M6: Dev Mode: compare changes against any saved version

crates/engine/src/cmd/file.rs

@@ -337,7 +337,7 @@ fn version_index(cmd: &str, ds: &DocState, p: &Value) -> Result<usize> {
     if i < ds.versions.len() { Ok(i) } else { Err(bad(cmd, format!("no version at index {i}"))) }
 }
 
-fn read_version(v: &Version) -> Result<Arc<Document>> {
+pub(crate) fn read_version(v: &Version) -> Result<Arc<Document>> {
     v.document().map_err(|e| EngineError::Other(format!("version “{}” can't be read: {e}", v.name)))
 }
 

crates/engine/src/cmd/section.rs

@@ -34,7 +34,7 @@ pub fn specs() -> Vec<CommandSpec> {
         spec!(
             "dev.compare",
             "Compare changes",
-            "{id? (default the first selected layer), show? (open the compare view in the app)} → {id, name, changed, snapshot, added, removed, modified, truncated, changes: [{id, name, type, change: added|removed|changed, depth, layers, properties?: [{section, property, before, after, text}]}]}  what changed in a ready-for-dev frame or section since it was marked (`snapshot` is false when that isn't known: a file from before snapshots were kept)",
+            "{id? (default the first selected layer), version? (a version id from version.list: compare with that saved version instead; any top-level frame or section), show? (open the compare view in the app)} → {id, name, changed, snapshot, added, removed, modified, truncated, version: {id, name, time} | null, changes: [{id, name, type, change: added|removed|changed, depth, layers, properties?: [{section, property, before, after, text}]}]}  what changed in a ready-for-dev frame or section since it was marked, or since the version (`snapshot` is false when that isn't known: a file from before snapshots were kept)",
             false,
             compare
         ),
@@ -104,14 +104,30 @@ fn resolve_change(s: &mut Session, p: &Value) -> Result<Value> {
 fn compare(s: &mut Session, p: &Value) -> Result<Value> {
     let cmd = "dev.compare";
     let id = targets(s, p).first().copied().ok_or_else(|| bad(cmd, "select a frame or section or pass `id`"))?;
-    let doc = s.doc()?;
+    let version = match get(p, "version") {
+        None | Some(Value::Null) => None,
+        Some(Value::String(v)) => Some(v.clone()),
+        Some(_) => return Err(bad(cmd, "version: a version id (version.list)")),
+    };
+    let ds = s.ds()?;
+    let doc = &ds.doc;
     let n = doc.node(id).ok_or_else(|| bad(cmd, "no such layer"))?;
-    if !has_status(doc, id) || n.dev_status != DevStatus::ReadyForDev {
-        return Err(bad(cmd, "compare a frame or section marked ready for dev"));
+    if !has_status(doc, id) {
+        return Err(bad(cmd, "compare a top-level frame or a section"));
     }
-    let v = serde_json::to_value(crate::devcompare::compare(doc, id)).unwrap_or(Value::Null);
+    let (cmp, against) = match &version {
+        Some(v) => {
+            let ver = ds.versions.iter().find(|x| x.id == *v).ok_or_else(|| bad(cmd, format!("no version `{v}`")))?;
+            let before = crate::cmd::file::read_version(ver)?;
+            (crate::devcompare::compare_with(&before, doc, id), json!({"id": ver.id, "name": ver.name, "time": ver.time}))
+        }
+        None if n.dev_status != DevStatus::ReadyForDev => return Err(bad(cmd, "compare a frame or section marked ready for dev, or pass `version`")),
+        None => (crate::devcompare::compare(doc, id), Value::Null),
+    };
+    let mut v = serde_json::to_value(cmp).unwrap_or(Value::Null);
+    v["version"] = against;
     if boolean(p, "show") == Some(true) {
-        s.request_ui("view.devCompare", json!({"id": id}));
+        s.request_ui("view.devCompare", json!({"id": id, "version": version}));
     }
     Ok(v)
 }