Create ROADMAP.md

Author: WendellXY

ROADMAP.md

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+# langcodec Roadmap
+
+This document outlines progressive, bite‑sized tasks to enhance langcodec and langcodec‑cli. It’s structured so we can pick items incrementally and track progress over time.
+
+Legend: [ ] todo, [x] done, [~] in progress
+
+## Recently Completed
+
+- [x] Android `<plurals>` parse/write support (library)
+- [x] `.strings` writer escaping (quotes, backslashes, control chars)
+- [x] Symmetric language matching for multi‑language formats (`xcstrings`, `csv`, `tsv`)
+- [x] CLI view prints “Type: Plural” and plural categories
+- [x] Conversion tests: CSV→Android, XCStrings→Android (with plurals)
+
+---
+
+## M1. Quality & Safety
+
+- [ ] Placeholder normalization and validation
+  - [ ] Mapping between iOS (`%1$@`, `%d`) and Android (`%1$s`, `%d`)
+  - [ ] Detect placeholder mismatches across languages; fail in strict mode, warn otherwise
+  - [ ] Auto‑fix option for common cases (`%@` → `%s`, `%1$@` → `%1$s`)
+  - [ ] Tests across `.strings`, Android, `.xcstrings`
+- [ ] Plural rules engine
+  - [ ] CLDR‑driven required category sets per locale (few/many/etc.)
+  - [ ] Validation pass: flag missing categories per key+locale
+  - [ ] CLI: `view --check-plurals` and `validate` output
+- [ ] Strict vs. permissive parsing
+  - [ ] Global setting in lib; CLI `--strict` flag
+  - [ ] Consistent error surfaces with actionable context
+- [ ] Better error context
+  - [ ] Include file path and entry id for parse/convert errors
+  - [ ] (Optional) capture line/column when parser knows it
+
+## M2. Formats
+
+- [ ] Apple `.stringsdict` (plurals/select)
+- [ ] Flutter `.arb`
+- [ ] Gettext `.po`
+- [ ] XLIFF 1.2 / 2.0
+- [ ] (Later) ICU MessageFormat v2 (exploration)
+
+For each new format:
+
+- [ ] Implement `Parser` and conversions to/from `Resource`
+- [ ] Round‑trip tests + cross‑conversion tests
+- [ ] CLI convert + view coverage
+- [ ] README updates
+
+## M3. CSV/TSV Schema
+
+- [ ] Optional extended columns: `comment`, `status`, `context`, `developer_note`
+- [ ] CLI: `--schema` flag (e.g., `basic`, `extended`, custom mapping)
+- [ ] Lossless round‑trip for supported metadata
+- [ ] Tests to ensure consistent ordering and schema stability
+
+## M4. CLI UX
+
+- [ ] `diff` subcommand
+  - [ ] Compare two files; output added/removed/changed keys by language
+  - [ ] Machine‑readable JSON output and pretty mode
+- [ ] `stats` subcommand
+  - [ ] Per‑language counts by `EntryStatus`, completion %, missing plurals
+- [ ] `normalize` subcommand
+  - [ ] Canonicalize whitespace, escapes, key casing; optional rules
+- [ ] Filters and export
+  - [ ] `view --where 'status=stale and lang in(en,fr)' --format csv`
+  - [ ] `--grep` for key/value regex
+- [ ] Stdio support: `-` for stdin/stdout across commands
+- [ ] Config file: `langcodec.toml` for project defaults (langs, merge strategy, schema, placeholder policy)
+
+## M5. Developer Experience
+
+- [ ] API ergonomics
+  - [ ] Borrowed iterators and helpers: `iter_keys()`, `iter_entries(lang)`
+  - [ ] Mutators: `rename_key`, `bulk_rename`, `map_values`
+- [ ] Deterministic ordering everywhere (keys, languages)
+- [ ] Provenance tracking (source file, optional line) per entry
+- [ ] Benchmarks (Criterion) for parse/convert/merge
+
+## M6. Ecosystem & Distribution
+
+- [ ] WASM target (browser/Node) for view/convert/diff in web tools
+- [ ] GitHub Action templates
+  - [ ] Validate PRs, enforce placeholder policy, fail on regressions
+  - [ ] Example workflows in `.github/workflows/examples/`
+- [ ] Documentation site
+  - [ ] Task‑oriented guides (convert recipes, plural pitfalls, placeholder mapping)
+  - [ ] API docs deep links; examples gallery
+
+## Testing Strategy
+
+- [ ] Start with unit tests near each format parser/writer
+- [ ] Add conversion matrix tests for common paths (strings↔android↔xcstrings↔csv/tsv)
+- [ ] Property tests where feasible (e.g., round‑trip invariants)
+- [ ] Large sample corpora in `tests/data/` for regression
+
+## Contribution Guide Enhancements
+
+- [ ] Add coding standards and commit message conventions
+- [ ] Issue templates for formats vs CLI vs core
+- [ ] Local dev quickstart and common cargo commands
+
+## Release Checklist (per minor)
+
+- [ ] Update README Supported Formats table
+- [ ] Changelog highlights (breaking changes, new formats, CLI flags)
+- [ ] Version bumps in workspace `Cargo.toml` and README
+- [ ] Tag + GitHub release notes
+
+---
+
+If you pick up an item, feel free to mark it with [~] and open a PR referencing this roadmap.