Properly handle "--keep-build-dir" option in platformio ci command (#4061)

This fixes #4011 and possible "FileExists" errors when the "platformio ci"
command by safely copying sources to the build folder

HISTORY.rst

@@ -12,6 +12,7 @@ PlatformIO Core 5
 ~~~~~~~~~~~~~~~~~~
 
 - Fixed a "KeyError: Invalid board option 'build.cpu'" when using a precompiled library with a board that does not have a CPU field in the manifest (`issue #4056 <https://github.com/platformio/platformio-core/issues/4056>`_)
+- Fixed a "FileExist" error when the `platformio ci <https://docs.platformio.org/en/latest/userguide/cmd_ci.html>`__ command is used in pair with the ``--keep-build-dir`` option (`issue #4011 <https://github.com/platformio/platformio-core/issues/4011>`_)
 
 5.2.0 (2021-09-13)
 ~~~~~~~~~~~~~~~~~~

platformio/commands/ci.py

@@ -122,7 +122,7 @@ def cli(  # pylint: disable=too-many-arguments, too-many-branches
             fs.rmtree(build_dir)
 
 
-def _copy_contents(dst_dir, contents):
+def _copy_contents(dst_dir, contents):  # pylint: disable=too-many-branches
     items = {"dirs": set(), "files": set()}
 
     for path in contents:
@@ -134,14 +134,15 @@ def _copy_contents(dst_dir, contents):
     dst_dir_name = os.path.basename(dst_dir)
 
     if dst_dir_name == "src" and len(items["dirs"]) == 1:
+        if not os.path.isdir(dst_dir):
             shutil.copytree(list(items["dirs"]).pop(), dst_dir, symlinks=True)
     else:
         if not os.path.isdir(dst_dir):
             os.makedirs(dst_dir)
         for d in items["dirs"]:
-            shutil.copytree(
-                d, os.path.join(dst_dir, os.path.basename(d)), symlinks=True
-            )
+            src_dst_dir = os.path.join(dst_dir, os.path.basename(d))
+            if not os.path.isdir(src_dst_dir):
+                shutil.copytree(d, src_dst_dir, symlinks=True)
 
     if not items["files"]:
         return

tests/commands/test_ci.py

@@ -88,6 +88,69 @@ def test_ci_keep_build_dir(clirunner, tmpdir_factory, validate_cliresult):
     assert "board: metro" in result.output
 
 
+def test_ci_keep_build_dir_single_src_dir(
+    clirunner, tmpdir_factory, validate_cliresult
+):
+    build_dir = str(tmpdir_factory.mktemp("ci_build_dir"))
+
+    # Run two times to detect possible "AlreadyExists" errors
+    for _ in range(2):
+        result = clirunner.invoke(
+            cmd_ci,
+            [
+                join("examples", "wiring-blink", "src"),
+                "-b",
+                "uno",
+                "--build-dir",
+                build_dir,
+                "--keep-build-dir",
+            ],
+        )
+        validate_cliresult(result)
+
+
+def test_ci_keep_build_dir_nested_src_dirs(
+    clirunner, tmpdir_factory, validate_cliresult
+):
+
+    build_dir = str(tmpdir_factory.mktemp("ci_build_dir"))
+
+    # Split default Arduino project in two parts
+    src_dir1 = tmpdir_factory.mktemp("src_1")
+    src_dir1.join("src1.cpp").write(
+        """
+void setup() {}
+"""
+    )
+
+    src_dir2 = tmpdir_factory.mktemp("src_2")
+    src_dir2.join("src2.cpp").write(
+        """
+void loop() {}
+"""
+    )
+
+    src_dir1 = str(src_dir1)
+    src_dir2 = str(src_dir2)
+
+    # Run two times to detect possible "AlreadyExists" errors
+    for _ in range(2):
+        result = clirunner.invoke(
+            cmd_ci,
+            [
+                src_dir1,
+                src_dir2,
+                "-b",
+                "teensy40",
+                "--build-dir",
+                build_dir,
+                "--keep-build-dir",
+            ],
+        )
+
+        validate_cliresult(result)
+
+
 def test_ci_project_conf(clirunner, validate_cliresult):
     project_dir = join("examples", "wiring-blink")
     result = clirunner.invoke(