## Changes
Introduce `libs/vfs` for an implementation of `fs.FS` and friends that
_includes_ the absolute path it is anchored to.
This is needed for:
1. Intercepting file operations to inject custom logic (e.g., logging,
access control).
2. Traversing directories to find specific leaf directories (e.g.,
`.git`).
3. Converting virtual paths to OS-native paths.
Options 2 and 3 are not possible with the standard `fs.FS` interface.
They are needed such that we can provide an instance to the sync package
and still detect the containing `.git` directory and convert paths to
native paths.
This change focuses on making the following packages use `vfs.Path`:
* libs/fileset
* libs/git
* libs/sync
All entries returned by `fileset.All` are now slash-separated. This has
2 consequences:
* The sync snapshot now always uses slash-separated paths
* We don't need to call `filepath.FromSlash` as much as we did
## Tests
* All unit tests pass
* All integration tests pass
* Manually confirmed that a deployment made on Windows by a previous
version of the CLI can be deployed by a new version of the CLI while
retaining the validity of the local sync snapshot as well as the remote
deployment state.
## Changes
This PR pays some tech debt by refactoring sync diff computation into
interfaces that are more robust.
Specifically:
1. Refactor the single diff computation function into a `SnapshotState`
class that computes the target state only based on the current local
files making it more robust and not carrying over state from previous
iterations.
2. Adds new validations for the sync state which make sure that the
invariants that downstream code expects are actually held true. This
prevents a class of issues where these invariants break and the
synchroniser behaves unexpectedly.
Note, this does not change the existing schema for the snapshot, only
the way the diff is computed, and thus is backwards compatible (ie does
not require a schema version bump).
## Tests
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Pieter Noordhuis
shreyas-goenka