refactor(i18n): move Settings-only strings into src/lib/i18n/settings.*.ts

CONTRIBUTING.md

@@ -89,9 +89,13 @@ running terminals: see [development](docs/development.md#checks).
 - **Theme colors:** edit them only in the theme blocks of `src/styles.css`. Never edit
   `src/lib/themes.generated.ts` or the generated copies in DESIGN.md, `index.html` and
   `public/manifest.webmanifest`; run `bun run generate:themes`.
-- **UI text:** every new `t("…")` string needs an entry in `src/lib/i18n.ko.ts`, `i18n.ja.ts`
-  and `i18n.zh.ts`, with the same placeholders. `bun run test:unit` fails on a missing, unused or
-  untranslated entry.
+- **UI text:** every new `t("…")` string needs a Korean, Japanese and Simplified Chinese entry with
+  the same placeholders. A string that only one feature's files use goes in that feature's files in
+  `src/lib/i18n/` when it has them (`settings.ko.ts`, `settings.ja.ts` and `settings.zh.ts` for the
+  Settings dialog; each file's header lists its feature's files). Any other string goes in
+  `src/lib/i18n.ko.ts`, `i18n.ja.ts` and `i18n.zh.ts`, and so does a feature's string once another
+  feature uses it too. `bun run test:unit` fails on a missing, unused or untranslated entry, and on one
+  the three languages keep in different files.
 - **UI languages:** the app keeps English, Korean, Japanese and Simplified Chinese and does not take
   new ones. Every language has to translate each later string, so a PR that adds a language is
   closed.

src/lib/i18n.test.ts

@@ -1,9 +1,9 @@
 import { describe, expect, it } from "bun:test";
 import { readFileSync } from "node:fs";
 import { join } from "node:path";
-import { JA } from "./i18n.ja.ts";
-import { KO } from "./i18n.ko.ts";
-import { ZH } from "./i18n.zh.ts";
+import { JA, JA_PARTS } from "./i18n.ja.ts";
+import { KO, KO_PARTS } from "./i18n.ko.ts";
+import { ZH, ZH_PARTS } from "./i18n.zh.ts";
 import { resolveLanguage, translate } from "./i18n.ts";
 
 const root = join(import.meta.dir, "..");
@@ -16,7 +16,8 @@ const root = join(import.meta.dir, "..");
 function keysInCode(): Map<string, string[]> {
   const found = new Map<string, string[]>();
   for (const file of new Bun.Glob("**/*.{ts,tsx}").scanSync({ cwd: root })) {
-    if (file.endsWith(".test.ts") || /i18n\.\w+\.ts$/.test(file)) continue;
+    // the dictionaries: i18n.ko.ts and the like, and the parts in lib/i18n/
+    if (file.endsWith(".test.ts") || /i18n\.\w+\.ts$/.test(file) || /^lib[\\/]i18n[\\/]/.test(file)) continue;
     const text = readFileSync(join(root, file), "utf8");
     for (const match of text.matchAll(/(?<![\w.])(?:t|tt)\(/g)) {
       const firstArg = firstArgument(text, match.index + match[0].length);
@@ -112,6 +113,34 @@ describe.each(Object.entries(DICTIONARIES))("%s dictionary", (_name, dictionary)
   });
 });
 
+/** Parts in src/lib/i18n/ hold the keys only one feature uses; the base dictionary holds the rest. */
+const PARTS = { Korean: [KO, KO_PARTS], Japanese: [JA, JA_PARTS], Chinese: [ZH, ZH_PARTS] } as const;
+
+describe("dictionary parts", () => {
+  it.each(Object.entries(PARTS))("%s keeps each key in one part", (_name, [dictionary, parts]) => {
+    // the dictionary is the parts spread together, and a spread keeps only the last copy of a key
+    const seen = new Map<string, string>();
+    const twice = Object.entries(parts).flatMap(([part, entries]) => Object.keys(entries).flatMap((key) => {
+      const first = seen.get(key);
+      seen.set(key, part);
+      return first === undefined ? [] : [`${key} (${first}, ${part})`];
+    }));
+    expect(twice).toEqual([]);
+    expect(Object.keys(dictionary).length).toBe(seen.size);
+  });
+
+  it("puts each key in the same part in every language", () => {
+    const placement = (parts: Record<string, Record<string, string>>) => Object.fromEntries(Object.entries(parts).map(([part, entries]) => [part, Object.keys(entries).sort()]));
+    expect(placement(JA_PARTS)).toEqual(placement(KO_PARTS));
+    expect(placement(ZH_PARTS)).toEqual(placement(KO_PARTS));
+  });
+
+  it("keeps each part file at 400 lines or fewer", () => {
+    const long = [...new Bun.Glob("lib/i18n/*.ts").scanSync({ cwd: root })].filter((file) => readFileSync(join(root, file), "utf8").split("\n").length > 400);
+    expect(long).toEqual([]);
+  });
+});
+
 describe("translate", () => {
   it("fills placeholders, falls back to English, and leaves unknown placeholders alone", () => {
     expect(translate("en", "Worked for {duration}", { duration: "7s" })).toBe("Worked for 7s");