Function apply_patch 

pub fn apply_patch<F>(
    tree: &FileTree,
    patch: &Patch,
    get_payload_blob: F,
) -> Result<FileTree, ApplyError>
where
    F: FnMut(&Patch) -> Option<Hash>,

Apply a single patch to a FileTree, producing a new FileTree.

Operation Semantics

Operation	Precondition	Effect
Create	Path must NOT exist	Insert path → blob hash
Modify	Path must exist	Update blob hash
Delete	Path must exist	Remove path
Move	Old path must exist, new must NOT	Rename
Metadata	Path must exist (if specified)	No tree change
Merge	N/A	No tree change (merge commits carry no payload)
Identity	N/A	No change

Arguments

• tree - The current file tree state
• patch - The patch to apply
• get_payload_blob - Function to resolve the patch payload to a CAS hash. For Modify/Create, the payload is a hex-encoded CAS hash; this function parses it and returns the actual hash.