The lager dependency is used only with old Erlang versions

mix.exs

@@ -44,7 +44,7 @@ defmodule Ejabberd.MixProject do
      applications: [:idna, :inets, :kernel, :sasl, :ssl, :stdlib,
                     :base64url, :fast_tls, :fast_xml, :fast_yaml, :jiffy, :jose,
                     :p1_utils, :stringprep, :yconf],
-     included_applications: [:lager, :mnesia, :os_mon,
+     included_applications: [:mnesia, :os_mon,
                              :cache_tab, :eimp, :mqtree, :p1_acme,
                              :p1_oauth2, :pkix, :xmpp]
      ++ cond_apps()]
@@ -118,7 +118,6 @@ defmodule Ejabberd.MixProject do
      {:idna, "~> 6.0"},
      {:jiffy, "~> 1.0.5"},
      {:jose, "~> 1.11.1"},
-     {:lager, "~> 3.9.1"},
      {:mqtree, "~> 1.0"},
      {:p1_acme, "~> 1.0"},
      {:p1_oauth2, "~> 0.6"},
@@ -147,6 +146,7 @@ defmodule Ejabberd.MixProject do
                          {config(:redis), {:eredis, "~> 1.2.0"}},
                          {config(:sip), {:esip, "~> 1.0"}},
                          {config(:zlib), {:ezlib, "~> 1.0"}},
+                         {if_version_below('22', true), {:lager, "~> 3.9.1"}},
                          {config(:lua), {:luerl, "~> 1.0"}},
                          {config(:mysql), {:p1_mysql, "~> 1.0"}},
                          {config(:pgsql), {:p1_pgsql, "~> 1.1"}},
@@ -159,6 +159,7 @@ defmodule Ejabberd.MixProject do
     for {:true, app} <- [{config(:pam), :epam},
                          {config(:lua), :luerl},
                          {config(:redis), :eredis},
+                         {if_version_below('22', true), :lager},
                          {config(:mysql), :p1_mysql},
                          {config(:sip), :esip},
                          {config(:odbc), :odbc},

rebar.config

@@ -39,7 +39,9 @@
         {idna, ".*", {git, "https://github.com/benoitc/erlang-idna", {tag, "6.0.0"}}},
         {jiffy, ".*", {git, "https://github.com/davisp/jiffy", {tag, "1.0.5"}}},
         {jose, ".*", {git, "https://github.com/potatosalad/erlang-jose", {tag, "1.11.1"}}},
-        {lager, ".*", {git, "https://github.com/erlang-lager/lager", {tag, "3.9.1"}}},
+        {if_version_below, "22",
+         {lager, ".*", {git, "https://github.com/erlang-lager/lager", {tag, "3.9.1"}}}
+        },
         {if_var_true, lua,
          {if_not_rebar3,
           {luerl, ".*", {git, "https://github.com/rvirding/luerl", {tag, "1.0"}}}

src/ejabberd.app.src.script

@@ -16,13 +16,12 @@ Vars = case file:consult(filename:join([filename:dirname(SCRIPT), "..", "vars.co
   {registered, []},
   {applications, [kernel, sasl, ssl, stdlib]},
   {included_applications,
-    [inets, mnesia, os_mon,
+    [compiler, inets, mnesia, os_mon,
      cache_tab,
      eimp,
      fast_tls,
      fast_xml,
      fast_yaml,
-     lager,
      p1_acme,
      p1_utils,
      pkix,