fix: pass path to MDX file for remark plugins

Author: axe312ger

packages/gatsby-plugin-mdx/src/compile-mdx.ts

@@ -1,13 +1,13 @@
 import type { ProcessorOptions } from "@mdx-js/mdx"
-
-import { Node } from "gatsby"
+import type { IFileNode, IMdxNode } from "./types"
 
 // Compiles MDX into JS
 // This could be replaced by @mdx-js/mdx if MDX compile would
 // accept custom data passed to the unified pipeline via processor.data()
 export default async function compileMDX(
   source: string,
-  mdxNode: Node,
+  mdxNode: IMdxNode,
+  fileNode: IFileNode,
   options: ProcessorOptions
 ): Promise<string> {
   const { createProcessor } = await import(`@mdx-js/mdx`)
@@ -18,11 +18,9 @@ export default async function compileMDX(
   // If we could pass this via MDX loader config, this whole custom loader might be obsolete.
   processor.data(`mdxNode`, mdxNode)
 
-  console.dir(`@todo add path`, { mdxNode })
-
   const result = await processor.process(
     // Inject path to original file for remark plugins. See: https://github.com/gatsbyjs/gatsby/issues/26914
-    new VFile({ value: source, path: `/at/todo/foo.mdx` })
+    new VFile({ value: source, path: fileNode.absolutePath })
   )
 
   return result.toString()

packages/gatsby-plugin-mdx/src/gatsby-mdx-loader.ts

@@ -23,18 +23,9 @@ const gatsbyMDXLoader: LoaderDefinition = async function (source) {
     return source
   }
 
-  const { mdxNode } = res
-
-  return compileMDX(
-    source,
-    mdxNode || {
-      id: ``,
-      children: [],
-      parent: ``,
-      internal: { contentDigest: ``, owner: ``, type: `` },
-    },
-    options
-  )
+  const { mdxNode, fileNode } = res
+
+  return compileMDX(source, mdxNode, fileNode, options)
 }
 
 export default gatsbyMDXLoader

packages/gatsby-plugin-mdx/src/gatsby-node.ts

@@ -133,6 +133,14 @@ export const preprocessSource: GatsbyNode["preprocessSource"] = async (
       parent: ``,
       internal: { contentDigest: ``, owner: ``, type: `` },
     },
+    {
+      id: ``,
+      children: [],
+      parent: ``,
+      internal: { contentDigest: ``, owner: ``, type: `` },
+      absolutePath: filename,
+      sourceInstanceName: `mocked`,
+    },
     mdxOptions
   )