M3: importing a file keeps its own variables and styles when their ids are already taken

`file.import` of a FigCraft file kept the document's style, variable or
collection for every id both files used, and the pasted layers kept
those ids. Ids are numbered per file, so two files made apart share
them, and the imported layers were bound to the document's unrelated
variables, modes and styles.

`append_pages` now gives the incoming file new ids first (`Renames`):
- an incoming style, variable or collection is shared, as before, only
  when the document has the same under its id and everything it names
  is shared too (the same file imported again); a collection and its
  variables are shared only together; library copies keep their ids;
- every other id the document already uses gets a new one from its
  allocators, which now take ids to avoid (the incoming file's own);
- layers' style links, bindings, explicit modes and prototype actions,
  styles' bindings, variables' collections, aliases, calculations and
  extensions, and the renamed collections' mode ids follow.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/doc/src/ids.rs

@@ -14,6 +14,8 @@
 //! space 0. The session server accepts a new object only with an id in its creator's space or
 //! space 0, so two people never make the same id.
 
+use std::collections::BTreeSet;
+
 use crate::{CollectionId, Document, ModeId, NodeId, StyleId, VariableId};
 
 /// What style ids start with.
@@ -74,25 +76,42 @@ impl Document {
 
     /// A new style id.
     pub fn new_style_id(&mut self) -> StyleId {
-        let taken: Vec<u64> = self.styles.iter().filter_map(|s| id_number(&s.id, STYLE_ID_PREFIX)).collect();
+        self.new_style_id_avoiding(&BTreeSet::new())
+    }
+
+    /// A new style id that is none of `avoid` either: ids of styles about to come in with a file
+    /// being imported.
+    pub fn new_style_id_avoiding(&mut self, avoid: &BTreeSet<StyleId>) -> StyleId {
+        let taken: Vec<u64> = self.styles.iter().map(|s| &s.id).chain(avoid).filter_map(|id| id_number(id, STYLE_ID_PREFIX)).collect();
         if let Some(n) = self.session_number(taken) {
             return format!("{STYLE_ID_PREFIX}{n}");
         }
         (self.styles.len() + 1..)
             .map(|k| format!("{STYLE_ID_PREFIX}{k}"))
-            .find(|id| self.style(id).is_none())
+            .find(|id| self.style(id).is_none() && !avoid.contains(id))
             .unwrap_or_else(|| format!("{STYLE_ID_PREFIX}0"))
     }
 
     /// A new variable id.
     pub fn new_variable_id(&mut self) -> VariableId {
-        let taken: Vec<u64> = self.variables.variables.iter().filter_map(|v| id_number(&v.id, VARIABLE_ID_PREFIX)).collect();
+        self.new_variable_id_avoiding(&BTreeSet::new())
+    }
+
+    /// A new variable id that is none of `avoid` either (see [`Self::new_style_id_avoiding`]).
+    pub fn new_variable_id_avoiding(&mut self, avoid: &BTreeSet<VariableId>) -> VariableId {
+        let taken = self.variables.variables.iter().map(|v| &v.id).chain(avoid).filter_map(|id| id_number(id, VARIABLE_ID_PREFIX)).collect();
         self.new_numbered_id(VARIABLE_ID_PREFIX, taken)
     }
 
     /// A new variable collection id.
     pub fn new_collection_id(&mut self) -> CollectionId {
-        let taken: Vec<u64> = self.variables.collections.iter().filter_map(|c| id_number(&c.id, COLLECTION_ID_PREFIX)).collect();
+        self.new_collection_id_avoiding(&BTreeSet::new())
+    }
+
+    /// A new variable collection id that is none of `avoid` either (see
+    /// [`Self::new_style_id_avoiding`]).
+    pub fn new_collection_id_avoiding(&mut self, avoid: &BTreeSet<CollectionId>) -> CollectionId {
+        let taken = self.variables.collections.iter().map(|c| &c.id).chain(avoid).filter_map(|id| id_number(id, COLLECTION_ID_PREFIX)).collect();
         self.new_numbered_id(COLLECTION_ID_PREFIX, taken)
     }
 

crates/doc/src/ids_tests.rs

@@ -1,6 +1,8 @@
 //! Ids of styles, variables, collections, modes and comments: unchanged outside a live session,
 //! from the client's own space during one.
 
+use std::collections::BTreeSet;
+
 use crate::ids::{COLLECTION_ID_PREFIX, id_number, id_space, mode_number, space_of};
 use crate::{Collection, Comment, Document, Message, Mode, NodeId, NodeKind, Style, StyleKind};
 
@@ -93,6 +95,20 @@ fn ids_of_the_space_already_in_the_document_stay_taken() {
     assert_eq!(e.new_style_id(), format!("S:{}", C3 | 1));
 }
 
+#[test]
+fn new_ids_can_avoid_ids_about_to_come_in() {
+    let mut d = Document::new("a");
+    d.styles.push(style("S:1"));
+    let avoid: BTreeSet<String> = ["S:2", "S:3", "VariableID:4", "VariableCollectionId:2", "lib:VariableID:9"].map(String::from).into();
+    assert_eq!(d.new_style_id_avoiding(&avoid), "S:4");
+    assert_eq!(d.new_variable_id_avoiding(&avoid), "VariableID:5");
+    assert_eq!(d.new_collection_id_avoiding(&avoid), "VariableCollectionId:3");
+    // In a session the numbers come from the client's space, above those of it to avoid.
+    let avoid: BTreeSet<String> = [format!("VariableID:{}", C3 | 7)].into();
+    d.set_client_id(3);
+    assert_eq!(d.new_variable_id_avoiding(&avoid), format!("VariableID:{}", C3 | 8));
+}
+
 #[test]
 fn the_highest_space_counts_every_kind_of_id() {
     let mut d = Document::new("a");

crates/engine/src/cmd/file.rs

@@ -15,6 +15,7 @@ use crate::params::{bool_of, boolean, get, id, num, num_or, req_index, req_strin
 use crate::{DocState, EngineError, Result, Session, bad, spec};
 
 mod export;
+mod import_ids;
 mod load;
 mod open;
 mod save;

crates/engine/src/cmd/file/import_ids.rs

@@ -0,0 +1,254 @@
+//! Ids a file being imported brings that the document already uses for something else.
+//!
+//! Style, variable and collection ids are numbered per file (`S:1`, `VariableID:1`,
+//! `VariableCollectionId:1`; see [`figcraft_doc::ids`]), so two files made apart use the same ones
+//! for unrelated things. Kept as they were, the imported layers would show the document's
+//! variables and styles instead of their own.
+
+use std::collections::{BTreeMap, BTreeSet};
+
+use figcraft_doc::ids::MODE_ID_INFIX;
+use figcraft_doc::proto::{Action, Expr, MAX_EXPR_DEPTH, walk_mut};
+use figcraft_doc::{Document, ModeId, NodeId, NodeKind, VariableValue, Variables};
+
+/// A style, variable or collection of the file being imported.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord)]
+enum Asset<'a> {
+    Style(&'a str),
+    Variable(&'a str),
+    Collection(&'a str),
+}
+
+/// New ids for styles, variables and collections of a file being imported (its id → the new one).
+#[derive(Debug, Default)]
+pub(super) struct Renames {
+    styles: BTreeMap<String, String>,
+    variables: BTreeMap<String, String>,
+    collections: BTreeMap<String, String>,
+}
+
+impl Renames {
+    /// The new ids `other`'s styles, variables and collections take when appended to `doc`.
+    ///
+    /// One whose id `doc` doesn't use keeps it. One `doc` already has is shared and keeps its id:
+    /// the same content under the same id, naming only things that are shared too (the same file
+    /// imported again). A collection and its variables are shared only all together, so variables
+    /// of one file never join a collection of another. Library copies keep their ids and are shared
+    /// with the document's copies, as before (`merge_store` records them). Every other id `doc`
+    /// already uses is replaced by a new one from `doc`'s allocators, clear of `other`'s ids too.
+    pub(super) fn new(doc: &mut Document, other: &Document) -> Renames {
+        let (theirs, libs) = (&other.variables, &other.libraries);
+        // Each with whether `doc` has the same under its id (None: nothing there), and whether
+        // it's a library copy.
+        let styles = other.styles.iter().map(|s| {
+            let here = doc.styles.iter().find(|m| m.id == s.id);
+            (Asset::Style(&s.id), here.map(|m| m == s), libs.style_import(&s.id).is_some())
+        });
+        let colls = theirs.collections.iter().map(|c| {
+            let here = doc.variables.collection_by_id(&c.id);
+            (Asset::Collection(&c.id), here.map(|m| m == c), libs.collection_import(&c.id).is_some())
+        });
+        let vars = theirs.variables.iter().map(|v| {
+            let here = doc.variables.get_by_id(&v.id);
+            (Asset::Variable(&v.id), here.map(|m| m == v), libs.variable_import(&v.id).is_some())
+        });
+        // `taken`: ids `doc` uses; `differs`: what `doc` doesn't have the same of.
+        let (mut taken, mut copies, mut differs) = (BTreeSet::new(), BTreeSet::new(), BTreeSet::new());
+        for (a, same, copy) in styles.chain(colls).chain(vars) {
+            match same {
+                None => {
+                    differs.insert(a);
+                }
+                Some(same) => {
+                    taken.insert(a);
+                    if copy {
+                        copies.insert(a);
+                    } else if !same {
+                        differs.insert(a);
+                    }
+                }
+            }
+        }
+        // What differs makes what names it differ (library copies aside), and a collection and its
+        // variables differ together.
+        let mut named_by: BTreeMap<Asset, Vec<Asset>> = BTreeMap::new();
+        for v in &theirs.variables {
+            let (var, coll) = (Asset::Variable(&v.id), Asset::Collection(&v.collection));
+            named_by.entry(coll).or_default().push(var);
+            named_by.entry(var).or_default().push(coll);
+            for r in v.values.values().flat_map(VariableValue::references).chain(&v.extends) {
+                named_by.entry(Asset::Variable(r)).or_default().push(var);
+            }
+        }
+        for c in &theirs.collections {
+            if let Some(e) = &c.extends {
+                named_by.entry(Asset::Collection(e)).or_default().push(Asset::Collection(&c.id));
+            }
+        }
+        for s in &other.styles {
+            for v in s.bound.values() {
+                named_by.entry(Asset::Variable(v)).or_default().push(Asset::Style(&s.id));
+            }
+        }
+        let mut todo: Vec<Asset> = differs.iter().copied().collect();
+        while let Some(a) = todo.pop() {
+            for &n in named_by.get(&a).into_iter().flatten() {
+                if !copies.contains(&n) && differs.insert(n) {
+                    todo.push(n);
+                }
+            }
+        }
+        let renamed = |a: Asset| taken.contains(&a) && differs.contains(&a);
+        Renames {
+            collections: fresh(
+                theirs.collections.iter().map(|c| &c.id),
+                |id| renamed(Asset::Collection(id)),
+                |avoid| doc.new_collection_id_avoiding(avoid),
+            ),
+            variables: fresh(theirs.variables.iter().map(|v| &v.id), |id| renamed(Asset::Variable(id)), |avoid| doc.new_variable_id_avoiding(avoid)),
+            styles: fresh(other.styles.iter().map(|s| &s.id), |id| renamed(Asset::Style(id)), |avoid| doc.new_style_id_avoiding(avoid)),
+        }
+    }
+
+    pub(super) fn is_empty(&self) -> bool {
+        self.styles.is_empty() && self.variables.is_empty() && self.collections.is_empty()
+    }
+
+    /// `other` with the renamed styles, variables and collections under their new ids, and what
+    /// names them following: layers' style links (text ranges too), bindings, explicit modes and
+    /// prototype actions; styles' bindings; variables' collections, aliases and calculations; what
+    /// extended collections and their variables extend; and the ids of the renamed collections'
+    /// modes, which name their collection (`<collection>/mode<k>`).
+    pub(super) fn applied(&self, other: &Document) -> Document {
+        let theirs = &other.variables;
+        let mut doc = other.clone();
+        let (styles, vars, colls) = (&self.styles, &self.variables, &self.collections);
+        for s in &mut doc.styles {
+            rename(styles, &mut s.id);
+            s.bound.values_mut().for_each(|v| rename(vars, v));
+        }
+        for c in &mut doc.variables.collections {
+            for m in &mut c.modes {
+                self.mode(theirs, &c.id, &mut m.id);
+            }
+            for id in std::iter::once(&mut c.id).chain(&mut c.extends) {
+                rename(colls, id);
+            }
+        }
+        for v in &mut doc.variables.variables {
+            let values = std::mem::take(&mut v.values).into_iter().map(|(mut mode, mut val)| {
+                self.mode(theirs, &v.collection, &mut mode);
+                val.references_mut().into_iter().for_each(|r| rename(vars, r));
+                (mode, val)
+            });
+            v.values = values.collect();
+            let overrides = std::mem::take(&mut v.overrides).into_iter().map(|mut mode| {
+                self.mode(theirs, &v.collection, &mut mode);
+                mode
+            });
+            v.overrides = overrides.collect();
+            rename(colls, &mut v.collection);
+            for id in std::iter::once(&mut v.id).chain(&mut v.extends) {
+                rename(vars, id);
+            }
+        }
+        let ids: Vec<NodeId> = doc.ids().collect();
+        for id in ids {
+            let Some(n) = doc.node_mut(id) else { continue };
+            let links = [&mut n.styles.fill, &mut n.styles.stroke, &mut n.styles.effect, &mut n.styles.grid, &mut n.styles.text];
+            for s in links.into_iter().flatten() {
+                rename(styles, s);
+            }
+            if let NodeKind::Text(t) = &mut n.kind {
+                t.map_text_styles(|s| Some(styles.get(s).cloned().unwrap_or_else(|| s.to_string())));
+            }
+            n.bound.values_mut().for_each(|v| rename(vars, v));
+            n.var_modes = std::mem::take(&mut n.var_modes)
+                .into_iter()
+                .map(|(mut c, mut mode)| {
+                    self.mode(theirs, &c, &mut mode);
+                    rename(colls, &mut c);
+                    (c, mode)
+                })
+                .collect();
+            for it in &mut n.interactions {
+                walk_mut(&mut it.actions, &mut |a| self.action(theirs, a));
+            }
+        }
+        doc
+    }
+
+    /// Rename mode `mode` of collection `of` (`theirs`: the imported file's variables as they were).
+    /// A mode id names the collection it was made in: `of`, or one `of` extends (an extended
+    /// collection has the modes of the one it extends). Library copies keep their library's mode
+    /// ids, which may name one of the file's own collections.
+    fn mode(&self, theirs: &Variables, of: &str, mode: &mut ModeId) {
+        let mut at = Some(of);
+        for _ in 0..=theirs.collections.len() {
+            let Some(c) = at else { return };
+            if let Some(k) = mode.strip_prefix(c).and_then(|rest| rest.strip_prefix(MODE_ID_INFIX)) {
+                if let Some(new) = self.collections.get(c) {
+                    *mode = format!("{new}{MODE_ID_INFIX}{k}");
+                }
+                return;
+            }
+            at = theirs.collection_by_id(c).and_then(|c| c.extends.as_deref());
+        }
+    }
+
+    /// Rename what one prototype action names (not the actions nested in it).
+    fn action(&self, theirs: &Variables, a: &mut Action) {
+        match a {
+            Action::SetVariable { variable, expr, .. } => {
+                rename(&self.variables, variable);
+                if let Some(e) = expr {
+                    self.expr(theirs, e, 0);
+                }
+            }
+            Action::SetVariableMode { collection, mode } => {
+                self.mode(theirs, collection, mode);
+                rename(&self.collections, collection);
+            }
+            Action::Conditional { blocks } => blocks.iter_mut().filter_map(|b| b.condition.as_mut()).for_each(|c| self.expr(theirs, c, 0)),
+            _ => {}
+        }
+    }
+
+    fn expr(&self, theirs: &Variables, e: &mut Expr, depth: usize) {
+        match e {
+            Expr::Value(v) => v.references_mut().into_iter().for_each(|r| rename(&self.variables, r)),
+            Expr::Op { args, .. } if depth < MAX_EXPR_DEPTH => args.iter_mut().for_each(|a| self.expr(theirs, a, depth + 1)),
+            Expr::Op { .. } => {}
+            Expr::Mode { collection } => rename(&self.collections, collection),
+            Expr::InMode { variable, mode } => {
+                if let Some(v) = theirs.get_by_id(variable) {
+                    self.mode(theirs, &v.collection, mode);
+                }
+                rename(&self.variables, variable);
+            }
+        }
+    }
+}
+
+/// New ids, from `new_id`, for those of `ids` that `pick` picks; each clear of all of `ids`.
+fn fresh<'a>(
+    ids: impl Iterator<Item = &'a String> + Clone,
+    pick: impl Fn(&str) -> bool,
+    mut new_id: impl FnMut(&BTreeSet<String>) -> String,
+) -> BTreeMap<String, String> {
+    let mut avoid: BTreeSet<String> = ids.clone().cloned().collect();
+    let mut out = BTreeMap::new();
+    for id in ids.filter(|id| pick(id)) {
+        let new = new_id(&avoid);
+        avoid.insert(new.clone());
+        out.insert(id.clone(), new);
+    }
+    out
+}
+
+/// `id` as `map` renames it.
+fn rename(map: &BTreeMap<String, String>, id: &mut String) {
+    if let Some(new) = map.get(id.as_str()) {
+        *id = new.clone();
+    }
+}

crates/engine/src/cmd/file/open.rs

@@ -1,3 +1,4 @@
+use super::import_ids::Renames;
 use super::load::{ext, file_stem, import_summary, load_path, load_with, read, rest_images, sibling_variables, variables_param};
 use super::*;
 
@@ -218,8 +219,18 @@ pub(super) fn import(s: &mut Session, p: &Value) -> Result<Value> {
 /// Append `other`'s pages (with their settings and flows, its images, styles and variables) to
 /// `doc`. Ids are remapped across all pages at once, so instances keep their main, instance layers
 /// their source and interactions and flows their targets wherever those are. Styles, variables and
-/// collections whose id the document already has are kept as they are.
+/// collections the document already has (the same under the same id, as when a file comes in
+/// again) and library copies are shared; others whose id the document uses for something else get
+/// new ids, and what comes in names them by those ([`Renames`]).
 pub(super) fn append_pages(doc: &mut Document, other: &Document) -> Result<Vec<NodeId>> {
+    let renames = Renames::new(doc, other);
+    let renamed;
+    let other = if renames.is_empty() {
+        other
+    } else {
+        renamed = renames.applied(other);
+        &renamed
+    };
     for (k, v) in &other.images {
         doc.images.entry(k.clone()).or_insert_with(|| v.clone());
     }

crates/engine/src/import_ids_tests.rs

@@ -0,0 +1,172 @@
+//! `file.import` of a file whose style, variable and collection ids the document already uses for
+//! other things: ids are numbered per file, so two files made apart share them. The imported
+//! layers keep their own variables, modes and styles, and a file imported again still shares what
+//! it brought the first time.
+
+use base64::Engine as _;
+use figcraft_doc::proto::Action;
+use figcraft_doc::{Document, Node, NodeId, VariableValue};
+use serde_json::{Value, json};
+
+use crate::Session;
+use crate::components::tests::ex;
+use crate::params::id_of;
+
+fn idv(v: &Value) -> NodeId {
+    id_of(&v["id"]).unwrap()
+}
+
+fn var_id(s: &Session, name: &str) -> String {
+    s.doc().unwrap().variables.get(name).unwrap().id.clone()
+}
+
+fn fill(s: &Session, id: NodeId) -> String {
+    s.doc().unwrap().node(id).unwrap().fills.first().and_then(|p| p.solid_color()).map(|c| c.to_hex()).unwrap_or_default()
+}
+
+/// The document's file: collection A (Light, Dark) with colours `a1`…`a4`, paint style `Host`
+/// and a frame filled with `a1`.
+fn host() -> (Session, NodeId) {
+    let mut s = Session::new();
+    ex(&mut s, "variable.createCollection", json!({"name": "A", "modes": ["Light", "Dark"]}));
+    for i in 1..=4 {
+        ex(&mut s, "variable.create", json!({"collection": "A", "name": format!("a{i}"), "type": "color", "value": format!("#A{i}0000")}));
+    }
+    ex(&mut s, "style.create", json!({"type": "paint", "name": "Host", "value": "#FF0000"}));
+    let f = idv(&ex(&mut s, "frame.create", json!({"x": 0, "y": 0, "width": 50, "height": 50, "name": "Host frame"})));
+    ex(&mut s, "variable.bind", json!({"ids": [f], "field": "fill", "variable": "a1"}));
+    (s, f)
+}
+
+/// Another file made apart: collection B (Light, Dark) with `b1` (green in each mode), `b2` (an
+/// alias of `b1`) and `size`; paint style `Brand` bound to `b1`. Frame `Card` shows B in Dark, its
+/// corners bound to `size`; in it `Swatch` is filled with `b2` and on click sets B to Dark and
+/// `size` to `size + 1`, and `Styled` uses `Brand`.
+fn other() -> Session {
+    let mut s = Session::new();
+    ex(&mut s, "variable.createCollection", json!({"name": "B", "modes": ["Light", "Dark"]}));
+    ex(&mut s, "variable.create", json!({"collection": "B", "name": "b1", "type": "color", "values": {"Light": "#00B000", "Dark": "#004000"}}));
+    ex(&mut s, "variable.create", json!({"collection": "B", "name": "b2", "type": "color", "value": {"alias": "b1"}}));
+    ex(&mut s, "variable.create", json!({"collection": "B", "name": "size", "type": "number", "value": 8}));
+    let brand = ex(&mut s, "style.create", json!({"type": "paint", "name": "Brand", "value": "#00B000"}))["id"].clone();
+    ex(&mut s, "style.bind", json!({"style": brand, "field": "fill", "variable": "b1"}));
+    let card = idv(&ex(&mut s, "frame.create", json!({"x": 0, "y": 0, "width": 200, "height": 100, "name": "Card"})));
+    ex(&mut s, "variable.setMode", json!({"ids": [card], "collection": "B", "mode": "Dark"}));
+    ex(&mut s, "variable.bind", json!({"ids": [card], "field": "cornerRadius", "variable": "size"}));
+    let swatch = idv(&ex(&mut s, "shape.rectangle", json!({"x": 10, "y": 10, "width": 40, "height": 40, "parent": card, "name": "Swatch"})));
+    ex(&mut s, "variable.bind", json!({"ids": [swatch], "field": "fill", "variable": "b2"}));
+    let actions = json!([
+        {"type": "setVariableMode", "collection": "B", "mode": "Dark"},
+        {"type": "setVariable", "variable": "size", "expression": "size + 1"}
+    ]);
+    ex(&mut s, "proto.interaction.add", json!({"id": swatch, "actions": actions}));
+    let styled = idv(&ex(&mut s, "shape.rectangle", json!({"x": 60, "y": 10, "width": 40, "height": 40, "parent": card, "name": "Styled"})));
+    ex(&mut s, "style.apply", json!({"ids": [styled], "style": "Brand"}));
+    s
+}
+
+fn import(s: &mut Session, file: &Session) -> Value {
+    let bytes = figcraft_format::save_bytes(file.doc().unwrap(), None).unwrap();
+    let data = base64::engine::general_purpose::STANDARD.encode(bytes);
+    ex(s, "file.import", json!({"data": data, "name": "other.figcraft"}))
+}
+
+/// The layers on the pages after the first `kept` pages.
+fn layers_after(doc: &Document, kept: usize) -> Vec<&Node> {
+    doc.pages[kept..].iter().flat_map(|p| doc.subtree(*p).into_iter().skip(1)).filter_map(|id| doc.node(id)).collect()
+}
+
+fn layer<'a>(doc: &'a Document, kept: usize, name: &str) -> &'a Node {
+    layers_after(doc, kept).into_iter().find(|n| n.name == name).unwrap()
+}
+
+#[test]
+fn imported_layers_keep_their_own_variables_and_styles_when_the_ids_are_taken() {
+    let (mut s, frame) = host();
+    let file = other();
+    assert_eq!(var_id(&file, "b1"), var_id(&s, "a1"), "the ids must collide for this test");
+    assert_eq!(file.doc().unwrap().styles[0].id, s.doc().unwrap().styles[0].id);
+    let before = s.doc().unwrap().clone();
+    import(&mut s, &file);
+    let doc = s.doc().unwrap();
+    assert_eq!(doc.variables.variables.len(), 4 + 3);
+    assert_eq!(doc.variables.collections.iter().map(|c| c.name.as_str()).collect::<Vec<_>>(), ["A", "B"]);
+    assert_eq!(doc.styles.iter().map(|st| st.name.as_str()).collect::<Vec<_>>(), ["Host", "Brand"]);
+    // The document's own are as they were.
+    assert_eq!(doc.variables.variables[..4], before.variables.variables[..]);
+    assert_eq!(doc.variables.collections[0], before.variables.collections[0]);
+    assert_eq!(doc.styles[0], before.styles[0]);
+    // Everything imported names B's variables, B and Brand.
+    let b = doc.variables.collection("B").unwrap().id.clone();
+    let imported = layers_after(doc, before.pages.len());
+    assert!(imported.iter().any(|n| !n.bound.is_empty()));
+    for n in imported {
+        for v in n.bound.values() {
+            assert_eq!(doc.variables.get_by_id(v).unwrap().collection, b, "{}: {v}", n.name);
+        }
+        assert!(n.var_modes.keys().all(|c| *c == b), "{}: {:?}", n.name, n.var_modes);
+        if let Some(st) = &n.styles.fill {
+            assert_eq!(doc.styles.iter().find(|x| x.id == *st).unwrap().name, "Brand");
+        }
+    }
+    let brand = doc.styles.iter().find(|st| st.name == "Brand").unwrap();
+    assert_eq!(brand.bound.values().map(|v| doc.variables.get_by_id(v).unwrap().name.as_str()).collect::<Vec<_>>(), ["b1"]);
+    // Bindings applied again leave the imported layers alone.
+    let swatch = layer(doc, before.pages.len(), "Swatch").id;
+    let a2 = var_id(&s, "a2");
+    ex(&mut s, "variable.set", json!({"variable": a2, "value": "#123456"}));
+    assert_eq!(fill(&s, swatch), "004000");
+    assert_eq!(fill(&s, frame), "A10000");
+    assert!(s.doc().unwrap().validate().is_empty());
+}
+
+#[test]
+fn an_alias_a_frame_mode_and_prototype_actions_follow_the_renamed_collection() {
+    let (mut s, _) = host();
+    let file = other();
+    let kept = s.doc().unwrap().pages.len();
+    import(&mut s, &file);
+    let doc = s.doc().unwrap();
+    let vars = &doc.variables;
+    let b = vars.collection("B").unwrap();
+    let in_b = |name: &str| vars.variables.iter().find(|v| v.name == name && v.collection == b.id).unwrap();
+    let (b1, b2, size) = (in_b("b1"), in_b("b2"), in_b("size"));
+    assert!(b2.values.values().all(|v| *v == VariableValue::Alias(b1.id.clone())), "{:?}", b2.values);
+    // B's mode ids name B's new id, and its variables' values are by those.
+    let modes: Vec<&str> = b.modes.iter().map(|m| m.id.as_str()).collect();
+    assert_eq!(modes, [format!("{}/mode1", b.id), format!("{}/mode2", b.id)]);
+    assert!([b1, b2, size].iter().all(|v| v.values.keys().all(|m| modes.contains(&m.as_str()))));
+    // The frame shows B in Dark: its mode is one of B's.
+    let card = layer(doc, kept, "Card");
+    let dark = b.find_mode("Dark").unwrap().id.clone();
+    assert_eq!(card.var_modes.iter().collect::<Vec<_>>(), [(&b.id, &dark)]);
+    assert_eq!(card.bound.get("cornerRadius"), Some(&size.id));
+    let swatch = layer(doc, kept, "Swatch");
+    assert_eq!(swatch.bound.get("fill"), Some(&b2.id));
+    let shown = vars.resolve(&b2.id, &doc.modes_for(swatch.id));
+    assert!(matches!(shown, Some(VariableValue::Color(c)) if c.to_hex() == "004000"), "{shown:?}");
+    let actions = &swatch.interactions[0].actions;
+    assert_eq!(actions[0], Action::SetVariableMode { collection: b.id.clone(), mode: dark });
+    let Action::SetVariable { variable, expr: Some(e), .. } = &actions[1] else { panic!("{actions:?}") };
+    assert_eq!((variable, e.variables()), (&size.id, vec![size.id.as_str()]));
+}
+
+#[test]
+fn importing_the_same_file_again_shares_what_it_brought() {
+    let file = other();
+    let mut s = other();
+    let before = s.doc().unwrap().clone();
+    import(&mut s, &file);
+    let doc = s.doc().unwrap();
+    assert_eq!(doc.variables, before.variables);
+    assert_eq!(doc.styles, before.styles);
+    let swatch = layer(doc, before.pages.len(), "Swatch");
+    assert_eq!(swatch.bound.get("fill"), Some(&var_id(&s, "b2")));
+    // A file imported into an empty one, then again: one copy of its variables.
+    let mut t = Session::new();
+    import(&mut t, &file);
+    import(&mut t, &file);
+    let doc = t.doc().unwrap();
+    assert_eq!((doc.variables.variables.len(), doc.variables.collections.len(), doc.styles.len()), (3, 1, 1));
+    assert!(layers_after(doc, 1).iter().flat_map(|n| n.bound.values()).all(|v| doc.variables.get_by_id(v).is_some()));
+}

crates/engine/src/lib.rs

@@ -367,6 +367,8 @@ mod images_left_in_file_tests;
 #[cfg(test)]
 mod import_export_tests;
 #[cfg(test)]
+mod import_ids_tests;
+#[cfg(test)]
 mod import_journal_tests;
 #[cfg(test)]
 mod inspect_behaviour_tests;

crates/engine/src/library_variables_tests.rs

@@ -385,6 +385,34 @@ fn library_components_keep_their_variable_bindings() {
     let _ = std::fs::remove_dir_all(&d);
 }
 
+#[test]
+fn a_file_bringing_older_copies_of_the_same_library_variables_shares_them() {
+    let d = dir("older-copies");
+    let lib_path = path_str(&d.join("kit.figcraft"));
+    let mut lib = Session::new();
+    theme(&mut lib);
+    let lid = publish_to(&mut lib, &lib_path);
+    let mut s = Session::new();
+    ex(&mut s, "library.add", json!({"path": lib_path}));
+    let r = idv(&ex(&mut s, "shape.rectangle", json!({"width": 10, "height": 10, "name": "Swatch"})));
+    ex(&mut s, "library.bindVariable", json!({"library": lid, "variable": "primary", "field": "fill", "ids": [r]}));
+    let old_path = path_str(&d.join("old.figcraft"));
+    ex(&mut s, "file.saveAs", json!({"path": old_path}));
+    // The copies take an update; the saved file keeps the older ones under the same ids.
+    ex(&mut lib, "variable.set", json!({"variable": "primary", "mode": "Light", "value": "#444444"}));
+    republish(&mut lib);
+    ex(&mut s, "library.acceptUpdates", json!({}));
+    let before = s.doc().unwrap().clone();
+    ex(&mut s, "file.import", json!({"path": old_path}));
+    let doc = s.doc().unwrap();
+    assert_eq!((&doc.variables, &doc.libraries.variables), (&before.variables, &before.libraries.variables), "shared by id, as before");
+    let swatches: Vec<&Node> = doc.nodes().filter(|n| n.name == "Swatch").collect();
+    assert_eq!(swatches.len(), 2);
+    assert!(swatches.iter().all(|n| n.bound.get("fill") == Some(&copy_of(&s, "primary").id)));
+    healthy(&s);
+    let _ = std::fs::remove_dir_all(&d);
+}
+
 #[test]
 fn library_variable_commands_fail_cleanly() {
     let mut s = Session::new();