Docs: document E044 and E045

Also, make sure BEL, BS, and DEL show up on the web page for E045.

Author: strager

docs/errors/E044.md

@@ -0,0 +1,26 @@
+# E044: unexpected characters in number literal
+
+```config-for-examples
+{
+  "globals": {
+    "pi": true
+  }
+}
+```
+
+Letters are allowed in number literals in certain situations, such as in
+`123n`, `1e6`, and `0xff`. It is an error to include other letters or letters in
+the wrong spot:
+
+    let gazillion = 10000000000000000000000000N;
+    let pi = 3.14l;
+    let tau = 2pi;
+
+To fix this error, use the correct letter or remove the extraneous letter:
+
+    let gazillion = 10000000000000000000000000n;
+    let pi = 3.14;
+
+Alternatively, use the `*` operator to multiply a variable by a number:
+
+    let tau = 2*pi;

docs/errors/E045.md

@@ -0,0 +1,14 @@
+# E045: unexpected control character
+
+JavaScript treats some Unicode control characters, such as newlines, tabs, and
+form feeds, as whitespace. Most other control characters are now allowed outside
+string literals and template literals:
+
+     
+
+To fix this error, delete the extra control characters, or put them inside a
+comment:
+
+    /*
+     
+    */

website/public/errors/index.ejs.html

@@ -47,16 +47,33 @@
         text-decoration: none;
       }
 
-      .unicode-bom:before {
-        content: "BOM";
+      .unicode-bom:before,
+      .unicode-bel:before,
+      .unicode-bs:before,
+      .unicode-del:before {
         background-color: #edbf66;
         border: 1px solid red;
         border-radius: 5px;
         padding: 1px 3px;
       }
+      .unicode-bom:before {
+        content: "BOM";
+      }
+      .unicode-bel:before {
+        content: "BEL";
+      }
+      .unicode-bs:before {
+        content: "BS";
+      }
+      .unicode-del:before {
+        content: "DEL";
+      }
 
       @media (prefers-color-scheme: dark) {
-        .unicode-bom:before {
+        .unicode-bom:before,
+        .unicode-bel:before,
+        .unicode-bs:before,
+        .unicode-del:before {
           background-color: #884444;
         }
       }

website/src/error-documentation.mjs

@@ -76,6 +76,8 @@ markdownParser.renderer.rules = {
       );
     }
 
+    codeHTML = wrapASCIIControlCharacters(codeHTML);
+
     env.codeBlockIndex += 1;
     return `<figure><pre><code>${codeHTML}</code></pre></figure>`;
   },
@@ -306,6 +308,18 @@ export async function loadErrorDocumentationFilesAsync(rootPath) {
 
 export class ProblemsError extends Error {}
 
+function wrapASCIIControlCharacters(html) {
+  let CONTROL_CHARACTER_TO_CSS_CLASS = {
+    "\u0007": "unicode-bel",
+    "\u0008": "unicode-bs",
+    "\u007f": "unicode-del",
+  };
+  return html.replace(/[\u0007\u0008\u007f]/g, (controlCharacter) => {
+    let cssClass = CONTROL_CHARACTER_TO_CSS_CLASS[controlCharacter];
+    return `<span class='${cssClass}'>${controlCharacter}</span>`;
+  });
+}
+
 // quick-lint-js finds bugs in JavaScript programs.
 // Copyright (C) 2020  Matthew "strager" Glazar
 //

website/test/test-error-documentation.mjs

@@ -172,6 +172,17 @@ wasn't that neat?
     );
   });
 
+  it("html wraps weird control characters", () => {
+    let doc = ErrorDocumentation.parseString(
+      "file.md",
+      "code:\n\n```\n" + "BEL:\u0007\n" + "BS:\u0008\n" + "DEL:\u007f\n" + "```"
+    );
+    let html = doc.toHTML();
+    expect(html).toContain("BEL:<span class='unicode-bel'>\u0007</span>");
+    expect(html).toContain("BS:<span class='unicode-bs'>\u0008</span>");
+    expect(html).toContain("DEL:<span class='unicode-del'>\u007f</span>");
+  });
+
   it("many possibilities of html code has bom", () => {
     const possibilities = [
       "<mark>\u{feff}hello</mark>",