refactor: hide the type of digest errors (#13786)

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

Author: rgrinberg

src/dune_cache/shared.ml

@@ -173,39 +173,11 @@ let compute_target_digests_or_raise_error
   | Error errors ->
     let missing, errors =
       let process_target (target, error) =
-        match error with
-        | Cached_digest.Digest_result.Error.No_such_file -> Left target
-        | Broken_symlink ->
-          let error = Pp.verbatim "Broken symbolic link" in
-          Right (target, error)
-        | Cyclic_symlink ->
-          let error = Pp.verbatim "Cyclic symbolic link" in
-          Right (target, error)
-        | Unexpected_kind file_kind ->
-          let error =
-            Pp.verbatim
-              (sprintf
-                 "Unexpected file kind %S (%s)"
-                 (File_kind.to_string file_kind)
-                 (File_kind.to_string_hum file_kind))
-          in
-          Right (target, error)
-        | Unix_error (error, syscall, arg) ->
-          let unix_error = Unix_error.Detailed.create error ~syscall ~arg in
-          Right (target, Unix_error.Detailed.pp unix_error)
-        | Unrecognized exn ->
-          let error =
-            Pp.verbatim
-              (match exn with
-               | Sys_error msg ->
-                 let prefix =
-                   let expected_syscall_path = Path.to_string (Path.build target) in
-                   expected_syscall_path ^ ": "
-                 in
-                 String.drop_prefix_if_exists ~prefix msg
-               | exn -> Printexc.to_string exn)
-          in
-          Right (target, error)
+        if Cached_digest.Digest_result.Error.no_such_file error
+        then Left target
+        else (
+          let error = Cached_digest.Digest_result.Error.pp error (Path.build target) in
+          Right (target, error))
       in
       Nonempty_list.to_list errors |> List.partition_map ~f:process_target
     in

src/dune_digest/cached_digest.ml

@@ -189,6 +189,36 @@ module Digest_result = struct
       | Unix_error of Unix_error.Detailed.t
       | Unrecognized of exn
 
+    let no_such_file = function
+      | No_such_file -> true
+      | _ -> false
+    ;;
+
+    let pp t path =
+      match t with
+      | No_such_file -> Pp.verbatim "No such file"
+      | Broken_symlink -> Pp.verbatim "Broken symbolic link"
+      | Cyclic_symlink -> Pp.verbatim "Cyclic symbolic link"
+      | Unexpected_kind file_kind ->
+        Pp.verbatimf
+          "Unexpected file kind %S (%s)"
+          (File_kind.to_string file_kind)
+          (File_kind.to_string_hum file_kind)
+      | Unix_error (error, syscall, arg) ->
+        let unix_error = Unix_error.Detailed.create error ~syscall ~arg in
+        Unix_error.Detailed.pp unix_error
+      | Unrecognized exn ->
+        Pp.verbatim
+          (match exn with
+           | Sys_error msg ->
+             let prefix =
+               let expected_syscall_path = Path.to_string path in
+               expected_syscall_path ^ ": "
+             in
+             String.drop_prefix_if_exists ~prefix msg
+           | exn -> Printexc.to_string exn)
+    ;;
+
     let equal x y =
       match x, y with
       | No_such_file, No_such_file -> true

src/dune_digest/cached_digest.mli

@@ -4,14 +4,10 @@ open Import
 
 module Digest_result : sig
   module Error : sig
-    type t =
-      | No_such_file
-      | Broken_symlink
-      | Cyclic_symlink
-      | Unexpected_kind of File_kind.t
-      | Unix_error of Unix_error.Detailed.t (** Can't be [ENOENT]. *)
-      | Unrecognized of exn
+    type t
 
+    val no_such_file : t -> bool
+    val pp : t -> Path.t -> _ Pp.t
     val to_dyn : t -> Dyn.t
   end
 

src/dune_engine/fs_memo.ml

@@ -316,16 +316,12 @@ let file_digest_exn ?loc path =
   file_digest path
   >>= function
   | Ok digest -> Memo.return digest
-  | Error No_such_file -> report_user_error []
-  | Error Broken_symlink -> report_user_error [ Pp.text "Broken symbolic link" ]
-  | Error Cyclic_symlink -> report_user_error [ Pp.text "Cyclic symbolic link" ]
-  | Error (Unexpected_kind st_kind) ->
-    report_user_error
-      [ Pp.textf "This is not a regular file (%s)" (File_kind.to_string st_kind) ]
-  | Error (Unix_error unix_error) ->
-    report_user_error [ Unix_error.Detailed.pp_reason unix_error ]
-  | Error (Unrecognized exn) ->
-    report_user_error [ Pp.textf "%s" (Printexc.to_string exn) ]
+  | Error e ->
+    if Cached_digest.Digest_result.Error.no_such_file e
+    then report_user_error []
+    else
+      report_user_error
+        [ Cached_digest.Digest_result.Error.pp e (Path.outside_build_dir path) ]
 ;;
 
 let dir_contents ?(force_update = false) path =