Emit leaner code on with var <-

Author: sabiwara

lib/elixir/src/elixir_clauses.erl

@@ -169,11 +169,16 @@ with(Meta, Args, S, E) ->
 
   {{with, Meta, EExprs ++ [[{do, EDo} | EOpts]]}, S3, E}.
 
-expand_with({'<-', Meta, [Left, Right]}, {S, E, _HasMatch}) ->
+expand_with({'<-', Meta, [Left, Right]}, {S, E, HasMatch}) ->
   {ERight, SR, ER} = elixir_expand:expand(Right, S, E),
   SM = elixir_env:reset_read(SR, S),
   {[ELeft], SL, EL} = head([Left], SM, ER),
-  {{'<-', Meta, [ELeft, ERight]}, {SL, EL, true}};
+  NewHasMatch =
+    case ELeft of
+      {Var, _, Ctx} when is_atom(Var), is_atom(Ctx) -> HasMatch;
+      _ -> true
+    end,
+  {{'<-', Meta, [ELeft, ERight]}, {SL, EL, NewHasMatch}};
 expand_with(Expr, {S, E, HasMatch}) ->
   {EExpr, SE, EE} = elixir_expand:expand(Expr, S, E),
   {EExpr, {SE, EE, HasMatch}}.

lib/elixir/src/elixir_erl_pass.erl

@@ -435,6 +435,8 @@ with_else_closure(Meta, TranslatedClauses, S) ->
   FunCall = {call, Ann, FunErlVar, [ArgErlVar]},
   {{clause, Ann, [ArgErlVar], [], [FunCall]}, FunAssign, SA}.
 
+translate_with_do([{'<-', Meta, [{Var, _, Ctx} = Left, Expr]} | Rest], Ann, Do, Else, S) when is_atom(Var), is_atom(Ctx) ->
+  translate_with_do([{'=', Meta, [Left, Expr]} | Rest], Ann, Do, Else, S);
 translate_with_do([{'<-', Meta, [Left, Expr]} | Rest], _Ann, Do, Else, S) ->
   Ann = ?ann(Meta),
   {Args, Guards} = elixir_utils:extract_guards(Left),