From 0baa07cdf2754748bbc2d969bf83f08c0976fb78 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Mon, 15 Aug 2016 15:34:06 +0200
Subject: Fix overridden BIFs

The filters in a list comprehension can be guard expressions or
an ordinary expressions.

If a guard expression is used as a filter, an exception will basically
mean the same as 'false':

  t() ->
    L = [{some_tag,42},an_atom],
    [X || X <- L, element(1, X) =:= some_tag]
    %% Returns [{some_tag,42}]

On the other hand, if an ordinary expression is used as a filter, there
will be an exception:

  my_element(N, T) -> element(N, T).

  t() ->
    L = [{some_tag,42},an_atom],
    [X || X <- L, my_element(1, X) =:= some_tag]
    %% Causes a 'badarg' exception when element(1, an_atom) is evaluated

It has been allowed for several releases to override a BIF with
a local function. Thus, if we define a function called element/2,
it will be called instead of the BIF element/2 within the module.
We must use the "erlang:" prefix to call the BIF.

Therefore, the following code is expected to work the same way as in
our second example above:

-compile({no_auto_import,[element/2]}).

element(N, T) ->
    erlang:element(N, T).

t() ->
    L = [{some_tag,42},an_atom],
    [X || X <- L, element(1, X) =:= some_tag].
    %% Causes a 'badarg' exception when element(1, an_atom) is evaluated

But the compiler refuses to compile the code with the following
diagnostic:

  call to local/imported function element/2 is illegal in guard
---
 lib/debugger/test/Makefile                 |  1 +
 lib/debugger/test/overridden_bif_SUITE.erl | 99 ++++++++++++++++++++++++++++++
 lib/debugger/test/test_lib.erl             |  7 +++
 3 files changed, 107 insertions(+)
 create mode 100644 lib/debugger/test/overridden_bif_SUITE.erl

(limited to 'lib/debugger/test')

diff --git a/lib/debugger/test/Makefile b/lib/debugger/test/Makefile
index 125abcacda..efb6d9ed8b 100644
--- a/lib/debugger/test/Makefile
+++ b/lib/debugger/test/Makefile
@@ -46,6 +46,7 @@ MODULES= \
 	lc_SUITE \
 	line_number_SUITE \
 	map_SUITE \
+	overridden_bif_SUITE \
 	record_SUITE \
 	trycatch_SUITE \
 	test_lib \
diff --git a/lib/debugger/test/overridden_bif_SUITE.erl b/lib/debugger/test/overridden_bif_SUITE.erl
new file mode 100644
index 0000000000..04bef3c0a2
--- /dev/null
+++ b/lib/debugger/test/overridden_bif_SUITE.erl
@@ -0,0 +1,99 @@
+%%
+%% %CopyrightBegin%
+%%
+%% Copyright Ericsson AB 2001-2016. All Rights Reserved.
+%%
+%% Licensed under the Apache License, Version 2.0 (the "License");
+%% you may not use this file except in compliance with the License.
+%% You may obtain a copy of the License at
+%%
+%%     http://www.apache.org/licenses/LICENSE-2.0
+%%
+%% Unless required by applicable law or agreed to in writing, software
+%% distributed under the License is distributed on an "AS IS" BASIS,
+%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%% See the License for the specific language governing permissions and
+%% limitations under the License.
+%%
+%% %CopyrightEnd%
+%%
+-module(overridden_bif_SUITE).
+-compile({no_auto_import,[is_reference/1,size/1]}).
+
+-export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1,
+	 init_per_group/2,end_per_group/2,
+	 init_per_testcase/2,end_per_testcase/2,
+	 overridden_bif/1]).
+
+-include_lib("common_test/include/ct.hrl").
+
+%% Used by overridden_bif/1.
+-import(gb_sets, [size/1]).
+-import(test_lib, [binary/1]).
+
+suite() ->
+    [{ct_hooks,[ts_install_cth]},
+     {timetrap,{minutes,1}}].
+
+all() ->
+    [overridden_bif].
+
+groups() ->
+    [].
+
+init_per_suite(Config) ->
+    test_lib:interpret(?MODULE),
+    Config.
+
+end_per_suite(_Config) ->
+    ok.
+
+init_per_group(_GroupName, Config) ->
+    Config.
+
+end_per_group(_GroupName, Config) ->
+    Config.
+
+
+init_per_testcase(Case, Config) when is_atom(Case), is_list(Config) ->
+    Config.
+
+end_per_testcase(Case, Config) when is_atom(Case), is_list(Config) ->
+    ok.
+
+overridden_bif(_Config) ->
+    L = [-3,-2,-1,0,1,2,3,4],
+    [-3,0,3] = do_overridden_bif_1(L),
+    [-2,0,2,4] = do_overridden_bif_2(L),
+    [3] = do_overridden_bif_3(L),
+    [2,4] = do_overridden_bif_4(L),
+
+    Set = gb_sets:from_list(L),
+    [Set] = do_overridden_bif_5([gb_sets:singleton(42),Set]),
+
+    [100,0] = do_overridden_bif_6([100|L]),
+    ok.
+
+do_overridden_bif_1(L) ->
+    [E || E <- L, is_reference(E)].
+
+do_overridden_bif_2(L) ->
+    [E || E <- L, port(E)].
+
+do_overridden_bif_3(L) ->
+    [E || E <- L, (is_reference(E) andalso E > 0)].
+
+do_overridden_bif_4(L) ->
+    [E || E <- L, (port(E) andalso E > 0)].
+
+do_overridden_bif_5(L) ->
+    [E || E <- L, size(E) > 1].
+
+do_overridden_bif_6(L) ->
+    [E || E <- L, binary(E)].
+
+is_reference(N) ->
+    N rem 3 =:= 0.
+
+port(N) ->
+    N rem 2 =:= 0.
diff --git a/lib/debugger/test/test_lib.erl b/lib/debugger/test/test_lib.erl
index b9ac486694..7e98d210e8 100644
--- a/lib/debugger/test/test_lib.erl
+++ b/lib/debugger/test/test_lib.erl
@@ -23,8 +23,15 @@
 
 -export([interpret/1]).
 
+%% Used by test case that override BIFs.
+-export([binary/1]).
+
 interpret(Mod) when is_atom(Mod) ->
     case lists:member(Mod, int:interpreted()) of
 	true -> ok;
 	false -> {module,Mod} = i:ii(Mod)
     end.
+
+%% This is for overridden_bif_SUITE.
+binary(N) ->
+    N rem 10 =:= 0.
-- 
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