Don't crash when obsolete guard overrides local function

The compiler would crash in v3_codegen when trying to compile the
following code:

  is_port(_) -> false.
  foo(P) when port(P) -> ok.

We *could* have the compiler interpret the code as:

  is_port(_) -> false.
  foo(P) when erlang:is_port(P) -> ok.

But that would encourage using the obsolete form of the guard tests.
Note that the following code is illegal:

  is_port(_) -> false.
  foo(P) when is_port(P) -> ok.

It produces the following diagnostic:

  call to local/imported function is_port/1 is illegal in guard

Therefore, we should refuse to compile the code.

1 files changed, 9 insertions, 1 deletions

diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index d916eb3eef..4ee3950882 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -1554,7 +1554,15 @@ guard(Config) when is_list(Config) ->
             [],
             {errors,[{1,erl_lint,illegal_guard_expr},
                      {2,erl_lint,illegal_guard_expr}],
-             []}}
+             []}},
+           {guard10,
+            <<"is_port(_) -> false.
+               t(P) when port(P) -> ok.
+            ">>,
+            [],
+            {error,
+	     [{2,erl_lint,{obsolete_guard_overridden,port}}],
+	     [{2,erl_lint,{obsolete_guard,{port,1}}}]}}
 	  ],
     [] = run(Config, Ts1),
     ok.