Read env var REBAR_CACHE_DIR on rebar3 only once

Instead of reading every time that rebar_dir:global_cache_dir/1 is
called

src/rebar3.erl

@@ -129,13 +129,20 @@ run_aux(State, RawArgs) ->
     %% Initializing project_plugins which can override default providers
     State6 = rebar_plugins:project_plugins_install(State5),
     State7 = rebar_plugins:top_level_install(State6),
-    State8 = rebar_state:default(State7, rebar_state:opts(State7)),
+    State8 = case os:getenv("REBAR_CACHE_DIR") of
+                false ->
+                    State7;
+                ConfigFile ->
+                    rebar_state:set(State7, global_rebar_dir, ConfigFile)
+            end,
+
+    State9 = rebar_state:default(State8, rebar_state:opts(State8)),
 
     {Task, Args} = parse_args(RawArgs),
 
-    State9 = rebar_state:code_paths(State8, default, code:get_path()),
+    State10 = rebar_state:code_paths(State9, default, code:get_path()),
 
-    rebar_core:init_command(rebar_state:command_args(State9, Args), Task).
+    rebar_core:init_command(rebar_state:command_args(State10, Args), Task).
 
 init_config() ->
     %% Initialize logging system

src/rebar_dir.erl

@@ -94,14 +94,8 @@ global_config() ->
 
 -spec global_cache_dir(rebar_dict()) -> file:filename_all().
 global_cache_dir(Opts) ->
-    RebarCacheDir = case os:getenv("REBAR_CACHE_DIR") of
-        false ->
-            Home = home_dir(),
-            filename:join([Home, ".cache", "rebar3"]);
-        ConfigFile ->
-            ConfigFile
-    end,
-    rebar_opts:get(Opts, global_rebar_dir, RebarCacheDir).
+    Home = home_dir(),
+    rebar_opts:get(Opts, global_rebar_dir, filename:join([Home, ".cache", "rebar3"])).
 
 local_cache_dir(Dir) ->
     filename:join(Dir, ".rebar3").

test/rebar_dir_SUITE.erl

@@ -25,6 +25,7 @@ init_per_testcase(default_global_cache_dir, Config) ->
                             ,{root_dir, AppsDir}]),
     [{apps, AppsDir}, {checkouts, CheckoutsDir}, {state, NewState} | Config];
 init_per_testcase(overwrite_default_global_cache_dir, Config) ->
+    os:putenv("REBAR_CACHE_DIR", ?config(priv_dir, Config)),
     [{apps, AppsDir}, {checkouts, CheckoutsDir}, {state, _State} | Config] = rebar_test_utils:init_rebar_state(Config),
     NewState = rebar_state:new([{base_dir, filename:join([AppsDir, "_build"])}
                             ,{root_dir, AppsDir}]),
@@ -189,7 +190,6 @@ default_global_cache_dir(Config) ->
     ?assertEqual(Expected, rebar_dir:global_cache_dir(rebar_state:opts(State))).
 
 overwrite_default_global_cache_dir(Config) ->
-    os:putenv("REBAR_CACHE_DIR", ?config(priv_dir, Config)),
     RebarConfig = [{erl_opts, []}],
     {ok, State} = rebar_test_utils:run_and_check(Config, RebarConfig, ["compile"], return),
     Expected = ?config(priv_dir, Config),