Change the default source code mount
If you add the image or dockerFile properties to devcontainer.json, VS Code will automatically "bind" mount your current workspace folder into the container. If git is present on the host's PATH and the folder containing .devcontainer/devcontainer.json is within a git repository, the current workspace mounted will be the root of the repository. If git is not present on the host's PATH, the current workspace mounted will be the folder containing .devcontainer/devcontainer.json.
While this is convenient, you may want to change mount settings, alter the type of mount, location, or run in a remote dev container.
You can use the workspaceMount property in devcontainer.json to change the automatic mounting behavior. It expects the same value as the Docker CLI --mount flag.
For example:
"workspaceMount": "source=${localWorkspaceFolder}/sub-folder,target=/workspace,type=bind",
"workspaceFolder": "/workspace"
This also allows you to do something like a named volume mount instead of a bind mount, which can be useful particularly when using a remote Docker Host or you want to store your entire source tree in a volume.
If you've already built the container and connected to it, run Dev Containers: Rebuild Container from the Command Palette (F1) to pick up the change. Otherwise run Dev Containers: Open Folder in Container... to connect to the container.