Fix parent/child warnings (gatsbyjs#84)

The parent child warnings described in gatsbyjs#83 were the result of us
trying to stuff fileNode into Mdx graphql types. As it turns out, this
is not necessary because you can query the parent using fragments
which more accurately reflect the existence or non-existence of parent
types. This also means you could query the base contentful/remote CMS
types when trying to add slug fields, etc.

Additionally, we unified the code paths that create nodes for all
sources and transformers. Since we now use the public APIs, we can
have more confidence that people can do everything we can in core when
creating new content types.

packages/gatsby-plugin-mdx/on-create-node.js

@@ -1,74 +1,43 @@
-const crypto = require("crypto");
+const { isFunction } = require("lodash");
+const debug = require("debug")("gatsby-mdx:on-create-node");
+
 const defaultOptions = require("./utils/default-options");
-const mdx = require("./utils/mdx");
-const extractExports = require("./utils/extract-exports");
 const createMDXNode = require("./utils/create-mdx-node");
 
 module.exports = async (
   { node, getNode, loadNodeContent, actions, createNodeId },
   pluginOptions
 ) => {
-  const { extensions, ...options } = defaultOptions(pluginOptions);
-  const { createNode, createParentChildLink } = actions;
+  const options = defaultOptions(pluginOptions);
 
+  /**
+   * transformerOptions can be a function or a {transformer, filter} object
+   */
   if (Object.keys(options.transformers).includes(node.internal.type)) {
-    createMDXNode(
-      {
-        node,
-        transform: options.transformers[node.internal.type],
-        createNode,
-        getNode,
-        createNodeId
-      },
-      actions,
-      pluginOptions
+    const transformerOptions = options.transformers[node.internal.type];
+    const transformerFn = isFunction(transformerOptions)
+      ? transformerOptions
+      : transformerOptions.transformer;
+    const filterFn = transformerOptions ? transformerOptions.filter : undefined;
+    debug(
+      `${node.internal.type} has transformerFn ${isFunction(transformerFn)}`
     );
-  }
-  // We only care about markdown content.
-  // replace with mediaType when mime-db is merged
-  //    node.internal.mediaType !== `text/mdx`
-  if (!extensions.includes(node.ext)) {
-    return;
-  }
-
-  const nodeContent = await loadNodeContent(node);
-  const code = await mdx(nodeContent, options);
-
-  // extract all the exports
-  const { frontmatter, ...nodeExports } = extractExports(code);
-
-  const mdxNode = {
-    id: createNodeId(`${node.id} >>> Mdx`),
-    children: [],
-    parent: node.id,
-    internal: {
-      content: nodeContent,
-      type: `Mdx`
+    debug(`${node.internal.type} has filterFn ${isFunction(filterFn)}`);
+    if (transformerFn) {
+      if ((isFunction(filterFn) && filterFn({ node })) || !filterFn) {
+        debug(`processing node ${node.id}`);
+        await createMDXNode(
+          {
+            createNodeId,
+            getNode,
+            loadNodeContent,
+            node,
+            transform: transformerFn
+          },
+          actions,
+          { __internalMdxTypeName: "Mdx", ...pluginOptions }
+        );
+      }
     }
-  };
-
-  mdxNode.frontmatter = {
-    title: ``, // always include a title
-    ...frontmatter,
-    _PARENT: node.id
-  };
-
-  mdxNode.excerpt = frontmatter.excerpt;
-  mdxNode.exports = nodeExports;
-  mdxNode.rawBody = nodeContent;
-
-  // Add path to the markdown file path
-  if (node.internal.type === `File`) {
-    mdxNode.fileAbsolutePath = node.absolutePath;
-    mdxNode.relativePath = node.relativePath;
-    mdxNode.fileNode = node;
   }
-
-  mdxNode.internal.contentDigest = crypto
-    .createHash(`md5`)
-    .update(JSON.stringify(mdxNode))
-    .digest(`hex`);
-
-  createNode(mdxNode);
-  createParentChildLink({ parent: node, child: mdxNode });
 };

packages/gatsby-plugin-mdx/utils/create-mdx-node.js

@@ -1,26 +1,34 @@
 const crypto = require("crypto");
+const debug = require("debug")("gatsby-mdx:utils/create-mdx-node");
+
 const mdx = require("./mdx");
 const extractExports = require("./extract-exports");
 
 module.exports = async (
-  { node, transform, getNode, createNodeId },
+  { node, transform, loadNodeContent, getNode, createNodeId },
   { createNode, createParentChildLink },
-  options
+  { __internalMdxTypeName, ...options }
 ) => {
-  const { meta, content: nodeContent } = transform({ node, getNode });
+  const nodeType = __internalMdxTypeName || `${node.internal.type}Mdx`;
+  debug(`creating node for nodeType \`${nodeType}\``);
+  const { meta, content: nodeContent } = await transform({
+    node,
+    getNode,
+    loadNodeContent
+  });
 
   const code = await mdx(nodeContent, options);
 
   // extract all the exports
   const { frontmatter, ...nodeExports } = extractExports(code);
 
   const mdxNode = {
-    id: createNodeId(`${node.id} >>> ${node.internal.type}Mdx`),
+    id: createNodeId(`${node.id} >>> ${nodeType}`),
     children: [],
     parent: node.id,
     internal: {
       content: nodeContent,
-      type: `${node.internal.type}Mdx`
+      type: nodeType
     }
   };
 

packages/gatsby-plugin-mdx/utils/default-options.js

@@ -19,6 +19,18 @@ module.exports = pluginOptions => {
     pluginOptions
   );
 
+  // ensure File transformer is always ours
+  options.transformers.File = {
+    transformer: async ({ loadNodeContent, node }) => {
+      const mdxContent = await loadNodeContent(node);
+      return { meta: undefined, content: mdxContent };
+    },
+    // We only care about markdown content.
+    // replace with mediaType when mime-db is merged
+    //    node.internal.mediaType !== `text/mdx`
+    filter: ({ node }) => options.extensions.includes(node.ext)
+  };
+
   // support single layout set in the `defaultLayouts` option
   if (options.defaultLayouts && isString(options.defaultLayouts)) {
     options.defaultLayouts = {