Add visual indicator to lexical errors in code snippets

src/components/Code.astro

@@ -1,10 +1,17 @@
 ---
 import { native_highlighter } from "../lexer/highlighter";
+import CodeError from "./docs/CodeError.astro";
 
 const { thpcode } = Astro.props;
 
-const native_html = await native_highlighter(thpcode);
+const [native_html, error_message] = await native_highlighter(thpcode);
 ---
 
 <pre
-    class="language-thp"><code class="language-thp" set:html={native_html} /><span class="absolute top-2 right-2 inline-block text-sm select-none opacity-75">thp</span></pre>
+    class="language-thp"><code class="language-thp" set:html={native_html} /><span class="absolute top-2 right-2 inline-block text-sm select-none opacity-75">thp
+    </span></pre>
+{
+    error_message !== null && (
+        <CodeError error_type="Lexical">{error_message}</CodeError>
+    )
+}

src/components/docs/CodeError.astro

@@ -0,0 +1,8 @@
+---
+const { error_type = "Unknown" } = Astro.props;
+---
+
+<div class="px-4 py-2 rounded bg-red-200 dark:bg-red-950">
+    <span class="inline-block font-bold">{error_type} error:</span>
+    <slot />
+</div>

src/lexer/highlighter.ts

@@ -45,13 +45,13 @@ export interface LexError {
 }
 
 
-export async function native_highlighter(code: string): Promise<string> {
+export async function native_highlighter(code: string): Promise<[string, string | null]> {
     let formatted_code = leftTrimDedent(code).join("\n");
 
     const result = await native_lex(formatted_code);
 
     if (result.Err) {
-        throw new Error(JSON.stringify(result.Err.Lex) + "\n" + code);
+        return lex_error_highlighter(formatted_code, result.Err!.Lex);
     }
 
     const tokens = result.Ok!;
@@ -82,7 +82,27 @@ export async function native_highlighter(code: string): Promise<string> {
         current_pos = token_end;
     }
 
-    return output;
+    return [output, null];
+}
+
+
+/**
+ * Highlights code that has a lexic error
+ */
+function lex_error_highlighter(code: string, error: LexError): [string, string] {
+    // Create a single error token
+
+    const err_pos = error.position;
+    const before_err = code.substring(0, err_pos);
+    const err_str = code[err_pos];
+    const after_err = code.substring(err_pos + 1);
+
+    const token = `<span class="token underline decoration-wavy decoration-red-500">${err_str}</span>`;
+
+    const all = `${before_err}${token}${after_err}`;
+
+    // TODO: Transform absolute posijion (error.position) into line:column
+    return [all, error.reason + " at position " + error.position]
 }
 
 function translate_token_type(tt: TokenType, value: string): string {

src/pages/learn/classes/readonly.mdx

@@ -5,3 +5,11 @@ title: Readonly
 import Code from "../../../components/Code.astro"
 
 # Readonly
+
+<Code thpcode={`
+class Caño
+{
+}
+`} />
+
+

src/pages/learn/templating/control-flow.mdx

@@ -57,11 +57,11 @@ fun UserDetail(User user) -> HTML
 {
     <div>
         @match user.type
-        case ::Admin
+        @case ::Admin
         {
             <button>Delete resource</button>
         }
-        case ::User
+        @case ::User
         {
             <button disable>Not allowed</button>
         }