perf(gatsby): Shortcut trivial queries by id

While there is a check for queries by `id`, this one circumvents a few more steps. It prevents having to build up an array based on type. Instead, if it sees a query by `id`, it will immediately just fetch that node directly.

This makes many sites that use plain queries by id a helluvalot faster. One site that made me look into this problem went down from 4.5 hours to about 5 minutes.

packages/gatsby/src/redux/nodes.js

@@ -103,6 +103,34 @@ exports.saveResolvedNodes = async (nodeTypeNames, resolver) => {
   }
 }
 
+/**
+ * Get node and save path dependency.
+ *
+ * @param {string} typeName
+ * @param {string} id
+ * @returns {Object|void} node
+ */
+const getResolvedNode = (typeName, id) => {
+  const { nodesByType, resolvedNodesCache } = store.getState()
+  const nodes /*: Map<mixed> */ = nodesByType.get(typeName)
+
+  if (!nodes) return undefined
+
+  let node = nodes.get(id)
+
+  if (!node) return undefined
+
+  const resolvedNodes = resolvedNodesCache.get(typeName)
+
+  if (resolvedNodes) {
+    node.__gatsby_resolved = resolvedNodes.get(id)
+  }
+
+  return node
+}
+
+exports.getResolvedNode = getResolvedNode
+
 const addResolvedNodes = (typeName, arr) => {
   const { nodesByType, resolvedNodesCache } = store.getState()
   const nodes /*: Map<mixed> */ = nodesByType.get(typeName)

packages/gatsby/src/redux/run-sift.js

@@ -86,7 +86,7 @@ function handleMany(siftArgs, nodes, sort, resolvedFields) {
   if (!result || !result.length) return null
 
   // Sort results.
-  if (sort) {
+  if (sort && result.length > 1) {
     // create functions that return the item to compare on
     const dottedFields = objectToDottedField(resolvedFields)
     const dottedFieldKeys = Object.keys(dottedFields)
@@ -123,9 +123,24 @@ function handleMany(siftArgs, nodes, sort, resolvedFields) {
  *   if `firstOnly` is true
  */
 const runSift = (args: Object) => {
-  const { getNode, addResolvedNodes } = require(`./nodes`)
+  const { getNode, addResolvedNodes, getResolvedNode } = require(`./nodes`)
 
   const { nodeTypeNames } = args
+  if (
+    args.queryArgs?.filter &&
+    Object.getOwnPropertyNames(args.queryArgs.filter).length === 1 &&
+    typeof args.queryArgs.filter?.id?.eq === `string`
+  ) {
+    // The args have an id.eq which subsumes all other queries
+    // Since the id of every node is unique there can only ever be one node found this way. Find it and return it.
+    let id = args.queryArgs.filter.id.eq
+    let node = undefined
+    nodeTypeNames.some(typeName => {
+      node = getResolvedNode(typeName, id)
+      return !!node
+    })
+    if (node) return [node]
+  }
 
   let nodes = []