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Most errors happening during ppxlib rewriting process are ultimately turned into
error extension nodes.
Undefined derivers are turned into error nodes
$ echo "type t = int [@@deriving undefined]" >> undefined_deriver.ml
$ ./deriver.exe undefined_deriver.ml
type t = int[@@deriving undefined]
include
struct
let _ = fun (_ : t) -> ()
[%%ocaml.error
"Ppxlib.Deriving: 'undefined' is not a supported type deriving generator"]
end[@@ocaml.doc "@inline"][@@merlin.hide ]
Error nodes are generated when parsing of payload fails.
export_string expects only one argument, a string, and output it.
Anything else will embed an error extension node
$ echo "let _ = [%export_string \"string\"]" > parsing_payload_extension.ml
$ echo "let _ = [%export_string \"string\" \"other\"]" >> parsing_payload_extension.ml
$ echo "let _ = [%export_string identifier]" >> parsing_payload_extension.ml
$ ./extender.exe parsing_payload_extension.ml
[%%ocaml.error "constant expected"]
[%%ocaml.error "constant expected"]
let _ = "string"
let _ = [%export_string "string" "other"]
let _ = [%export_string identifier]
$ echo "type a = int [@@deriving a_string]" > parsing_payload_deriver.ml
$ echo "type b = int [@@deriving a_string unexpected_args]" >> parsing_payload_deriver.ml
$ ./deriver.exe parsing_payload_deriver.ml
type a = int[@@deriving a_string]
include struct let _ = fun (_ : a) -> ()
let _ = "derived_string" end[@@ocaml.doc "@inline"][@@merlin.hide
]
type b = int[@@deriving a_string unexpected_args]
include
struct
let _ = fun (_ : b) -> ()
[%%ocaml.error
"Ppxlib.Deriving: non-optional labelled argument or record expected"]
end[@@ocaml.doc "@inline"][@@merlin.hide ]
Error nodes are generated when dependent derivers are not applied.
$ echo "type a = int [@@deriving a_dependent_string]" > dependent_derivers.ml
$ ./deriver.exe dependent_derivers.ml
type a = int[@@deriving a_dependent_string]
include
struct
let _ = fun (_ : a) -> ()
[%%ocaml.error
"Deriver a_string is needed for a_dependent_string, you need to add it before in the list"]
let _ = "derived_string"
end[@@ocaml.doc "@inline"][@@merlin.hide ]
$ echo "type b = int [@@deriving a_dependent_string, a_string]" > dependent_derivers.ml
$ ./deriver.exe dependent_derivers.ml
type b = int[@@deriving (a_dependent_string, a_string)]
include
struct
let _ = fun (_ : b) -> ()
[%%ocaml.error
"Deriver a_string is needed for a_dependent_string, you need to add it before in the list"]
let _ = "derived_string"
let _ = "derived_string"
end[@@ocaml.doc "@inline"][@@merlin.hide ]
$ echo "type b = int [@@deriving a_string, a_dependent_string]" > dependent_derivers.ml
$ ./deriver.exe dependent_derivers.ml
type b = int[@@deriving (a_string, a_dependent_string)]
include
struct
let _ = fun (_ : b) -> ()
let _ = "derived_string"
let _ = "derived_string"
end[@@ocaml.doc "@inline"][@@merlin.hide ]
Flag `-raise-embedded-errors` raises the first embedded error in the AST.
$ echo "let () = ()" > embedded_error.ml
$ echo "module T = struct [%%ocaml.error \"error 1\"] end" >> embedded_error.ml
$ echo "[%%ocaml.error \"error 2\"]" >> embedded_error.ml
$ ./extender.exe embedded_error.ml -raise-embedded-errors
File "embedded_error.ml", line 2, characters 21-32:
2 | module T = struct [%%ocaml.error "error 1"] end
^^^^^^^^^^^
Error: error 1
[1]
Undeprecated `[@@@deriving.end]` runs just fine.
$ echo "type t [@@deriving_inline a_string] [@@@deriving.end]" > embedded_error.ml
$ ./deriver.exe embedded_error.ml -diff-cmd "diff -u --label source --label derived"
type t[@@deriving_inline a_string]
[@@@deriving.end ]
--- source
+++ derived
@@ -1 +1,4 @@
-type t [@@deriving_inline a_string] [@@@deriving.end]
+type t [@@deriving_inline a_string]
+let _ = fun (_ : t) -> ()
+let _ = "derived_string"
+[@@@deriving.end]
[1]
Deprecated `[@@@deriving.end]` produces an error.
$ echo "type t [@@deriving_inline a_string] [@@@deriving.end]" > embedded_error.ml
$ ./deriver.exe embedded_error.ml -allow-deriving-end false
[%%ocaml.error
"ppxlib: [@@@deriving.end] is deprecated, please use [@@@ppxlib.inline.end]. If you need the deprecated attribute temporarily, pass [-allow-deriving-end] to the ppx driver)."]
type t[@@deriving_inline a_string]
[@@@deriving.end ]
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