Improve error message for pipe syntax (#7520)

Author: cknitt

CHANGELOG.md

@@ -30,7 +30,8 @@
 - Allow oneliner formatting when including module with single type alias. https://github.com/rescript-lang/rescript/pull/7502
 - Improve error messages for JSX type mismatches, passing objects where record is expected, passing array literal where tuple is expected, and more. https://github.com/rescript-lang/rescript/pull/7500
 - Show in error messages when coercion can be used to fix a type mismatch. https://github.com/rescript-lang/rescript/pull/7505
-- Remove deprecated pipe last (|>) syntax. https://github.com/rescript-lang/rescript/pull/7512
+- Remove deprecated pipe last (`|>`) syntax. https://github.com/rescript-lang/rescript/pull/7512
+- Improve error message for pipe (`->`) syntax. https://github.com/rescript-lang/rescript/pull/7520
 
 # 12.0.0-alpha.13
 

compiler/frontend/ast_exp_apply.ml

@@ -197,7 +197,8 @@ let app_exp_mapper (e : exp) (self : Bs_ast_mapper.mapper) : exp =
       | _ -> Location.raise_errorf ~loc "invalid #= assignment"))
   | Some {op = "->"; loc} ->
     Location.raise_errorf ~loc
-      "invalid |. syntax, it can only be used as binary operator"
+      "Invalid pipe syntax. The pipe symbol (->) can only be used as a binary \
+       operator."
   | Some {op = "##"; loc} ->
     Location.raise_errorf ~loc
       "Js object ## expect syntax like obj##(paint (a,b)) "