Merge #1165: Make SVG unique_id linear for repeated layer names (@Silvertree2010)

crates/svg/src/lib.rs

@@ -79,6 +79,8 @@ struct W<'a> {
     clip: Option<String>,
     /// `id` attributes written so far.
     used_ids: std::collections::BTreeSet<String>,
+    /// The next `_k` suffix to try per base id, so repeated names don't rescan from `_2`.
+    next_suffix: std::collections::HashMap<String, usize>,
 }
 
 /// ` clip-path="url(#…)"` for a clip path id (else nothing).
@@ -549,7 +551,15 @@ impl W<'_> {
     fn unique_id(&mut self, name: &str) -> String {
         let base: String = name.chars().take(200).map(|c| if c.is_whitespace() || c.is_control() { '_' } else { c }).collect();
         let base = if base.is_empty() { "layer".to_string() } else { base };
-        let id = (1..).map(|k| if k == 1 { base.clone() } else { format!("{base}_{k}") }).find(|i| !self.used_ids.contains(i)).unwrap_or(base);
+        let next = self.next_suffix.entry(base.clone()).or_insert(1);
+        let id = loop {
+            let k = *next;
+            *next += 1;
+            let candidate = if k == 1 { base.clone() } else { format!("{base}_{k}") };
+            if !self.used_ids.contains(&candidate) {
+                break candidate;
+            }
+        };
         self.used_ids.insert(id.clone());
         id
     }
@@ -1004,6 +1014,7 @@ pub fn try_export_svg(doc: &Document, ids: &[NodeId], opts: &SvgOptions) -> Resu
         mask: None,
         clip: None,
         used_ids: Default::default(),
+        next_suffix: Default::default(),
     };
     for id in ids {
         let parent_xf = doc.node(*id).and_then(|n| n.parent).map(|p| doc.world_transform(p)).unwrap_or(Affine::IDENTITY);

crates/svg/src/tests.rs

@@ -179,3 +179,32 @@ fn point_joins_equal_to_the_layer_join_keep_a_plain_stroke() {
     assert!(svg_with(StrokeJoin::Miter).contains("stroke-width=\"2\""), "equal joins stay a stroke");
     assert!(!svg_with(StrokeJoin::Round).contains("stroke-width="), "a differing join is drawn as an outline");
 }
+
+#[test]
+fn unique_id_is_linear_for_repeated_names() {
+    let d = Document::new("t");
+    let opts = SvgOptions::default();
+    let mut w = W {
+        doc: &d,
+        roots: &[],
+        page: Affine::IDENTITY,
+        defs: String::new(),
+        body: String::new(),
+        next: 0,
+        opts: &opts,
+        mask: None,
+        clip: None,
+        used_ids: Default::default(),
+        next_suffix: Default::default(),
+    };
+    assert_eq!(w.unique_id("a"), "a");
+    assert_eq!(w.unique_id("a_3"), "a_3");
+    assert_eq!(w.unique_id("a"), "a_2");
+    assert_eq!(w.unique_id("a"), "a_4");
+    let start = std::time::Instant::now();
+    for _ in 0..30_000 {
+        w.unique_id("Rectangle");
+    }
+    assert_eq!(w.unique_id("Rectangle"), "Rectangle_30001");
+    assert!(start.elapsed() < std::time::Duration::from_secs(2), "unique_id is quadratic: {:?}", start.elapsed());
+}