error handling

Author: Laurie Barth

packages/gatsby-plugin-theme-ui/gatsby-node.js

@@ -4,10 +4,25 @@ exports.onPreInit = (__, options) => {
         options.themeModulePath = require(themeModulePath)
     }
     if(prismPreset) {
-      options.prismPreset = require(`@theme-ui/prism/presets/${prismPreset}.json`)
+      try {
+        options.prismPreset = require(`@theme-ui/prism/presets/${prismPreset}.json`)
+      } catch {
+        reporter.error(`It appears the prism dependency is not installed. Try running \`${generateInstallInstructions()} @theme-ui/prism\``)
+      }
     }
 }
 
+function generateInstallInstructions() {
+  const { getConfigStore } = require(`gatsby-core-utils`)
+
+  const packageMangerConfigKey = `cli.packageManager`
+  const PACKAGE_MANGER = getConfigStore().get(packageMangerConfigKey) || `yarn`
+
+  const installKeyWord = PACKAGE_MANGER === `yarn` ? "add" : "install"
+
+  return `${PACKAGE_MANGER} ${installKeyWord}`
+}
+
 exports.createSchemaCustomization = ({ actions }) => {
     const { createTypes } = actions
 

packages/gatsby-plugin-theme-ui/package.json

@@ -7,7 +7,8 @@
   "peerDependencies": {
     "gatsby": "^2.13.1",
     "theme-ui": "^0.3.0",
-    "@theme-ui/prism": "0.3.0"
+    "@theme-ui/prism": "0.3.0",
+    "gatsby-core-utils": "^1.2.0"
   },
   "keywords": [
     "gatsby",