Source file ppx.ml
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open Ppxlib
module Builder = Ast_builder.Default
type target = Native | Js
let mode = ref Native
module Platform = struct
let pattern = Ast_pattern.(__')
let collect_expressions ~loc first second =
match (first.pc_lhs.ppat_desc, second.pc_lhs.ppat_desc) with
| ( Ppat_construct
({ txt = Lident "Server" | Ldot (Lident "Runtime", "Server"); _ }, _),
Ppat_construct
({ txt = Lident "Client" | Ldot (Lident "Runtime", "Client"); _ }, _)
) ->
Ok (first.pc_rhs, second.pc_rhs)
| ( Ppat_construct
({ txt = Lident "Client" | Ldot (Lident "Runtime", "Client"); _ }, _),
Ppat_construct
({ txt = Lident "Server" | Ldot (Lident "Runtime", "Server"); _ }, _)
) ->
Ok (second.pc_rhs, first.pc_rhs)
| _ ->
Error
[%expr
[%ocaml.error
"[browser_only] switch%%platform requires 2 cases: `Server` and \
`Client`"]]
let switch_platform_requires_a_match ~loc =
[%expr
[%ocaml.error
"[browser_ppx] switch%%platform requires a match expression"]]
let handler ~ctxt:_ { txt = payload; loc } =
match payload with
| PStr [ { pstr_desc = Pstr_eval (expression, _); _ } ] -> (
match expression.pexp_desc with
| Pexp_match (_expression, cases) -> (
match cases with
| [ first; second ] -> (
match collect_expressions ~loc first second with
| Ok (server_expr, client_expr) -> (
match !mode with
| Js -> client_expr
| Native -> server_expr)
| Error error_msg_expr -> error_msg_expr)
| _ -> switch_platform_requires_a_match ~loc)
| _ -> switch_platform_requires_a_match ~loc)
| _ -> switch_platform_requires_a_match ~loc
let rule =
Context_free.Rule.extension
(Extension.V3.declare "platform" Extension.Context.expression pattern
handler)
end
let remove_type_constraint pattern =
match pattern with
| { ppat_desc = Ppat_constraint (pattern, _); _ } -> pattern
| _ -> pattern
let rec last_expr_to_raise_impossible ~loc original_name expr =
match expr.pexp_desc with
| Pexp_constraint (expr, _) ->
last_expr_to_raise_impossible ~loc original_name expr
| Pexp_fun (arg_label, _arg_expression, fun_pattern, expression) ->
let new_fun_pattern = remove_type_constraint fun_pattern in
let fn =
Builder.pexp_fun ~loc arg_label None new_fun_pattern
(last_expr_to_raise_impossible ~loc original_name expression)
in
{ fn with pexp_attributes = expr.pexp_attributes }
| _ ->
[%expr
Runtime.fail_impossible_action_in_ssr
[%e Builder.estring ~loc original_name]]
module Browser_only = struct
let get_function_name pattern =
match pattern with Ppat_var { txt = name; _ } -> name | _ -> "<unkwnown>"
let error_only_works_on ~loc =
[%expr
[%ocaml.error
"[browser_ppx] browser_only works on function definitions or values. \
If there's another case where it can be helpful, feel free to open an \
issue in https://github.com/ml-in-barcelona/server-reason-react."]]
let remove_alert_browser_only ~loc =
Builder.attribute ~loc ~name:{ txt = "alert"; loc }
~payload:(PStr [ [%stri "-browser_only"] ])
let browser_only_fun ~loc arg_label pattern expression =
let stringified = Ppxlib.Pprintast.string_of_expression expression in
let message = Builder.estring ~loc stringified in
let fn =
Builder.pexp_fun ~loc arg_label None pattern
[%expr Runtime.fail_impossible_action_in_ssr [%e message]]
in
{ fn with pexp_attributes = expression.pexp_attributes }
let browser_only_value_binding pattern expression =
let loc = pattern.ppat_loc in
match pattern with
| [%pat? ()] -> Builder.value_binding ~loc ~pat:pattern ~expr:[%expr ()]
| _ -> (
match expression.pexp_desc with
| Pexp_constraint
( {
pexp_desc =
Pexp_fun (_arg_label, _arg_expression, _fun_pattern, _expr);
_;
},
_type_constraint ) ->
let function_name = get_function_name pattern.ppat_desc in
let expr =
last_expr_to_raise_impossible ~loc function_name expression
in
let vb = Builder.value_binding ~loc ~pat:pattern ~expr in
{ vb with pvb_attributes = [ remove_alert_browser_only ~loc ] }
| Pexp_fun (_arg_label, _arg_expression, _fun_pattern, _expr) ->
let function_name = get_function_name pattern.ppat_desc in
let expr =
last_expr_to_raise_impossible ~loc function_name expression
in
let vb = Builder.value_binding ~loc ~pat:pattern ~expr in
{ vb with pvb_attributes = [ remove_alert_browser_only ~loc ] }
| Pexp_ident { txt = longident; loc } ->
let stringified = Ppxlib.Longident.name longident in
let message = Builder.estring ~loc stringified in
let vb =
Builder.value_binding ~loc ~pat:pattern
~expr:[%expr Runtime.fail_impossible_action_in_ssr [%e message]]
in
{ vb with pvb_attributes = [ remove_alert_browser_only ~loc ] }
| _ ->
Builder.value_binding ~loc ~pat:pattern
~expr:(error_only_works_on ~loc))
let extractor = Ast_pattern.(single_expr_payload __)
let expression_handler ~ctxt payload =
let loc = Expansion_context.Extension.extension_point_loc ctxt in
match !mode with
| Js -> payload
| Native -> (
match payload.pexp_desc with
| Pexp_apply (expression, _) ->
let stringified =
Ppxlib.Pprintast.string_of_expression expression
in
let message = Builder.estring ~loc stringified in
[%expr Runtime.fail_impossible_action_in_ssr [%e message]]
| Pexp_constraint
( {
pexp_desc =
Pexp_fun (arg_label, _arg_expression, pattern, expression);
},
type_constraint ) ->
let fn = browser_only_fun ~loc arg_label pattern expression in
Builder.pexp_constraint ~loc
{ fn with pexp_attributes = expression.pexp_attributes }
type_constraint
| Pexp_fun (arg_label, _arg_expression, pattern, expr) ->
let function_name = get_function_name pattern.ppat_desc in
let new_fun_pattern = remove_type_constraint pattern in
Builder.pexp_fun ~loc arg_label None new_fun_pattern
(last_expr_to_raise_impossible ~loc function_name expr)
| Pexp_let (rec_flag, value_bindings, expression) ->
let pexp_let =
Builder.pexp_let ~loc rec_flag
(List.map
(fun binding ->
browser_only_value_binding binding.pvb_pat binding.pvb_expr)
value_bindings)
expression
in
[%expr [%e pexp_let]]
| _ -> error_only_works_on ~loc)
let expression_rule =
Context_free.Rule.extension
(Extension.V3.declare "browser_only" Extension.Context.expression
extractor expression_handler)
let make_vb_with_browser_only ~loc ?type_constraint pattern expression =
match type_constraint with
| Some type_constraint ->
[%stri
let[@warning "-27-32"] ([%p pattern] :
([%t type_constraint]
[@alert
browser_only
"This expression is marked to only run \
on the browser where JavaScript can \
run. You can only use it inside a \
let%browser_only function."])) =
([%e expression] [@alert "-browser_only"])]
| None ->
[%stri
let[@warning "-27-32"] ([%p pattern]
[@alert
browser_only
"This expression is marked to only run on the browser where \
JavaScript can run. You can only use it inside a \
let%browser_only function."]) =
([%e expression] [@alert "-browser_only"])]
let =
let open Ast_pattern in
let =
pstr_value __ (value_binding ~pat:__ ~expr:__ ^:: nil)
in
pstr @@ extractor_in_let ^:: nil
let structure_item_handler ~ctxt rec_flag pattern expression =
let loc = Expansion_context.Extension.extension_point_loc ctxt in
let do_nothing rec_flag =
match rec_flag with
| Recursive -> [%stri let rec [%p pattern] = [%e expression]]
| Nonrecursive -> [%stri let [%p pattern] = [%e expression]]
in
match !mode with
| Js -> do_nothing rec_flag
| Native -> (
match expression.pexp_desc with
| Pexp_constraint
( {
pexp_desc =
Pexp_fun (arg_label, _arg_expression, fun_pattern, expr);
_;
},
type_constraint ) ->
let original_function_name = get_function_name pattern.ppat_desc in
let new_fun_pattern = remove_type_constraint fun_pattern in
let fn =
Builder.pexp_fun ~loc arg_label None new_fun_pattern
(last_expr_to_raise_impossible ~loc original_function_name expr)
in
let item = { fn with pexp_attributes = expr.pexp_attributes } in
make_vb_with_browser_only ~loc ~type_constraint pattern item
| Pexp_fun (arg_label, _arg_expression, fun_pattern, expr) ->
let original_function_name = get_function_name pattern.ppat_desc in
let new_fun_pattern = remove_type_constraint fun_pattern in
let fn =
Builder.pexp_fun ~loc arg_label None new_fun_pattern
(last_expr_to_raise_impossible ~loc original_function_name expr)
in
let item = { fn with pexp_attributes = expr.pexp_attributes } in
make_vb_with_browser_only ~loc pattern item
| Pexp_ident { txt = _longident; loc } ->
let item = [%expr Obj.magic ()] in
make_vb_with_browser_only ~loc pattern item
| Pexp_newtype (name, expr) ->
let original_function_name = name.txt in
let item =
last_expr_to_raise_impossible ~loc original_function_name expr
in
make_vb_with_browser_only ~loc pattern item
| _expr -> do_nothing rec_flag)
let structure_item_rule =
Context_free.Rule.extension
(Extension.V3.declare "browser_only" Extension.Context.structure_item
extractor structure_item_handler)
end
let () =
Driver.add_arg "-js"
(Unit (fun () -> mode := Js))
~doc:"preprocess for js build";
Driver.V2.register_transformation "browser_ppx"
~rules:
[
Browser_only.expression_rule;
Browser_only.structure_item_rule;
Platform.rule;
]