Support 500 pages in the dev server (#131)

* Support 500 pages

* Document custom 400/500 pages

* Remove search from any pages not the 500 page

* fix(kitchen-sink): add snowpack.config.js

* fix(examples): add snowpack.config.js

* style: redesign built-in 500 page

Co-authored-by: Nate Moore <nate@skypack.dev>

12 files changed, 233 insertions, 15 deletions

diff --git a/README.md b/README.md
index eb55208eb..7b3c6257e 100644
--- a/README.md
+++ b/README.md
@@ -210,9 +210,18 @@ Now upload the contents of `/_site_` to your favorite static site host.
 
 👉 [**Full API Reference**][docs-api]
 
+## 👩🏽‍💻 CLI
+
+👉 [**Command Line Docs**][docs-cli]
+
+## 🏗 Development Server
+
+👉 [**Dev Server Docs**][docs-dev]
+
 [config]: #%EF%B8%8F-configuration
 [docs-api]: ./docs/api.md
 [docs-collections]: ./docs/collections.md
+[docs-dev]: ./docs/dev.md
 [docs-styling]: ./docs/styling.md
 [example-blog]: ./examples/blog
 [fetch-content]: ./docs/api.md#fetchcontent
@@ -220,3 +229,4 @@ Now upload the contents of `/_site_` to your favorite static site host.
 [mdn-io]: https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API
 [mdn-ric]: https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback
 [routing]: #-routing
+[docs-cli]: ./docs/cli.md
diff --git a/docs/cli.md b/docs/cli.md
index c413323d5..67f0ae631 100644
--- a/docs/cli.md
+++ b/docs/cli.md
@@ -34,6 +34,8 @@ Print the help message and exit.
 
 Runs the Astro development server. This starts an HTTP server that responds to requests for pages stored in `astro/pages` (or which folder is specified in your [configuration](../README.md##%EF%B8%8F-configuration)).
 
+See the [dev server](./dev.md) docs for more information on how the dev server works.
+
 __Flags__
 
 ##### `--port`
diff --git a/docs/dev.md b/docs/dev.md
new file mode 100644
index 000000000..7b811d7d3
--- /dev/null
+++ b/docs/dev.md
@@ -0,0 +1,51 @@
+# Development Server
+
+The development server comes as part of the Astro CLI. Start the server with:
+
+```shell
+astro dev
+```
+
+In your project root. You can specify an alternative
+
+## Special routes
+
+The dev server will serve the following special routes:
+
+### /400
+
+This is a custom __400__ status code page. You can add this route by adding a page component to your `astro/pages` folder:
+
+```
+├── astro/
+│   ├── components/
+│   └── pages/
+│       └── 400.astro
+```
+
+For any URL you visit that doesn't have a corresponding page, the `400.astro` file will be used.
+
+### /500
+
+This is a custom __500__ status code page. You can add this route by adding a page component to your `astro/pages` folder:
+
+```astro
+├── astro/
+│   ├── components/
+│   └── pages/
+│       └── 500.astro
+```
+
+This page is used any time an error occurs in the dev server.
+
+The 500 page will receive an `error` query parameter which you can access with:
+
+```
+---
+const error = import.meta.request.url.searchParams.get('error');
+---
+
+<strong>{error}</strong>
+```
+
+A default error page is included with Astro so you will get pretty error messages even without adding a custom 500 page.
\ No newline at end of file
diff --git a/examples/blog/snowpack.config.js b/examples/blog/snowpack.config.js
new file mode 100644
index 000000000..5a800b10f
--- /dev/null
+++ b/examples/blog/snowpack.config.js
@@ -0,0 +1,3 @@
+module.exports = {
+  workspaceRoot: '../../'
+};
diff --git a/examples/kitchen-sink/snowpack.config.js b/examples/kitchen-sink/snowpack.config.js
new file mode 100644
index 000000000..5a800b10f
--- /dev/null
+++ b/examples/kitchen-sink/snowpack.config.js
@@ -0,0 +1,3 @@
+module.exports = {
+  workspaceRoot: '../../'
+};
diff --git a/examples/snowpack/package-lock.json b/examples/snowpack/package-lock.json
index b802bc687..22de83842 100644
--- a/examples/snowpack/package-lock.json
+++ b/examples/snowpack/package-lock.json
@@ -975,6 +975,7 @@
     "astro": {
       "version": "file:../..",
       "requires": {
+        "@babel/code-frame": "^7.12.13",
         "@babel/generator": "^7.13.9",
         "@babel/parser": "^7.13.15",
         "@babel/traverse": "^7.13.15",
diff --git a/examples/tailwindcss/snowpack.config.js b/examples/tailwindcss/snowpack.config.js
new file mode 100644
index 000000000..5a800b10f
--- /dev/null
+++ b/examples/tailwindcss/snowpack.config.js
@@ -0,0 +1,3 @@
+module.exports = {
+  workspaceRoot: '../../'
+};
diff --git a/package.json b/package.json
index dbb929b3e..f8a489571 100644
--- a/package.json
+++ b/package.json
@@ -22,7 +22,7 @@
   ],
   "scripts": {
     "build": "npm run build:core && npm run build:parser",
-    "build:core": "tsc -p tsconfig.json",
+    "build:core": "tsc -p tsconfig.json && cp src/frontend/500.astro lib/frontend/500.astro",
     "build:parser": "tsc -p tsconfig.parser.json",
     "postbuild:parser": "echo '{ \"type\": \"commonjs\" }' > parser/package.json",
     "dev": "tsc --watch",
diff --git a/src/dev.ts b/src/dev.ts
index 505a99425..4ca8e28e9 100644
--- a/src/dev.ts
+++ b/src/dev.ts
@@ -72,7 +72,17 @@ export default async function dev(astroConfig: AstroConfig) {
           }
         }
         res.statusCode = 500;
-        res.end(formatErrorForBrowser(result.error));
+
+        let errorResult = await runtime.load(`/500?error=${encodeURIComponent(result.error.stack || result.error.toString())}`);
+        if(errorResult.statusCode === 200) {
+          if (errorResult.contentType) {
+            res.setHeader('Content-Type', errorResult.contentType);
+          }
+          res.write(errorResult.contents);
+        } else {
+          res.write(result.error.toString());
+        }
+        res.end();
         break;
       }
     }
@@ -85,9 +95,3 @@ export default async function dev(astroConfig: AstroConfig) {
     info(logging, 'dev server', `${green('Local:')} http://${hostname}:${port}/`);
   });
 }
-
-/** Format error message */
-function formatErrorForBrowser(err: Error) {
-  // TODO make this pretty.
-  return err.toString();
-}
diff --git a/src/frontend/500.astro b/src/frontend/500.astro
new file mode 100644
index 000000000..af7b901e9
--- /dev/null
+++ b/src/frontend/500.astro
@@ -0,0 +1,128 @@
+---
+import Prism from 'astro/components/Prism.astro';
+let title = 'Uh oh...';
+
+const error = import.meta.request.url.searchParams.get('error');
+---
+
+<!doctype html>
+<html lang="en">
+  <head>
+    <title>Error 500</title>
+    <link rel="preconnect"href="https://fonts.gstatic.com">
+    <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=IBM+Plex+Mono&family=IBM+Plex+Sans&display=swap">
+    <link rel="stylesheet" href="http://cdn.skypack.dev/prism-themes/themes/prism-material-dark.css">
+
+    <style>
+      * {
+        box-sizing: border-box;
+        margin: 0;
+      }
+
+      :global(:root) {
+        --font-sans: "IBM Plex Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
+        --font-mono: "IBM Plex Mono", Consolas, "Andale Mono WT", "Andale Mono",
+            "Lucida Console", "Lucida Sans Typewriter", "DejaVu Sans Mono",
+            "Bitstream Vera Sans Mono", "Liberation Mono", "Nimbus Mono L", Monaco,
+            "Courier New", Courier, monospace;
+        --color-gray-800: #1F2937;
+        --color-gray-500: #6B7280;
+        --color-gray-400: #9CA3AF;
+        --color-gray-100: #F3F4F6;
+        --color-red: #FF1639;
+      }
+
+      html, body {
+        width: 100vw;
+        height: 100%;
+        min-height: 100vh;
+
+        font-family: var(--font-sans);
+        font-weight: 400;
+        background: var(--color-gray-100);
+        text-align: center;
+      }
+
+      body {
+        display: grid;
+        place-content: center;
+      }
+
+      header {
+        display: flex;
+        flex-direction: column;
+        align-items: center;
+        font-family: var(--font-sans);
+        font-size: 2.5rem;
+        font-size: clamp(24px, calc(2vw + 1rem), 2.5rem);
+      }
+
+      header h1 {
+        margin: 0.25em;
+        margin-right: 0;
+        font-weight: 400;
+        letter-spacing: -2px;
+        line-height: 1;
+      }
+
+      header h1 .title {
+        color: var(--color-gray-400);
+        white-space: nowrap;
+      }
+
+      header svg {
+        margin-bottom: -0.125em;
+        color: var(--color-red);
+      }
+
+      p {
+        font-size: 1.75rem;
+        font-size: clamp(14px, calc(2vw + 0.5rem), 1.75rem);
+        flex: 1;
+      }
+
+      .error-message {
+        display: grid;
+        justify-content: center;
+        margin-top: 4rem;
+      }
+
+      .error-message :global(code[class*="language-"]) {
+        background: var(--color-gray-800);
+      }
+      .error-message :global(pre) {
+        margin: 0;
+        font-family: var(--font-mono);
+        font-size: 0.85rem;
+        background: var(--color-gray-800);
+        border-radius: 8px;
+      }
+
+      .error-message :global(.token.punctuation) {
+        color: var(--color-gray-400);
+      }
+
+      .error-message :global(.token.operator) {
+        color: var(--color-gray-400);
+      }
+    </style>
+  </head>
+  <body>
+    <main>
+      <header>
+        <svg xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24" stroke="currentColor" width="1.75em" height="1.75em">
+          <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M12 9v2m0 4h.01m-6.938 4h13.856c1.54 0 2.502-1.667 1.732-3L13.732 4c-.77-1.333-2.694-1.333-3.464 0L3.34 16c-.77 1.333.192 3 1.732 3z" />
+        </svg>
+        <h1><span class="error">500 Error </span><span class="title">{title}</span></h1>
+      </header>
+
+      <article>
+        <p>Astro had some trouble loading this page.</p>
+
+        <div class="error-message">
+          <Prism lang="shell" code={error} />
+        </div>
+      </article>
+    </main>
+  </body>
+</html>
diff --git a/src/runtime.ts b/src/runtime.ts
index 330ca013b..a394d93c4 100644
--- a/src/runtime.ts
+++ b/src/runtime.ts
@@ -195,11 +195,20 @@ async function load(config: RuntimeConfig, rawPathname: string | undefined): Pro
       collection.data = data;
     }
 
+    const requestURL = new URL(fullurl.toString());
+
+    // For first release query params are not passed to components.
+    // An exception is made for dev server specific routes.
+    if(reqPath !== '/500') {
+      requestURL.search = '';
+    }
+
     let html = (await mod.exports.__renderPage({
       request: {
         host: fullurl.hostname,
         path: fullurl.pathname,
         href: fullurl.toString(),
+        url: requestURL
       },
       children: [],
       props: { collection },
diff --git a/src/search.ts b/src/search.ts
index d4ed73f96..c141e4a77 100644
--- a/src/search.ts
+++ b/src/search.ts
@@ -91,6 +91,17 @@ export function searchForPage(url: URL, astroRoot: URL): SearchResult {
     }
   }
 
+  if(reqPath === '/500') {
+    return {
+      statusCode: 200,
+      location: {
+        fileURL: new URL('./frontend/500.astro', import.meta.url),
+        snowpackURL: `/_astro_internal/500.astro.js`
+      },
+      pathname: reqPath
+    };
+  }
+
   return {
     statusCode: 404,
   };
@@ -128,10 +139,3 @@ function loadCollection(url: string, astroRoot: URL): { currentPage?: number; lo
     }
   }
 }
-
-/** convert a value to a number, if possible */
-function maybeNum(val: string): string | number {
-  const num = parseFloat(val);
-  if (num.toString() === val) return num;
-  return val;
-}