Custom rule to identify unused goog.require() calls

package.json

@@ -35,6 +35,7 @@
     "browserify": "13.1.0",
     "closure-util": "1.15.0",
     "derequire": "2.0.3",
+    "eslint-plugin-openlayers-internal": "file:test/rules",
     "fs-extra": "0.30.0",
     "glob": "7.0.5",
     "handlebars": "4.0.5",
@@ -82,6 +83,9 @@
       "goog": false,
       "proj4": false
     },
+    "plugins": [
+      "openlayers-internal"
+    ],
     "rules": {
       "no-console": [
         2,
@@ -91,7 +95,8 @@
           ]
         }
       ],
-      "no-constant-condition": 0
+      "no-constant-condition": 0,
+      "openlayers-internal/no-unused-requires": 2
     }
   },
   "ext": [

test/rules/.eslintrc

@@ -0,0 +1,5 @@
+{
+  "env": {
+    "es6": true
+  }
+}

test/rules/index.js

@@ -0,0 +1,5 @@
+module.exports = {
+  rules: {
+    'no-unused-requires': require('./no-unused-requires').rule
+  }
+};

test/rules/no-unused-requires.js

@@ -0,0 +1,100 @@
+function isGoogRequire(node) {
+  const callee = node.callee;
+  return callee.type === 'MemberExpression' &&
+      callee.object.type === 'Identifier' && callee.object.name === 'goog' &&
+      callee.property.type === 'Identifier' && !callee.property.computed && callee.property.name === 'require';
+}
+
+function getName(node) {
+  if (node.type !== 'MemberExpression') {
+    return;
+  }
+  if (node.property.type !== 'Identifier' || node.property.computed) {
+    return;
+  }
+  let objectName;
+  if (node.object.type === 'Identifier' && !node.object.computed) {
+    objectName = node.object.name;
+  } else if (node.object.type === 'MemberExpression' && !node.object.computed) {
+    objectName = getName(node.object);
+  }
+  if (!objectName) {
+    return;
+  }
+  return `${objectName}.${node.property.name}`;
+}
+
+exports.rule = {
+  meta: {
+    docs: {
+      description: 'disallow unused goog.require() calls'
+    },
+    schema: []
+  },
+  create: function(context) {
+
+    // a lookup of goog.require() nodes by argument
+    const requireNodes = {};
+
+    // used names from member expressions that match the goog.require() arg
+    const usedNames = {};
+
+    return {
+
+      CallExpression: function(node) {
+
+        if (isGoogRequire(node)) {
+          if (node.arguments.length !== 1) {
+            return context.report(node, 'Expected one argument for goog.require()');
+          }
+          const arg = node.arguments[0];
+          if (arg.type !== 'Literal' || !arg.value || typeof arg.value !== 'string') {
+            return context.report(node, 'Expected goog.require() to be called with a string');
+          }
+          const name = arg.value;
+          if (name in requireNodes) {
+            return context.report(node, `Duplicate goog.require('${name}')`);
+          }
+          requireNodes[name] = node;
+        }
+
+      },
+
+      MemberExpression: function(node) {
+        const name = getName(node);
+        if (name in requireNodes) {
+          const requiredAncestor = context.getAncestors().some(ancestorNode => !!requireNodes[getName(ancestorNode)]);
+          if (!requiredAncestor) {
+            usedNames[name] = true;
+          }
+        }
+      },
+
+      Identifier: function(node) {
+        const name = node.name;
+        if (name in requireNodes) {
+          const ancestors = context.getAncestors();
+          if (ancestors.length && ancestors[0].type === 'MemberExpression') {
+            const requiredAncestor = context.getAncestors().some(ancestorNode => !!requireNodes[getName(ancestorNode)]);
+            if (!requiredAncestor) {
+              usedNames[name] = true;
+            }
+          } else {
+            usedNames[name] = true;
+          }
+        }
+      },
+
+      'Program:exit': function(node) {
+        const source = context.getSourceCode();
+        for (let name in requireNodes) {
+          if (!usedNames[name]) {
+            const unusedRequire = requireNodes[name];
+            context.report(unusedRequire, `Unused ${source.getText(unusedRequire)}`);
+          }
+        }
+      }
+
+    };
+  }
+};

test/rules/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "eslint-plugin-openlayers-internal",
+  "version": "1.0.0",
+  "description": "Custom ESLint rules for the OpenLayers project",
+  "main": "index.js"
+}