feat(i18n): add `Astro.currentLocale` (#9101)

17 files changed, 222 insertions, 16 deletions

diff --git a/.changeset/quick-toes-peel.md b/.changeset/quick-toes-peel.md
new file mode 100644
index 000000000..25d5c13c7
--- /dev/null
+++ b/.changeset/quick-toes-peel.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Add a new property `Astro.currentLocale`, available when `i18n` is enabled.
diff --git a/packages/astro/src/@types/astro.ts b/packages/astro/src/@types/astro.ts
index f15cf7d09..6477f7383 100644
--- a/packages/astro/src/@types/astro.ts
+++ b/packages/astro/src/@types/astro.ts
@@ -2112,6 +2112,11 @@ interface AstroSharedContext<
 	 */
 
 	preferredLocaleList: string[] | undefined;
+
+	/**
+	 * The current locale computed from the URL of the request. It matches the locales in `i18n.locales`, and returns `undefined` otherwise.
+	 */
+	currentLocale: string | undefined;
 }
 
 export interface APIContext<
@@ -2241,6 +2246,11 @@ export interface APIContext<
 	 * [quality value]: https://developer.mozilla.org/en-US/docs/Glossary/Quality_values
 	 */
 	preferredLocaleList: string[] | undefined;
+
+	/**
+	 * The current locale computed from the URL of the request. It matches the locales in `i18n.locales`, and returns `undefined` otherwise.
+	 */
+	currentLocale: string | undefined;
 }
 
 export type EndpointOutput =
diff --git a/packages/astro/src/core/app/index.ts b/packages/astro/src/core/app/index.ts
index ec7990119..b297171a4 100644
--- a/packages/astro/src/core/app/index.ts
+++ b/packages/astro/src/core/app/index.ts
@@ -234,7 +234,9 @@ export class App {
 				status,
 				env: this.#pipeline.env,
 				mod: handler as any,
-				locales: this.#manifest.i18n ? this.#manifest.i18n.locales : undefined,
+				locales: this.#manifest.i18n?.locales,
+				routingStrategy: this.#manifest.i18n?.routingStrategy,
+				defaultLocale: this.#manifest.i18n?.defaultLocale,
 			});
 		} else {
 			const pathname = prependForwardSlash(this.removeBase(url.pathname));
@@ -269,7 +271,9 @@ export class App {
 				status,
 				mod,
 				env: this.#pipeline.env,
-				locales: this.#manifest.i18n ? this.#manifest.i18n.locales : undefined,
+				locales: this.#manifest.i18n?.locales,
+				routingStrategy: this.#manifest.i18n?.routingStrategy,
+				defaultLocale: this.#manifest.i18n?.defaultLocale,
 			});
 		}
 	}
diff --git a/packages/astro/src/core/build/generate.ts b/packages/astro/src/core/build/generate.ts
index 02837cf69..20854f779 100644
--- a/packages/astro/src/core/build/generate.ts
+++ b/packages/astro/src/core/build/generate.ts
@@ -558,7 +558,9 @@ async function generatePath(pathname: string, gopts: GeneratePathOptions, pipeli
 		route: pageData.route,
 		env: pipeline.getEnvironment(),
 		mod,
-		locales: i18n ? i18n.locales : undefined,
+		locales: i18n?.locales,
+		routingStrategy: i18n?.routingStrategy,
+		defaultLocale: i18n?.defaultLocale,
 	});
 
 	let body: string | Uint8Array;
diff --git a/packages/astro/src/core/endpoint/index.ts b/packages/astro/src/core/endpoint/index.ts
index 33c659dca..80af2358d 100644
--- a/packages/astro/src/core/endpoint/index.ts
+++ b/packages/astro/src/core/endpoint/index.ts
@@ -12,7 +12,11 @@ import { ASTRO_VERSION } from '../constants.js';
 import { AstroCookies, attachCookiesToResponse } from '../cookies/index.js';
 import { AstroError, AstroErrorData } from '../errors/index.js';
 import { callMiddleware } from '../middleware/callMiddleware.js';
-import { computePreferredLocale, computePreferredLocaleList } from '../render/context.js';
+import {
+	computeCurrentLocale,
+	computePreferredLocale,
+	computePreferredLocaleList,
+} from '../render/context.js';
 import { type Environment, type RenderContext } from '../render/index.js';
 
 const encoder = new TextEncoder();
@@ -27,6 +31,8 @@ type CreateAPIContext = {
 	props: Record<string, any>;
 	adapterName?: string;
 	locales: string[] | undefined;
+	routingStrategy: 'prefix-always' | 'prefix-other-locales' | undefined;
+	defaultLocale: string | undefined;
 };
 
 /**
@@ -41,9 +47,12 @@ export function createAPIContext({
 	props,
 	adapterName,
 	locales,
+	routingStrategy,
+	defaultLocale,
 }: CreateAPIContext): APIContext {
 	let preferredLocale: string | undefined = undefined;
 	let preferredLocaleList: string[] | undefined = undefined;
+	let currentLocale: string | undefined = undefined;
 
 	const context = {
 		cookies: new AstroCookies(request),
@@ -83,6 +92,16 @@ export function createAPIContext({
 
 			return undefined;
 		},
+		get currentLocale(): string | undefined {
+			if (currentLocale) {
+				return currentLocale;
+			}
+			if (locales) {
+				currentLocale = computeCurrentLocale(request, locales, routingStrategy, defaultLocale);
+			}
+
+			return currentLocale;
+		},
 		url: new URL(request.url),
 		get clientAddress() {
 			if (clientAddressSymbol in request) {
@@ -153,8 +172,7 @@ export async function callEndpoint<MiddlewareResult = Response | EndpointOutput>
 	mod: EndpointHandler,
 	env: Environment,
 	ctx: RenderContext,
-	onRequest: MiddlewareHandler<MiddlewareResult> | undefined,
-	locales: undefined | string[]
+	onRequest: MiddlewareHandler<MiddlewareResult> | undefined
 ): Promise<Response> {
 	const context = createAPIContext({
 		request: ctx.request,
@@ -162,7 +180,9 @@ export async function callEndpoint<MiddlewareResult = Response | EndpointOutput>
 		props: ctx.props,
 		site: env.site,
 		adapterName: env.adapterName,
-		locales,
+		routingStrategy: ctx.routingStrategy,
+		defaultLocale: ctx.defaultLocale,
+		locales: ctx.locales,
 	});
 
 	let response;
diff --git a/packages/astro/src/core/middleware/index.ts b/packages/astro/src/core/middleware/index.ts
index 77da30aee..c02761351 100644
--- a/packages/astro/src/core/middleware/index.ts
+++ b/packages/astro/src/core/middleware/index.ts
@@ -35,6 +35,8 @@ function createContext({ request, params, userDefinedLocales = [] }: CreateConte
 		props: {},
 		site: undefined,
 		locales: userDefinedLocales,
+		defaultLocale: undefined,
+		routingStrategy: undefined,
 	});
 }
 
diff --git a/packages/astro/src/core/pipeline.ts b/packages/astro/src/core/pipeline.ts
index bd203b437..87f833ee5 100644
--- a/packages/astro/src/core/pipeline.ts
+++ b/packages/astro/src/core/pipeline.ts
@@ -128,6 +128,8 @@ export class Pipeline {
 			site: env.site,
 			adapterName: env.adapterName,
 			locales: renderContext.locales,
+			routingStrategy: renderContext.routingStrategy,
+			defaultLocale: renderContext.defaultLocale,
 		});
 
 		switch (renderContext.route.type) {
@@ -158,13 +160,7 @@ export class Pipeline {
 				}
 			}
 			case 'endpoint': {
-				return await callEndpoint(
-					mod as any as EndpointHandler,
-					env,
-					renderContext,
-					onRequest,
-					renderContext.locales
-				);
+				return await callEndpoint(mod as any as EndpointHandler, env, renderContext, onRequest);
 			}
 			default:
 				throw new Error(`Couldn't find route of type [${renderContext.route.type}]`);
diff --git a/packages/astro/src/core/render/context.ts b/packages/astro/src/core/render/context.ts
index 851c41bc5..0f0bf39b0 100644
--- a/packages/astro/src/core/render/context.ts
+++ b/packages/astro/src/core/render/context.ts
@@ -29,6 +29,8 @@ export interface RenderContext {
 	props: Props;
 	locals?: object;
 	locales: string[] | undefined;
+	defaultLocale: string | undefined;
+	routingStrategy: 'prefix-always' | 'prefix-other-locales' | undefined;
 }
 
 export type CreateRenderContextArgs = Partial<
@@ -60,6 +62,8 @@ export async function createRenderContext(
 		params,
 		props,
 		locales: options.locales,
+		routingStrategy: options.routingStrategy,
+		defaultLocale: options.defaultLocale,
 	};
 
 	// We define a custom property, so we can check the value passed to locals
@@ -208,3 +212,23 @@ export function computePreferredLocaleList(request: Request, locales: string[])
 
 	return result;
 }
+
+export function computeCurrentLocale(
+	request: Request,
+	locales: string[],
+	routingStrategy: 'prefix-always' | 'prefix-other-locales' | undefined,
+	defaultLocale: string | undefined
+): undefined | string {
+	const requestUrl = new URL(request.url);
+	for (const segment of requestUrl.pathname.split('/')) {
+		for (const locale of locales) {
+			if (normalizeTheLocale(locale) === normalizeTheLocale(segment)) {
+				return locale;
+			}
+		}
+	}
+	if (routingStrategy === 'prefix-other-locales') {
+		return defaultLocale;
+	}
+	return undefined;
+}
diff --git a/packages/astro/src/core/render/core.ts b/packages/astro/src/core/render/core.ts
index da9675f10..ed9ea7fdb 100644
--- a/packages/astro/src/core/render/core.ts
+++ b/packages/astro/src/core/render/core.ts
@@ -60,6 +60,8 @@ export async function renderPage({ mod, renderContext, env, cookies }: RenderPag
 		cookies,
 		locals: renderContext.locals ?? {},
 		locales: renderContext.locales,
+		defaultLocale: renderContext.defaultLocale,
+		routingStrategy: renderContext.routingStrategy,
 	});
 
 	// TODO: Remove in Astro 4.0
diff --git a/packages/astro/src/core/render/result.ts b/packages/astro/src/core/render/result.ts
index 91dc545df..e9c8302a1 100644
--- a/packages/astro/src/core/render/result.ts
+++ b/packages/astro/src/core/render/result.ts
@@ -12,7 +12,11 @@ import { chunkToString } from '../../runtime/server/render/index.js';
 import { AstroCookies } from '../cookies/index.js';
 import { AstroError, AstroErrorData } from '../errors/index.js';
 import type { Logger } from '../logger/core.js';
-import { computePreferredLocale, computePreferredLocaleList } from './context.js';
+import {
+	computeCurrentLocale,
+	computePreferredLocale,
+	computePreferredLocaleList,
+} from './context.js';
 
 const clientAddressSymbol = Symbol.for('astro.clientAddress');
 const responseSentSymbol = Symbol.for('astro.responseSent');
@@ -47,6 +51,8 @@ export interface CreateResultArgs {
 	locals: App.Locals;
 	cookies?: AstroCookies;
 	locales: string[] | undefined;
+	defaultLocale: string | undefined;
+	routingStrategy: 'prefix-always' | 'prefix-other-locales' | undefined;
 }
 
 function getFunctionExpression(slot: any) {
@@ -148,6 +154,7 @@ export function createResult(args: CreateResultArgs): SSRResult {
 	let cookies: AstroCookies | undefined = args.cookies;
 	let preferredLocale: string | undefined = undefined;
 	let preferredLocaleList: string[] | undefined = undefined;
+	let currentLocale: string | undefined = undefined;
 
 	// Create the result object that will be passed into the render function.
 	// This object starts here as an empty shell (not yet the result) but then
@@ -218,6 +225,24 @@ export function createResult(args: CreateResultArgs): SSRResult {
 
 					return undefined;
 				},
+				get currentLocale(): string | undefined {
+					if (currentLocale) {
+						return currentLocale;
+					}
+					if (args.locales) {
+						currentLocale = computeCurrentLocale(
+							request,
+							args.locales,
+							args.routingStrategy,
+							args.defaultLocale
+						);
+						if (currentLocale) {
+							return currentLocale;
+						}
+					}
+
+					return undefined;
+				},
 				params,
 				props,
 				locals,
diff --git a/packages/astro/src/vite-plugin-astro-server/route.ts b/packages/astro/src/vite-plugin-astro-server/route.ts
index 7468f8819..48f89db04 100644
--- a/packages/astro/src/vite-plugin-astro-server/route.ts
+++ b/packages/astro/src/vite-plugin-astro-server/route.ts
@@ -215,6 +215,9 @@ export async function handleRoute({
 				env,
 				mod,
 				route,
+				locales: manifest.i18n?.locales,
+				routingStrategy: manifest.i18n?.routingStrategy,
+				defaultLocale: manifest.i18n?.defaultLocale,
 			});
 		} else {
 			return handle404Response(origin, incomingRequest, incomingResponse);
@@ -271,7 +274,9 @@ export async function handleRoute({
 			route: options.route,
 			mod,
 			env,
-			locales: i18n ? i18n.locales : undefined,
+			locales: i18n?.locales,
+			routingStrategy: i18n?.routingStrategy,
+			defaultLocale: i18n?.defaultLocale,
 		});
 	}
 
diff --git a/packages/astro/test/fixtures/i18n-routing-prefix-always/src/pages/en/start.astro b/packages/astro/test/fixtures/i18n-routing-prefix-always/src/pages/en/start.astro
index 990baecd9..92e189636 100644
--- a/packages/astro/test/fixtures/i18n-routing-prefix-always/src/pages/en/start.astro
+++ b/packages/astro/test/fixtures/i18n-routing-prefix-always/src/pages/en/start.astro
@@ -1,8 +1,13 @@
+---
+const currentLocale = Astro.currentLocale;
+---
 <html>
 <head>
 	<title>Astro</title>
 </head>
 <body>
 Start
+Current Locale: {currentLocale ? currentLocale : "none"}
+
 </body>
 </html>
diff --git a/packages/astro/test/fixtures/i18n-routing-prefix-always/src/pages/pt/start.astro b/packages/astro/test/fixtures/i18n-routing-prefix-always/src/pages/pt/start.astro
index 5a4a84c2c..6f82c3790 100644
--- a/packages/astro/test/fixtures/i18n-routing-prefix-always/src/pages/pt/start.astro
+++ b/packages/astro/test/fixtures/i18n-routing-prefix-always/src/pages/pt/start.astro
@@ -1,8 +1,12 @@
+---
+const currentLocale = Astro.currentLocale;
+---
 <html>
 <head>
 	<title>Astro</title>
 </head>
 <body>
 Oi essa e start
+Current Locale: {currentLocale ? currentLocale : "none"}
 </body>
 </html>
diff --git a/packages/astro/test/fixtures/i18n-routing/src/pages/current-locale.astro b/packages/astro/test/fixtures/i18n-routing/src/pages/current-locale.astro
new file mode 100644
index 000000000..64af0118b
--- /dev/null
+++ b/packages/astro/test/fixtures/i18n-routing/src/pages/current-locale.astro
@@ -0,0 +1,12 @@
+---
+const currentLocale = Astro.currentLocale;
+---
+
+<html>
+<head>
+	<title>Astro</title>
+</head>
+<body>
+	Current Locale: {currentLocale ? currentLocale : "none"}
+</body>
+</html>
diff --git a/packages/astro/test/fixtures/i18n-routing/src/pages/dynamic/[id].astro b/packages/astro/test/fixtures/i18n-routing/src/pages/dynamic/[id].astro
new file mode 100644
index 000000000..58141fec0
--- /dev/null
+++ b/packages/astro/test/fixtures/i18n-routing/src/pages/dynamic/[id].astro
@@ -0,0 +1,19 @@
+
+---
+export function getStaticPaths() {
+    return [
+        { id: "lorem" }
+    ]
+}
+const currentLocale = Astro.currentLocale;
+
+---
+
+<html>
+<head>
+    <title>Astro</title>
+</head>
+<body>
+Current Locale: {currentLocale ? currentLocale : "none"}
+</body>
+</html>
diff --git a/packages/astro/test/fixtures/i18n-routing/src/pages/pt/start.astro b/packages/astro/test/fixtures/i18n-routing/src/pages/pt/start.astro
index 15a63a7b8..9a37428ca 100644
--- a/packages/astro/test/fixtures/i18n-routing/src/pages/pt/start.astro
+++ b/packages/astro/test/fixtures/i18n-routing/src/pages/pt/start.astro
@@ -1,8 +1,12 @@
+---
+const currentLocale = Astro.currentLocale;
+---
 <html>
 <head>
 	<title>Astro</title>
 </head>
 <body>
 Hola
+Current Locale: {currentLocale ? currentLocale : "none"}
 </body>
 </html>
diff --git a/packages/astro/test/i18-routing.test.js b/packages/astro/test/i18n-routing.test.js
index a7e8b318d..f305a5747 100644
--- a/packages/astro/test/i18-routing.test.js
+++ b/packages/astro/test/i18n-routing.test.js
@@ -991,6 +991,73 @@ describe('[SSR] i18n routing', () => {
 			});
 		});
 	});
+
+	describe('current locale', () => {
+		describe('with [prefix-other-locales]', () => {
+			/** @type {import('./test-utils').Fixture} */
+			let fixture;
+
+			before(async () => {
+				fixture = await loadFixture({
+					root: './fixtures/i18n-routing/',
+					output: 'server',
+					adapter: testAdapter(),
+				});
+				await fixture.build();
+				app = await fixture.loadTestAdapterApp();
+			});
+
+			it('should return the default locale', async () => {
+				let request = new Request('http://example.com/current-locale', {});
+				let response = await app.render(request);
+				expect(response.status).to.equal(200);
+				expect(await response.text()).includes('Current Locale: en');
+			});
+
+			it('should return the default locale of the current URL', async () => {
+				let request = new Request('http://example.com/pt/start', {});
+				let response = await app.render(request);
+				expect(response.status).to.equal(200);
+				expect(await response.text()).includes('Current Locale: pt');
+			});
+
+			it('should return the default locale when a route is dynamic', async () => {
+				let request = new Request('http://example.com/dynamic/lorem', {});
+				let response = await app.render(request);
+				expect(response.status).to.equal(200);
+				expect(await response.text()).includes('Current Locale: en');
+			});
+		});
+
+		describe('with [prefix-always]', () => {
+			/** @type {import('./test-utils').Fixture} */
+			let fixture;
+
+			before(async () => {
+				fixture = await loadFixture({
+					root: './fixtures/i18n-routing-prefix-always/',
+					output: 'server',
+					adapter: testAdapter(),
+				});
+				await fixture.build();
+				app = await fixture.loadTestAdapterApp();
+			});
+
+			it('should return the locale of the current URL (en)', async () => {
+				let request = new Request('http://example.com/en/start', {});
+				let response = await app.render(request);
+				expect(response.status).to.equal(200);
+				expect(await response.text()).includes('Current Locale: en');
+			});
+
+			it('should return the locale of the current URL (pt)', async () => {
+				let request = new Request('http://example.com/pt/start', {});
+				let response = await app.render(request);
+				expect(response.status).to.equal(200);
+				expect(await response.text()).includes('Current Locale: pt');
+			});
+		});
+	});
 });
 
 describe('i18n routing does not break assets and endpoints', () => {