build: Add eslint rules for React hooks

These make components with simple state (only a few variables) easier to
read and maintain. See https://reactjs.org/docs/hooks-intro.html for
details. Hook are available since React 16.8, and we already depend on 16.10.

We don't have any hooks yet in our code. This enables the ESLint plugin
to guide us right from the start.

.eslintrc.json

@@ -13,7 +13,7 @@
         },
         "sourceType": "module"
     },
-    "plugins": ["flowtype", "react", "cockpit", "jsx-a11y"],
+    "plugins": ["flowtype", "react", "react-hooks", "cockpit", "jsx-a11y"],
     "rules": {
         "indent": ["error", 4,
             {
@@ -28,6 +28,9 @@
         "react/jsx-indent": ["error", 4],
         "semi": ["error", "always", { "omitLastInOneLineBlock": true }],
 
+        "react-hooks/rules-of-hooks": "error",
+        "react-hooks/exhaustive-deps": "error",
+
         "camelcase": "off",
         "comma-dangle": "off",
         "curly": "off",

package.json

@@ -55,11 +55,12 @@
     "eslint-plugin-cockpit": "file:eslint-plugin-cockpit",
     "eslint-plugin-flowtype": "^4.2.0",
     "eslint-plugin-import": "^2.18.2",
+    "eslint-plugin-jsx-a11y": "^6.2.3",
     "eslint-plugin-node": "^9.1.0",
     "eslint-plugin-promise": "^4.2.1",
     "eslint-plugin-react": "^7.15.1",
+    "eslint-plugin-react-hooks": "^2.1.2",
     "eslint-plugin-standard": "^4.0.1",
-    "eslint-plugin-jsx-a11y": "^6.2.3",
     "html-webpack-plugin": "^3.2.0",
     "htmlparser": "^1.7.7",
     "imports-loader": "^0.6.5",