Fix an issue when platformio ci recompiles project if `--keep-build-dir` option is passed // Resolve #2109

HISTORY.rst

@@ -10,6 +10,8 @@ PlatformIO 4.0
 * Added Python 3.5+ support
   (`issue #895 <https://github.com/platformio/platformio-core/issues/895>`_)
 * Fixed an issue with slow updating of PlatformIO Core packages on Windows
+* Fixed an issue when `platformio ci <https://docs.platformio.org/en/latest/userguide/cmd_ci.html>`__ recompiles project if ``--keep-build-dir`` option is passed
+  (`issue #2109 <https://github.com/platformio/platformio-core/issues/2109>`_)
 
 PlatformIO 3.0
 --------------

platformio/commands/ci.py

@@ -84,7 +84,11 @@ def cli(  # pylint: disable=too-many-arguments
 
     try:
         app.set_session_var("force_option", True)
-        _clean_dir(build_dir)
+
+        if not keep_build_dir and isdir(build_dir):
+            util.rmtree_(build_dir)
+        if not isdir(build_dir):
+            makedirs(build_dir)
 
         for dir_name, patterns in dict(lib=lib, src=src).items():
             if not patterns:
@@ -116,11 +120,6 @@ def cli(  # pylint: disable=too-many-arguments
             util.rmtree_(build_dir)
 
 
-def _clean_dir(dirpath):
-    util.rmtree_(dirpath)
-    makedirs(dirpath)
-
-
 def _copy_contents(dst_dir, contents):
     items = {"dirs": set(), "files": set()}