Add Sync tool to "make relive" with Rebar3

How to use:
- Compile ejabberd with Rebar3
- Start ejabberd with "make relive"
- Edit some ejabberd source code file
- Save the file, and Sync will compile and reload it automatically

I've added src_dirs option so Sync doesn't act on dependencies,
which would produce many garbage log lines.
However, now it only works if the parent directory is named "ejabberd"

Sync requires at least Erlang/OTP 21, which introduced the
new try-catch syntax to retrieve the stacktrace
https://www.erlang.org/patches/otp-21.0

References:
https://hex.pm/packages/sync
https://github.com/rustyio/sync

.gitignore

@@ -34,6 +34,7 @@
 /priv/bin/captcha*sh
 /priv/sql
 /rel/ejabberd
+/recompile.log
 /_build
 /database/
 /.rebar

Makefile.in

@@ -150,6 +150,7 @@ ifeq ($(REBAR_ENABLE_ELIXIR),true)
   ELIXIR_LIBDIR_RAW=$(shell elixir -e "IO.puts(:filename.dirname(:code.lib_dir(:elixir)))" -e ":erlang.halt")
   ELIXIR_LIBDIR=":$(ELIXIR_LIBDIR_RAW)"
   EXPLICIT_ELIXIR_COMPILE=MIX_ENV=default mix compile.elixir
+  EXPLICIT_ELIXIR_COMPILE_DEV=MIX_ENV=dev mix compile.elixir
   PREPARE_ELIXIR_SCRIPTS=$(MKDIR_P) rel/overlays; cp $(ELIXIR_LIBDIR_RAW)/../bin/iex rel/overlays/; cp $(ELIXIR_LIBDIR_RAW)/../bin/elixir rel/overlays/; sed -i 's|ERTS_BIN=$$|ERTS_BIN=$$SCRIPT_PATH/../../erts-{{erts_vsn}}/bin/|' rel/overlays/elixir
 endif
 ifeq "$(REBAR_VER)" "3"
@@ -170,7 +171,7 @@ endif
   CLEANARG=--all
   REBARREL=$(REBAR) as prod tar
   REBARDEV=$(REBAR) as dev release
-  RELIVECMD=$(REBAR) relive
+  RELIVECMD=$(REBAR) as dev relive
   REL_LIB_DIR = _build/dev/rel/ejabberd/lib
   COPY_REL_TARGET = dev
   GET_DEPS_TRANSLATIONS=$(REBAR) as translations $(GET_DEPS)
@@ -377,6 +378,7 @@ uninstall-librel:
 #
 
 relive:
+	$(EXPLICIT_ELIXIR_COMPILE_DEV)
 	$(RELIVECMD)
 
 relivelibdir=$(shell pwd)/$(DEPSDIR)

rebar.config

@@ -274,6 +274,7 @@
                                        {copy, "ejabberdctl.cfg.example", "conf/ejabberdctl.cfg"},
                                        {copy, "ejabberd.yml.example", "conf/ejabberd.yml"}]}]}]},
             {dev, [{post_hooks, [{release, "rel/setup-dev.sh rebar3"}]},
+                   {deps, [{if_version_above, "20", sync}]},
                    {relx, [{debug_info, keep},
                            {dev_mode, true},
                            {include_erts, true},
@@ -289,6 +290,7 @@
 
 {alias, [{relive, [{shell, "--apps ejabberd \
                             --config rel/relive.config \
+                            --eval sync:go(). \
                             --script rel/relive.escript \
                             --name ejabberd@localhost"}]}
 ]}.

rel/relive.config

@@ -1,3 +1,4 @@
 [{mnesia, [{dir, "_build/relive/database"}]},
+ {sync,[{src_dirs, {replace, [{"ejabberd/src", []}]}}]},
  {ejabberd, [{config, "_build/relive/conf/ejabberd.yml"},
              {log_path, "_build/relive/logs/ejabberd.log"}]}].