Merge pull request #11202 from Julow/nix-result-fmt-crash

test: Repro 'dune fmt' crash in presence of Nix result

src/dune_engine/hooks.ml

@@ -26,9 +26,13 @@ module Make () = struct
     match !exns with
     | [] -> ()
     | exns ->
-      let exns = List.rev exns in
-      let open Dyn in
-      Code_error.raise "hooks failed" [ "exns", (list Exn_with_backtrace.to_dyn) exns ]
+      (match exns with
+       | [ { exn = User_error.E _ as e; backtrace = _ } ] -> raise e
+       | _ ->
+         let exns = List.rev exns in
+         Code_error.raise
+           "hooks failed"
+           [ "exns", (Dyn.list Exn_with_backtrace.to_dyn) exns ])
   ;;
 end
 

src/promote/diff_promotion.ml

@@ -52,7 +52,13 @@ module File = struct
   let do_promote ~correction_file ~dst =
     Path.Source.unlink_no_err dst;
     let chmod = Path.Permissions.add Path.Permissions.write in
-    Io.copy_file ~chmod ~src:correction_file ~dst:(Path.source dst) ()
+    match Io.copy_file ~chmod ~src:correction_file ~dst:(Path.source dst) () with
+    | () -> ()
+    | exception Unix.Unix_error (e, _, _) ->
+      User_error.raise
+        [ Pp.textf "failed to promote %s" (Path.Source.to_string dst)
+        ; Pp.text (Unix.error_message e)
+        ]
   ;;
 
   let correction_file { src; staging; _ } = Path.build (Option.value staging ~default:src)

test/blackbox-tests/test-cases/read-only-symlink-target.t/dune

@@ -0,0 +1,2 @@
+(executable
+ (name ocamlformat))

test/blackbox-tests/test-cases/read-only-symlink-target.t/dune-project

@@ -0,0 +1 @@
+(lang dune 2.8)

test/blackbox-tests/test-cases/read-only-symlink-target.t/ocamlformat.ml

@@ -0,0 +1,2 @@
+(* Avoid adding dependencies to this cram test *)
+let () = print_endline "(* formatted *)"

test/blackbox-tests/test-cases/read-only-symlink-target.t/run.t

@@ -0,0 +1,22 @@
+Nix can leave a symlink to a store path in the tree, often called 'result'.
+'dune fmt' crashes because of that.
+
+  $ RESULT=`mktemp -d`
+  $ echo "let x  = 2" > "$RESULT/foo.ml"
+  $ chmod -R a-w "$RESULT"
+  $ ln -s "$RESULT" result
+
+This command should succeed:
+
+  $ dune fmt
+  File "result/foo.ml", line 1, characters 0-0:
+  Error: Files _build/default/result/foo.ml and
+  _build/default/result/.formatted/foo.ml differ.
+  Promoting _build/default/result/.formatted/foo.ml to result/foo.ml.
+  Error: failed to promote result/foo.ml
+  Permission denied
+  [1]
+
+Allow Dune to remove temporary files (calling Dune crashes without this):
+
+  $ chmod -R u+w "$RESULT"