Merge pull request #3754 from Silvertree2010/fix/3595-audit-dxf-import-paper-layouts-a

Fix quadratic paper layout de-duplication in DXF import

crates/cad/src/import/reader.rs

@@ -423,6 +423,7 @@ fn font_family(g: &[Pair<'_>]) -> String {
 /// objects but with paper-space art has one paper layout.
 fn layouts(objects: &[Record<'_>], block_records: &HashMap<String, String>, entities: &[Record<'_>]) -> Vec<LayoutDef> {
     let mut paper: Vec<(i64, LayoutDef)> = vec![];
+    let mut seen = std::collections::HashSet::new();
     for r in objects.iter().filter(|r| r.kind == "LAYOUT") {
         // The layout's own groups follow its subclass marker.
         let own = r.g.iter().position(|p| p.code == 100 && p.value.trim() == "AcDbLayout").and_then(|i| r.g.get(i + 1..)).unwrap_or(&[]);
@@ -432,7 +433,7 @@ fn layouts(objects: &[Record<'_>], block_records: &HashMap<String, String>, enti
             continue;
         }
         let Some(block) = block else { continue };
-        if !paper.iter().any(|(_, l)| l.name.eq_ignore_ascii_case(name)) {
+        if seen.insert(name.to_ascii_lowercase()) {
             paper.push((own.int_or(71, i64::MAX), LayoutDef { name: name.to_string(), block: Some(block) }));
         }
     }

crates/cad/src/import/tests.rs

@@ -1061,3 +1061,32 @@ fn entities_extruded_along_minus_z_are_mirrored() {
     let b = bounds(&leaves(&doc)[0]);
     assert!((b.center().x + 50.0).abs() < 1e-6, "the centre's x is mirrored: {b:?}");
 }
+
+/// A drawing with one paper block record (handle `A`) and a LAYOUT object per name.
+fn with_layouts(names: &[String]) -> Vec<u8> {
+    let mut s = String::from(
+        "  0\nSECTION\n  2\nTABLES\n  0\nTABLE\n  2\nBLOCK_RECORD\n  0\nBLOCK_RECORD\n  5\nA\n  2\n*Paper_Space\n  0\nENDTAB\n  0\nENDSEC\n  0\nSECTION\n  2\nOBJECTS\n",
+    );
+    for n in names {
+        s.push_str(&format!("  0\nLAYOUT\n100\nAcDbLayout\n  1\n{n}\n330\nA\n"));
+    }
+    s.push_str("  0\nENDSEC\n  0\nEOF\n");
+    s.into_bytes()
+}
+
+#[test]
+fn many_paper_layouts_are_read_in_linear_time() {
+    let names: Vec<String> = (0..100_000).map(|i| format!("L{i}")).collect();
+    let bytes = with_layouts(&names);
+    let t = std::time::Instant::now();
+    let info = info(&bytes).unwrap();
+    assert_eq!(info.layouts.len(), names.len() + 1);
+    assert!(t.elapsed() < std::time::Duration::from_secs(5), "layout de-duplication is quadratic: {:?}", t.elapsed());
+}
+
+#[test]
+fn paper_layout_names_are_unique_ignoring_case() {
+    let names = ["Layout1", "LAYOUT1", "Other"].map(String::from);
+    let info = info(&with_layouts(&names)).unwrap();
+    assert_eq!(info.layouts, ["Model", "Layout1", "Other"]);
+}