googlefonts configuration option (**experimental and temporary**)

ref. #423

Author: Fil

docs/config.md

@@ -300,3 +300,11 @@ The set of replacements for straight double and single quotes used when the [**t
 ## linkify <a href="https://github.com/observablehq/framework/releases/tag/v1.7.0" class="observablehq-version-badge" data-version="^1.7.0" title="Added in 1.7.0"></a>
 
 If true (the default), automatically convert URL-like text to links in Markdown.
+
+<!--
+
+## googlefonts <a href="https://github.com/observablehq/framework/pull/1588" class="observablehq-version-badge" data-version="prerelease" title="Added in #1588"></a>
+
+The URL of a Google Fonts resource. This is a **temporary** configuration element, which will be superseded when fonts are self-hosted (see [#423](https://github.com/observablehq/framework/issues/423)).
+
+-->

src/build.ts

@@ -49,7 +49,7 @@ export async function build(
   {config}: BuildOptions,
   effects: BuildEffects = new FileBuildEffects(config.output, join(config.root, ".observablehq", "cache"))
 ): Promise<void> {
-  const {root, loaders, normalizePath} = config;
+  const {root, loaders, normalizePath, googlefonts} = config;
   Telemetry.record({event: "build", step: "start"});
 
   // Make sure all files are readable before starting to write output files.
@@ -79,7 +79,7 @@ export async function build(
       effects.logger.log(faint("(skipped)"));
       continue;
     }
-    const resolvers = await getResolvers(page, {root, path: sourceFile, normalizePath, loaders});
+    const resolvers = await getResolvers(page, {root, path: sourceFile, normalizePath, loaders, googlefonts});
     const elapsed = Math.floor(performance.now() - start);
     for (const f of resolvers.assets) files.add(resolvePath(sourceFile, f));
     for (const f of resolvers.files) files.add(resolvePath(sourceFile, f));

src/config.ts

@@ -84,6 +84,7 @@ export interface Config {
   head: PageFragmentFunction | string | null; // defaults to null
   header: PageFragmentFunction | string | null; // defaults to null
   footer: PageFragmentFunction | string | null; // defaults to “Built with Observable on [date].”
+  googlefonts: string | null; // defaults to Source Pro URL
   toc: TableOfContents;
   style: null | Style; // defaults to {theme: ["light", "dark"]}
   search: SearchConfig | null; // default to null
@@ -105,6 +106,7 @@ export interface ConfigSpec {
   head?: unknown;
   header?: unknown;
   footer?: unknown;
+  googlefonts?: unknown;
   interpreters?: unknown;
   title?: unknown;
   pages?: unknown;
@@ -239,6 +241,12 @@ export function normalizeConfig(spec: ConfigSpec = {}, defaultRoot?: string, wat
   const head = pageFragment(spec.head === undefined ? "" : spec.head);
   const header = pageFragment(spec.header === undefined ? "" : spec.header);
   const footer = pageFragment(spec.footer === undefined ? defaultFooter() : spec.footer);
+  const googlefonts =
+    spec.googlefonts === undefined
+      ? "https://fonts.googleapis.com/css2?family=Source+Serif+Pro:ital,wght@0,400;0,600;0,700;1,400;1,600;1,700&display=swap"
+      : spec.googlefonts === null
+      ? null
+      : String(spec.googlefonts);
   const search = spec.search == null || spec.search === false ? null : normalizeSearch(spec.search as any);
   const interpreters = normalizeInterpreters(spec.interpreters as any);
   const config: Config = {
@@ -253,6 +261,7 @@ export function normalizeConfig(spec: ConfigSpec = {}, defaultRoot?: string, wat
     head,
     header,
     footer,
+    googlefonts,
     toc,
     style,
     search,

src/preview.ts

@@ -305,7 +305,7 @@ function handleWatch(socket: WebSocket, req: IncomingMessage, configPromise: Pro
 
   async function watcher(event: WatchEventType, force = false) {
     if (!path || !config) throw new Error("not initialized");
-    const {root, loaders, normalizePath} = config;
+    const {root, loaders, normalizePath, googlefonts} = config;
     switch (event) {
       case "rename": {
         markdownWatcher?.close();
@@ -336,7 +336,7 @@ function handleWatch(socket: WebSocket, req: IncomingMessage, configPromise: Pro
           clearTimeout(emptyTimeout);
           emptyTimeout = null;
         }
-        const resolvers = await getResolvers(page, {root, path, loaders, normalizePath});
+        const resolvers = await getResolvers(page, {root, path, loaders, normalizePath, googlefonts});
         if (hash === resolvers.hash) break;
         const previousHash = hash!;
         const previousHtml = html!;
@@ -373,10 +373,10 @@ function handleWatch(socket: WebSocket, req: IncomingMessage, configPromise: Pro
     if (path.endsWith("/")) path += "index";
     path = join(dirname(path), basename(path, ".html") + ".md");
     config = await configPromise;
-    const {root, loaders, normalizePath} = config;
+    const {root, loaders, normalizePath, googlefonts} = config;
     const source = await readFile(join(root, path), "utf8");
     const page = parseMarkdown(source, {path, ...config});
-    const resolvers = await getResolvers(page, {root, path, loaders, normalizePath});
+    const resolvers = await getResolvers(page, {root, path, loaders, normalizePath, googlefonts});
     if (resolvers.hash !== initialHash) return void send({type: "reload"});
     hash = resolvers.hash;
     html = getHtml(page, resolvers);

src/resolvers.ts

@@ -33,6 +33,7 @@ export interface ResolversConfig {
   path: string;
   normalizePath: (path: string) => string;
   loaders: LoaderResolver;
+  googlefonts: string | null;
 }
 
 const defaultImports = [
@@ -83,7 +84,7 @@ export const builtins = new Map<string, string>([
  */
 export async function getResolvers(
   page: MarkdownPage,
-  {root, path, normalizePath, loaders}: ResolversConfig
+  {root, path, normalizePath, loaders, googlefonts}: ResolversConfig
 ): Promise<Resolvers> {
   const hash = createHash("sha256").update(page.body).update(JSON.stringify(page.data));
   const assets = new Set<string>();
@@ -107,7 +108,7 @@ export async function getResolvers(
 
   // Add stylesheets. TODO Instead of hard-coding Source Serif Pro, parse the
   // page’s stylesheet to look for external imports.
-  stylesheets.add("https://fonts.googleapis.com/css2?family=Source+Serif+Pro:ital,wght@0,400;0,600;0,700;1,400;1,600;1,700&display=swap"); // prettier-ignore
+  if (googlefonts) stylesheets.add(googlefonts);
   if (page.style) stylesheets.add(page.style);
 
   // Collect directly-attached files, local imports, and static imports.

test/config-test.ts

@@ -38,6 +38,8 @@ describe("readConfig(undefined, root)", () => {
       header: "",
       footer:
         'Built with <a href="https://observablehq.com/" target="_blank">Observable</a> on <a title="2024-01-10T16:00:00">Jan 10, 2024</a>.',
+      googlefonts:
+        "https://fonts.googleapis.com/css2?family=Source+Serif+Pro:ital,wght@0,400;0,600;0,700;1,400;1,600;1,700&display=swap",
       search: null,
       watchPath: resolve("test/input/build/config/observablehq.config.js")
     });
@@ -62,6 +64,8 @@ describe("readConfig(undefined, root)", () => {
       header: "",
       footer:
         'Built with <a href="https://observablehq.com/" target="_blank">Observable</a> on <a title="2024-01-10T16:00:00">Jan 10, 2024</a>.',
+      googlefonts:
+        "https://fonts.googleapis.com/css2?family=Source+Serif+Pro:ital,wght@0,400;0,600;0,700;1,400;1,600;1,700&display=swap",
       search: null,
       watchPath: undefined
     });