Add a custom runner for tests

This custom runner allows to display the result of a test in the same
way on Unix and Windows (by mapping Windows error codes to their
equivalent result on Unix)
It also uses GitHub CI formats when available so that test failures are
referenced as such at their positions in the logs

tools/dune

@@ -0,0 +1,5 @@
+(executable
+ (name runner)
+ (public_name runner)
+ (package multicoretests)
+ (libraries unix))

tools/runner.ml

@@ -0,0 +1,131 @@
+(* Custom runner for the tests so that:
+   - error codes on Windows are turned back into their Unix meaninrgs
+   - anchors are added to CI logs with relevant information *)
+
+let use_github_anchors = Sys.getenv_opt "CI" = Some "true"
+
+let signals =
+  let open Sys in
+  [
+    (sigabrt, "ABRT");
+    (sigalrm, "ALRM");
+    (sigfpe, "FPE");
+    (sighup, "HUP");
+    (sigill, "ILL");
+    (sigint, "INT");
+    (sigkill, "KILL");
+    (sigpipe, "PIPE");
+    (sigquit, "QUIT");
+    (sigsegv, "SEGV");
+    (sigterm, "TERM");
+    (sigusr1, "USR1");
+    (sigusr2, "USR2");
+    (sigchld, "CHLD");
+    (sigcont, "CONT");
+    (sigstop, "STOP");
+    (sigtstp, "TSTP");
+    (sigttin, "TTIN");
+    (sigttou, "TTOU");
+    (sigvtalrm, "VTALRM");
+    (sigprof, "PROF");
+    (sigbus, "BUS");
+    (sigpoll, "POLL");
+    (sigsys, "SYS");
+    (sigtrap, "TRAP");
+    (sigurg, "URG");
+    (sigxcpu, "XCPU");
+    (sigxfsz, "XFSZ");
+  ]
+
+let error fmt cmd msg =
+  if use_github_anchors then
+    Format.fprintf fmt "\n::error title=%s in %s::%s in %s\n%!" msg cmd msg cmd
+  else Format.fprintf fmt "\nError: %s in %s\n%!" msg cmd
+
+let pp_status_unix fmt cmd status =
+  let open Unix in
+  (match status with
+  | WEXITED 0 -> ()
+  | WEXITED s -> error fmt cmd (Printf.sprintf "Exit %d" s)
+  | WSIGNALED s ->
+      let msg =
+        match List.assoc_opt s signals with
+        | Some signal -> "Signal " ^ signal
+        | None -> Printf.sprintf "Unknown signal %d" s
+      in
+      error fmt cmd msg
+  | WSTOPPED s ->
+      let msg =
+        match List.assoc_opt s signals with
+        | Some signal -> "Stop with signal " ^ signal
+        | None -> Printf.sprintf "Stop with unknown signal %d" s
+      in
+      error fmt cmd msg);
+  status = WEXITED 0
+
+(* Under Windows, there is no such thing as terminating due to a
+   signal, so the WSIGNALED and WSTOPPED cases are dead code.
+
+   The strategy is to use conventional exit values (which are 32-bit,
+   not just 8-bit like on Unix) to describe the cause.
+   The documentation of ”NTSTATUS Values” list {e many} cases, too
+   many to handle them all. This is where the value akin to SEGV comes
+   from. Other special cases will be caught as they appear.
+
+   The value used to match ABRT comes from the code of the abort
+   function in the standard library.
+
+   {{:https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-erref/596a1078-e883-4972-9bbc-49e60bebca55}NTSTATUS Values}
+*)
+let pp_status_win fmt cmd status =
+  let open Unix in
+  (match status with
+  | WEXITED 0 -> ()
+  | WEXITED 3 -> error fmt cmd "Signal ABRT"
+  | WEXITED -1073741819 (* 0xC0000005 *) -> error fmt cmd "Signal SEGV"
+  | WEXITED s -> error fmt cmd (Printf.sprintf "Exit %d" s)
+  (* Those last 2 cases are dead code on Windows *)
+  | WSIGNALED s ->
+      let msg =
+        match List.assoc_opt s signals with
+        | Some signal -> "Signal " ^ signal
+        | None -> Printf.sprintf "Unknown signal %d" s
+      in
+      error fmt cmd msg
+  | WSTOPPED s ->
+      let msg =
+        match List.assoc_opt s signals with
+        | Some signal -> "Stop with signal " ^ signal
+        | None -> Printf.sprintf "Stop with unknown signal %d" s
+      in
+      error fmt cmd msg);
+  status = WEXITED 0
+
+let pp_status = if Sys.win32 then pp_status_win else pp_status_unix
+
+let run ofmt efmt argv =
+  let argv =
+    match argv with [| cmd |] -> [| cmd; "--verbose" |] | _ -> argv
+  in
+  let testdir = Filename.basename (Sys.getcwd ()) in
+  let exe, cmd =
+    if Filename.is_implicit argv.(0) then
+      ( Filename.concat Filename.current_dir_name argv.(0),
+        Filename.concat testdir argv.(0) )
+    else (argv.(0), argv.(0))
+  in
+  let cmdline = String.concat " " (Array.to_list argv) in
+  Format.fprintf ofmt "\n\nStarting (in %s) %s:\n%!" testdir cmdline;
+  let pid = Unix.(create_process exe argv stdin stdout stderr) in
+  let _, status = Unix.waitpid [] pid in
+  pp_status efmt cmd status
+
+let _ =
+  let open Format in
+  if Array.length Sys.argv < 2 then (
+    fprintf err_formatter
+      "\nError: %s expects the\n  command to run as argument\n%!" Sys.argv.(0);
+    exit 1);
+  let cmd = Array.sub Sys.argv 1 (Array.length Sys.argv - 1) in
+  let success = run std_formatter err_formatter cmd in
+  if not success then exit 1