package ppx_hash
A ppx rewriter that generates hash functions from type expressions and definitions
Install
Dune Dependency
Authors
Maintainers
Sources
ppx_hash-v0.16.0.tar.gz
sha256=9b012546b7b9278bfd536f802fb6da88a11ebb5340d8aa47e9bf49acbf13b6e5
doc/src/ppx_hash.expander/ppx_hash_expander.ml.html
Source file ppx_hash_expander.ml
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open Base open Ppxlib open Ast_builder.Default module Attrs = struct let ignore_label_declaration = Attribute.declare "hash.ignore" Attribute.Context.label_declaration Ast_pattern.(pstr nil) () ;; let ignore_core_type = Attribute.declare "hash.ignore" Attribute.Context.core_type Ast_pattern.(pstr nil) () ;; let no_hashing_label_declaration = Attribute.declare "hash.no_hashing" Attribute.Context.label_declaration Ast_pattern.(pstr nil) () ;; end let str_attributes = [ Attribute.T Attrs.ignore_core_type ; Attribute.T Attrs.ignore_label_declaration ; Attribute.T Attrs.no_hashing_label_declaration ] ;; let is_ignored_gen attrs t = List.exists attrs ~f:(fun attr -> Option.is_some (Attribute.get attr t)) ;; let core_type_is_ignored ct = is_ignored_gen [ Attrs.ignore_core_type; Ppx_compare_expander.Compare.Attrs.ignore_core_type ] ct ;; let should_ignore_label_declaration ld = let warning = "[@hash.no_hashing] is deprecated. Use [@hash.ignore]." in let is_ignored = is_ignored_gen [ Attrs.ignore_label_declaration ; Ppx_compare_expander.Compare.Attrs.ignore_label_declaration ] ld (* Avoid confusing errors with [ { mutable field : (value[@ignore]) } ] vs [ { mutable field : value [@ignore] } ] by treating them the same. *) || core_type_is_ignored ld.pld_type in match Attribute.get Attrs.no_hashing_label_declaration ld with | None -> (if is_ignored then `ignore else `incorporate), None | Some () -> `ignore, Some (attribute_of_warning ld.pld_loc warning) ;; (* Generate code to compute hash values of type [t] in folding style, following the structure of the type. Incorporate all structure when computing hash values, to maximise hash quality. Don't attempt to detect/avoid cycles - just loop. *) let hash_state_t ~loc = [%type: Ppx_hash_lib.Std.Hash.state] let hash_fold_type ~loc ty = let loc = { loc with loc_ghost = true } in [%type: [%t hash_state_t ~loc] -> [%t ty] -> [%t hash_state_t ~loc]] ;; let hash_type ~loc ty = let loc = { loc with loc_ghost = true } in [%type: [%t ty] -> Ppx_hash_lib.Std.Hash.hash_value] ;; (* [expr] is an expression that doesn't use the [hsv] variable. Currently it's there only for documentation value, but conceptually it can be thought of as an abstract type *) type expr = expression (* Represents an expression that produces a hash value and uses the variable [hsv] in a linear way (mixes it in exactly once). You can think of it as a body of a function of type [Hash.state -> Hash.state] *) module Hsv_expr : sig type t val identity : loc:location -> t val invoke_hash_fold_t : loc:location -> hash_fold_t:expr -> t:expr -> t val compose : loc:location -> t -> t -> t val compile_error : loc:location -> string -> t (** the [_unchecked] functions all break abstraction in some way *) val of_expression_unchecked : expr -> t (** the returned [expression] uses the binding [hsv] bound by [pattern] *) val to_expression : loc:location -> t -> pattern * expression (* [case] is binding a variable that's not [hsv] and uses [hsv] on the rhs exactly once *) type case val compile_error_case : loc:location -> string -> case val pexp_match : loc:location -> expr -> case list -> t (* [lhs] should not bind [hsv] *) val case : lhs:pattern -> guard:expr option -> rhs:t -> case (* [value_binding]s should not bind or use [hsv] *) val pexp_let : loc:location -> rec_flag -> value_binding list -> t -> t val with_attributes : f:(attribute list -> attribute list) -> t -> t end = struct type t = expression type nonrec case = case let invoke_hash_fold_t ~loc ~hash_fold_t ~t = eapply ~loc hash_fold_t [ [%expr hsv]; t ] let identity ~loc = [%expr hsv] let compose ~loc a b = [%expr let hsv = [%e a] in [%e b]] ;; let to_expression ~loc x = [%pat? hsv], x let of_expression_unchecked x = x let pexp_match = pexp_match let case = case let pexp_let = pexp_let let with_attributes ~f x = { x with pexp_attributes = f x.pexp_attributes } let compile_error ~loc s = pexp_extension ~loc (Location.Error.to_extension (Location.Error.createf ~loc "%s" s)) ;; let compile_error_case ~loc s = case ~lhs:(ppat_any ~loc) ~guard:None ~rhs:(compile_error ~loc s) ;; end let hash_fold_int ~loc i : Hsv_expr.t = Hsv_expr.invoke_hash_fold_t ~loc ~hash_fold_t:[%expr Ppx_hash_lib.Std.Hash.fold_int] ~t:(eint ~loc i) ;; let special_case_types_named_t = function | `hash_fold -> false | `hash -> true ;; let hash_fold_ tn = match tn with | "t" when special_case_types_named_t `hash_fold -> "hash_fold" | _ -> "hash_fold_" ^ tn ;; let hash_ tn = match tn with | "t" when special_case_types_named_t `hash -> "hash" | _ -> "hash_" ^ tn ;; (** renames [x] avoiding collision with [type_name] *) let rigid_type_var ~type_name x = let prefix = "rigid_" in if String.equal x type_name || String.is_prefix x ~prefix then prefix ^ x ^ "_of_type_" ^ type_name else x ;; let make_type_rigid ~type_name = let map = object inherit Ast_traverse.map as super method! core_type ty = let ptyp_desc = let () = (* making sure [type_name] is the only free type variable *) match ty.ptyp_desc with | Ptyp_constr (name, _args) -> (match name.txt with | Ldot _ | Lapply _ -> () | Lident name -> if not (String.equal name type_name) then Location.raise_errorf ~loc:ty.ptyp_loc "ppx_hash: make_type_rigid: unexpected type %S. expected to only \ find %S" (string_of_core_type ty) type_name; ()) | _ -> () in match ty.ptyp_desc with | Ptyp_var s -> Ptyp_constr (Located.lident ~loc:ty.ptyp_loc (rigid_type_var ~type_name s), []) | desc -> super#core_type_desc desc in { ty with ptyp_desc } end in map#core_type ;; (* The only names we assume to be in scope are [hash_fold_<TY>] So we are sure [tp_name] (which start with an [_]) will not capture them. *) let tp_name n = Printf.sprintf "_hash_fold_%s" n let with_tuple loc (value : expr) xs (f : (expr * core_type) list -> Hsv_expr.t) : Hsv_expr.t = let names = List.mapi ~f:(fun i t -> Printf.sprintf "e%d" i, t) xs in let pattern = let l = List.map ~f:(fun (n, _) -> pvar ~loc n) names in ppat_tuple ~loc l in let e = f (List.map ~f:(fun (n, t) -> evar ~loc n, t) names) in let binding = value_binding ~loc ~pat:pattern ~expr:value in Hsv_expr.pexp_let ~loc Nonrecursive [ binding ] e ;; let hash_ignore ~loc value = Hsv_expr.pexp_let ~loc Nonrecursive [ value_binding ~loc ~pat:[%pat? _] ~expr:value ] (Hsv_expr.identity ~loc) ;; let ghostify_located (t : 'a loc) : 'a loc = { t with loc = { t.loc with loc_ghost = true } } ;; let rec hash_applied ty value = let loc = { ty.ptyp_loc with loc_ghost = true } in match ty.ptyp_desc with | Ptyp_constr (name, ta) -> let args = List.map ta ~f:(hash_fold_of_ty_fun ~type_constraint:false) in Hsv_expr.invoke_hash_fold_t ~loc ~hash_fold_t:(type_constr_conv ~loc name ~f:hash_fold_ args) ~t:value | _ -> assert false and hash_fold_of_tuple ~loc tys value = with_tuple loc value tys (fun elems1 -> List.fold_right elems1 ~init:(Hsv_expr.identity ~loc) ~f:(fun (v, t) (result : Hsv_expr.t) -> Hsv_expr.compose ~loc (hash_fold_of_ty t v) result)) and hash_variant ~loc row_fields value = let map row = match row.prf_desc with | Rtag ({ txt = cnstr; _ }, true, _) | Rtag ({ txt = cnstr; _ }, _, []) -> Hsv_expr.case ~guard:None ~lhs:(ppat_variant ~loc cnstr None) ~rhs:(hash_fold_int ~loc (Ocaml_common.Btype.hash_variant cnstr)) | Rtag ({ txt = cnstr; _ }, false, tp :: _) -> let v = "_v" in let body = Hsv_expr.compose ~loc (hash_fold_int ~loc (Ocaml_common.Btype.hash_variant cnstr)) (hash_fold_of_ty tp (evar ~loc v)) in Hsv_expr.case ~guard:None ~lhs:(ppat_variant ~loc cnstr (Some (pvar ~loc v))) ~rhs:body | Rinherit ({ ptyp_desc = Ptyp_constr (id, _); _ } as ty) -> (* Generated code from.. type 'a id = 'a [@@deriving hash] type t = [ `a | [ `b ] id ] [@@deriving hash] doesn't compile: Also see the "sadly" note in: ppx_compare_expander.ml *) let v = "_v" in Hsv_expr.case ~guard:None ~lhs:(ppat_alias ~loc (ppat_type ~loc (ghostify_located id)) (Located.mk ~loc v)) ~rhs:(hash_applied ty (evar ~loc v)) | Rinherit ty -> let s = string_of_core_type ty in Hsv_expr.compile_error_case ~loc (Printf.sprintf "ppx_hash: impossible variant case: %s" s) in Hsv_expr.pexp_match ~loc value (List.map ~f:map row_fields) and branch_of_sum hsv ~loc cd = match cd.pcd_args with | Pcstr_tuple [] -> let pcnstr = pconstruct cd None in Hsv_expr.case ~guard:None ~lhs:pcnstr ~rhs:hsv | Pcstr_tuple tps -> let ids_ty = List.mapi tps ~f:(fun i ty -> Printf.sprintf "_a%d" i, ty) in let lpatt = List.map ids_ty ~f:(fun (l, _ty) -> pvar ~loc l) |> ppat_tuple ~loc and body = List.fold_left ids_ty ~init:(Hsv_expr.identity ~loc) ~f:(fun expr (l, ty) -> Hsv_expr.compose ~loc expr (hash_fold_of_ty ty (evar ~loc l))) in Hsv_expr.case ~guard:None ~lhs:(pconstruct cd (Some lpatt)) ~rhs:(Hsv_expr.compose ~loc hsv body) | Pcstr_record lds -> let arg = "_ir" in let pat = pvar ~loc arg in let v = evar ~loc arg in let body = hash_fold_of_record ~loc lds v in Hsv_expr.case ~guard:None ~lhs:(pconstruct cd (Some pat)) ~rhs:(Hsv_expr.compose ~loc hsv body) and branches_of_sum = function | [ cd ] -> (* this is an optimization: we don't need to mix in the constructor tag if the type only has one constructor *) let loc = cd.pcd_loc in [ branch_of_sum (Hsv_expr.identity ~loc) ~loc cd ] | cds -> List.mapi cds ~f:(fun i cd -> let loc = cd.pcd_loc in let hsv = hash_fold_int ~loc i in branch_of_sum hsv ~loc cd) and hash_sum ~loc cds value = Hsv_expr.pexp_match ~loc value (branches_of_sum cds) and hash_fold_of_ty ty value = let loc = { ty.ptyp_loc with loc_ghost = true } in if core_type_is_ignored ty then hash_ignore ~loc value else ( match ty.ptyp_desc with | Ptyp_constr _ -> hash_applied ty value | Ptyp_tuple tys -> hash_fold_of_tuple ~loc tys value | Ptyp_var name -> Hsv_expr.invoke_hash_fold_t ~loc ~hash_fold_t:(evar ~loc (tp_name name)) ~t:value | Ptyp_arrow _ -> Hsv_expr.compile_error ~loc "ppx_hash: functions can not be hashed." | Ptyp_variant (row_fields, Closed, _) -> hash_variant ~loc row_fields value | _ -> let s = string_of_core_type ty in Hsv_expr.compile_error ~loc (Printf.sprintf "ppx_hash: unsupported type: %s" s)) and hash_fold_of_ty_fun ~type_constraint ty = let loc = { ty.ptyp_loc with loc_ghost = true } in let arg = "arg" in let maybe_constrained_arg = if type_constraint then ppat_constraint ~loc (pvar ~loc arg) ty else pvar ~loc arg in let hsv_pat, hsv_expr = Hsv_expr.to_expression ~loc (hash_fold_of_ty ty (evar ~loc arg)) in eta_reduce_if_possible [%expr fun [%p hsv_pat] [%p maybe_constrained_arg] -> [%e hsv_expr]] and hash_fold_of_record ~loc lds value = let is_evar = function | { pexp_desc = Pexp_ident _; _ } -> true | _ -> false in assert (is_evar value); List.fold_left lds ~init:(Hsv_expr.identity ~loc) ~f:(fun hsv ld -> Hsv_expr.compose ~loc hsv (let loc = ld.pld_loc in let label = Located.map lident ld.pld_name in let should_ignore, should_warn = should_ignore_label_declaration ld in let field_handling = match ld.pld_mutable, should_ignore with | Mutable, `incorporate -> `error "require [@hash.ignore] or [@compare.ignore] on mutable record field" | (Mutable | Immutable), `ignore -> `ignore | Immutable, `incorporate -> `incorporate in let hsv = match field_handling with | `error s -> Hsv_expr.compile_error ~loc (Printf.sprintf "ppx_hash: %s" s) | `incorporate -> hash_fold_of_ty ld.pld_type (pexp_field ~loc value label) | `ignore -> Hsv_expr.identity ~loc in match should_warn with | None -> hsv | Some attribute -> Hsv_expr.with_attributes ~f:(fun attributes -> attribute :: attributes) hsv)) ;; let hash_fold_of_abstract ~loc type_name value = let str = Printf.sprintf "hash called on the type %s, which is abstract in an implementation." type_name in Hsv_expr.of_expression_unchecked [%expr let _ = hsv in let _ = [%e value] in failwith [%e estring ~loc str]] ;; (** this does not change behavior (keeps the expression side-effect if any), but it can make the compiler happy when the expression occurs on the rhs of an [let rec] binding. *) let eta_expand ~loc f = [%expr let func = [%e f] in fun x -> func x] ;; let recognize_simple_type ty = match ty.ptyp_desc with | Ptyp_constr (lident, []) -> Some lident | _ -> None ;; let hash_of_ty_fun ~special_case_simple_types ~type_constraint ty = let loc = { ty.ptyp_loc with loc_ghost = true } in let arg = "arg" in let maybe_constrained_arg = if type_constraint then ppat_constraint ~loc (pvar ~loc arg) ty else pvar ~loc arg in match recognize_simple_type ty with | Some lident when special_case_simple_types -> unapplied_type_constr_conv ~loc lident ~f:hash_ | _ -> let hsv_pat, hsv_expr = Hsv_expr.to_expression ~loc (hash_fold_of_ty ty (evar ~loc arg)) in [%expr fun [%p maybe_constrained_arg] -> Ppx_hash_lib.Std.Hash.get_hash_value (let [%p hsv_pat] = Ppx_hash_lib.Std.Hash.create () in [%e hsv_expr])] ;; let hash_structure_item_of_td td = let loc = td.ptype_loc in match td.ptype_params with | _ :: _ -> [] | [] -> [ (let bnd = pvar ~loc (hash_ td.ptype_name.txt) in let typ = combinator_type_of_type_declaration td ~f:hash_type in let pat = ppat_constraint ~loc bnd typ in let expected_scope, expr = let is_simple_type ty = match recognize_simple_type ty with | Some _ -> true | None -> false in match td.ptype_kind, td.ptype_manifest with | Ptype_abstract, Some ty when is_simple_type ty -> ( `uses_rhs , hash_of_ty_fun ~special_case_simple_types:true ~type_constraint:false ty ) | _ -> ( `uses_hash_fold_t_being_defined , hash_of_ty_fun ~special_case_simple_types:false ~type_constraint:false { ptyp_loc = loc ; ptyp_loc_stack = [] ; ptyp_attributes = [] ; ptyp_desc = Ptyp_constr ({ loc; txt = Lident td.ptype_name.txt }, []) } ) in expected_scope, value_binding ~loc ~pat ~expr:(eta_expand ~loc expr)) ] ;; let hash_fold_structure_item_of_td td ~rec_flag = let loc = { td.ptype_loc with loc_ghost = true } in let arg = "arg" in let body = let v = evar ~loc arg in match td.ptype_kind with | Ptype_variant cds -> hash_sum ~loc cds v | Ptype_record lds -> hash_fold_of_record ~loc lds v | Ptype_open -> Hsv_expr.compile_error ~loc "ppx_hash: open types are not supported" | Ptype_abstract -> (match td.ptype_manifest with | None -> hash_fold_of_abstract ~loc td.ptype_name.txt v | Some ty -> (match ty.ptyp_desc with | Ptyp_variant (_, Open, _) | Ptyp_variant (_, Closed, Some (_ :: _)) -> Hsv_expr.compile_error ~loc:ty.ptyp_loc "ppx_hash: cannot hash open polymorphic variant types" | Ptyp_variant (row_fields, _, _) -> hash_variant ~loc row_fields v | _ -> hash_fold_of_ty ty v)) in let vars = List.map td.ptype_params ~f:(fun p -> get_type_param_name p) in let extra_names = List.map vars ~f:(fun x -> tp_name x.txt) in let hsv_pat, hsv_expr = Hsv_expr.to_expression ~loc body in let patts = List.map extra_names ~f:(pvar ~loc) @ [ hsv_pat; pvar ~loc arg ] in let bnd = pvar ~loc (hash_fold_ td.ptype_name.txt) in let scheme = combinator_type_of_type_declaration td ~f:hash_fold_type in let pat = ppat_constraint ~loc bnd (ptyp_poly ~loc vars scheme) in let expr = eta_reduce_if_possible_and_nonrec ~rec_flag (eabstract ~loc patts hsv_expr) in let use_rigid_variables = match td.ptype_kind with | Ptype_variant _ -> true | _ -> false in let expr = if use_rigid_variables then ( let type_name = td.ptype_name.txt in List.fold_right vars ~f:(fun s -> pexp_newtype ~loc { txt = rigid_type_var ~type_name s.txt; loc = s.loc }) ~init:(pexp_constraint ~loc expr (make_type_rigid ~type_name scheme))) else expr in value_binding ~loc ~pat ~expr ;; let pstr_value ~loc rec_flag bindings = match bindings with | [] -> [] | nonempty_bindings -> (* [pstr_value] with zero bindings is invalid *) [ pstr_value ~loc rec_flag nonempty_bindings ] ;; let str_type_decl ~loc ~path:_ (rec_flag, tds) = let tds = List.map tds ~f:name_type_params_in_td in let rec_flag = (object inherit type_is_recursive rec_flag tds as super method! label_declaration ld = match fst (should_ignore_label_declaration ld) with | `ignore -> () | `incorporate -> super#label_declaration ld method! core_type ty = if core_type_is_ignored ty then () else super#core_type ty end) #go () in let hash_fold_bindings = List.map ~f:(hash_fold_structure_item_of_td ~rec_flag) tds in let hash_bindings = List.concat (List.map ~f:hash_structure_item_of_td tds) in match rec_flag with | Recursive -> (* if we wanted to maximize the scope hygiene here this would be, in this order: - recursive group of [hash_fold] - nonrecursive group of [hash] that are [`uses_hash_fold_t_being_defined] - recursive group of [hash] that are [`uses_rhs] but fighting the "unused rec flag" warning is just way too hard *) pstr_value ~loc Recursive (hash_fold_bindings @ List.map ~f:snd hash_bindings) | Nonrecursive -> let rely_on_hash_fold_t, use_rhs = List.partition_map hash_bindings ~f:(function | `uses_hash_fold_t_being_defined, binding -> First binding | `uses_rhs, binding -> Second binding) in pstr_value ~loc Nonrecursive (hash_fold_bindings @ use_rhs) @ pstr_value ~loc Nonrecursive rely_on_hash_fold_t ;; let mk_sig ~loc:_ ~path:_ (_rec_flag, tds) = List.concat (List.map tds ~f:(fun td -> let monomorphic = List.is_empty td.ptype_params in let definition ~f_type ~f_name = let type_ = combinator_type_of_type_declaration td ~f:f_type in let name = let tn = td.ptype_name.txt in f_name tn in let loc = td.ptype_loc in psig_value ~loc (value_description ~loc ~name:{ td.ptype_name with txt = name } ~type_ ~prim:[]) in List.concat [ [ definition ~f_type:hash_fold_type ~f_name:hash_fold_ ] ; (if monomorphic then [ definition ~f_type:hash_type ~f_name:hash_ ] else []) ])) ;; let sig_type_decl ~loc ~path (rec_flag, tds) = match mk_named_sig ~loc ~sg_name:"Ppx_hash_lib.Hashable.S" ~handle_polymorphic_variant:true tds with | Some include_info -> [ psig_include ~loc include_info ] | None -> mk_sig ~loc ~path (rec_flag, tds) ;; let hash_fold_core_type ty = hash_fold_of_ty_fun ~type_constraint:true ty let hash_core_type ty = hash_of_ty_fun ~special_case_simple_types:true ~type_constraint:true ty ;;
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