[json-loader] Only log file events if we're past bootstrap (#4826)

* Don't emit new file node until previous is finished processing

This is an experiment to use
[xstate](http://davidkpiano.github.io/xstate/docs/#/) to setup state
machines to better handle complex state changes as we sometimes have.

Ideally this happens in core and then gatsby-source-filesystem
just has a simple queue and emits a new file node every time
the system returns to idle.

In a future refactor we'll do that plus refactor other parts of core
that should be handled in a state machine e.g. pages-query-runner.js

This PR also reinforced the need for us to implement
[tracing](https://github.com/jaegertracing/jaeger) in core / plugins
as that'd make it far far easier to understand what's happening and
when.

* Document state machine and remove extraneous Chokidar states

* Remove console.log

* Only log file events if we're past bootstrap

packages/gatsby-source-filesystem/src/gatsby-node.js

@@ -26,13 +26,20 @@ const fsMachine = Machine({
         CHOKIDAR_NOT_READY: {
           on: {
             CHOKIDAR_READY: "CHOKIDAR_WATCHING",
+            BOOTSTRAP_FINISHED: "CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED",
           },
         },
         CHOKIDAR_WATCHING: {
           on: {
+            BOOTSTRAP_FINISHED: "CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED",
             CHOKIDAR_READY: "CHOKIDAR_WATCHING",
           },
         },
+        CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED: {
+          on: {
+            CHOKIDAR_READY: "CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED",
+          },
+        },
       },
     },
     PROCESSING: {
@@ -152,20 +159,32 @@ See docs here - https://www.gatsbyjs.org/packages/gatsby-source-filesystem/
 
   watcher.on(`add`, path => {
     if (currentState.value.CHOKIDAR !== `CHOKIDAR_NOT_READY`) {
-      reporter.info(`added file at ${path}`)
+      if (
+        currentState.value.CHOKIDAR === `CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED`
+      ) {
+        reporter.info(`added file at ${path}`)
+      }
       createAndProcessNode(path).catch(err => reporter.error(err))
     } else {
       pathQueue.push(path)
     }
   })
 
   watcher.on(`change`, path => {
-    reporter.info(`changed file at ${path}`)
+    if (
+      currentState.value.CHOKIDAR === `CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED`
+    ) {
+      reporter.info(`changed file at ${path}`)
+    }
     createAndProcessNode(path).catch(err => reporter.error(err))
   })
 
   watcher.on(`unlink`, path => {
-    reporter.info(`file deleted at ${path}`)
+    if (
+      currentState.value.CHOKIDAR === `CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED`
+    ) {
+      reporter.info(`file deleted at ${path}`)
+    }
     const node = getNode(createNodeId(path))
     // It's possible the file node was never created as sometimes tools will
     // write and then immediately delete temporary files to the file system.
@@ -177,15 +196,23 @@ See docs here - https://www.gatsbyjs.org/packages/gatsby-source-filesystem/
 
   watcher.on(`addDir`, path => {
     if (currentState.value.CHOKIDAR !== `CHOKIDAR_NOT_READY`) {
-      reporter.info(`added directory at ${path}`)
+      if (
+        currentState.value.CHOKIDAR === `CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED`
+      ) {
+        reporter.info(`added directory at ${path}`)
+      }
       createAndProcessNode(path).catch(err => reporter.error(err))
     } else {
       pathQueue.push(path)
     }
   })
 
   watcher.on(`unlinkDir`, path => {
-    reporter.info(`directory deleted at ${path}`)
+    if (
+      currentState.value.CHOKIDAR === `CHOKIDAR_WATCHING_BOOTSTRAP_FINISHED`
+    ) {
+      reporter.info(`directory deleted at ${path}`)
+    }
     const node = getNode(createNodeId(path))
     deleteNode(node.id, node)
   })