Read cell formatting from .xls files

.xls (Excel 97-2003) import used only each cell's number format. It now
also reads the BIFF8 formatting records (Font, XF, Palette and Style),
so opened sheets keep their fonts, solid and pattern fills, borders
(including diagonals), alignment (rotation, indent, wrap, shrink),
locked and hidden protection, the workbook's custom colour palette, its
Normal font as the default, and its user-defined cell styles.

The decoding lives in a new xls/styles.rs; xls/mod.rs gains the record
arms and the build call. Short or malformed formatting records keep the
fields present and add one warning instead of refusing the workbook.
Tests build the records in code, including truncation and byte mutation.

Also merges origin/main, keeping its dialog-sheet, WINDOW2 and XF
number-format handling; the XF arm now goes through the new styles
module, which covers the number format too.

docs/file-format-parity.md

@@ -1,6 +1,6 @@
 # File-format parity
 
-> **Last reviewed:** 2026-10-11 · **Last updated:** 2026-10-21 · **Change:** minor (.xls dialog sheets are skipped instead of read as worksheets; `.xls` import reads each sheet's display options from WINDOW2: right-to-left, gridlines, headings, zeros, formulas; XLSX text boxes and shapes keep their paragraphs' right-to-left direction on save; CSV/TSV/TXT can open with every field kept as text via `file.open {csvAsText}`; formulas over Excel's 8,192 characters, and `%` or call chains past the nesting limit, are parse errors instead of stack overflows when a file is opened; XLSX PivotTables read and write `rowGrandTotals`/`colGrandTotals` the way Excel does, so a table saved with only one grand total opens with the right one; HTML export keeps right-to-left; CSV and text import detects likely Windows-1256 Arabic when invalid UTF-8 has Arabic byte runs; other invalid UTF-8 remains Windows-1252; HTML export places pictures and charts, as inline SVG, at their anchors) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
+> **Last reviewed:** 2026-10-11 · **Last updated:** 2026-10-21 · **Change:** minor (`.xls` import reads cell formatting: fonts, fills, borders, alignment, protection, palette, user cell styles; .xls dialog sheets are skipped instead of read as worksheets; `.xls` import reads each sheet's display options from WINDOW2: right-to-left, gridlines, headings, zeros, formulas; XLSX text boxes and shapes keep their paragraphs' right-to-left direction on save; CSV/TSV/TXT can open with every field kept as text via `file.open {csvAsText}`; formulas over Excel's 8,192 characters, and `%` or call chains past the nesting limit, are parse errors instead of stack overflows when a file is opened; XLSX PivotTables read and write `rowGrandTotals`/`colGrandTotals` the way Excel does, so a table saved with only one grand total opens with the right one; HTML export keeps right-to-left; CSV and text import detects likely Windows-1256 Arabic when invalid UTF-8 has Arabic byte runs; other invalid UTF-8 remains Windows-1252; HTML export places pictures and charts, as inline SVG, at their anchors) · **Target:** Microsoft Excel (Microsoft 365), Excel for Mac 16.113.4
 
 Every format Excel opens or saves, with GridCraft's read and write support, fidelity and tests.
 Part of [target-app-parity.md](target-app-parity.md). **File formats: ~50% ready, 80–120 h**
@@ -54,7 +54,7 @@ values) is still dropped.
 | `.xlsm` Macro-Enabled Workbook | R/W | yes | yes, macros kept, not run | The VBA project is kept byte-for-byte and written back only into `.xlsm`/`.xltm` (#6); macros never run. Saved with the macro-enabled workbook content type | `roundtrip.rs` (`vba_project_roundtrip`, `package_kind_sets_workbook_content_type`), engine `io.rs` (`macros_are_saved_only_into_xlsm`) |
 | `.xltx` / `.xltm` templates | R/W | yes | partial | Saved with the template (and macro-enabled template) content type, chosen by extension; `.xltm` keeps a VBA project, `.xltx` drops it; "new from template" behaviour missing | `roundtrip.rs` (`package_kind_sets_workbook_content_type`), engine `io.rs` |
 | `.xlsb` Binary Workbook | R/W | **values only** (#101) | no | Names, visibility, numbers, text, booleans, errors, merges, cached formula results; no formulas, formatting, charts, names | `xlsb_tests.rs` |
-| `.xls` Excel 97-2003 (BIFF8) | R/W | **yes, partial** (#121) | no (Save As `.xlsx`) | Clean-room from [MS-CFB] and [MS-XLS]. Read: worksheets and visibility, shared strings, numbers, text, booleans, errors, formulas (text for the common tokens, shared and array formulas, 3-D refs, names, newer functions called by name) with cached results, number formats (dates display as dates), 1904 date system, merges, column widths, row heights, defined names, print area and titles, calculation settings (mode, iteration with its maximum iterations and change, precision as displayed), sheet display options (right-to-left, gridlines, headings, zero values, formulas; a truncated WINDOW2 is ignored). Not read: fonts, fills, borders, alignment, charts, pictures, comments, CF, validation, hyperlinks, freeze panes, external links (formula kept as its value). Chart and macro sheets skipped with a warning; encrypted (FILEPASS) and BIFF5 (Excel 5.0/95) files refused with a message. Opens as a new unsaved workbook. Unverified on a real-world corpus | `xls_tests.rs` |
+| `.xls` Excel 97-2003 (BIFF8) | R/W | **yes, partial** (#121) | no (Save As `.xlsx`) | Clean-room from [MS-CFB] and [MS-XLS]. Read: worksheets and visibility, shared strings, numbers, text, booleans, errors, formulas (text for the common tokens, shared and array formulas, 3-D refs, names, newer functions called by name) with cached results, number formats (dates display as dates), cell formatting (fonts, solid and pattern fills, borders with diagonals, alignment with rotation, indent, wrap and shrink, locked and hidden, the custom colour palette, the Normal font as the workbook default, user-defined cell styles), 1904 date system, merges, column widths, row heights, defined names, print area and titles, calculation settings (mode, iteration with its maximum iterations and change, precision as displayed), sheet display options (right-to-left, gridlines, headings, zero values, formulas; a truncated WINDOW2 is ignored). Not read: exact colours beyond the 56-colour palette (XFExt: theme colours and tints show as the palette colour Excel stored next to them), rich-text runs inside a cell, charts, pictures, comments, CF, validation, hyperlinks, freeze panes, external links (formula kept as its value). Chart and macro sheets skipped with a warning; encrypted (FILEPASS) and BIFF5 (Excel 5.0/95) files refused with a message. Opens as a new unsaved workbook. Unverified on a real-world corpus | `xls_tests.rs`, `xls_style_tests.rs` |
 | `.xlt` Excel 97-2003 template | R/W | yes (read as `.xls`) | no | | — |
 | `.xlam` / `.xla` add-ins | R/W | no | no | VBA; out of scope | — |
 | `.xml` XML Spreadsheet 2003 | R/W | no | no | Simple to support | — |
@@ -100,7 +100,7 @@ refresh. Counted under features (Get & Transform, ~10% ready), not here.
 | Real-world XLSX corpus run (craftrules test-corpora standard), and confirm Excel opens our output with no repair prompt (owner runs Excel) | 15–25 |
 | Preserve the rest of the unmodelled XLSX content (slicers, timelines, data model, table query tables, `extLst` entries); pass-through landed for the rest (#330) | 6–10 |
 | Streaming XLSX reader for very large files (#175), part-size limits that degrade instead of failing | 10–15 |
-| Legacy `.xls` (BIFF8): styles (fonts, fills, borders, alignment), comments, CF, validation, pictures and charts on import; corpus run; then write | 10–15 |
+| Legacy `.xls` (BIFF8): exact theme colours (XFExt), comments, CF, validation, pictures and charts on import; corpus run; then write | 10–15 |
 | Encrypted workbooks: save with password (#11) | 4–6 |
 | XLSB and ODS: formulas and formatting on import; then write | 10–15 |
 | CSV/text: encoding choice, `.prn`, `.dif`, `.slk`, XML Spreadsheet 2003 | 4–7 |
@@ -132,6 +132,7 @@ refresh. Counted under features (Get & Transform, ~10% ready), not here.
 | 2026-10-15 | minor | XLSX: formulas and PivotTable sources quote sheet names like Excel (a leading `.`, R1C1-like and cell-like names), so `'.x'!A1` no longer saves as `.x!A1`, which Excel could not open (#1458) |
 | 2026-10-15 | minor | XLSX text preserves CR and CRLF across save/reopen; shared strings use `_x000D_` and other XML text uses `
` (#1488) |
 | 2026-10-15 | minor | XLSX save keeps legacy `INDEX`/`MATCH` formulas scalar instead of marking them as dynamic arrays (#1505) |
+| 2026-10-14 | minor | `.xls` import reads cell formatting from the Font, XF, Palette and Style records: fonts, fills, borders, alignment, protection, the custom palette, the Normal font and user cell styles |
 | 2026-10-14 | trivial | Formula parser: text longer than Excel's 8,192 characters, and postfix chains (`1%%%…`, `f(1)(1)…`) past the 256-level nesting limit, are parse errors (the cell keeps its formula text and cached value) instead of trees deep enough to overflow the stack when a hostile file is opened, saved or dropped |
 | 2026-10-14 | minor | XLSX formulas read with dynamic-array metadata (`cm`) keep it on save, so Excel does not recalculate them with implicit intersection |
 | 2026-10-14 | minor | PDF export writes clickable annotations for safe cell URLs and destinations on printed pages; CLI `convert` accepts `.pdf` output (#954) |