mount_paths can delete a directory in the container

[pickledish]

Description

One task A creates a directory in a container, then a later task B which depends on A, when using mount_paths, can remove that directory. I've tested and the same does not happen with input_paths.

Instructions to reproduce the bug

Here is my Toast file. The package.json contains Vite and some other stuff:

image: node:20
command_prefix: set -euxo pipefail
location: /scratch
tasks:
  deps:
    input_paths:
    - package.json
    - package-lock.json
    command: |
      npm install
  dev:
    cache: false
    dependencies:
    - deps
    mount_paths:
    - .
    ports:
    - 5173:5173
    command: |
      npm run dev

When trying to use toast dev, the command fails (vite is not found), and getting a shell into the container I found that the node_modules directory that had been created by the deps task was gone. Replacing mount_paths with input_paths in the above example, changing nothing else, fixes the problem (the node_modules dir exists and vite etc can be used).

Environment information:

$ toast -v
Toast 0.47.5

$ sw_vers
ProductName:    macOS
ProductVersion: 11.7.8
BuildVersion:   20G1351

Might this be because mounting . of the host to /scratch inside the container overrides all existing contents in /scratch? This would be a surprising difference between the behaviors of mount_paths and input_paths ("for each file in this directory, copy the file into the container") which otherwise look and work the same. Anyway, if this behavior is intended, then feel free to close the issue, thanks!

[stepchowfun]

Hi @pickledish, thank you for opening this issue. Unless I'm misunderstanding, this is the intended behavior and highlights one of the key differences between mount_paths and input_paths: mount_paths just exposes the host file system to the container, and any changes made by containers to mounted paths (such as deleting directories) are persisted between runs. However, you can also use the mount_readonly toastfile option if you want to disallow changes to the host file system. With input_paths, the container is operating on a copy of the files from the host, so the files on the host are unaffected by whatever happens inside the container.