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Document snapshot pipeline

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This commit is contained in:
Lucien Greathouse
2019-09-26 14:28:04 -07:00
parent 91d12aeb4f
commit 87227c96ed
3 changed files with 51 additions and 14 deletions
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32
src/snapshot/mod.rs
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@@ -1,8 +1,32 @@
//! This module defines the instance snapshot subsystem of Rojo.
//!
//! It defines a way to define the instance tree of a project as a pure function
//! of the filesystem by providing a lightweight instance 'snapshot' type, a
//! method to generate minimal patches, and a method that applies those patches.
//! Snapshots define a way to define the instance tree of a project as a pure
//! function of the filesystem by providing a lightweight instance 'snapshot'
//! type, a method to generate minimal patches, and a method that applies those
//! patches.
//!
//! Changes in Rojo go through a pipeline of transformations once they hit the
//! snapshot subsystem.
//!
//! 1. Instance snapshots are generated by Rojo's snapshot middleware,
//! representing a set of instances and their metadata. These will
//! usually contain data that hasn't actually changed, and how coarsely
//! the snapshots happen is defined outside this part of the code.
//!
//! 2. Input snapshots are turned into `PatchSet` objects by Rojo's diffing
//! algorithm via `compute_patch_set`. This operation doesn't mutate the
//! instance tree, so work at this point can be thrown away.
//!
//! `PatchSet` prescribe what changes need to be applied to the current
//! tree to get the next tree. It isn't useful for describing those
//! changes after the fact, since Rojo needs to assign IDs to created
//! instances, which happens during patch application, not generation!
//!
//! 3. Patch sets are applied to the tree with `apply_patch_set`, which
//! mutates the relevant instances. `apply_patch_set` returns a new
//! object, `AppliedPatchSet`. Applied patch sets describe the transform
//! that was applied, and are suitable for cases where another tree needs
//! to be synchronized with Rojo's, like the Rojo Studio plugin.
//!
//! The aim with this approach is to reduce the number of bugs that arise from
//! attempting to manually update instances in response to filesystem updates.
@@ -26,7 +50,7 @@ mod patch_compute;
mod tree;
pub use instance_snapshot::InstanceSnapshot;
pub use metadata::*;
pub use metadata::InstanceMetadata;
pub use patch::*;
pub use patch_apply::apply_patch_set;
pub use patch_compute::compute_patch_set;