ppxlib

Standard library for ppx rewriters
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Library ppxlib
Module Ppxlib . Attribute

This module provides hygiene for attributes. The goal is to report misuses of attributes to the user as soon as possible so that no mistyped attribute get silently ignored.

type ('context, 'payload) t

Type of declared attribute.

The 'context type parameter describes where the attribute is expected and the 'payload one what its payload should contain.

type packed =
| T : ( _, _ ) t -> packed
module Context : sig ... end
val declare : string -> 'a Context.t -> ( Astlib.Ast_500.Parsetree.payload, 'b, 'c ) Ast_pattern.t -> 'b -> ( 'a, 'c ) t

declare fully_qualified_name context payload_pattern k declares an attribute. k is used to build the value resulting from parsing the payload.

For instance if a rewriter named "foo" expect the attribute @@default on record field declaration with an expression as payload:

let default =
  Attribute.declare "foo.default" Attribute.Context.label_declaration
    Ast_pattern.(pstr (pstr_eval __ nil))
    (fun x -> x)

fully_qualified_name is expected to be a dot-separated list of names. When matching, any full suffix will be accepted. So for instance an attribute declared with name "foo.bar.default" will match exactly these attribute names: "default", "bar.default" and "foo.bar.default".

Additionally it is possible to prevent a suffix to be shortened by prefixing it with '@'. So for instance an attribute declared with name "foo.@bar.default" will match exactly these attribute names: "bar.default" and "foo.bar.default".

When matching against a list of attributes on an item, if several matches are possible, the longest one is used. For instance using the attribute "foo.default" declared in the previous example, on this code it will match the @foo.default 0 attribute:

type t = { x : int [@default 42] [@foo.default 0] } 

This is to allow the user to specify a @default attribute for all re-writers that use it but still put a specific one for one specific re-writer.

It is not allowed to declare an attribute with a name that matches a previously-defined one on the same context. For instance trying to declare the same attribute twice will fail.

val declare_with_name_loc : string -> 'a Context.t -> ( Astlib.Ast_500.Parsetree.payload, 'b, 'c ) Ast_pattern.t -> ( name_loc:Location.t -> 'b ) -> ( 'a, 'c ) t

Same as declare but the callback receives the location of the name of the attribute.

val name : ( _, _ ) t -> string
val context : ( 'a, _ ) t -> 'a Context.t
val get_res : ( 'a, 'b ) t -> ?mark_as_seen:bool -> 'a -> ( 'b option, Location.Error.t Stdppx.NonEmptyList.t ) result

Gets the associated attribute value. Marks the attribute as seen unless mark_as_seen=false. Returns an Error if the attribute is duplicated

val get : ( 'a, 'b ) t -> ?mark_as_seen:bool -> 'a -> 'b option

See get_res. Raises a located error if the attribute is duplicated

val consume_res : ( 'a, 'b ) t -> 'a -> ( ('a * 'b) option, Location.Error.t Stdppx.NonEmptyList.t ) result

consume_res t x returns the value associated to attribute t on x if present as well as x with t removed.

val consume : ( 'a, 'b ) t -> 'a -> ('a * 'b) option

See consume_res. Raises a located exception in case of error.

val remove_seen_res : 'a Context.t -> packed list -> 'a -> ( 'a, Location.Error.t Stdppx.NonEmptyList.t ) result

remove_seen x attrs removes the set of attributes matched by elements of attrs. Only remove them if they where seen by get or consume.

val remove_seen : 'a Context.t -> packed list -> 'a -> 'a

See remove_seen_res. Raises in case of error.

module Floating : sig ... end
val explicitly_drop : Ast_traverse.iter

Code that is voluntarily dropped by a rewriter needs to be given to this object. All attributes inside will be marked as handled.

val check_unused : Ast_traverse.iter

Raise if there are unused attributes.

val collect_unused_attributes_errors : Location.Error.t list Ast_traverse.fold

Collect all errors due to unused attributes.

val collect : Ast_traverse.iter

Collect all attribute names. To be used in conjunction with check_all_seen.

val collect_unseen_errors : unit -> Location.Error.t list
val check_all_seen : unit -> unit

Check that all attributes collected by freshen_and_collect have been:

  • matched at least once by one of: get, consume or Floating.convert
  • seen by check_unused (to allow allowlisted attributed to pass through)

This helps with faulty ppx rewriters that silently drop attributes.

val mark_as_handled_manually : Astlib.Ast_500.Parsetree.attribute -> unit

Mark an attribute as seen and handled. This is only to make ppx rewriters that don't use ppxlib works well with the ones that do use it.

val dropped_so_far_structure : Astlib.Ast_500.Parsetree.structure_item list -> string Loc.t list

Return the list of attributes that have been dropped so far: attributes that haven't been marked and are not present in the given AST. This is used to debug extensions that drop attributes.

val dropped_so_far_signature : Astlib.Ast_500.Parsetree.signature_item list -> string Loc.t list
val reset_checks : unit -> unit
val pattern : ( 'a, 'b ) t -> ( 'a, 'c, 'd ) Ast_pattern.t -> ( 'a, 'b option -> 'c, 'd ) Ast_pattern.t
val pattern_res : ( 'a, 'b ) t -> ( 'a, 'c, 'd ) Ast_pattern.t -> ( 'a, 'b option -> 'c, ( 'd, Location.Error.t Stdppx.NonEmptyList.t ) result ) Ast_pattern.t