fix: getFileInfo does not add .html extension in url when build.format is file (#4849)

* Create appendExtension

* Add html to file URLs if build.format is file

* Add changeset

.changeset/light-shrimps-draw.md

@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+append .html to the file URL in case build.format says file

packages/astro/src/core/path.ts

@@ -1,3 +1,7 @@
+export function appendExtension(path: string, extension: string) {
+	return path + '.' + extension;
+}
+
 export function appendForwardSlash(path: string) {
 	return path.endsWith('/') ? path : path + '/';
 }

packages/astro/src/vite-plugin-utils/index.ts

@@ -1,6 +1,6 @@
 import { Data } from 'vfile';
 import type { AstroConfig, MarkdownAstroData } from '../@types/astro';
-import { appendForwardSlash } from '../core/path.js';
+import { appendForwardSlash, appendExtension } from '../core/path.js';
 
 export function getFileInfo(id: string, config: AstroConfig) {
 	const sitePathname = appendForwardSlash(
@@ -14,6 +14,9 @@ export function getFileInfo(id: string, config: AstroConfig) {
 	if (fileUrl && config.trailingSlash === 'always') {
 		fileUrl = appendForwardSlash(fileUrl);
 	}
+	if (fileUrl && config.build.format === 'file') {
+		fileUrl = appendExtension(fileUrl, 'html');
+	}
 	return { fileId, fileUrl };
 }