Implement Syncback to support converting Roblox files to a Rojo project (#937)

This is a very large commit.
Consider checking the linked PR for more information.

src/snapshot_middleware/rbxmx.rs

@@ -2,8 +2,12 @@ use std::path::Path;
 
 use anyhow::Context;
 use memofs::Vfs;
+use rbx_xml::EncodeOptions;
 
-use crate::snapshot::{InstanceContext, InstanceMetadata, InstanceSnapshot};
+use crate::{
+    snapshot::{InstanceContext, InstanceMetadata, InstanceSnapshot},
+    syncback::{FsSnapshot, SyncbackReturn, SyncbackSnapshot},
+};
 
 pub fn snapshot_rbxmx(
     context: &InstanceContext,
@@ -15,7 +19,7 @@ pub fn snapshot_rbxmx(
         .property_behavior(rbx_xml::DecodePropertyBehavior::ReadUnknown);
 
     let temp_tree = rbx_xml::from_reader(vfs.read(path)?.as_slice(), options)
-        .with_context(|| format!("Malformed rbxm file: {}", path.display()))?;
+        .with_context(|| format!("Malformed rbxmx file: {}", path.display()))?;
 
     let root_instance = temp_tree.root();
     let children = root_instance.children();
@@ -41,6 +45,32 @@ pub fn snapshot_rbxmx(
     }
 }
 
+pub fn syncback_rbxmx<'sync>(
+    snapshot: &SyncbackSnapshot<'sync>,
+) -> anyhow::Result<SyncbackReturn<'sync>> {
+    let inst = snapshot.new_inst();
+
+    let options =
+        EncodeOptions::new().property_behavior(rbx_xml::EncodePropertyBehavior::WriteUnknown);
+
+    // Long-term, we probably want to have some logic for if this contains a
+    // script. That's a future endeavor though.
+    let mut serialized = Vec::new();
+    rbx_xml::to_writer(
+        &mut serialized,
+        snapshot.new_tree(),
+        &[inst.referent()],
+        options,
+    )
+    .context("failed to serialize new rbxmx")?;
+
+    Ok(SyncbackReturn {
+        fs_snapshot: FsSnapshot::new().with_added_file(&snapshot.path, serialized),
+        children: Vec::new(),
+        removed_children: Vec::new(),
+    })
+}
+
 #[cfg(test)]
 mod test {
     use super::*;