Catch and exit if someone mistakenly puts their gatsby-config.js in t…

…he src directory fixes #2674

packages/gatsby/src/bootstrap/get-config-file.js

@@ -4,6 +4,7 @@ const fs = require(`fs-extra`)
 const testRequireError = require(`../utils/test-require-error`)
 const report = require(`gatsby-cli/lib/reporter`)
 const chalk = require(`chalk`)
+const path = require(`path`)
 
 function isNearMatch(
   fileName: string,
@@ -18,7 +19,7 @@ module.exports = async function getConfigFile(
   configName: string,
   distance: number = 3
 ) {
-  const configPath = `${rootDir}/${configName}`
+  const configPath = path.join(rootDir, configName)
   let configModule
   try {
     configModule = require(configPath)
@@ -41,6 +42,13 @@ module.exports = async function getConfigFile(
       )
       console.log(``)
       process.exit(1)
+    } else if (fs.existsSync(path.join(rootDir, `src`, configName))) {
+      console.log(``)
+      report.error(
+        `Your gatsby-config.js file is in the wrong place. You've placed in the src/ directory. It must instead be at the root of your site next to your package.json file.`
+      )
+      console.log(``)
+      process.exit(1)
     }
   }