Add application:get_key/3

The new function provides a default value for a configuration
parameter.

3 files changed, 29 insertions, 4 deletions

diff --git a/lib/kernel/doc/src/application.xml b/lib/kernel/doc/src/application.xml
index 51a3311ec2..3513e2b592 100644
--- a/lib/kernel/doc/src/application.xml
+++ b/lib/kernel/doc/src/application.xml
@@ -108,12 +108,14 @@
     <func>
       <name name="get_env" arity="1"/>
       <name name="get_env" arity="2"/>
+      <name name="get_env" arity="3"/>
       <fsummary>Get the value of a configuration parameter</fsummary>
       <desc>
         <p>Returns the value of the configuration parameter <c><anno>Par</anno></c>
           for <c><anno>Application</anno></c>. If the application argument is
           omitted, it defaults to the application of the calling
-          process.</p>
+          process. If <c><anno>Def</anno></c> value is provided, it is returned
+          when no configuration parameter <c><anno>Par</anno></c> is defined.</p>
         <p>If the specified application is not loaded, or
           the configuration parameter does not exist, or if the process
           executing the call does not belong to any application,
diff --git a/lib/kernel/src/application.erl b/lib/kernel/src/application.erl
index 9b7c4aa7b8..4e65883be7 100644
--- a/lib/kernel/src/application.erl
+++ b/lib/kernel/src/application.erl
@@ -23,7 +23,7 @@
 	 which_applications/0, which_applications/1,
 	 loaded_applications/0, permit/2]).
 -export([set_env/3, set_env/4, unset_env/2, unset_env/3]).
--export([get_env/1, get_env/2, get_all_env/0, get_all_env/1]).
+-export([get_env/1, get_env/2, get_env/3, get_all_env/0, get_all_env/1]).
 -export([get_key/1, get_key/2, get_all_key/0, get_all_key/1]).
 -export([get_application/0, get_application/1, info/0]).
 -export([start_type/0]).
@@ -264,6 +264,20 @@ get_env(Key) ->
 get_env(Application, Key) -> 
     application_controller:get_env(Application, Key).
 
+-spec get_env(Application, Par, Def) -> Val when
+      Application :: atom(),
+      Par :: atom(),
+      Def :: term(),
+      Val :: term().
+
+get_env(Application, Key, Def) ->
+    case get_env(Application, Key) of
+    {ok, Val} ->
+        Val;
+    undefined ->
+        Def
+    end.
+
 -spec get_all_env() -> Env when
       Env :: [{Par :: atom(), Val :: term()}].
 
diff --git a/lib/kernel/test/application_SUITE.erl b/lib/kernel/test/application_SUITE.erl
index f469a0af98..412a969b13 100644
--- a/lib/kernel/test/application_SUITE.erl
+++ b/lib/kernel/test/application_SUITE.erl
@@ -27,7 +27,7 @@
 	 otp_1586/1, otp_2078/1, otp_2012/1, otp_2718/1, otp_2973/1,
 	 otp_3002/1, otp_3184/1, otp_4066/1, otp_4227/1, otp_5363/1,
 	 otp_5606/1,
-	 start_phases/1, get_key/1, 
+	 start_phases/1, get_key/1, get_env/1,
 	 permit_false_start_local/1, permit_false_start_dist/1, script_start/1, 
 	 nodedown_start/1, init2973/0, loop2973/0, loop5606/1]).
 
@@ -49,7 +49,7 @@ all() ->
     [failover, failover_comp, permissions, load,
      load_use_cache, {group, reported_bugs}, start_phases,
      script_start, nodedown_start, permit_false_start_local,
-     permit_false_start_dist, get_key,
+     permit_false_start_dist, get_key, get_env,
      {group, distr_changed}, config_change, shutdown_func, shutdown_timeout].
 
 groups() -> 
@@ -1503,6 +1503,15 @@ loop5606(Pid) ->
 	    Pid ! {self(), Res}
     end.
 	    
+get_env(suite) -> [];
+get_env(doc) ->
+    ["Tests get_env/* functions"];
+get_env(Conf) when is_list(Conf) ->
+    ?line {ok, _}   = application:get_env(kernel, error_logger),
+    ?line undefined = application:get_env(undefined_app, a),
+    ?line undefined = application:get_env(kernel, error_logger_xyz),
+    ?line default   = application:get_env(kernel, error_logger_xyz, default),
+    ok.
 
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