ val store_field_elt : 'field t -> 'field -> 'field Cvar.t
 
 val alloc_var : 'field t -> unit -> 'field Cvar.t
 
+val id : _ t -> int
+
 val has_witness : _ t -> bool
 
 val as_prover : _ t -> bool

src/base/runners.ml

@@ -59,7 +59,11 @@ struct
         ~aux:(pack_field_vec aux) ~system ~eval_constraints:true
         ~with_witness:true ()
     in
-    let _, x = run t0 state in
+    let id = Run_state.id state in
+    let state, x = run t0 state in
+    let final_id = Run_state.id state in
+    if id <> final_id then
+      failwith "Snarky's internal state has been clobbered." ;
     (x, get_value)
 
   let run_and_check' ~run t0 =
@@ -84,8 +88,13 @@ struct
         ~aux:(pack_field_vec aux) ~system ~eval_constraints:true
         ~with_witness:true ()
     in
+    let id = Run_state.id state in
     let res = run t0 state in
-    map res ~f:(function _, x -> (x, get_value))
+    map res ~f:(function state, x ->
+        let final_id = Run_state.id state in
+        if id <> final_id then
+          failwith "Snarky's internal state has been clobbered." ;
+        (x, get_value) )
 
   let run_and_check_deferred' ~map ~return ~run t0 =
     match
@@ -107,7 +116,12 @@ struct
       Runner.State.make ~num_inputs ~input ~next_auxiliary ~aux
         ~with_witness:true ()
     in
-    match run t0 state with _, x -> x
+    let id = Run_state.id state in
+    let state, x = run t0 state in
+    let final_id = Run_state.id state in
+    if id <> final_id then
+      failwith "Snarky's internal state has been clobbered." ;
+    x
 
   let run_and_check_exn ~run t =
     let x, get_value = run_and_check_exn' ~run t in
@@ -220,6 +234,7 @@ struct
           Runner.State.make ~num_inputs ~input ~next_auxiliary ~aux ~system
             ~with_witness:false ()
         in
+        let id = Run_state.id state in
         let state, () =
           (* create constraints to validate the input (using the input [Typ]'s [check]) *)
           let checked =
@@ -230,6 +245,9 @@ struct
         in
         let run_computation k = k var state in
         let finish_computation (state, res) =
+          let final_id = Run_state.id state in
+          if id <> final_id then
+            failwith "Snarky's internal state has been clobbered." ;
           let res, _ = return_typ.var_to_fields res in
           let retvar, _ = return_typ.var_to_fields retvar in
           let _state =
@@ -332,8 +350,12 @@ struct
             ~next_auxiliary ~aux:(pack_field_vec aux) ~handler
             ~with_witness:true ()
         in
+        let id = Run_state.id state in
         let run_computation t0 = t0 input_var state in
         let finish_witness_generation (state, res) =
+          let final_id = Run_state.id state in
+          if id <> final_id then
+            failwith "Snarky's internal state has been clobbered." ;
           let (Typ return_typ) = return_typ in
           let res_fields, auxiliary_output_data =
             return_typ.var_to_fields res