Bug: CWD was not being created for workspaces

The code was creating the cwd folder but when the workspace was
mounted in to the buildroot it was hiding the folder created in it
behind the bind mounted workspace.

However buy using the bubble warp `--dir` directive to ensure that cwd
exists then we can cover both workspace and non workspace situation with
the same method.

2 files changed, 9 insertions, 8 deletions

diff --git a/buildstream/sandbox/_sandboxbwrap.py b/buildstream/sandbox/_sandboxbwrap.py
index 88b697dca..8ba1ff824 100644
--- a/buildstream/sandbox/_sandboxbwrap.py
+++ b/buildstream/sandbox/_sandboxbwrap.py
@@ -120,9 +120,6 @@ class SandboxBwrap(Sandbox):
             bwrap_command += ['--unshare-uts', '--hostname', 'buildstream']
             bwrap_command += ['--unshare-ipc']
 
-        if cwd is not None:
-            bwrap_command += ['--chdir', cwd]
-
         # Give it a proc and tmpfs
         bwrap_command += [
             '--proc', '/proc',
@@ -163,6 +160,10 @@ class SandboxBwrap(Sandbox):
         if flags & SandboxFlags.ROOT_READ_ONLY:
             bwrap_command += ["--remount-ro", "/"]
 
+        if cwd is not None:
+            bwrap_command += ['--dir', cwd]
+            bwrap_command += ['--chdir', cwd]
+
         # Set UID and GUI
         if self.user_ns_available:
             bwrap_command += ['--unshare-user']
@@ -191,11 +192,6 @@ class SandboxBwrap(Sandbox):
         with ExitStack() as stack:
             stack.enter_context(mount_map.mounted(self))
 
-            # Ensure the cwd exists
-            if cwd is not None:
-                workdir = os.path.join(root_mount_source, cwd.lstrip(os.sep))
-                os.makedirs(workdir, exist_ok=True)
-
             # If we're interactive, we want to inherit our stdin,
             # otherwise redirect to /dev/null, ensuring process
             # disconnected from terminal.
diff --git a/buildstream/sandbox/sandbox.py b/buildstream/sandbox/sandbox.py
index 9d34f0195..9192df7c2 100644
--- a/buildstream/sandbox/sandbox.py
+++ b/buildstream/sandbox/sandbox.py
@@ -197,6 +197,11 @@ class Sandbox():
     def run(self, command, flags, *, cwd=None, env=None):
         """Run a command in the sandbox.
 
+        Note:
+            When reimplementing this function for sandbox specific implementations it is the sandbox's and probably
+            this functions responsibility to ensure that cwd is created correctly and that if a workspace is used
+            then the directory must be correctly created to take this in to account.
+
         Args:
             command (list): The command to run in the sandboxed environment, as a list
                             of strings starting with the binary to run.