add warning 109 to signal top-level expressions have type unit

Author: bobzhang

typing/typecore.ml

@@ -4873,6 +4873,11 @@ let type_expression env sexp =
   Typetexp.reset_type_variables();
   begin_def();
   let exp = type_exp env sexp in
+  if Warnings.is_active Bs_toplevel_expression_unit then 
+    (try unify env exp.exp_type 
+      (instance_def Predef.type_unit) with 
+    | Unify _ 
+    | Tags _  -> Location.prerr_warning sexp.pexp_loc Bs_toplevel_expression_unit);
   end_def();
   if not (is_nonexpansive exp) then generalize_expansive env exp.exp_type;
   generalize exp.exp_type;

utils/warnings.ml

@@ -105,6 +105,7 @@ type t =
   | Bs_unimplemented_primitive of string    (* 106 *)
   | Bs_integer_literal_overflow              (* 107 *)
   | Bs_uninterpreted_delimiters of string   (* 108 *)
+  | Bs_toplevel_expression_unit             (* 109 *)
 #end  
 ;;
 
@@ -193,10 +194,11 @@ let number = function
   | Bs_unimplemented_primitive _ -> 106
   | Bs_integer_literal_overflow -> 107
   | Bs_uninterpreted_delimiters _ -> 108
+  | Bs_toplevel_expression_unit -> 109
 #end  
 ;;
 
-let last_warning_number = 108
+let last_warning_number = 109
 let letter_all = 
   let rec loop i = if i = 0 then [] else i :: loop (i - 1) in
   loop last_warning_number
@@ -331,7 +333,7 @@ let parse_options errflag s =
   current := {error; active}
 
 (* If you change these, don't forget to change them in man/ocamlc.m *)
-let defaults_w = "+a-4-6-7-9-27-29-32..42-44-45-48-50-60-102";;
+let defaults_w = "+a-4-6-7-9-27-29-32..42-44-45-48-50-60-102-109";;
 let defaults_warn_error = "-a+31";;
 
 let () = 
@@ -609,6 +611,8 @@ let message = function
       "Integer literal exceeds the range of representable integers of type int"
   | Bs_uninterpreted_delimiters s -> 
       "Uninterpreted delimiters " ^ s  
+  | Bs_toplevel_expression_unit -> 
+      "Toplevel expression is expected to have unit type."    
 #end      
 ;;
 
@@ -744,7 +748,8 @@ let descriptions =
    105, "External name is inferred from val name is unsafe from refactoring when changing value name";
    106, "Unimplemented primitive used:";
    107, "Integer literal exceeds the range of representable integers of type int";
-   108, "Uninterpreted delimiters (for unicode)"  
+   108, "Uninterpreted delimiters (for unicode)" ;
+   109, "Toplevel expression has unit type"   
 #end   
   ]
 ;;

utils/warnings.mli

@@ -97,6 +97,7 @@ type t =
   | Bs_unimplemented_primitive of string    (* 106 *)
   | Bs_integer_literal_overflow              (* 107 *)
   | Bs_uninterpreted_delimiters of string   (* 108 *)
+  | Bs_toplevel_expression_unit             (* 109 *)
 #end        
 ;;