Issue a warning when a named fun is constructed but not used

2 files changed, 6 insertions, 1 deletions

diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index 1cdbac5693..40f324b839 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -305,6 +305,10 @@ expr(#c_let{}=Let, Ctxt, Sub) ->
 	    %% Now recursively re-process the new expression.
 	    expr(Expr, Ctxt, sub_new_preserve_types(Sub))
     end;
+expr(#c_letrec{body=#c_var{}}=Letrec, effect, _Sub) ->
+    %% This is named fun in an 'effect' context. Warn and ignore.
+    add_warning(Letrec, useless_building),
+    void();
 expr(#c_letrec{defs=Fs0,body=B0}=Letrec, Ctxt, Sub) ->
     Fs1 = map(fun ({Name,Fb}) ->
 		      {Name,expr(Fb, {letrec,Ctxt}, Sub)}
diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index e30bfa729c..59863f52ec 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -2088,7 +2088,8 @@ cexpr(#ifun{anno=#a{us=Us0}=A0,name={named,Name},fc=#iclause{pats=Ps}}=Fun0,
             RecVar = #c_var{name={Name,length(Ps)}},
             Let = #c_let{vars=[#c_var{name=Name}],arg=RecVar,body=Body},
             CFun1 = CFun0#c_fun{body=Let},
-            Letrec = #c_letrec{defs=[{RecVar,CFun1}],
+            Letrec = #c_letrec{anno=A0#a.anno,
+			       defs=[{RecVar,CFun1}],
                                body=RecVar},
             {Letrec,[],Us1,St1}
     end;