Edit the absolute link linter

Allow JavaScript code as the value of the `href` attribute. This allows
us to import assets as MDX modules so we can refer to the asset paths in
HTML tags. Otherwise, the linter encounters a runtime exception and
fails even if there is a comment that ignores messages from the linter.

An example of the linter failing is gravitational/teleport#51193, which
imports a bot avatar logo as a module so users can download it.

server/lint-teleport-docs-links.test.ts

@@ -0,0 +1,48 @@
+import { describe, expect, test } from "@jest/globals";
+import { remarkLintTeleportDocsLinks } from "./lint-teleport-docs-links";
+import { VFile } from "vfile";
+import { remark } from "remark";
+import mdx from "remark-mdx";
+
+const getReasons = (value: string) => {
+  return remark()
+    .use(mdx as any)
+    .use(remarkLintTeleportDocsLinks as any)
+    .processSync(new VFile({ value, path: "mypath.mdx" }) as any)
+    .messages.map((m) => m.reason);
+};
+
+describe("server/lint-absolute-docs-links", () => {
+  interface testCase {
+    description: string;
+    input: string;
+    expected: Array<string>;
+  }
+
+  const testCases: Array<testCase> = [
+    {
+      description: "absolute docs path in a Markdown link href",
+      input: "This is a [link](https://goteleport.com/docs/installation)",
+      expected: [
+        "Link reference https://goteleport.com/docs/installation must be a relative link to an *.mdx page",
+      ],
+    },
+    {
+      description: "absolute docs path in an a tag",
+      input: "<a href='https://goteleport.com/docs/installation'>here</a>",
+      expected: [
+        "Component href https://goteleport.com/docs/installation must be a relative link to an *.mdx page",
+      ],
+    },
+    {
+      description: "JavaScript identifier as href value",
+      input:
+        "You can <a href={BotLogo} download>download</a> our avatar to set as your Bot Icon.",
+      expected: [],
+    },
+  ];
+
+  test.each(testCases)("$description", (tc) => {
+    expect(getReasons(tc.input)).toEqual(tc.expected);
+  });
+});

server/lint-teleport-docs-links.ts

@@ -24,6 +24,11 @@ const isMdxComponentWithHref = (node: Node): node is MdxAnyElement => {
 };
 
 const isAnAbsoluteDocsLink = (href: string): boolean => {
+  // The href is not a string value, and is likely an AST node object. Skip
+  // the absolute link check.
+  if (typeof href != "string") {
+    return false;
+  }
   return (
     href.startsWith("/docs") || href.startsWith("https://goteleport.com/docs")
   );
@@ -35,7 +40,9 @@ export const remarkLintTeleportDocsLinks = lintRule(
     visit(root, undefined, (node: Node) => {
       if (node.type == "link" && isAnAbsoluteDocsLink((node as Link).url)) {
         vfile.message(
-          `Link reference ${(node as Link).url} must be a relative link to an *.mdx page`,
+          `Link reference ${
+            (node as Link).url
+          } must be a relative link to an *.mdx page`,
           node.position
         );
         return;