Managed target directories

Cargo normally writes build outputs to <workspace>/target. Deleting a worktree deletes useful outputs, while abandoning a checkout leaves gigabytes behind indefinitely.

Managed targets are enabled by default. For a checkout without an existing target/, the first build is enough:

mbx build

mbx places the target directory under its cache root and leaves a symlink at target, so familiar paths continue to work:

target -> <cache root>/targets/v1/<checkout digest>

Collection

mbx records the checkout associated with each target view. Once that checkout no longer exists, mbx gc can remove its target directory. Cached compilations shared with a live checkout remain protected.

Managed target directories are collected when their checkout disappears; they are not counted against gc.max_size. The size budget covers cached objects and action results.

When mbx leaves a target alone

mbx does not override an explicit target directory supplied by:

• --target-dir
• CARGO_TARGET_DIR
• Cargo's build.target-dir configuration

Existing target directories

When an interactive mbx command finds an existing real target/, it offers to remove the old outputs and replace the directory with a managed link:

Use a managed target directory?
mbx can remove /path/to/project/target and replace it with a managed target that is pruned after this checkout is deleted.

“Keep it” is selected by default. Declining leaves every output untouched and the Cargo command continues normally. Non-interactive runs never prompt or remove the directory.

After acceptance, mbx temporarily moves the old directory aside. It removes those outputs only after the managed link and its collection record both succeed, then reports how much space the old outputs occupied. If placement fails, mbx restores the original directory.

mbx does not offer removal for an explicitly configured target directory or a symlink it does not own.

Disable managed targets

Set MBX_TARGET_VIEWS=0, or configure:

[target]
views = false

Turning placement off does not delete a target directory mbx already manages. The existing target link continues to work, and collection can still reclaim the directory after its checkout disappears.

Windows

Creating the link requires Developer Mode or a privileged process on Windows. If Windows cannot create it, mbx lets Cargo use its ordinary target directory.