Error message: Suggest module in place of value where it makes sense (#7384)

* suggest existing module name in scope when it makes sense for missing values

* add another test

* changelog

Author: zth

CHANGELOG.md

@@ -21,6 +21,10 @@
 
 - Better representation of JSX in AST. https://github.com/rescript-lang/rescript/pull/7286
 
+#### :nail_care: Polish
+
+- Improve error message for missing value when the identifier is also the name of a module in scope. https://github.com/rescript-lang/rescript/pull/7384
+
 # 12.0.0-alpha.11
 
 #### :bug: Bug fix

compiler/ml/typetexp.ml

@@ -841,7 +841,7 @@ let report_error env ppf = function
         Printtyp.reset_and_mark_loops_list [ty; ty'];
         fprintf ppf "@[<hov>Method '%s' has type %a,@ which should be %a@]" l
           Printtyp.type_expr ty Printtyp.type_expr ty')
-  | Unbound_value lid ->
+  | Unbound_value lid -> (
     (* modified *)
     (match lid with
     | Ldot (outer, inner) ->
@@ -850,7 +850,29 @@ let report_error env ppf = function
     | other_ident ->
       Format.fprintf ppf "The value %a can't be found" Printtyp.longident
         other_ident);
-    super_spellcheck ppf Env.fold_values env lid |> ignore
+    let did_spellcheck = super_spellcheck ppf Env.fold_values env lid in
+    (* For cases such as when the user refers to something that's a value with 
+      a lowercase identifier in JS but a module in ReScript.
+      
+      'Console' is a typical example, where JS is `console.log` and ReScript is `Console.log`. *)
+    (* TODO(codemods) Add codemod for refering to the module instead. *)
+    let as_module =
+      match lid with
+      | Lident name -> (
+        try
+          Some
+            (env
+            |> Env.lookup_module ~load:false
+                 (Lident (String.capitalize_ascii name)))
+        with _ -> None)
+      | _ -> None
+    in
+    match as_module with
+    | None -> ()
+    | Some module_path ->
+      Format.fprintf ppf "@,@[<v 2>@,@[%s to use the module @{<info>%a@}?@]@]"
+        (if did_spellcheck then "Or did you mean" else "Maybe you meant")
+        Printtyp.path module_path)
   | Unbound_module lid ->
     (* modified *)
     (match lid with

tests/build_tests/super_errors/expected/suggest_module_for_missing_identifier.res.expected

@@ -0,0 +1,10 @@
+
+  We've found a bug for you!
+  /.../fixtures/suggest_module_for_missing_identifier.res:1:1-7
+
+  1 │ console.log("Hello")
+  2 │ 
+
+  The value console can't be found
+
+  Maybe you meant to use the module Console?

tests/build_tests/super_errors/expected/suggest_module_for_missing_identifier_with_spellcheck.res.expected

@@ -0,0 +1,13 @@
+
+  We've found a bug for you!
+  /.../fixtures/suggest_module_for_missing_identifier_with_spellcheck.res:2:1-7
+
+  1 │ let consol = 1
+  2 │ console.log("Hello")
+  3 │ 
+
+  The value console can't be found
+  
+  Hint: Did you mean consol?
+
+  Or did you mean to use the module Console?

tests/build_tests/super_errors/fixtures/suggest_module_for_missing_identifier.res

@@ -0,0 +1 @@
+console.log("Hello")

tests/build_tests/super_errors/fixtures/suggest_module_for_missing_identifier_with_spellcheck.res

@@ -0,0 +1,2 @@
+let consol = 1
+console.log("Hello")

tests/build_tests/super_errors/input.js

@@ -10,8 +10,8 @@ const { bsc } = setup(import.meta.dirname);
 
 const expectedDir = path.join(import.meta.dirname, "expected");
 
-const fixtures = readdirSync("fixtures").filter(
-  fileName => path.extname(fileName) === ".res",
+const fixtures = readdirSync(path.join(import.meta.dirname, "fixtures")).filter(
+  (fileName) => path.extname(fileName) === ".res"
 );
 
 const prefix = ["-w", "+A", "-bs-jsx", "4"];