feature: Suggest candidates when alias not found

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

<!-- ps-id: 8eef5d92-83a8-4141-9bc8-234ddb4136ce -->

bin/alias.ml

@@ -79,14 +79,31 @@ let dep_on_alias_rec_multi_contexts ~dir:src_dir ~name ~contexts =
   let* dir =
     Action_builder.of_memo (find_dir_specified_on_command_line ~dir:src_dir)
   in
-  let+ is_nonempty_list =
+  let* is_nonempty_list =
     Action_builder.all
       (List.map contexts ~f:(fun ctx ->
            Action_builder.dep_on_alias_rec name ctx dir))
   in
+  let+ load_dir =
+    Action_builder.of_memo
+    @@ Load_rules.load_dir ~dir:(Path.source (Source_tree.Dir.path dir))
+  in
   let is_nonempty = List.exists is_nonempty_list ~f:Fun.id in
   if (not is_nonempty) && not (Dune_engine.Alias.is_standard name) then
-    User_error.raise
+    let hints =
+      let aliases =
+        match load_dir with
+        | Build build -> build.aliases
+        | _ ->
+          Printf.printf "Oh no, the map is not there!\n";
+          Alias.Name.Map.empty
+      in
+      User_message.did_you_mean
+        (Alias.Name.to_string name)
+        ~candidates:
+          (Alias.Name.Map.keys aliases |> List.map ~f:Alias.Name.to_string)
+    in
+    User_error.raise ~hints
       [ Pp.textf "Alias %S specified on the command line is empty."
           (Dune_engine.Alias.Name.to_string name)
       ; Pp.textf "It is not defined in %s or any of its descendants."

test/blackbox-tests/test-cases/alias-candidates.t/dune

@@ -0,0 +1,4 @@
+(rule
+ (alias foo)
+ (action
+  (echo "Hello, world from \"foo\"!")))

test/blackbox-tests/test-cases/alias-candidates.t/dune-project

@@ -0,0 +1 @@
+(lang dune 3.7)

test/blackbox-tests/test-cases/alias-candidates.t/run.t

@@ -0,0 +1,11 @@
+Dune should suggest similar aliases when it cannot find one. 
+
+We have an alias "foo" but let's try to build something misspeled:
+  $ dune build @fou
+  Error: Alias "fou" specified on the command line is empty.
+  It is not defined in . or any of its descendants.
+  Oh no, the map is not there!
+  [1]
+
+  $ dune build @foo
+  Hello, world from "foo"!