Do not use symlink when writing and reading log files.

CHANGES.md

@@ -1,3 +1,8 @@
+### dev
+
+- Fix a bug when running test concurently. Alcotest could fail to
+  output the content of the log file. (#353, @hhugo)
+
 ### 1.5.0 (2021-10-09)
 
 - Make Alcotest compatible with `js_of_ocaml.3.11.0`. Users can depend on the

src/alcotest-engine/log_trap.ml

@@ -9,7 +9,13 @@ module Make
 struct
   open Promise.Syntax
 
-  type state = { root : string; uuid : string; suite_name : string }
+  type state = {
+    root : string;
+    uuid : string;
+    suite_name : string;
+    has_alias : bool;
+  }
+
   type t = Inactive | Active of state
 
   (** Take a string path and collapse a leading [$HOME] path segment to [~]. *)
@@ -30,7 +36,8 @@ struct
 
   let active ~root ~uuid ~suite_name =
     Platform.prepare_log_trap ~root ~uuid ~name:suite_name;
-    Active { root; uuid; suite_name }
+    let has_alias = Platform.file_exists (Filename.concat root suite_name) in
+    Active { root; uuid; suite_name; has_alias }
 
   let pp_path = Fmt.using maybe_collapse_home Fmt.string
 
@@ -63,31 +70,31 @@ struct
         in
         ListLabels.iter display_lines ~f:(Fmt.pf ppf "%s@\n")
 
-  let log_dir { suite_name; uuid; root } =
-    (* We don't create symlinks on Windows. *)
-    let via_symlink = not Sys.win32 in
+  let log_dir ~via_symlink { suite_name; uuid; root; has_alias } =
+    let via_symlink = via_symlink && has_alias in
     Filename.concat root (if via_symlink then suite_name else uuid)
 
-  let output_fpath t tname = Filename.concat (log_dir t) (Test_name.file tname)
+  let output_fpath ~via_symlink t tname =
+    Filename.concat (log_dir ~via_symlink t) (Test_name.file tname)
 
   let active_or_exn = function
     | Active t -> t
     | Inactive -> failwith "internal error: no log location"
 
   let pp_current_run_dir t ppf =
     let t = active_or_exn t in
-    pp_path ppf (log_dir t)
+    pp_path ppf (log_dir ~via_symlink:true t)
 
   let pp_log_location t tname ppf =
     let t = active_or_exn t in
-    let path = output_fpath t tname in
+    let path = output_fpath ~via_symlink:true t tname in
     pp_path ppf path
 
   let recover_logs t ~tail tname =
     match t with
     | Inactive -> None
     | Active t -> (
-        let fpath = output_fpath t tname in
+        let fpath = output_fpath ~via_symlink:false t tname in
         match Platform.file_exists fpath with
         | false -> None
         | true -> Some (fun ppf -> pp_tail tail fpath ppf))
@@ -96,7 +103,9 @@ struct
     match t with
     | Inactive -> f x
     | Active t ->
-        let fd = Platform.open_write_only (output_fpath t tname) in
+        let fd =
+          Platform.open_write_only (output_fpath ~via_symlink:false t tname)
+        in
         let* () = Promise.return () in
         let+ a = Platform.with_redirect fd (fun () -> f x) in
         Platform.close fd;