SVG: made-up ids skip every id the file names

An id the importer writes into an element no longer matches a style sheet's
#id selector or a <use> link that no element matched before. The ids are
read from the decoded attribute values and text of the file, once.

crates/svg/src/import/prepass.rs

@@ -40,8 +40,9 @@ pub(crate) struct Edits {
     list: Vec<(std::ops::Range<usize>, String)>,
     /// The ids made up so far, by element.
     ids: HashMap<roxmltree::NodeId, String>,
-    /// The ids in the file and those made up, read when the first id is made up.
-    taken: Option<HashSet<String>>,
+    /// The numbers `n` of the `{MADE_UP_ID}n` the file names (as an element's id, in a style
+    /// sheet's `#id` selector or in a `#id` link to no element), read when the first id is made up.
+    taken: Option<HashSet<usize>>,
     /// The number the next made-up id is tried with: the numbers below it are made up or taken.
     next: usize,
     /// Declarations added to elements' `style`s, by element: (where they go, whether the element
@@ -55,7 +56,7 @@ impl Edits {
     }
 
     /// The id of element `n` (in `svg`), made up and written in when it has none. A made-up id is
-    /// one no element of the file has.
+    /// one the file does not name ([`named_made_up_ids`]).
     pub(super) fn id(&mut self, svg: &str, n: XNode) -> String {
         if let Some(id) = n.attribute("id").filter(|id| !id.is_empty()) {
             return id.to_string();
@@ -63,15 +64,12 @@ impl Edits {
         if let Some(id) = self.ids.get(&n.id()) {
             return id.clone();
         }
-        let taken = self.taken.get_or_insert_with(|| n.document().descendants().filter_map(|e| e.attribute("id")).map(str::to_string).collect());
-        let id = loop {
-            let id = format!("{MADE_UP_ID}{}", self.next);
+        let taken = self.taken.get_or_insert_with(|| named_made_up_ids(n.document()));
+        while taken.contains(&self.next) {
             self.next += 1;
-            if !taken.contains(&id) {
-                break id;
-            }
-        };
-        taken.insert(id.clone());
+        }
+        let id = format!("{MADE_UP_ID}{}", self.next);
+        self.next += 1;
         self.set(svg, n, "id", &id);
         self.ids.insert(n.id(), id.clone());
         id
@@ -121,6 +119,24 @@ impl Edits {
     }
 }
 
+/// The number after each [`MADE_UP_ID`] followed by digits in the attribute values and text of
+/// `xml`, read with their character references decoded (numbers too large for a `usize` left out).
+fn named_made_up_ids(xml: &roxmltree::Document) -> HashSet<usize> {
+    fn numbers(s: &str) -> impl Iterator<Item = usize> + '_ {
+        s.match_indices(MADE_UP_ID).filter_map(|(at, _)| {
+            let rest = s.get(at + MADE_UP_ID.len()..)?;
+            let digits = rest.bytes().take_while(u8::is_ascii_digit).count();
+            rest.get(..digits)?.parse().ok()
+        })
+    }
+    let mut taken = HashSet::new();
+    for n in xml.descendants() {
+        taken.extend(n.attributes().flat_map(|a| numbers(a.value())));
+        taken.extend(n.text().filter(|_| n.is_text()).into_iter().flat_map(numbers));
+    }
+    taken
+}
+
 /// usvg reads `<a href>` and `<use>` as plain groups, drops what isn't displayed and reads linked
 /// files on its own. Before it runs, the SVG is changed so that what we keep can be found:
 /// * every `<a href>` and every `<use>` of a `<symbol>` gets an id when it has none

crates/svg/tests/it/basic_shapes.rs

@@ -209,3 +209,29 @@ fn circles_import_without_changing_ids_or_style_matches() {
     assert_eq!(img.over_white(30, 30), [0, 0, 255]);
     assert_eq!(img.over_white(130, 30), [255, 0, 0]);
 }
+
+#[test]
+fn circles_import_without_an_id_the_file_names() {
+    // A style sheet's rule for an id no element has does not reach the circle.
+    let svg = r##"<svg xmlns="http://www.w3.org/2000/svg" width="200" height="200">
+        <style>#vectorcraft-id-0 { fill: #ff0000 }</style>
+        <circle cx="30" cy="30" r="20" fill="#000000"/></svg>"##;
+    let img = render_artboard(&import(svg).unwrap());
+    assert_eq!(img.over_white(30, 30), [0, 0, 0]);
+}
+
+#[test]
+fn circles_import_without_an_id_a_use_names() {
+    // A `<use>` of an id no element has does not show the circle, nor does one that writes the
+    // id with a character reference.
+    for href in ["#vectorcraft-id-0", "#vectorcraft-id-&#48;"] {
+        let svg = format!(
+            r##"<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" width="200" height="200">
+            <circle cx="30" cy="30" r="20" fill="#000000"/>
+            <use xlink:href="{href}" x="100"/></svg>"##
+        );
+        let img = render_artboard(&import(&svg).unwrap());
+        assert_eq!(img.over_white(30, 30), [0, 0, 0], "{href}");
+        assert_eq!(img.over_white(130, 30), [255, 255, 255], "{href}");
+    }
+}