Allow rules with directory targets to be disabled (#10367)

Previously attempting to disable a rule with a directory target would
cause dune to crash.

Fixes #10310

Signed-off-by: Stephen Sherratt <stephen@sherra.tt>

src/dune_rules/dir_status.ml

@@ -85,32 +85,36 @@ let error_no_module_consumer ~loc (qualification : Include_subdirs.qualification
     ]
 ;;
 
-let extract_directory_targets ~dir stanzas =
+let extract_directory_targets ~dir ~expander stanzas =
   Memo.List.fold_left stanzas ~init:Path.Build.Map.empty ~f:(fun acc stanza ->
     match Stanza.repr stanza with
-    | Rule_conf.T { targets = Static { targets = l; _ }; loc = rule_loc; _ } ->
-      List.fold_left l ~init:acc ~f:(fun acc (target, kind) ->
-        let loc = String_with_vars.loc target in
-        match (kind : Targets_spec.Kind.t) with
-        | File -> acc
-        | Directory ->
-          (match String_with_vars.text_only target with
-           | None ->
-             User_error.raise
-               ~loc
-               [ Pp.text "Variables are not allowed in directory targets." ]
-           | Some target ->
-             let dir_target = Path.Build.relative ~error_loc:loc dir target in
-             if Path.Build.is_descendant dir_target ~of_:dir
-             then
-               (* We ignore duplicates here as duplicates are detected and
-                  reported by [Load_rules]. *)
-               Path.Build.Map.set acc dir_target rule_loc
-             else
-               (* This will be checked when we interpret the stanza
-                  completely, so just ignore this rule for now. *)
-               acc))
-      |> Memo.return
+    | Rule_conf.T { targets = Static { targets = l; _ }; loc = rule_loc; enabled_if; _ }
+      ->
+      let+ available = Expander.eval_blang expander enabled_if in
+      if not available
+      then acc
+      else
+        List.fold_left l ~init:acc ~f:(fun acc (target, kind) ->
+          let loc = String_with_vars.loc target in
+          match (kind : Targets_spec.Kind.t) with
+          | File -> acc
+          | Directory ->
+            (match String_with_vars.text_only target with
+             | None ->
+               User_error.raise
+                 ~loc
+                 [ Pp.text "Variables are not allowed in directory targets." ]
+             | Some target ->
+               let dir_target = Path.Build.relative ~error_loc:loc dir target in
+               if Path.Build.is_descendant dir_target ~of_:dir
+               then
+                 (* We ignore duplicates here as duplicates are detected and
+                    reported by [Load_rules]. *)
+                 Path.Build.Map.set acc dir_target rule_loc
+               else
+                 (* This will be checked when we interpret the stanza
+                    completely, so just ignore this rule for now. *)
+                 acc))
     | Coq_stanza.Theory.T m ->
       (* It's unfortunate that we need to pull in the coq rules here. But
          we don't have a generic mechanism for this yet. *)
@@ -257,15 +261,15 @@ end = struct
   ;;
 end
 
-let directory_targets t ~dir =
+let directory_targets t ~dir ~expander =
   match t with
   | Lock_dir | Generated | Source_only _ | Is_component_of_a_group_but_not_the_root _ ->
     Memo.return Path.Build.Map.empty
   | Standalone (_, dune_file) ->
-    Dune_file.stanzas dune_file >>= extract_directory_targets ~dir
+    Dune_file.stanzas dune_file >>= extract_directory_targets ~dir ~expander
   | Group_root { components; dune_file; _ } ->
     let f ~dir stanzas acc =
-      extract_directory_targets ~dir stanzas >>| Path.Build.Map.superpose acc
+      extract_directory_targets ~dir ~expander stanzas >>| Path.Build.Map.superpose acc
     in
     let* init =
       let* stanzas = Dune_file.stanzas dune_file in

src/dune_rules/dir_status.mli

@@ -42,4 +42,8 @@ module DB : sig
   val get : dir:Path.Build.t -> t Memo.t
 end
 
-val directory_targets : t -> dir:Path.Build.t -> Loc.t Path.Build.Map.t Memo.t
+val directory_targets
+  :  t
+  -> dir:Path.Build.t
+  -> expander:Expander.t
+  -> Loc.t Path.Build.Map.t Memo.t

src/dune_rules/gen_rules.ml

@@ -518,7 +518,10 @@ let gen_rules_regular_directory sctx ~src_dir ~components ~dir =
       in
       let+ rules =
         let+ make_rules =
-          let+ directory_targets = Dir_status.directory_targets dir_status ~dir in
+          let* expander = sctx >>= Super_context.expander ~dir in
+          let+ directory_targets =
+            Dir_status.directory_targets dir_status ~dir ~expander
+          in
           let allowed_subdirs =
             let automatic = Automatic_subdir.subdirs components in
             let toplevel =

test/blackbox-tests/test-cases/gh10310.t

@@ -1,5 +1,5 @@
-Reproduces a bug where if a rule with a directory target is excluded with
-enabled_if then dune crashes.
+Make sure that dune can handle rules with directory targets that are disabled
+with enabled_if.
 
   $ cat > dune-project <<EOF
   > (lang dune 3.14)
@@ -13,11 +13,4 @@ enabled_if then dune crashes.
   >  (action (progn)))
   > EOF
 
-  $ dune build 2>&1 | head -n 7
-  Internal error, please report upstream including the contents of _build/log.
-  Description:
-    ("gen_rules returned a set of directory targets that doesn't match the set of directory targets from returned rules",
-    { dir = In_build_dir "default"
-    ; mismatched_directories =
-        map { "default/x" : { message = "not generated"; loc = "dune:1" } }
-    })
+  $ dune build