Better error message on capitalized type

src/res_core.ml

@@ -728,8 +728,14 @@ let parseValuePath p =
   | Lident ident -> Longident.Lident ident
   | Uident ident ->
     Parser.next p;
-    Parser.expect Dot p;
-    aux p (Lident ident)
+    begin match p.token with
+      | Dot ->
+        Parser.next p;
+        aux p (Lident ident)
+      | _ ->
+        Parser.err p (Diagnostics.message "Identifier needs to be lower-cased.");
+        Longident.Lident ident
+    end
   | token ->
     Parser.err p (Diagnostics.unexpected token p.breadcrumbs);
     Longident.Lident "_"
@@ -5223,7 +5229,21 @@ and parseTypeDefinitionOrExtension ~attrs p =
       Asttypes.Nonrecursive
     | _ -> Asttypes.Nonrecursive
   in
-  let name = parseValuePath p in
+  let name = match p.token with
+  | Uident ident ->
+    let identStartPos = p.startPos in
+    let identEndPos = p.endPos in
+    Parser.next p;
+    begin match p.token with
+    | Dot ->
+      Parser.next p;
+      parseValuePathTail p identStartPos (Longident.Lident ident)
+    | _ ->
+      Parser.err p ~startPos:identStartPos ~endPos:identEndPos (Diagnostics.message "Type names need to start with a lower-cased letter.");
+      Location.mkloc (Longident.Lident ident) (mkLoc identStartPos identEndPos)
+    end
+    | _ -> parseValuePath p
+  in
   let params = parseTypeParams ~parent:name p in
   match p.Parser.token with
   | PlusEqual ->

tests/parsing/errors/typeDef/expected/typeDef.res.txt

@@ -29,21 +29,35 @@
   10 │ // missing type
   11 │ type state =
   12 │ 
+  13 │ // name cannot be capitalized
 
   Missing a type here
 
 
   Syntax error!
-  tests/parsing/errors/typeDef/typeDef.res:12:1
+  tests/parsing/errors/typeDef/typeDef.res:14:1-4
 
-  10 │ // missing type
-  11 │ type state =
   12 │ 
+  13 │ // name cannot be capitalized
+  14 │ type User = string
+  15 │ 
 
   Missing a type here
 
+
+  Syntax error!
+  tests/parsing/errors/typeDef/typeDef.res:14:6-9
+
+  12 │ 
+  13 │ // name cannot be capitalized
+  14 │ type User = string
+  15 │ 
+
+  Type names need to start with a lower-cased letter.
+
 type stack =
   | Empty 
 type nonrec bar = string
 type nonrec t = [%rescript.typehole ]
-type nonrec state = [%rescript.typehole ]
+type nonrec state = [%rescript.typehole ]
+type nonrec User = string

tests/parsing/errors/typeDef/typeDef.res

@@ -9,3 +9,6 @@ type t =
 
 // missing type
 type state =
+
+// name cannot be capitalized
+type User = string