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/test_lib.erl | 7 +++++++
 1 file changed, 7 insertions(+)

(limited to 'lib/debugger/test/test_lib.erl')

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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