[erlang-bugs 7] possible supervisor bug in r14b02

[Filipe David Manana]

Hi,

In R14B02 I noticed that for a child with a "temporary" restart_type,
we discard its A component of the MFA tuple when adding the childspec
to the list of the supervisor's children [1].

When the child terminates, its spec is never removed from the list of
the supervisor's children specs.
Then if we call supervisor:restart_child/2 after the child terminates,
the handle_call clause for restart_child gets the childspec with an
MFA  that is {M, F, undefined} [2]. At that point do_start_child will
call apply(M, F, undefined) [3] which will cause the supervisor to
reply with an error, instead of returning {ok, Pid} as in previous
releases. An example for the returned error:

 {error,{'EXIT',{badarg,[{erlang,apply,[gen_server,start_link,undefined]},
                              {supervisor,do_start_child,2},
                              {supervisor,handle_call,3},
                              {gen_server,handle_msg,5},
                              {proc_lib,init_p_do_apply,3}]}}}

The patch at [4] fixes the issue for me. The particular code that is
no longer working in R14B02 but worked on all previous releases, is
from Apache CouchDB, see [5]

This issue was introuced by OTP-9064 (reading from the R14B02 release notes).
Was this intended behaviour? It doesn't make much sense for me to keep
a temporary childspec in the supervisor once the child terminates, so
I believe deleting it from the state is the right thing to do.

[1] - https://github.com/erlang/otp/blob/dev/lib/stdlib/src/supervisor.erl#L787
[2] - https://github.com/erlang/otp/blob/dev/lib/stdlib/src/supervisor.erl#L314
[3] - https://github.com/erlang/otp/blob/dev/lib/stdlib/src/supervisor.erl#L246
[4] - https://github.com/fdmanana/otp/commit/2697042aa9ebab2fcd208c93b7f454b25bc580d4
[5] - https://github.com/apache/couchdb/blob/trunk/src/couchdb/couch_replicator.erl#L119

-- 
Filipe David Manana,
fdmanana@REDACTED, fdmanana@REDACTED

"Reasonable men adapt themselves to the world.
 Unreasonable men adapt the world to themselves.
 That's why all progress depends on unreasonable men."