Properly handle redundant boolean clauses in sys_core_fold

Boolean case expressions with redundant clauses could make the compiler
crash:

    case X == 0 of
        false -> no;
        false -> no;
        true -> yes
    end.

Reported-by: Ulf Norell

3 files changed, 39 insertions, 7 deletions

diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index 6fdeea51d1..058abd3357 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -1810,9 +1810,14 @@ opt_bool_clauses([#c_clause{pats=[#c_literal{val=Lit}],
 	true ->
 	    %% This clause will match.
 	    C = C0#c_clause{body=opt_bool_case(B)},
-	    case Lit of
-		false -> [C|opt_bool_clauses(Cs, SeenT, true)];
-		true -> [C|opt_bool_clauses(Cs, true, SeenF)]
+	    case {Lit,SeenT,SeenF} of
+                {false,_,false} ->
+                    [C|opt_bool_clauses(Cs, SeenT, true)];
+                {true,false,_} ->
+                    [C|opt_bool_clauses(Cs, true, SeenF)];
+                _ ->
+                    add_warning(C, nomatch_shadow),
+                    opt_bool_clauses(Cs, SeenT, SeenF)
 	    end
     end;
 opt_bool_clauses([#c_clause{pats=Ps,guard=#c_literal{val=true}}=C|Cs], SeenT, SeenF) ->
diff --git a/lib/compiler/test/core_fold_SUITE.erl b/lib/compiler/test/core_fold_SUITE.erl
index 8151dc1b16..9c986576d5 100644
--- a/lib/compiler/test/core_fold_SUITE.erl
+++ b/lib/compiler/test/core_fold_SUITE.erl
@@ -23,7 +23,7 @@
 	 t_element/1,setelement/1,t_length/1,append/1,t_apply/1,bifs/1,
 	 eq/1,nested_call_in_case/1,guard_try_catch/1,coverage/1,
 	 unused_multiple_values_error/1,unused_multiple_values/1,
-	 multiple_aliases/1]).
+	 multiple_aliases/1,redundant_boolean_clauses/1]).
 
 -export([foo/0,foo/1,foo/2,foo/3]).
 
@@ -40,7 +40,7 @@ groups() ->
       [t_element,setelement,t_length,append,t_apply,bifs,
        eq,nested_call_in_case,guard_try_catch,coverage,
        unused_multiple_values_error,unused_multiple_values,
-       multiple_aliases]}].
+       multiple_aliases,redundant_boolean_clauses]}].
 
 
 init_per_suite(Config) ->
@@ -365,4 +365,13 @@ run_once() ->
     ok.
 
 
+redundant_boolean_clauses(Config) when is_list(Config) ->
+  X = id(0),
+  yes = case X == 0 of
+            false -> no;
+            false -> no;
+            true -> yes
+        end.
+
+
 id(I) -> I.
diff --git a/lib/compiler/test/warnings_SUITE.erl b/lib/compiler/test/warnings_SUITE.erl
index f63299ea35..de56a59e12 100644
--- a/lib/compiler/test/warnings_SUITE.erl
+++ b/lib/compiler/test/warnings_SUITE.erl
@@ -38,7 +38,7 @@
 -export([pattern/1,pattern2/1,pattern3/1,pattern4/1,
 	 guard/1,bad_arith/1,bool_cases/1,bad_apply/1,
          files/1,effect/1,bin_opt_info/1,bin_construction/1, comprehensions/1,
-         maps/1]).
+         maps/1,redundant_boolean_clauses/1]).
 
 % Default timetrap timeout (set in init_per_testcase).
 -define(default_timeout, ?t:minutes(2)).
@@ -62,7 +62,8 @@ groups() ->
     [{p,test_lib:parallel(),
       [pattern,pattern2,pattern3,pattern4,guard,
        bad_arith,bool_cases,bad_apply,files,effect,
-       bin_opt_info,bin_construction,comprehensions,maps]}].
+       bin_opt_info,bin_construction,comprehensions,maps,
+       redundant_boolean_clauses]}].
 
 init_per_suite(Config) ->
     Config.
@@ -201,6 +202,8 @@ pattern4(Config) when is_list(Config) ->
 	   [nowarn_unused_vars],
 	   {warnings,
 	    [{9,sys_core_fold,no_clause_match},
+             {11,sys_core_fold,nomatch_shadow},
+             {15,sys_core_fold,nomatch_shadow},
 	     {18,sys_core_fold,no_clause_match},
 	     {23,sys_core_fold,no_clause_match},
 	     {33,sys_core_fold,no_clause_match}
@@ -573,6 +576,21 @@ maps(Config) when is_list(Config) ->
     run(Config, Ts),
     ok.
 
+redundant_boolean_clauses(Config) when is_list(Config) ->
+    Ts = [{redundant_boolean_clauses,
+           <<"
+             t(X) ->
+                 case X == 0 of
+                     false -> no;
+                     false -> no;
+                     true -> yes
+                 end.
+           ">>,
+           [],
+           {warnings,[{5,sys_core_fold,nomatch_shadow}]}}],
+    run(Config, Ts),
+    ok.
+
 %%%
 %%% End of test cases.
 %%%