Avoid formatting read-only files

otherlibs/stdune/src/fpath.ml

@@ -217,3 +217,9 @@ let traverse =
 let traverse_files ~dir ~init ~f =
   traverse ~dir ~init ~on_dir:(fun ~dir:_ _fname acc -> acc) ~on_file:f
 ;;
+
+let is_rw p =
+  match Unix.access p Unix.[ R_OK; W_OK ] with
+  | () -> true
+  | exception Unix.Unix_error _ -> false
+;;

otherlibs/stdune/src/fpath.mli

@@ -64,3 +64,6 @@ val traverse_files
   -> init:'acc
   -> f:(dir:string -> Filename.t -> 'acc -> 'acc)
   -> 'acc
+
+(** Is readable and writable. *)
+val is_rw : string -> bool

otherlibs/stdune/src/path.ml

@@ -1436,6 +1436,7 @@ module Source = struct
 
   let is_in_build_dir s = is_in_build_dir (path_of_local s)
   let to_local t = t
+  let is_rw t = Fpath.is_rw (to_string t)
 end
 
 let set_of_source_paths set = Source.Set.to_list set |> Set.of_list_map ~f:source

otherlibs/stdune/src/path.mli

@@ -109,6 +109,9 @@ module Source : sig
   val descendant : t -> of_:t -> t option
   val to_local : t -> Local.t
 
+  (** Whether the file at the given path is readable and writable. *)
+  val is_rw : t -> bool
+
   module Table : Hashtbl.S with type key = t
 end
 

src/dune_rules/format_rules.ml

@@ -138,6 +138,9 @@ let gen_rules_output
      let* dialect, kind =
        Path.Source.extension file |> Dialect.DB.find_by_extension dialects
      in
+     (* Avoid setting up rules that will fail during promotion due to the
+        source file not being writable. *)
+     let* () = Option.some_if (Path.Source.is_rw file) () in
      let* () =
        Option.some_if (Format_config.includes config (Dialect (Dialect.name dialect))) ()
      in

test/blackbox-tests/test-cases/dialects/good.t/run.t

@@ -2,6 +2,8 @@ Test the (dialect ...) stanza inside the dune-project file.
 
   $ dune exec ./main.exe
 
+  $ chmod a+w *
+
   $ dune build @fmt
   Formatting main.mf
   Formatting main.mfi

test/blackbox-tests/test-cases/dialects/no_impl.t/run.t

@@ -2,6 +2,8 @@ Test the (dialect ...) stanza inside the `dune-project` file.
 
   $ dune exec ./main.exe
 
+  $ chmod a+w *
+
   $ dune build @fmt
   fake ocamlformat is running: "--impl" "fmt.ml"
   fake ocamlformat is running: "--impl" "main.ml"

test/blackbox-tests/test-cases/dialects/no_intf_good.t/run.t

@@ -2,6 +2,8 @@ Test the (dialect ...) stanza inside the dune-project file.
 
   $ dune exec ./main.exe
 
+  $ chmod a+w *
+
   $ dune build @fmt
   fake ocamlformat is running: "--impl" "fmt.ml"
   Formatting main.mf

test/blackbox-tests/test-cases/formatting/feature.t/run.t

@@ -3,6 +3,10 @@ Note about versioning:
 - in (lang dune 1.x), no formatting rules are set up by default.
 - (lang dune 2.0) behaves as if (using fmt 1.2) is set.
 
+Turn every symlinks into writable files belonging to the sandbox as formatting
+rules are not generated for read-only files:
+  $ find . -type l | while read f; do (rm "$f"; cat > $f) < $f; done
+
 Formatting can be checked using the @fmt target:
 
   $ touch .ocamlformat

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

@@ -6,20 +6,9 @@ Nix can leave a symlink to a store path in the tree, often called 'result'.
   $ chmod -R a-w "$RESULT"
   $ ln -s "$RESULT" result
 
-This command should succeed:
+Formatting 'foo.ml' shouldn't be attempted and this command should succeed:
 
   $ dune fmt
-  File "ocamlformat.ml", line 1, characters 0-0:
-  Error: Files _build/default/ocamlformat.ml and
-  _build/default/.formatted/ocamlformat.ml differ.
-  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/.formatted/ocamlformat.ml to ocamlformat.ml.
-  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):