Correct error behavior of is_map_key/2 in guards

Consider the following functions:

    foo() -> bar(not_a_map).

    bar(M) when not is_map_key(a, M) -> ok;
    bar(_) -> error.

What will `foo/0` return? It depends. If the module is compiled
with the default compiler options, the return value will be
`ok`. If the module is compiled with the `inline` option,
the return value will be `error`.

The correct value is `error`, because the call to `is_map_key/2`
when the second argument is not a map should fail the entire
guard. That is the way other failing guards BIFs are handled.
For example:

    foo() -> bar(not_a_tuple).

    bar(T) when not element(1, T) -> ok;
    bar(_) -> error.

`foo/0` always returns `error` (whether the code is inlined
or not).

This bug can be fixed by changing the classification of `is_map_key/2`
in the `erl_internal` module. It is now classified as a type test,
which is incorrect because type tests should not fail. Reclassifying
it as a plain guard BIF corrects the bug.

This correction also fixes the internal consistency check
failure which was reported in:

https://bugs.erlang.org/browse/ERL-699

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/stdlib/src/erl_internal.erl b/lib/stdlib/src/erl_internal.erl
index b311a843c2..939abaff00 100644
--- a/lib/stdlib/src/erl_internal.erl
+++ b/lib/stdlib/src/erl_internal.erl
@@ -74,6 +74,7 @@ guard_bif(element, 2) -> true;
 guard_bif(float, 1) -> true;
 guard_bif(floor, 1) -> true;
 guard_bif(hd, 1) -> true;
+guard_bif(is_map_key, 2) -> true;
 guard_bif(length, 1) -> true;
 guard_bif(map_size, 1) -> true;
 guard_bif(map_get, 2) -> true;
@@ -109,7 +110,6 @@ new_type_test(is_function, 2) -> true;
 new_type_test(is_integer, 1) -> true;
 new_type_test(is_list, 1) -> true;
 new_type_test(is_map, 1) -> true;
-new_type_test(is_map_key, 2) -> true;
 new_type_test(is_number, 1) -> true;
 new_type_test(is_pid, 1) -> true;
 new_type_test(is_port, 1) -> true;