Architecture review fixes: partials carry the locale, mountable locales/, shared core words

src/i18n/view-locals.ts

@@ -4,7 +4,6 @@
 
 import { DEFAULT_LOCALE } from "./catalog.ts";
 import { ENGLISH } from "./english.ts";
-import type { RequestContext } from "../http/context.ts";
 import { localeHref, localeLabel, textDirection } from "./locale.ts";
 import type { Translate } from "./translate.ts";
 
@@ -19,28 +18,46 @@ export interface I18nLocals {
   dir: "ltr" | "rtl";
   locale: string;
   localeHref: (href: string) => string;
+  // The locale to carry as a hidden field, or null when the visitor never asked for one. A GET form
+  // replaces the whole query string, so a link-carrying wrapper can't reach it — the form must.
+  localeParam: string | null;
   localeSwitch: LocaleChoice[];
   locales: string[];
   t: Translate;
 }
 
+// Just the request fields a render needs, so this module stays a leaf of src/i18n/ rather than
+// depending on the HTTP layer that calls it.
+export interface I18nRequest {
+  locale: string;
+  localeHref: (href: string) => string;
+  locales: string[];
+  t: Translate;
+  url: URL;
+}
+
 // For a render with no request behind it — a partial exercised directly, a one-off render: English,
 // left-to-right, no language picker.
 export const ENGLISH_LOCALS: I18nLocals = {
   dir: "ltr",
   locale: DEFAULT_LOCALE,
   localeHref: (href) => href,
+  localeParam: null,
   localeSwitch: [],
   locales: [DEFAULT_LOCALE],
   t: ENGLISH,
 };
 
-export function i18nLocals(ctx: RequestContext): I18nLocals {
+export function i18nLocals(ctx: I18nRequest): I18nLocals {
   const here = `${ctx.url.pathname}${ctx.url.search}`;
+  // ctx.localeHref is a no-op unless the URL asked for a locale, so it is also the honest answer to
+  // "did it?" — asking the function that decides keeps the two from drifting apart.
+  const carried = ctx.localeHref("/") === "/" ? null : ctx.locale;
   return {
     dir: textDirection(ctx.locale),
     locale: ctx.locale,
     localeHref: (href) => ctx.localeHref(href),
+    localeParam: carried,
     localeSwitch: ctx.locales.map((tag) => ({ current: tag === ctx.locale, href: localeHref(here, tag), label: localeLabel(tag), tag })),
     locales: ctx.locales,
     t: ctx.t,