rescript-lang · cristianoc · Apr 18, 2023 · Apr 18, 2023 · Apr 18, 2023 · cristianoc
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -26,6 +26,7 @@
 - Fixed subtype checking for record types with "@as" attributes: The subtype relationship now takes into account the compatibility of "@as" attributes between corresponding fields, ensuring correctness in runtime representation.
  https://github.com/rescript-lang/rescript-compiler/issues/6158
 - Emit directive above header comment. https://github.com/rescript-lang/rescript-compiler/pull/6172
+- Add error message to private extension. https://github.com/rescript-lang/rescript-compiler/pull/6175
 
 #### :nail_care: Polish
 

diff --git a/jscomp/build_tests/super_errors/expected/private_without_body.res.expected b/jscomp/build_tests/super_errors/expected/private_without_body.res.expected
@@ -0,0 +1,9 @@
+
+  [1;31mWe've found a bug for you![0m
+  [36m/.../fixtures/private_without_body.res[0m:[2m1:1-9[0m
+
+  [1;31m1[0m [2m│[0m [1;31m%%private[0m
+  2 [2m│[0m let a = 2
+  3 [2m│[0m 
+
+  %%private extension expects a definition as its argument. Example: %%private(let a = "Hello")
diff --git a/jscomp/build_tests/super_errors/fixtures/private_without_body.res b/jscomp/build_tests/super_errors/fixtures/private_without_body.res
@@ -0,0 +1,2 @@
+%%private
+let a = 2
diff --git a/jscomp/frontend/bs_builtin_ppx.ml b/jscomp/frontend/bs_builtin_ppx.ml
@@ -474,6 +474,9 @@ let rec structure_mapper (self : mapper) (stru : Ast_structure.t) =
           :: next -> (
           match payload with
           | PStr work ->
+            if List.length work = 0 then
+              Location.raise_errorf ~loc
+                {|%%%%private extension expects a definition as its argument. Example: %%%%private(let a = "Hello")|};
             aux
               (Ext_list.rev_map_append work acc (fun x ->
                    self.structure_item self x))
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		%%private
		let a = 2
Copy link Collaborator cristianoc Apr 18, 2023 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Any way to make the error message more approachable. Not so clear why `a` "does not have a body". Copy link Contributor Author aspeddro Apr 18, 2023 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. The message highlights `%private`. It's not `a` that doesn't have a body, it's `%%private`. Maybe `%%private extension expects arguments`? Copy link Collaborator cristianoc Apr 18, 2023 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Yes: private expects the definition as argument. Copy link Collaborator cristianoc Apr 18, 2023 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Error: The '%%private' extension expects a definition as its argument. Example usage: %%private let a = (x) => x + 2; In this case, the '%%private' extension is missing a definition as its argument. Please provide a valid definition for the private extension to work as intended.