Add a better inference rule for vector literals

Mostly this improves typechecking in situations like the following,
where we are returning a bitvector with some length that satisfied
a property. In the example below, we are returning a vector of
length `'n` containing bitvectors of length `'m`, where `'n == 'm`
and `'n > 1`. Sail can now type-check this without any annotations.

```
register R : bool

register X : bits(32)

val test : unit -> {'n 'm, 'n > 1 & 'n == 'm. vector('n, bits('m))}

function test() = {
  if R then {
    [0b00, 0b11]
  } else {
    [match X { _ => 0b000 }, 0b001, 0b100]
  }
}
```

Previously one would need a lot of annotations to convince Sail that
this was ok, one on each vector literal.

Note that we don't rely on inferring the first element (any element
can be inferred), as can be seen in the second literal with the match.

src/lib/type_check.ml

@@ -2328,15 +2328,34 @@ let rec check_exp env (E_aux (exp_aux, (l, uannot)) as exp : uannot exp) (Typ_au
       in
       let checked_body = crule check_exp env body typ in
       annot_exp (E_internal_plet (tpat, bind_exp, checked_body)) typ
-  | E_vector vec, _ ->
-      let len, vtyp =
+  | E_vector vec, orig_typ -> begin
+      let literal_len = List.length vec in
+      let tyvars, nc, typ =
+        match destruct_exist_plain typ with Some (tyvars, nc, typ) -> (tyvars, nc, typ) | None -> ([], nc_true, typ)
+      in
+      let len, elem_typ, is_generic =
         match destruct_any_vector_typ l env typ with
-        | Destruct_vector (len, vtyp) -> (len, vtyp)
-        | Destruct_bitvector len -> (len, bit_typ)
+        | Destruct_vector (len, elem_typ) -> (len, elem_typ, true)
+        | Destruct_bitvector len -> (len, bit_typ, false)
+      in
+      let tyvars = List.fold_left (fun set kopt -> KidSet.add (kopt_kid kopt) set) KidSet.empty tyvars in
+      let tyvars, nc, elem_typ =
+        if not (KidSet.is_empty (KidSet.inter tyvars (tyvars_of_nexp len))) then (
+          let unifiers = unify_nexp l env tyvars len (nint literal_len) in
+          let elem_typ = subst_unifiers unifiers elem_typ in
+          let nc = KBindings.fold (fun v arg nc -> constraint_subst v arg nc) unifiers nc in
+          let tyvars = KBindings.fold (fun v _ tyvars -> KidSet.remove v tyvars) unifiers tyvars in
+          (tyvars, nc, elem_typ)
+        )
+        else if prove __POS__ env (nc_eq (nint literal_len) (nexp_simp len)) then (tyvars, nc, elem_typ)
+        else typ_error l "Vector literal with incorrect length"
       in
-      let checked_items = List.map (fun i -> crule check_exp env i vtyp) vec in
-      if prove __POS__ env (nc_eq (nint (List.length vec)) (nexp_simp len)) then annot_exp (E_vector checked_items) typ
-      else typ_error l "Vector literal with incorrect length" (* FIXME: improve error message *)
+      match check_or_infer_sequence ~at:l env vec tyvars nc elem_typ with
+      | Some (vec, elem_typ) ->
+          annot_exp (E_vector vec)
+            (if is_generic then vector_typ (nint literal_len) elem_typ else bitvector_typ (nint literal_len))
+      | None -> typ_error l ("This vector literal does not satisfy the constraint in " ^ string_of_typ (mk_typ orig_typ))
+    end
   | E_lit (L_aux (L_undef, _) as lit), _ ->
       if can_be_undefined ~at:l env typ then
         if is_typ_inhabited env (Env.expand_synonyms env typ) then annot_exp (E_lit lit) typ
@@ -2351,6 +2370,36 @@ let rec check_exp env (E_aux (exp_aux, (l, uannot)) as exp : uannot exp) (Typ_au
       let inferred_exp = irule infer_exp env exp in
       expect_subtype env inferred_exp typ
 
+(* This function will check that a sequence of expressions all have
+   the same type, where that type can have additional type variables
+   and constraints that must be instantiated (usually these
+   variables/constraints come from an existential). *)
+and check_or_infer_sequence ~at:l env xs tyvars nc typ =
+  let tyvars, nc, typ, xs =
+    List.fold_left
+      (fun (tyvars, nc, typ, xs) x ->
+        let goals = KidSet.inter tyvars (tyvars_of_typ typ) in
+        if not (KidSet.is_empty goals) then (
+          match irule infer_exp env x with
+          | exception Type_error _ -> (tyvars, nc, typ, Error x :: xs)
+          | x ->
+              let unifiers = unify l env goals typ (typ_of x) in
+              let typ = subst_unifiers unifiers typ in
+              let nc = KBindings.fold (fun v arg nc -> constraint_subst v arg nc) unifiers nc in
+              let tyvars = KBindings.fold (fun v _ tyvars -> KidSet.remove v tyvars) unifiers tyvars in
+              (tyvars, nc, typ, Ok x :: xs)
+        )
+        else (
+          let x = crule check_exp env x typ in
+          (tyvars, nc, typ, Ok x :: xs)
+        )
+      )
+      (tyvars, nc, typ, []) xs
+  in
+  if KidSet.is_empty tyvars && prove __POS__ env nc then
+    Some (List.rev_map (function Ok x -> x | Error x -> crule check_exp env x typ) xs, typ)
+  else None
+
 and check_block l env exps ret_typ =
   let final env exp = match ret_typ with Some typ -> crule check_exp env exp typ | None -> irule infer_exp env exp in
   let annot_exp exp typ exp_typ = E_aux (exp, (l, mk_expected_tannot env typ exp_typ)) in

test/typecheck/pass/Replicate/v2.expect

@@ -8,4 +8,4 @@ Explicit effect annotations are deprecated. They are no longer used and can be r
 pass/Replicate/v2.sail:13.4-30:
 13 |    replicate_bits(x, 'N / 'M)
    |    ^------------------------^
-   | Failed to prove constraint: ('M * 'ex249#) == 'N
+   | Failed to prove constraint: ('M * 'ex248#) == 'N

test/typecheck/pass/bool_constraint/v1.expect

@@ -9,13 +9,13 @@ All external bindings should be marked as either pure or impure
 12 |  if b then n else 4
    |                   ^
    | int(4) is not a subtype of {('m : Int), (('b & 'm == 'n) | (not('b) & 'm == 3)). int('m)}
-   | as (('b & 'ex240 == 'n) | (not('b) & 'ex240 == 3)) could not be proven
+   | as (('b & 'ex239 == 'n) | (not('b) & 'ex239 == 3)) could not be proven
    | 
-   | type variable 'ex240:
+   | type variable 'ex239:
    | pass/bool_constraint/v1.sail:9.25-73:
    | 9 |  (bool('b), int('n)) -> {'m, 'b & 'm == 'n | not('b) & 'm == 3. int('m)}
    |   |                         ^----------------------------------------------^ derived from here
    | pass/bool_constraint/v1.sail:12.19-20:
    | 12 |  if b then n else 4
    |    |                   ^ bound here
-   |    | has constraint: 4 == 'ex240
+   |    | has constraint: 4 == 'ex239

test/typecheck/pass/ex_vector_infer.sail

@@ -0,0 +1,17 @@
+default Order dec
+
+$include <prelude.sail>
+
+register R : bool
+
+register X : bits(32)
+
+val test : unit -> {'n 'm, 'n > 1 & 'n == 'm. vector('n, bits('m))}
+
+function test() = {
+  if R then {
+    [0b00, 0b11]
+  } else {
+    [match X { _ => 0b000 }, 0b001, 0b100]
+  }
+}

test/typecheck/pass/ex_vector_infer/v1.expect

@@ -0,0 +1,5 @@
+Type error:
+pass/ex_vector_infer/v1.sail:13.4-9:
+13 |    [0b1]
+   |    ^---^
+   | This vector literal does not satisfy the constraint in {('n : Int) ('m : Int), ('n > 1 & 'n == 'm). vector('n, bitvector('m))}

test/typecheck/pass/ex_vector_infer/v1.sail

@@ -0,0 +1,17 @@
+default Order dec
+
+$include <prelude.sail>
+
+register R : bool
+
+register X : bits(32)
+
+val test : unit -> {'n 'm, 'n > 1 & 'n == 'm. vector('n, bits('m))}
+
+function test() = {
+  if R then {
+    [0b1]
+  } else {
+    [match X { _ => 0b000 }, 0b001, 0b100]
+  }
+}

test/typecheck/pass/ex_vector_infer/v2.expect

@@ -0,0 +1,5 @@
+Type error:
+pass/ex_vector_infer/v2.sail:13.11-16:
+13 |    [0b00, 0b111]
+   |           ^---^
+   | Failed to prove constraint: 3 == 2

test/typecheck/pass/ex_vector_infer/v2.sail

@@ -0,0 +1,17 @@
+default Order dec
+
+$include <prelude.sail>
+
+register R : bool
+
+register X : bits(32)
+
+val test : unit -> {'n 'm, 'n > 1 & 'n == 'm. vector('n, bits('m))}
+
+function test() = {
+  if R then {
+    [0b00, 0b111]
+  } else {
+    [match X { _ => 0b000 }, 0b001, 0b100]
+  }
+}

test/typecheck/pass/existential_ast/v3.expect

@@ -9,4 +9,4 @@ Old set syntax, {|1, 2, 3|} can now be written as {1, 2, 3}.
 26 |  Some(Ctor1(a, x, c))
    |       ^------------^ checking function argument has type ast
    | Could not resolve quantifiers for Ctor1
-   | * 'ex335# in {32, 64}
+   | * 'ex334# in {32, 64}

test/typecheck/pass/existential_ast3/v1.expect

@@ -2,26 +2,26 @@
 pass/existential_ast3/v1.sail:17.48-65:
 17 |    if b == 0b0 then (64, unsigned(b @ a)) else (33, unsigned(a));
    |                                                ^---------------^
-   | (int(33), int('ex289)) is not a subtype of (int('ex284), int('ex285))
+   | (int(33), int('ex288)) is not a subtype of (int('ex283), int('ex284))
    | as false could not be proven
    | 
-   | type variable 'ex284:
+   | type variable 'ex283:
    | pass/existential_ast3/v1.sail:16.23-25:
    | 16 |  let (datasize, n) : {'d 'n, datasize('d) & 0 <= 'n < 'd. (int('d), int('n))} =
    |    |                       ^^ derived from here
    | pass/existential_ast3/v1.sail:17.48-65:
    | 17 |    if b == 0b0 then (64, unsigned(b @ a)) else (33, unsigned(a));
    |    |                                                ^---------------^ bound here
    | 
-   | type variable 'ex285:
+   | type variable 'ex284:
    | pass/existential_ast3/v1.sail:16.26-28:
    | 16 |  let (datasize, n) : {'d 'n, datasize('d) & 0 <= 'n < 'd. (int('d), int('n))} =
    |    |                          ^^ derived from here
    | pass/existential_ast3/v1.sail:17.48-65:
    | 17 |    if b == 0b0 then (64, unsigned(b @ a)) else (33, unsigned(a));
    |    |                                                ^---------------^ bound here
    | 
-   | type variable 'ex289:
+   | type variable 'ex288:
    | pass/existential_ast3/v1.sail:17.48-65:
    | 17 |    if b == 0b0 then (64, unsigned(b @ a)) else (33, unsigned(a));
    |    |                                                ^---------------^ bound here

test/typecheck/pass/existential_ast3/v2.expect

@@ -2,26 +2,26 @@
 pass/existential_ast3/v2.sail:17.48-65:
 17 |    if b == 0b0 then (64, unsigned(b @ a)) else (31, unsigned(a));
    |                                                ^---------------^
-   | (int(31), int('ex289)) is not a subtype of (int('ex284), int('ex285))
+   | (int(31), int('ex288)) is not a subtype of (int('ex283), int('ex284))
    | as false could not be proven
    | 
-   | type variable 'ex284:
+   | type variable 'ex283:
    | pass/existential_ast3/v2.sail:16.23-25:
    | 16 |  let (datasize, n) : {'d 'n, datasize('d) & 0 <= 'n < 'd. (int('d), int('n))} =
    |    |                       ^^ derived from here
    | pass/existential_ast3/v2.sail:17.48-65:
    | 17 |    if b == 0b0 then (64, unsigned(b @ a)) else (31, unsigned(a));
    |    |                                                ^---------------^ bound here
    | 
-   | type variable 'ex285:
+   | type variable 'ex284:
    | pass/existential_ast3/v2.sail:16.26-28:
    | 16 |  let (datasize, n) : {'d 'n, datasize('d) & 0 <= 'n < 'd. (int('d), int('n))} =
    |    |                          ^^ derived from here
    | pass/existential_ast3/v2.sail:17.48-65:
    | 17 |    if b == 0b0 then (64, unsigned(b @ a)) else (31, unsigned(a));
    |    |                                                ^---------------^ bound here
    | 
-   | type variable 'ex289:
+   | type variable 'ex288:
    | pass/existential_ast3/v2.sail:17.48-65:
    | 17 |    if b == 0b0 then (64, unsigned(b @ a)) else (31, unsigned(a));
    |    |                                                ^---------------^ bound here

test/typecheck/pass/existential_ast3/v3.expect

@@ -3,4 +3,4 @@
 25 |    Some(Ctor(64, unsigned(0b0 @ b @ a)))
    |         ^-----------------------------^ checking function argument has type ast
    | Could not resolve quantifiers for Ctor
-   | * (64 in {32, 64} & (0 <= 'ex326# & 'ex326# < 64))
+   | * (64 in {32, 64} & (0 <= 'ex325# & 'ex325# < 64))

test/typecheck/pass/existential_ast3/v4.expect

@@ -3,13 +3,13 @@
 36 |    if is_64 then 64 else 32;
    |                  ^^
    | int(64) is not a subtype of {('d : Int), (('is_64 & 'd == 63) | (not('is_64) & 'd == 32)). int('d)}
-   | as (('is_64 & 'ex342 == 63) | (not('is_64) & 'ex342 == 32)) could not be proven
+   | as (('is_64 & 'ex341 == 63) | (not('is_64) & 'ex341 == 32)) could not be proven
    | 
-   | type variable 'ex342:
+   | type variable 'ex341:
    | pass/existential_ast3/v4.sail:35.18-79:
    | 35 |  let 'datasize : {'d, ('is_64 & 'd == 63) | (not('is_64) & 'd == 32). int('d)} =
    |    |                  ^-----------------------------------------------------------^ derived from here
    | pass/existential_ast3/v4.sail:36.18-20:
    | 36 |    if is_64 then 64 else 32;
    |    |                  ^^ bound here
-   |    | has constraint: 64 == 'ex342
+   |    | has constraint: 64 == 'ex341

test/typecheck/pass/existential_ast3/v5.expect

@@ -3,13 +3,13 @@
 37 |  let n : range(0, 'datasize - 2) = if is_64 then unsigned(b @ a) else unsigned(a);
    |                                                  ^-------------^
    | range(0, 63) is not a subtype of range(0, ('datasize - 2))
-   | as (0 <= 'ex350 & 'ex350 <= ('datasize - 2)) could not be proven
+   | as (0 <= 'ex349 & 'ex349 <= ('datasize - 2)) could not be proven
    | 
-   | type variable 'ex350:
+   | type variable 'ex349:
    | pass/existential_ast3/v5.sail:37.10-33:
    | 37 |  let n : range(0, 'datasize - 2) = if is_64 then unsigned(b @ a) else unsigned(a);
    |    |          ^---------------------^ derived from here
    | pass/existential_ast3/v5.sail:37.50-65:
    | 37 |  let n : range(0, 'datasize - 2) = if is_64 then unsigned(b @ a) else unsigned(a);
    |    |                                                  ^-------------^ bound here
-   |    | has constraint: (0 <= 'ex350 & 'ex350 <= 63)
+   |    | has constraint: (0 <= 'ex349 & 'ex349 <= 63)

test/typecheck/pass/existential_ast3/v6.expect

@@ -3,13 +3,13 @@
 37 |  let n : range(0, 'datasize - 1) = if is_64 then unsigned(b @ a) else unsigned(b @ a);
    |                                                                       ^-------------^
    | range(0, 63) is not a subtype of range(0, ('datasize - 1))
-   | as (0 <= 'ex356 & 'ex356 <= ('datasize - 1)) could not be proven
+   | as (0 <= 'ex355 & 'ex355 <= ('datasize - 1)) could not be proven
    | 
-   | type variable 'ex356:
+   | type variable 'ex355:
    | pass/existential_ast3/v6.sail:37.10-33:
    | 37 |  let n : range(0, 'datasize - 1) = if is_64 then unsigned(b @ a) else unsigned(b @ a);
    |    |          ^---------------------^ derived from here
    | pass/existential_ast3/v6.sail:37.71-86:
    | 37 |  let n : range(0, 'datasize - 1) = if is_64 then unsigned(b @ a) else unsigned(b @ a);
    |    |                                                                       ^-------------^ bound here
-   |    | has constraint: (0 <= 'ex356 & 'ex356 <= 63)
+   |    | has constraint: (0 <= 'ex355 & 'ex355 <= 63)

test/typecheck/pass/if_infer/v1.expect

@@ -3,7 +3,7 @@
 10 |  let _ = 0b100[if R then 0 else f()];
    |          ^-------------------------^
    | Could not resolve quantifiers for bitvector_access
-   | * (0 <= 'ex241# & 'ex241# < 3)
+   | * (0 <= 'ex240# & 'ex240# < 3)
    | 
    | Caused by pass/if_infer/v1.sail:10.10-37:
    | 10 |  let _ = 0b100[if R then 0 else f()];

test/typecheck/pass/if_infer/v2.expect

@@ -3,7 +3,7 @@
 10 |  let _ = 0b1001[if R then 0 else f()];
    |          ^--------------------------^
    | Could not resolve quantifiers for bitvector_access
-   | * (0 <= 'ex241# & 'ex241# < 4)
+   | * (0 <= 'ex240# & 'ex240# < 4)
    | 
    | Caused by pass/if_infer/v2.sail:10.10-38:
    | 10 |  let _ = 0b1001[if R then 0 else f()];

test/typecheck/pass/reg_32_64/v3.expect

@@ -17,5 +17,5 @@ Explicit effect annotations are deprecated. They are no longer used and can be r
    | * sub_int
    |   pass/reg_32_64/v3.sail:29.15-17:
    |   29 |  reg_deref(R)['d - 1 .. 0]
-   |      |               ^^ checking function argument has type int('ex174#)
+   |      |               ^^ checking function argument has type int('ex173#)
    |      | Cannot re-write sizeof('d)