Add erlang:nif_error/1,2

A stub function that is supposed to be replaced by a NIF usually
calls erlang:error/1 to cause an exception if the NIF library
is not loaded. For example:

  foo() ->
      erlang:error(nif_not_loaded).

The problem is that although erlang:error/1 will normally never be
called, Dialyzer will think that any call to the function will fail
and thus generate false warnings. Adding a spec for the function
will not help because Dialyzer will not believe the spec.

Add erlang:nif_error/1,2 that work exactly like erlang:error/1,2.

Define the return types for both BIFs to be t_any().

erlang:nif_error is used like this:

  -spec foo() -> binary().

  foo() ->
      erlang:nif_error(nif_not_loaded).

(The -spec is optional but highly recommended, since Dialyzer
otherwise has no chance to figure out the types.)

4 files changed, 70 insertions, 0 deletions

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index e683f161f1..7ff52c5b50 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -2644,6 +2644,37 @@ os_prompt%</pre>
       </desc>
     </func>
     <func>
+      <name>erlang:nif_error(Reason)</name>
+      <fsummary>Stop execution with a given reason</fsummary>
+      <type>
+        <v>Reason = term()</v>
+      </type>
+      <desc>
+        <p>Works exactly like
+	 <seealso marker="#error/1">erlang:error/1</seealso>,
+	 but Dialyzer thinks that this BIF will return an arbitrary term.
+	 When used in a stub function for a NIF to generate an
+	 exception when the NIF library is not loaded, Dialyzer
+	 will not generate false warnings.</p>
+      </desc>
+    </func>
+    <func>
+      <name>erlang:nif_error(Reason, Args)</name>
+      <fsummary>Stop execution with a given reason</fsummary>
+      <type>
+        <v>Reason = term()</v>
+        <v>Args = [term()]</v>
+      </type>
+      <desc>
+        <p>Works exactly like
+	 <seealso marker="#error/2">erlang:error/2</seealso>,
+	 but Dialyzer thinks that this BIF will return an arbitrary term.
+	 When used in a stub function for a NIF to generate an
+	 exception when the NIF library is not loaded, Dialyzer
+	 will not generate false warnings.</p>
+      </desc>
+    </func>
+    <func>
       <name>node() -> Node</name>
       <fsummary>Name of the local node</fsummary>
       <type>
diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index 85bf584337..7a69dc6eff 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -1132,6 +1132,34 @@ BIF_RETTYPE error_2(Process* p, Eterm value, Eterm args)
 }
 
 /**********************************************************************/
+/*
+ * This is like exactly like error/1. The only difference is
+ * that Dialyzer thinks that it it will return an arbitrary term.
+ * It is useful in stub functions for NIFs.
+ */
+
+BIF_RETTYPE nif_error_1(Process* p, Eterm term)
+{
+    p->fvalue = term;
+    BIF_ERROR(p, EXC_ERROR);
+}
+
+/**********************************************************************/
+/*
+ * This is like exactly like error/2. The only difference is
+ * that Dialyzer thinks that it it will return an arbitrary term.
+ * It is useful in stub functions for NIFs.
+ */
+
+BIF_RETTYPE nif_error_2(Process* p, Eterm value, Eterm args)
+{
+    Eterm* hp = HAlloc(p, 3);
+
+    p->fvalue = TUPLE2(hp, value, args);
+    BIF_ERROR(p, EXC_ERROR_2);
+}
+
+/**********************************************************************/
 /* this is like throw/1 except that we set freason to EXC_EXIT */
 
 BIF_RETTYPE exit_1(BIF_ALIST_1)
diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index 9feb302a3d..e4713567de 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -793,6 +793,9 @@ bif binary:encode_unsigned/2
 bif binary:decode_unsigned/1
 bif binary:decode_unsigned/2
 
+bif erlang:nif_error/1
+bif erlang:nif_error/2
+
 #
 # Obsolete
 #
diff --git a/lib/hipe/cerl/erl_bif_types.erl b/lib/hipe/cerl/erl_bif_types.erl
index be3073c0e6..523c00b2be 100644
--- a/lib/hipe/cerl/erl_bif_types.erl
+++ b/lib/hipe/cerl/erl_bif_types.erl
@@ -1155,6 +1155,10 @@ type(erlang, monitor_node, 2, Xs) ->
 type(erlang, monitor_node, 3, Xs) ->
   strict(arg_types(erlang, monitor_node, 3), Xs,
 	 fun (_) -> t_atom('true') end);
+type(erlang, nif_error, 1, _) ->
+  t_any();
+type(erlang, nif_error, 2, Xs) ->
+  strict(arg_types(erlang, nif_error, 2), Xs, fun (_) -> t_any() end);
 type(erlang, node, 0, _) -> t_node();
 type(erlang, node, 1, Xs) ->
   strict(arg_types(erlang, node, 1), Xs, fun (_) -> t_node() end);
@@ -3628,6 +3632,10 @@ arg_types(erlang, monitor_node, 2) ->
   [t_node(), t_boolean()];
 arg_types(erlang, monitor_node, 3) ->
   [t_node(), t_boolean(), t_list(t_atom('allow_passive_connect'))];
+arg_types(erlang, nif_error, 1) ->
+  [t_any()];
+arg_types(erlang, nif_error, 2) ->
+  [t_any(), t_list()];
 arg_types(erlang, node, 0) ->
   [];
 arg_types(erlang, node, 1) ->