xlsx: share inline dxf number formats within a styles part (#3260)

* xlsx: share each custom number format across cell formats, cap font names at 31 characters

Every cell format record copied its font (name included) and built its
own copy of its number-format code, so many short records naming one
long font or code multiplied it in memory. Custom codes are now built
once and shared, and font names are cut to Excel's 31 characters.

* xlsx: drop stray worktree entries added by mistake

* address review: compare truncated theme font for the scheme link; intern inline dxf number formats

crates/xlsx/src/styles.rs

@@ -393,12 +393,14 @@ pub fn read_styles(root: &El, checkboxes: &[bool], minor_font: &str) -> StylesIn
             }
         }
     }
-    let dxfs = root.child("dxfs").map(|d| d.kids("dxf").map(|x| read_dxf(x, &palette, &shared_fmts)).collect()).unwrap_or_default();
+    // Inline dxf format codes are interned: a code repeated by many dxfs is one allocation.
+    let mut inline_fmts = HashMap::new();
+    let dxfs = root.child("dxfs").map(|d| d.kids("dxf").map(|x| read_dxf(x, &palette, &shared_fmts, &mut inline_fmts)).collect()).unwrap_or_default();
     StylesIn { xfs, dxfs, palette, named, num_fmts: fmts }
 }
 
 /// One differential format (`dxf`): the style it sets over a cell's own.
-fn read_dxf(x: &El, palette: &[u32], fmts: &HashMap<u32, NumFmt>) -> Style {
+fn read_dxf<'a>(x: &'a El, palette: &[u32], fmts: &HashMap<u32, NumFmt>, inline_fmts: &mut HashMap<&'a str, NumFmt>) -> Style {
     let mut s = Style::default();
     if let Some(e) = x.child("font") {
         let f = read_font(e, palette);
@@ -421,7 +423,7 @@ fn read_dxf(x: &El, palette: &[u32], fmts: &HashMap<u32, NumFmt>) -> Style {
     }
     if let Some(n) = x.child("numFmt") {
         if let Some(code) = n.attr("formatCode") {
-            s.num_fmt = NumFmt::new(code);
+            s.num_fmt = inline_fmts.entry(code).or_insert_with(|| NumFmt::new(code)).clone();
         } else if let Some(id) = n.attr_u32("numFmtId") {
             s.num_fmt = num_fmt_code(id, fmts);
         }

crates/xlsx/src/tests/fixtures.rs

@@ -869,3 +869,17 @@ fn every_skipped_drawing_object_is_reported() {
         assert_eq!(hits, 1, "object {n}: {:?}", rep.warnings);
     }
 }
+
+/// A number format code repeated by many differential formats is read into one allocation.
+#[test]
+fn inline_dxf_number_formats_are_shared() {
+    let code = format!("0.00{}", " \"x\"".repeat(50));
+    let dxfs: String = (0..3).map(|_| format!(r#"<dxf><numFmt numFmtId="170" formatCode="{}"/></dxf>"#, code.replace('"', "&quot;"))).collect();
+    let styles =
+        format!(r#"<styleSheet xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main"><dxfs count="3">{dxfs}</dxfs></styleSheet>"#);
+    let root = crate::xml::parse(styles.as_bytes()).unwrap();
+    let read = crate::styles::read_styles(&root, &[], "Calibri");
+    assert_eq!(read.dxfs.len(), 3);
+    assert_eq!(read.dxfs[0].num_fmt.as_str(), code);
+    assert!(read.dxfs.iter().all(|d| std::sync::Arc::ptr_eq(&d.num_fmt.0, &read.dxfs[0].num_fmt.0)));
+}