commit c316b6455b6d811bde30b5bf611c3d1e6748e45e
parent debc15ea196dabfeda7f1a3d9ce33a27b1410021
Author: Erik Loualiche <eloualic@umn.edu>
Date: Fri, 13 Mar 2026 17:34:08 -0500
docs: add xlset design spec — Excel cell writer
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Diffstat:
1 file changed, 176 insertions(+), 0 deletions(-)
diff --git a/docs/superpowers/specs/2026-03-13-xlset-design.md b/docs/superpowers/specs/2026-03-13-xlset-design.md
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+# xlset — Excel Cell Writer
+
+## Purpose
+
+A Rust CLI tool that modifies cells in existing `.xlsx` files using
+`umya-spreadsheet`. Preserves all formatting, formulas, charts, and
+structure it doesn't touch. Lives in the same repo as `xlcat` (the
+read-only viewer) but is a separate binary.
+
+## CLI Interface
+
+```
+xlset <file> <cell>=<value> [<cell>=<value> ...]
+xlset <file> --from <csv-file|->
+xlset <file> --sheet "Revenue" A1=42 B2="hello"
+xlset <file> --output other.xlsx A1=42
+```
+
+### Flags
+
+| Flag | Purpose |
+|------|---------|
+| `--sheet <name\|index>` | Target sheet (default: first sheet). Name or 0-based index. |
+| `--output <path>` | Write to a new file instead of modifying in-place. |
+| `--from <path\|->` | Read cell assignments from a CSV file or stdin (`-`). |
+
+## Cell Assignment Syntax
+
+Positional arguments after the file path are cell assignments:
+
+```
+A1=42 # auto-infer: integer
+B2=3.14 # auto-infer: float
+C3=true # auto-infer: boolean
+D4=2024-01-15 # auto-infer: date
+E5=hello world # auto-infer: string
+F6:str=07401 # explicit: force string (preserves leading zero)
+G7:num=42 # explicit: force number
+H8:bool=1 # explicit: force boolean
+I9:date=2024-01-15 # explicit: force date
+```
+
+### Type Tags
+
+Optional type tags override auto-inference: `:str`, `:num`, `:bool`, `:date`.
+Placed between the cell reference and the `=` sign.
+
+### Auto-Inference Rules (in order)
+
+1. If explicit type tag is present → use that type.
+2. `true` or `false` (case-insensitive) → boolean.
+3. Parseable as `i64` (no decimal point) → integer (stored as f64 in Excel).
+4. Parseable as `f64` → float.
+5. Matches `YYYY-MM-DD` pattern → date (stored as Excel serial number
+ with `yyyy-mm-dd` format code applied to the cell).
+6. Empty value after `=` (e.g., `A1=`) → empty string.
+7. Everything else → string.
+
+## `--from` CSV Format
+
+```csv
+cell,value
+A1,42
+B2,hello
+C3:str,07401
+```
+
+- First row is skipped if the first field does not parse as a valid cell
+ reference (e.g., a header like `cell,value` or `ref,val`).
+- Each row is a `cell,value` pair. Standard RFC 4180 CSV quoting applies —
+ values containing commas must be quoted: `A1,"hello, world"`.
+- Type tags work in the cell column: `C3:str,07401`.
+- Reads from a file path or `-` for stdin.
+- Can be combined with positional args. **Duplicate resolution:** last-write-wins,
+ with positional args applied after CSV. If the CSV sets `A1=42` and a
+ positional arg sets `A1=99`, the cell gets `99`.
+
+## Cell Address Parsing
+
+Supports standard Excel A1 notation:
+
+- Column: `A` through `XFD` (1 to 16384).
+- Row: `1` through `1048576`.
+- Examples: `A1`, `Z99`, `AA1`, `XFD1048576`.
+- Case-insensitive: `a1` = `A1`.
+
+Passed to umya-spreadsheet using its string-based cell reference API
+(e.g., `worksheet.get_cell_mut("A1")`).
+
+## Sheet Selection
+
+- `--sheet "Revenue"` selects by name.
+- `--sheet 0` selects by 0-based index.
+- If the argument matches a sheet name exactly, the name takes precedence
+ over interpreting it as an index (same behavior as xlcat).
+- Default: first sheet in the workbook.
+- If sheet not found: error listing available sheets.
+
+## Output Behavior
+
+- **Default:** modifies file in-place.
+- **`--output path.xlsx`:** writes to a new file, original untouched.
+- Errors are reported before any write occurs when possible.
+
+## Stderr Confirmation
+
+On success, prints to stderr:
+```
+xlset: updated 3 cells in Revenue (report.xlsx)
+```
+
+No output to stdout. This keeps xlset pipe-friendly.
+
+## Exit Codes
+
+| Code | Meaning |
+|------|---------|
+| 0 | Success |
+| 1 | Runtime error (file not found, corrupt, sheet missing, write failure) |
+| 2 | Invalid arguments (bad cell reference, bad type tag, bad CSV) |
+
+All error messages go to stderr.
+
+## Technology
+
+- **Language:** Rust
+- **Excel read/write:** `umya-spreadsheet` (round-trip editing, preserves formatting)
+- **CLI parsing:** `clap` (derive API, shared with xlcat)
+- **Cell parsing / type inference:** shared library code with xlcat
+- **No runtime dependencies** — single compiled binary
+
+## Project Structure
+
+Same repo, two binaries sharing a library:
+
+```
+Cargo.toml # [[bin]] entries for xlcat and xlset
+src/
+├── lib.rs # crate library root, re-exports modules
+├── bin/
+│ ├── xlcat.rs # xlcat entry point (moved from main.rs)
+│ └── xlset.rs # xlset entry point
+├── cell.rs # A1 notation parser, value type inference
+├── writer.rs # umya-spreadsheet write logic
+├── metadata.rs # existing (used by xlcat)
+├── reader.rs # existing (used by xlcat)
+└── formatter.rs # existing (used by xlcat)
+```
+
+`umya-spreadsheet` is added as a dependency. Existing calamine/polars deps
+remain for xlcat. Shared code in `lib.rs` and `cell.rs` must not import
+crate-specific types (polars, umya-spreadsheet) unconditionally — only
+the binary entry points and their dedicated modules should pull those in.
+With LTO enabled, the linker strips unused code per binary.
+
+## Error Handling
+
+- **File does not exist:** error. xlset operates on existing files only; it
+ does not create new workbooks.
+- **File is `.xls` (not `.xlsx`):** "xlset only supports .xlsx files."
+- **File not found:** clear error with path.
+- **File not writable:** "Cannot write to: <path>" with OS error.
+- **Invalid cell reference:** "Invalid cell reference: <ref>" with hint
+ (e.g., "Expected format: A1, B2, AA100").
+- **Invalid type tag:** "Unknown type tag: <tag>. Valid tags: str, num, bool, date".
+- **Sheet not found:** list available sheets in error message.
+- **CSV parse error:** "Error on line N: <detail>".
+- **No assignments:** "No cell assignments provided. Use positional args or --from."
+
+## Future Possibilities (Not in Scope)
+
+- Formula setting (`A1==SUM(B1:B10)`)
+- Range fill (`A1:A10=0`)
+- Cell deletion / clearing
+- Row/column insertion
+- Conditional updates (`--if-empty`)
