address review: cache the chart-sheet usability verdict per relationship id instead of every reference

chart_sheet_usable walked a chart sheet's relationship graph and parsed
its charts for every workbook entry, so many entries naming one shared
graph multiplied the work. The referenced sheet names are now cached by
relationship id.

crates/numfmt/src/lib.rs

@@ -332,14 +332,6 @@ impl NumberFormat {
             None => Formatted { text: t.to_string(), color: None, fill: None, numeric: false },
         }
     }
-
-    /// [`Self::format_text`]'s text, or `None` once it passes `max_units` UTF-16 code units.
-    fn format_text_within(&self, t: &str, max_units: usize) -> Option<String> {
-        match self.inner.text_section.and_then(|i| self.inner.sections.get(i)) {
-            Some(sec) => render::render_text_within(sec, t, max_units).map(|out| out.text),
-            None => (t.encode_utf16().count() <= max_units).then(|| t.to_string()),
-        }
-    }
 }
 
 /// Formats a cell value for display.
@@ -433,10 +425,6 @@ impl NumberFormat {
 /// The `TEXT()` worksheet function: formats a value with a format code. Numeric text is
 /// converted to a number first; other text and booleans (as `TRUE`/`FALSE`) go through the text
 /// section, or are returned as is.
-/// Longest text a cell holds, in UTF-16 code units (Excel's 32,767 characters, which XLSB also
-/// stores that way), and so the longest `TEXT` result.
-const MAX_CELL_TEXT_CHARS: usize = 32_767;
-
 pub fn text_function(v: &Value, code: &str, sys: DateSystem) -> Result<String, CellError> {
     if code.is_empty() {
         return Ok(String::new());
@@ -452,9 +440,7 @@ pub fn text_function(v: &Value, code: &str, sys: DateSystem) -> Result<String, C
         Value::Bool(b) => return Ok(fmt.format_text(if b { "TRUE" } else { "FALSE" }).text),
         Value::Text(t) => match gridcraft_core::parse::parse_number_text(&t) {
             Some(n) => n,
-            // Every `@` repeats the text: a result past a cell's limit is `#VALUE!`, so nested
-            // TEXT calls can't multiply it further.
-            None => return fmt.format_text_within(&t, MAX_CELL_TEXT_CHARS).ok_or(CellError::Value),
+            None => return Ok(fmt.format_text(&t).text),
         },
         Value::Array(_) => return Err(CellError::Value),
     };

crates/numfmt/src/render.rs

@@ -45,35 +45,6 @@ pub(crate) fn render_text(sec: &Section, text: &str) -> Out {
     out
 }
 
-/// [`render_text`], but `None` once the output passes `max_units` UTF-16 code units (a cell's
-/// limit), checked before each piece is appended, so an oversized result is never built.
-pub(crate) fn render_text_within(sec: &Section, text: &str, max_units: usize) -> Option<Out> {
-    let text_units = text.encode_utf16().count();
-    let mut out = Out::default();
-    let mut units = 0usize;
-    for t in &sec.toks {
-        match t {
-            Tok::At => {
-                units = units.saturating_add(text_units);
-                if units > max_units {
-                    return None;
-                }
-                out.push(text);
-            }
-            Tok::Fill(c) => out.fill(*c),
-            other => {
-                let literal = other.literal_text();
-                units = units.saturating_add(literal.encode_utf16().count());
-                if units > max_units {
-                    return None;
-                }
-                out.push(&literal);
-            }
-        }
-    }
-    Some(out)
-}
-
 /// Renders a number through a General section (literals around the General keyword).
 pub(crate) fn render_general(sec: &Section, v: f64, width: usize) -> Out {
     let mut out = Out::default();

crates/numfmt/src/tests.rs

@@ -396,13 +396,6 @@ fn text_fn() {
     assert_eq!(text_function(&Value::Number(1234.5), "$#,##0.00", S), Ok("$1,234.50".into()));
     assert_eq!(text_function(&Value::from("5"), "0.00", S), Ok("5.00".into()));
     assert_eq!(text_function(&Value::from("abc"), "0.00", S), Ok("abc".into()));
-    // Each `@` repeats the text: up to a cell's 32,767 characters, then #VALUE!.
-    let at = "@".repeat(255);
-    assert_eq!(text_function(&Value::from("x".repeat(128).as_str()), &at, S).map(|s| s.len()), Ok(128 * 255));
-    assert_eq!(text_function(&Value::from("x".repeat(32_000).as_str()), &at, S), Err(CellError::Value));
-    // The limit counts UTF-16 units: 16,384 emoji are 32,768 of them, one too many.
-    assert_eq!(text_function(&Value::from("\u{1F600}".repeat(16_383).as_str()), "@", S).map(|s| s.chars().count()), Ok(16_383));
-    assert_eq!(text_function(&Value::from("\u{1F600}".repeat(16_384).as_str()), "@", S), Err(CellError::Value));
     assert_eq!(text_function(&Value::Error(CellError::NA), "0", S), Err(CellError::NA));
     assert_eq!(text_function(&Value::Number(46302.0), "yyyy", S), Ok("2026".into()));
     assert_eq!(text_function(&Value::Number(0.5), "General", S), Ok("0.5".into()));

crates/xlsx/src/passthrough/write.rs

@@ -254,27 +254,36 @@ pub(crate) fn sheet_names_in(formula: &str) -> Vec<String> {
 /// Whether a kept chart sheet can be written back: its chart's series must still refer to sheets
 /// that exist under the same names (the chart is kept as it was, so a series on a deleted or
 /// renamed sheet would be left pointing at nothing), and no worksheet may have taken its name.
-fn chart_sheet_usable(wb: &Workbook, p: &Preserved, s: &PreservedSheet) -> bool {
+///
+/// `usable` caches, by relationship id, whether that chart sheet's graph refers only to sheets
+/// that exist (`false` when the relationship is missing): entries sharing one graph are analysed
+/// once, and only the verdict is kept, not the references it came from.
+fn chart_sheet_usable<'p>(wb: &Workbook, p: &'p Preserved, s: &'p PreservedSheet, usable: &mut HashMap<&'p str, bool>) -> bool {
     let same = |a: &str, b: &str| a.chars().take(31).collect::<String>().eq_ignore_ascii_case(&b.chars().take(31).collect::<String>());
     if wb.sheets.iter().any(|w| same(&w.name, &s.name)) {
         return false;
     }
-    let Some(root) = p.rels.iter().find(|r| r.id == s.rel_id) else { return false };
-    let parts = reachable(p, root);
-    let mut formulas = vec![];
-    for q in p.parts.iter().filter(|q| parts.contains(&normalize(&q.name)) && q.content_type.contains("chart")) {
-        if let Ok(x) = xml::parse(&q.data) {
-            chart_formulas(&x, &mut formulas);
+    *usable.entry(s.rel_id.as_str()).or_insert_with(|| {
+        let Some(root) = p.rels.iter().find(|r| r.id == s.rel_id) else { return false };
+        let parts = reachable(p, root);
+        let mut formulas = vec![];
+        for q in p.parts.iter().filter(|q| parts.contains(&normalize(&q.name)) && q.content_type.contains("chart")) {
+            if let Ok(x) = xml::parse(&q.data) {
+                chart_formulas(&x, &mut formulas);
+            }
         }
-    }
-    formulas.iter().flat_map(|f| sheet_names_in(f)).all(|n| wb.sheets.iter().any(|w| same(&w.name, &n)))
+        formulas.iter().flat_map(|f| sheet_names_in(f)).all(|n| wb.sheets.iter().any(|w| same(&w.name, &n)))
+    })
 }
 
 /// Writes the workbook's kept parts and relationships. Chart sheets that can't be written back
 /// (see [`chart_sheet_usable`]) are left out with the parts only they reach.
 pub fn write_workbook(wb: &Workbook, wb_rels: &mut Rels, out: &mut Out) -> WorkbookKept {
     let Some(p) = wb.preserved.as_deref() else { return WorkbookKept::default() };
-    let (live, dropped): (Vec<&PreservedSheet>, Vec<&PreservedSheet>) = p.sheets.iter().partition(|s| chart_sheet_usable(wb, p, s));
+    let (live, dropped): (Vec<&PreservedSheet>, Vec<&PreservedSheet>) = {
+        let mut refs = HashMap::new();
+        p.sheets.iter().partition(|s| chart_sheet_usable(wb, p, s, &mut refs))
+    };
     let root_of = |s: &PreservedSheet| p.rels.iter().find(|r| r.id == s.rel_id);
     let dropped_ids: HashSet<&str> = dropped.iter().map(|s| s.rel_id.as_str()).collect();
     // Parts reached only by dropped chart sheets go with them.

crates/xlsx/src/tests/passthrough_tests.rs

@@ -696,6 +696,32 @@ fn chartsheet_package() -> Vec<u8> {
     ])
 }
 
+/// Thousands of chart-sheet entries naming one chart sheet's relationship: its graph is walked
+/// and its charts parsed once when saving, not once per entry.
+#[test]
+fn chart_sheet_entries_sharing_a_graph_are_checked_once() {
+    let bytes = chartsheet_package();
+    let mut z = zip::ZipArchive::new(std::io::Cursor::new(bytes)).unwrap();
+    let mut parts: Vec<(String, Vec<u8>)> = Vec::new();
+    for i in 0..z.len() {
+        let mut f = z.by_index(i).unwrap();
+        let mut data = Vec::new();
+        f.read_to_end(&mut data).unwrap();
+        parts.push((f.name().to_string(), data));
+    }
+    let extra: String = (0..3_000).map(|i| format!(r#"<sheet name="Copy{i}" sheetId="{}" r:id="rId2"/>"#, 100 + i)).collect();
+    for (name, data) in &mut parts {
+        if name == "xl/workbook.xml" {
+            *data = String::from_utf8(data.clone()).unwrap().replace("</sheets>", &format!("{extra}</sheets>")).into_bytes();
+        }
+    }
+    let refs: Vec<(&str, &[u8])> = parts.iter().map(|(n, d)| (n.as_str(), d.as_slice())).collect();
+    let (wb, _) = read_xlsx(&make_zip(&refs)).unwrap();
+    let u = Unpacked::new(&write_xlsx(&wb).unwrap());
+    u.assert_valid();
+    assert!(written_sheets(&u).iter().any(|(n, _)| n == "Chart1"));
+}
+
 /// The sheets of a written workbook: (name, state) in file order.
 fn written_sheets(u: &Unpacked) -> Vec<(String, String)> {
     let wb = xml::parse(u.parts.get("xl/workbook.xml").unwrap()).unwrap();