Fix: Astro.site should default to localhost if not provided in config (#3552)

* Astro.site should be defaulted to localhost

* test: verify Astro.site default value

* chore: add changeset

* test: matching a URL regex to ignore specific port numbers

5 files changed, 80 insertions, 6 deletions

diff --git a/.changeset/brown-peas-destroy.md b/.changeset/brown-peas-destroy.md
new file mode 100644
index 000000000..f4bbb7586
--- /dev/null
+++ b/.changeset/brown-peas-destroy.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fix: Astro.site should default to localhost when not provided in a project's config
diff --git a/packages/astro/src/vite-plugin-astro/compile.ts b/packages/astro/src/vite-plugin-astro/compile.ts
index 09dcbbe57..356d602de 100644
--- a/packages/astro/src/vite-plugin-astro/compile.ts
+++ b/packages/astro/src/vite-plugin-astro/compile.ts
@@ -63,7 +63,7 @@ async function compile({
 		// For Windows compat, prepend the module ID with `/@fs`
 		pathname: `/@fs${prependForwardSlash(moduleId)}`,
 		projectRoot: config.root.toString(),
-		site: config.site ? new URL(config.base, config.site).toString() : undefined,
+		site: config.site ? new URL(config.base, config.site).toString() : `http://localhost:${config.server.port}/`,
 		sourcefile: filename,
 		sourcemap: 'both',
 		internalURL: `/@fs${prependForwardSlash(
diff --git a/packages/astro/src/vite-plugin-markdown/index.ts b/packages/astro/src/vite-plugin-markdown/index.ts
index 6712e0cbb..f64250bdd 100644
--- a/packages/astro/src/vite-plugin-markdown/index.ts
+++ b/packages/astro/src/vite-plugin-markdown/index.ts
@@ -165,7 +165,7 @@ ${setup}`.trim();
 				let { code: tsResult } = await transform(astroResult, {
 					pathname: '/@fs' + prependForwardSlash(fileUrl.pathname),
 					projectRoot: config.root.toString(),
-					site: config.site ? new URL(config.base, config.site).toString() : undefined,
+					site: config.site ? new URL(config.base, config.site).toString() : `http://localhost:${config.server.port}/`,
 					sourcefile: id,
 					sourcemap: 'inline',
 					// TODO: baseline flag
diff --git a/packages/astro/test/astro-global.test.js b/packages/astro/test/astro-global.test.js
index 799f89071..5a26270a0 100644
--- a/packages/astro/test/astro-global.test.js
+++ b/packages/astro/test/astro-global.test.js
@@ -8,6 +8,8 @@ describe('Astro Global', () => {
 	before(async () => {
 		fixture = await loadFixture({
 			root: './fixtures/astro-global/',
+			site: 'https://mysite.dev/',
+			base: '/blog'
 		});
 	});
 
@@ -85,3 +87,74 @@ describe('Astro Global', () => {
 		});
 	});
 });
+
+describe('Astro Global Defaults', () => {
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({
+			root: './fixtures/astro-global/'
+		});
+	});
+
+	describe('dev', () => {
+		let devServer;
+		let $;
+
+		before(async () => {
+			devServer = await fixture.startDevServer();
+			const html = await fixture.fetch('/blog/?foo=42').then((res) => res.text());
+			$ = cheerio.load(html);
+		});
+
+		after(async () => {
+			await devServer.stop();
+		});
+
+		it('Astro.request.url', async () => {
+			expect($('#pathname').text()).to.equal('');
+			expect($('#searchparams').text()).to.equal('');
+			expect($('#child-pathname').text()).to.equal('');
+			expect($('#nested-child-pathname').text()).to.equal('');
+		});
+	});
+
+	describe('build', () => {
+		before(async () => {
+			await fixture.build();
+		});
+
+		it('Astro.request.url', async () => {
+			const html = await fixture.readFile('/index.html');
+			const $ = cheerio.load(html);
+
+			expect($('#pathname').text()).to.equal('/');
+			expect($('#searchparams').text()).to.equal('{}');
+			expect($('#child-pathname').text()).to.equal('/');
+			expect($('#nested-child-pathname').text()).to.equal('/');
+		});
+
+		it('Astro.canonicalURL', async () => {
+			// given a URL, expect the following canonical URL
+			const canonicalURLs = {
+				'/index.html': /http:\/\/localhost:\d+\//,
+				'/post/post/index.html': /http:\/\/localhost:\d+\/post\/post\//,
+				'/posts/1/index.html': /http:\/\/localhost:\d+\/posts\//,
+				'/posts/2/index.html': /http:\/\/localhost:\d+\/posts\/2\//,
+			};
+
+			for (const [url, canonicalURL] of Object.entries(canonicalURLs)) {
+				const html = await fixture.readFile(url);
+
+				const $ = cheerio.load(html);
+				expect($('link[rel="canonical"]').attr('href')).to.match(canonicalURL);
+			}
+		});
+
+		it('Astro.site', async () => {
+			const html = await fixture.readFile('/index.html');
+			const $ = cheerio.load(html);
+			expect($('#site').attr('href')).to.match(/http:\/\/localhost:\d+\//);
+		});
+	});
+});
diff --git a/packages/astro/test/fixtures/astro-global/astro.config.mjs b/packages/astro/test/fixtures/astro-global/astro.config.mjs
deleted file mode 100644
index d87985387..000000000
--- a/packages/astro/test/fixtures/astro-global/astro.config.mjs
+++ /dev/null
@@ -1,4 +0,0 @@
-export default {
-	site: 'https://mysite.dev/',
-	base: '/blog'
-}