feature: Suggest candidates when alias not found

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

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

CHANGES.md

@@ -5,6 +5,8 @@ Unreleased
 - Fix parsing of OCaml errors that contain code excerpts with `...` in them.
   (#7008, @rgrinberg)
 
+- Dune now suggests other aliases when an alias is not found (#7004, @Alizter)
+
 - Pre-emptively clear screen in watch mode (#6987, fixes #6884, @rgrinberg)
 
 - Fix cross compilation configuration when a context with targets is itself a

bin/alias.ml

@@ -79,14 +79,40 @@ 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.all
+    @@ List.map contexts ~f:(fun ctx ->
+           let dir =
+             Source_tree.Dir.path dir
+             |> Path.Build.append_source (Context_name.build_dir ctx)
+             |> Path.build
+           in
+           Action_builder.of_memo @@ Load_rules.load_dir ~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 rec aliases t =
+        match (t : Load_rules.Loaded.t list) with
+        | Build build :: t ->
+          Alias.Name.Map.union
+            ~f:(fun _ a _ -> Some a)
+            build.aliases (aliases t)
+        | _ :: t -> aliases t
+        | _ -> Alias.Name.Map.empty
+      in
+      User_message.did_you_mean
+        (Alias.Name.to_string name)
+        ~candidates:
+          (Alias.Name.Map.keys (aliases load_dir)
+          |> 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 +1,8 @@
+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.
+  Hint: did you mean fmt or foo?
+  [1]

test/blackbox-tests/test-cases/generated-source-dir-overlap.t

@@ -19,6 +19,7 @@ If a generated directory is "overlaid" by a source dir, then things break.
   $ dune build @foo
   Error: Alias "foo" specified on the command line is empty.
   It is not defined in . or any of its descendants.
+  Hint: did you mean fmt?
   [1]
 
 The command above claims that @foo isn't defined, but it clearly is if we