Teach sys:get_status/1,2 to call Mod:format_status/2

Restore the ability for gen_server and gen_fsm callback
modules to format their own state for display under the
sys:get_status/1,2 calls.

This ability is extremely useful for new behavior modules
based on gen_server or gen_fsm, so that they can display
their status in a more meaningful way than just dumping
the state record. It is also generally useful for applications
wanting to display their gen_server or gen_fsm callback module
state in something other than the default manner.

Also document the previously undocumented the
gen_server:format_status/2 and gen_fsm:format_status/2 optional
callback functions that, if exported by the callback module, are
invoked when sys:get_status/1,2 are called.

Add unit tests to ensure that format_status/2 functions exported
from a gen_fsm callback module and a gen_server callback module
are called when sys:get_status/1,2 are called.

1 files changed, 10 insertions, 1 deletions

diff --git a/lib/stdlib/src/sys.erl b/lib/stdlib/src/sys.erl
index e0f2dbcd3c..12209c16d7 100644
--- a/lib/stdlib/src/sys.erl
+++ b/lib/stdlib/src/sys.erl
@@ -245,8 +245,17 @@ do_cmd(SysState, Other, _Parent, _Mod, Debug, Misc) ->
     {SysState, {error, {unknown_system_msg, Other}}, Debug, Misc}.
 
 get_status(SysState, Parent, Mod, Debug, Misc) ->
+    PDict = get(),
+    FmtMisc =
+        case erlang:function_exported(Mod, format_status, 2) of
+            true ->
+                FmtArgs = [PDict, SysState, Parent, Debug, Misc],
+                Mod:format_status(normal, FmtArgs);
+            _ ->
+                Misc
+        end,
     {status, self(), {module, Mod},
-     [get(), SysState, Parent, Debug, Misc]}.
+     [PDict, SysState, Parent, Debug, FmtMisc]}.
 
 %%-----------------------------------------------------------------
 %% These are the system debug commands.