[utils] make `read_file` return a `Result.t`

Summary: Small API improvement for better error messages.

Reviewed By: mbouaziz

Differential Revision: D5293334

fbshipit-source-id: ef7f7e2

infer/src/backend/InferPrint.re

@@ -1026,7 +1026,7 @@ let pp_summary_by_report_kind
 
 let pp_json_report_by_report_kind formats_by_report_kind fname =>
   switch (Utils.read_file fname) {
-  | Some report_lines =>
+  | Ok report_lines =>
     let pp_json_issues format_list report => {
       let pp_json_issue (format_kind, outf: Utils.outfile) =>
         switch format_kind {
@@ -1048,7 +1048,7 @@ let pp_json_report_by_report_kind formats_by_report_kind fname =>
       | _ => ()
       };
     List.iter f::pp_report_by_report_kind formats_by_report_kind
-  | None => failwithf "Error reading %s. Does the file exist?" fname
+  | Error error => failwithf "Error reading '%s': %s" fname error
   };
 
 let pp_lint_issues_by_report_kind formats_by_report_kind error_filter linereader procname error_log => {

infer/src/backend/StatsAggregator.re

@@ -71,8 +71,8 @@ let load_data_from_infer_deps file => {
   let lines = Utils.read_file file;
   try (
     switch lines {
-    | Some l => Ok (List.map f::extract_target_and_path l)
-    | None => raise (Failure ("Error reading '" ^ file ^ "'"))
+    | Ok l => Ok (List.map f::extract_target_and_path l)
+    | Error error => raise (Failure (Printf.sprintf "Error reading '%s': %s" file error))
     }
   ) {
   | Failure msg => Error msg

infer/src/backend/infer.ml

@@ -403,12 +403,15 @@ let analyze driver_mode =
 
 (** as the Config.fail_on_bug flag mandates, exit with error when an issue is reported *)
 let fail_on_issue_epilogue () =
-  let issues_json = DB.Results_dir.(path_to_filename Abs_root ["report.json"]) in
-  match Utils.read_file (DB.filename_to_string issues_json) with
-  | Some lines ->
+  let issues_json = DB.Results_dir.(path_to_filename Abs_root ["report.json"])
+                    |> DB.filename_to_string in
+  match Utils.read_file issues_json with
+  | Ok lines ->
       let issues = Jsonbug_j.report_of_string @@ String.concat ~sep:"" lines in
       if issues <> [] then exit Config.fail_on_issue_exit_code
-  | None -> ()
+  | Error error ->
+      L.internal_error "Failed to read report file '%s': %s@." issues_json error ;
+      ()
 
 let log_infer_args driver_mode =
   L.environment_info "INFER_ARGS = %s@\n"

infer/src/backend/mergeCapture.ml

@@ -29,9 +29,10 @@ let modified_targets = ref String.Set.empty
 
 let modified_file file =
   match Utils.read_file file with
-  | Some targets ->
+  | Ok targets ->
       modified_targets := List.fold ~f:String.Set.add ~init:String.Set.empty targets
-  | None ->
+  | Error error ->
+      L.user_error "Failed to read modified targets file '%s': %s@." file error ;
       ()
 
 type stats =
@@ -192,9 +193,11 @@ let process_merge_file deps_file =
         then slink ~stats ~skiplevels infer_out_src infer_out_dst
     | _ ->
         () in
-  Option.iter
-    ~f:(fun lines -> List.iter ~f:process_line lines)
-    (Utils.read_file deps_file);
+  (
+    match Utils.read_file deps_file with
+    | Ok lines -> List.iter ~f:process_line lines
+    | Error error -> L.internal_error "Couldn't read deps file '%s': %s" deps_file error
+  );
   create_multilinks ();
   L.progress "Captured results merged.@.";
   L.progress "Targets merged: %d@." stats.targets_merged;

infer/src/base/Config.ml

@@ -1509,10 +1509,11 @@ and specs_library =
         if Filename.is_relative path then
           failwith ("Failing because path " ^ path ^ " is not absolute") in
       match Utils.read_file (resolve fname) with
-      | Some pathlist ->
+      | Ok pathlist ->
           List.iter ~f:validate_path pathlist;
           pathlist
-      | None -> failwith ("cannot read file " ^ fname ^ " from cwd " ^ (Sys.getcwd ()))
+      | Error error ->
+          failwithf "cannot read file '%s' from cwd '%s': %s" fname (Sys.getcwd ()) error
     in
     (* Add the newline-separated directories listed in <file> to the list of directories to be
        searched for .spec files *)

infer/src/base/Multilinks.re

@@ -30,8 +30,10 @@ let reset_cache () => String.Table.clear multilink_files_cache;
 let read ::dir :option t => {
   let multilink_fname = Filename.concat dir multilink_file_name;
   switch (Utils.read_file multilink_fname) {
-  | None => None
-  | Some lines =>
+  | Error error =>
+    L.internal_error "Couldn't read multilink file '%s': %s@." multilink_fname error;
+    None
+  | Ok lines =>
     let links = create ();
     List.iter
       f::(fun line => String.Table.set links key::(Filename.basename line) data::line) lines;

infer/src/base/SourceFile.ml

@@ -10,6 +10,8 @@
 open! IStd
 open! PVariant
 
+module L = Logging
+
 let count_newlines (path: string): int =
   let f file = In_channel.fold_lines file ~init:0 ~f:(fun i _ -> i + 1) in
   In_channel.with_file path ~f
@@ -134,19 +136,22 @@ let create ?(warn_on_error=true) path =
     from_abs_path ~warn_on_error path
 
 let changed_files_set =
-  Option.bind Config.changed_files_index Utils.read_file |>
-  Option.map ~f:(
-    List.fold
-      ~f:(fun changed_files line ->
-          let source_file = create line in
-          let changed_files' = Set.add source_file changed_files in
-          (* Add source corresponding to changed header if it exists *)
-          match of_header source_file with
-          | Some src -> Set.add src changed_files'
-          | None -> changed_files'
-        )
-      ~init:Set.empty
-  )
+  match Config.changed_files_index with
+  | None ->
+      None
+  | Some index -> match Utils.read_file index with
+    | Ok lines ->
+        Some (List.fold lines ~init:Set.empty ~f:(fun changed_files line ->
+            let source_file = create line in
+            let changed_files' = Set.add source_file changed_files in
+            (* Add source corresponding to changed header if it exists *)
+            match of_header source_file with
+            | Some src -> Set.add src changed_files'
+            | None -> changed_files'
+          ))
+    | Error error ->
+        L.user_error "Error reading the changed files index '%s': %s@." index error ;
+        None
 
 module UNSAFE = struct
   let from_string str =

infer/src/base/Utils.ml

@@ -38,10 +38,10 @@ let read_file fname =
   with
   | End_of_file ->
       cleanup ();
-      Some (List.rev !res)
-  | Sys_error _ ->
+      Ok (List.rev !res)
+  | Sys_error error ->
       cleanup ();
-      None
+      Error error
 
 (** copy a source file, return the number of lines, or None in case of error *)
 let copy_file fname_from fname_to =

infer/src/base/Utils.mli

@@ -21,8 +21,8 @@ val string_crc_hex32 : string -> string
 (** copy a source file, return the number of lines, or None in case of error *)
 val copy_file : string -> string -> int option
 
-(** read a source file and return a list of lines, or None in case of error *)
-val read_file : string -> string list option
+(** read a source file and return a list of lines *)
+val read_file : string -> (string list, string) Result.t
 
 (** Convert a filename to an absolute one if it is relative, and normalize "." and ".." *)
 val filename_to_absolute : root:string -> string -> string