Improve lock warning message with clearer action guidance

Make the warning message more actionable by explicitly instructing users
what to check and what to do if the lock is stale. The message now tells
users to verify if the locking process is still running and provides the
exact command needed to resolve the issue (delete the lock file).

Signed-off-by: sabine <[email protected]>

Author: sabine

src/dune_util/global_lock.ml

@@ -105,14 +105,24 @@ let lock ~timeout =
            | `Failure ->
              let lock_held_by = Lock_held_by.read_lock_file () in
              User_warning.emit
-               [ Pp.textf
-                   "Build directory is locked by another dune process%s. Waiting for the \
-                    lock to be released... (lock file: %s)"
-                   (match lock_held_by with
-                    | Unknown -> ""
-                    | Pid_from_lockfile pid -> sprintf " (pid: %d)" pid)
-                   (Path.Build.to_string lock_file)
-               ];
+               ([ Pp.textf
+                    "Build directory is locked by another dune process%s. Waiting for the \
+                     lock to be released..."
+                    (match lock_held_by with
+                     | Unknown -> ""
+                     | Pid_from_lockfile pid -> sprintf " (pid: %d)" pid)
+                ]
+                @ (match lock_held_by with
+                   | Pid_from_lockfile _ ->
+                     [ Pp.textf
+                         "If this process is no longer running, delete the lock file: %s"
+                         (Path.Build.to_string lock_file)
+                     ]
+                   | Unknown ->
+                     [ Pp.textf
+                         "If no other dune process is running, delete the lock file: %s"
+                         (Path.Build.to_string lock_file)
+                     ]));
              `Failure)
         | Some timeout ->
           let warned = ref false in
@@ -121,20 +131,30 @@ let lock ~timeout =
                match Lock.lock () with
                | `Success -> `Stop
                | `Failure ->
-                 if not !warned
-                 then (
-                   warned := true;
-                   let lock_held_by = Lock_held_by.read_lock_file () in
-                   User_warning.emit
-                     [ Pp.textf
-                         "Build directory is locked by another dune process%s. Waiting for \
-                          the lock to be released... (lock file: %s)"
-                         (match lock_held_by with
-                          | Unknown -> ""
-                          | Pid_from_lockfile pid -> sprintf " (pid: %d)" pid)
-                         (Path.Build.to_string lock_file)
-                     ]);
-                 `Continue)
+                  if not !warned
+                  then (
+                    warned := true;
+                    let lock_held_by = Lock_held_by.read_lock_file () in
+                    User_warning.emit
+                      ([ Pp.textf
+                           "Build directory is locked by another dune process%s. Waiting for \
+                            the lock to be released..."
+                           (match lock_held_by with
+                            | Unknown -> ""
+                            | Pid_from_lockfile pid -> sprintf " (pid: %d)" pid)
+                       ]
+                       @ (match lock_held_by with
+                          | Pid_from_lockfile _ ->
+                            [ Pp.textf
+                                "If this process is no longer running, delete the lock file: %s"
+                                (Path.Build.to_string lock_file)
+                            ]
+                          | Unknown ->
+                            [ Pp.textf
+                                "If no other dune process is running, delete the lock file: %s"
+                                (Path.Build.to_string lock_file)
+                            ])));
+                  `Continue)
            with
            | `Timed_out -> `Failure
            | `Success -> `Success)