Potentially create global cache dir (rebar3) if it doesn't exist

src/rebar3_checkshell_inst.erl

@@ -22,8 +22,11 @@
 -spec put_executables() -> Result when
     Result :: ok | {error, nonempty_ubytes()}.
 put_executables() ->
+    GlobalCacheDirExists = filelib:is_dir(global_cache_dir()),
+    GlobalCacheDirResult = mkdir_global_cache(GlobalCacheDirExists),
+
     ArchCacheDirExists = filelib:is_dir(arch_cache_dir()),
-    CacheDirResult = mkdir_arch_cache(ArchCacheDirExists),
+    CacheDirResult = mkdir_arch_cache(ArchCacheDirExists, GlobalCacheDirResult),
 
     VsnCacheDirExists = filelib:is_dir(vsn_cache_dir()),
     VsnDirResult = mkdir_vsn_cache(VsnCacheDirExists, CacheDirResult),
@@ -105,13 +108,29 @@ executable_for(linux) ->
 executable_for(win32) ->
     "shellcheck.exe".
 
--spec mkdir_arch_cache(Exists) -> Result when
+-spec mkdir_global_cache(Exists) -> Result when
+    Exists :: boolean(),
+    Result :: ok | {error, file:posix()}.
+mkdir_global_cache(true = _Exists) ->
+    ok;
+mkdir_global_cache(false = _Exists) ->
+    GlobalCacheDir = global_cache_dir(),
+    _ = rebar_log:log(warn, "checkshell: creating global cache dir at ~p. Is this a CI env.?", [
+        GlobalCacheDir
+    ]),
+    filelib:ensure_path(GlobalCacheDir).
+
+-spec mkdir_arch_cache(Exists, GlobalCacheDirResult) -> Result when
     Exists :: boolean(),
+    GlobalCacheDirResult :: ok | {error, file:posix()},
     Result :: ok | {error, file:posix()}.
-mkdir_arch_cache(true = _Exists) ->
+mkdir_arch_cache(true = _Exists, _GlobalCacheDirResult) ->
     _ = rebar_log:log(debug, "checkshell: arch. cache dir exists", []),
     ok;
-mkdir_arch_cache(false = _Exists) ->
+mkdir_arch_cache(false = _Exists, {error, _FilePosix} = GlobalCacheDirResult) ->
+    _ = rebar_log:log(debug, "checkshell: (arch. cache) prior error ~p", [GlobalCacheDirResult]),
+    GlobalCacheDirResult;
+mkdir_arch_cache(false = _Exists, ok = _GlobalCacheDirResult) ->
     ArchFolderName = arch_folder_name(),
     ArchCacheDir = arch_cache_dir(),
     _ = rebar_log:log(info, "checkshell: creating cache/arch. dir (arch: ~p) at ~p", [