fix: expand %{deps} in (cat) properly

Signed-off-by: Ali Caglayan <alizter@gmail.com>

CHANGES.md

@@ -3,6 +3,9 @@ Unreleased
 
 - Add `dune show rules` as alias of the `dune rules` command. (#8000, @Alizter)
 
+- Fix `%{deps}` to expand properly in `(cat ...)` when containing 2 or more
+  items. (#8196, @Alizter)
+
 - Add `dune show installed-libraries` as an alias of the `dune
   installed-libraries` command. (#8135, @Alizter)
 

src/dune_rules/action_unexpanded.ml

@@ -68,6 +68,9 @@ module Action_expander : sig
     (* Evaluate a path in a position of dependency, such as in [(cat <dep>)] *)
     val dep : String_with_vars.t -> Path.t t
 
+    (* Evaluate paths in the position of dependencies, such as in [(cat <deps>)] *)
+    val deps : String_with_vars.t -> Path.t list t
+
     (* Evaluate a path in a position of optional dependency, such as in [(diff
        <dep_if_exists> ...)] *)
     val dep_if_exists : String_with_vars.t -> Path.t t
@@ -241,6 +244,14 @@ end = struct
         Value.to_path_in_build_or_external v
           ~error_loc:(String_with_vars.loc sw) ~dir:t.dir
 
+      let expand_paths t sw =
+        let+ v, vs = expand t ~mode:At_least_one sw in
+        List.map
+          ~f:
+            (Value.to_path_in_build_or_external
+               ~error_loc:(String_with_vars.loc sw) ~dir:t.dir)
+          (v :: vs)
+
       let expand_string env sw =
         let+ v = expand env ~mode:Single sw in
         Value.to_string v ~dir:(Path.build env.dir)
@@ -285,24 +296,26 @@ end = struct
       let path sw ~f = make ~expand:Expander.No_deps.expand_path sw ~f
     end
 
-    let register_dep x ~f env acc =
+    let register_deps x ~f env acc =
       Memo.return
         (if not env.infer then (x, acc)
          else
-           let x = Action_builder.memoize "dep" x in
+           let x = Action_builder.memoize "deps" x in
            ( x
            , { acc with
                deps =
                  (let+ x = x
                   and+ set = acc.deps in
-                  match f x with
-                  | None -> set
-                  | Some fn -> Path.Set.add set fn)
+                  Path.Set.union set (Path.Set.of_list (f x)))
              } ))
 
     let dep sw env acc =
       let fn = Expander.expand_path env sw in
-      register_dep fn ~f:Option.some env acc
+      register_deps fn ~f:List.singleton env acc
+
+    let deps sw env acc =
+      let fn = Expander.expand_paths env sw in
+      register_deps fn ~f:Fun.id env acc
 
     let dep_if_exists sw env acc =
       Memo.return
@@ -366,9 +379,9 @@ end = struct
         let args = Value.L.to_strings ~dir args in
         (prog, args)
       in
-      register_dep b env acc ~f:(function
-        | Ok p, _ -> Some p
-        | Error _, _ -> None)
+      register_deps b env acc ~f:(function
+        | Ok p, _ -> [ p ]
+        | Error _, _ -> [])
   end
 end
 
@@ -427,8 +440,8 @@ let rec expand (t : Dune_lang.Action.t) ~context : Action.t Action_expander.t =
     let l = List.concat l in
     O.Echo l
   | Cat xs ->
-    let+ xs = A.all (List.map xs ~f:E.dep) in
-    O.Cat xs
+    let+ xs = A.all (List.map xs ~f:E.deps) in
+    O.Cat (List.concat xs)
   | Copy (x, y) ->
     let+ x = E.dep x
     and+ y = E.target y in

test/blackbox-tests/test-cases/quoting/cat.t/run.t

@@ -13,9 +13,3 @@ arguments.
   > EOF
 
   $ dune build @foo
-  File "dune", line 5, characters 7-14:
-  5 |   (cat %{deps})))
-             ^^^^^^^
-  Error: Variable %{deps} expands to 2 values, however a single value is
-  expected here. Please quote this atom.
-  [1]