ms_transform: Fix incorrect `variable shadowed' warnings

Compile below module resulting incorrect warning:

$ cat tmp.erl
-module(tmp).
-export([tmp/1]).
-include_lib("stdlib/include/ms_transform.hrl").
tmp(X) when X > 100 ->
  Y=X,
  Y;
tmp(X) ->
  ets:fun2ms(fun(Y) -> {X, Y} end).

$ erlc tmp.erl
./tmp.erl:8: Warning: variable 'Y' shadowed in ms_transform fun head

The scope for a variable is its function clause. Variables bound in one
function clause should not interfere with other function clauses.

This patch removes incorrect passing of variable bindings from one
function clause to another.

Signed-off-by: Haitao Li <[email protected]>

2 files changed, 53 insertions, 9 deletions

diff --git a/lib/stdlib/src/ms_transform.erl b/lib/stdlib/src/ms_transform.erl
index 48e22e53fa..63b397f3a5 100644
--- a/lib/stdlib/src/ms_transform.erl
+++ b/lib/stdlib/src/ms_transform.erl
@@ -333,17 +333,18 @@ form({function,Line,Name0,Arity0,Clauses0}) ->
 form(AnyOther) ->
     AnyOther.
 function(Name, Arity, Clauses0) ->
-    {Clauses1,_} = clauses(Clauses0,gb_sets:new()),
+    Clauses1 = clauses(Clauses0),
     {Name,Arity,Clauses1}.
-clauses([C0|Cs],Bound) ->
-    {C1,Bound1} = clause(C0,Bound),
-    {C2,Bound2} = clauses(Cs,Bound1),
-    {[C1|C2],Bound2};
-clauses([],Bound) -> {[],Bound}.
+clauses([C0|Cs]) ->
+    C1 = clause(C0,gb_sets:new()),
+    C2 = clauses(Cs),
+    [C1|C2];
+clauses([]) -> [].
+
 clause({clause,Line,H0,G0,B0},Bound) ->
     {H1,Bound1} = copy(H0,Bound),
-    {B1,Bound2} = copy(B0,Bound1),
-    {{clause,Line,H1,G0,B1},Bound2}.
+    {B1,_Bound2} = copy(B0,Bound1),
+    {clause,Line,H1,G0,B1}.
 
 copy({call,Line,{remote,_Line2,{atom,_Line3,ets},{atom,_Line4,fun2ms}},
       As0},Bound) ->
diff --git a/lib/stdlib/test/ms_transform_SUITE.erl b/lib/stdlib/test/ms_transform_SUITE.erl
index 4e5df12798..c9688354b1 100644
--- a/lib/stdlib/test/ms_transform_SUITE.erl
+++ b/lib/stdlib/test/ms_transform_SUITE.erl
@@ -39,6 +39,7 @@
 -export([float_1_function/1]).
 -export([action_function/1]).
 -export([warnings/1]).
+-export([no_warnings/1]).
 -export([init_per_testcase/2, end_per_testcase/2]).
 
 init_per_testcase(_Func, Config) ->
@@ -55,7 +56,7 @@ all() ->
     [from_shell, basic_ets, basic_dbg, records,
      record_index, multipass, bitsyntax, record_defaults,
      andalso_orelse, float_1_function, action_function,
-     warnings, top_match, old_guards, autoimported,
+     warnings, no_warnings, top_match, old_guards, autoimported,
      semicolon].
 
 groups() -> 
@@ -155,6 +156,34 @@ warnings(Config) when is_list(Config) ->
 	compile_ww(Prog7),
     ok.
 
+no_warnings(suite) ->
+    [];
+no_warnings(doc) ->
+    ["Check that variables bound in other function clauses don't generate "
+     "warning"];
+no_warnings(Config) when is_list(Config) ->
+    ?line setup(Config),
+    Prog = <<"tmp(X) when X > 100 ->\n",
+	     "   Y=X,\n"
+	     "   Y;\n"
+	     "tmp(X) ->\n"
+	     "   ets:fun2ms(fun(Y) ->\n"
+	     "                  {X, 3*Y}\n"
+	     "              end)">>,
+    ?line [] = compile_no_ww(Prog),
+
+    Prog2 = <<"tmp(X) when X > 100 ->\n",
+	     "   Y=X,\n"
+	     "   Y;\n"
+	     "tmp(X) when X < 200 ->\n"
+	     "   ok;\n"
+	     "tmp(X) ->\n"
+	     "   ets:fun2ms(fun(Y) ->\n"
+	     "                  {X, 3*Y}\n"
+	     "              end)">>,
+    ?line [] = compile_no_ww(Prog2),
+    ok.
+
 andalso_orelse(suite) ->
     [];
 andalso_orelse(doc) ->
@@ -842,6 +871,20 @@ compile_ww(Records,Expr) ->
 					       nowarn_unused_record]),
     Wlist.
 
+compile_no_ww(Expr) ->
+    Prog = <<
+	"-module(tmp).\n",
+    "-include_lib(\"stdlib/include/ms_transform.hrl\").\n",
+    "-export([tmp/1]).\n\n",
+    Expr/binary,".\n">>,
+    FN=temp_name(),
+    file:write_file(FN,Prog),
+    {ok,Forms} = epp:parse_file(FN,"",""),
+    {ok,tmp,_Bin,Wlist} = compile:forms(Forms,[return_warnings,
+					       nowarn_unused_vars,
+					       nowarn_unused_record]),
+    Wlist.
+
 do_eval(String) ->
     {done,{ok,T,_},[]} = erl_scan:tokens(
 			   [],