feat(rules): add rule prefer-session-equals

closes #118

README.md

@@ -58,6 +58,7 @@ For a more thorough introduction, read the [setup guide](/docs/guides/setup.md).
 * [no-blaze-lifecycle-assignment](docs/rules/no-blaze-lifecycle-assignment.md): Prevent deprecated template lifecycle callback assignments
 * [no-zero-timeout](docs/rules/no-zero-timeout.md): Prevent usage of Meteor.setTimeout with zero delay
 * [blaze-consistent-eventmap-params](docs/rules/blaze-consistent-eventmap-params.md): Force consistent event handler parameters in event maps
+* [prefer-session-equals](docs/prefer-session-equals.md): Prefer `Session.equals` in conditions
 
 
 ## Core API

docs/rules/prefer-session-equals.md

@@ -0,0 +1,57 @@
+# Prefer `Session.equals` in conditions (prefer-session-equals)
+
+Using `Session.equals('foo', bar)` toggles fewer invalidations compared to `Session.get('foo') === bar`.
+
+
+## Rule Details
+
+While the above is only true for scalar types, this rule encourages use over `Session.equals` in all conditional statements.
+
+The following patterns are considered warnings:
+
+```js
+if (Session.get("foo")) {/* ... */}
+
+if (Session.get("foo") == bar) {/* ... */}
+
+if (Session.get("foo") === bar) {/* ... */}
+
+Session.get("foo") ? true : false
+
+Session.get("foo") === bar ? true : false
+```
+
+The following patterns are not warnings:
+
+```js
+if (Session.equals("foo", true)) {/* ... */}
+
+if (Session.equals("foo", 1)) {/* ... */}
+
+if (Session.equals("foo", "hello")) {/* ... */}
+
+if (Session.equals("foo", bar)) {/* ... */}
+
+if (_.isEqual(Session.get("foo"), otherValue)) {/* ... */}
+
+Session.equals("foo", true) ? true : false
+```
+
+```js
+const foo = Session.get("foo")
+if (foo === 'bar') {/* ... */}
+```
+
+## When Not To Use It
+
+Turn this rule off when you are comparing compound types, e.g. Arrays.
+
+
+## Further Reading
+
+- http://docs.meteor.com/#/full/session_equals
+
+
+## Possible Improvements
+
+* Track which variables were set through `Session.get` and warn when they are used in conditions

lib/index.js

@@ -5,6 +5,7 @@ module.exports = {
     'no-blaze-lifecycle-assignment': require('./rules/no-blaze-lifecycle-assignment'),
     'no-zero-timeout': require('./rules/no-zero-timeout'),
     'blaze-consistent-eventmap-params': require('./rules/blaze-consistent-eventmap-params'),
+    'prefer-session-equals': require('./rules/prefer-session-equals'),
   },
   configs: {
     parserOptions: {
@@ -19,6 +20,7 @@ module.exports = {
         'meteor/no-blaze-lifecycle-assignment': 2,
         'meteor/no-zero-timeout': 2,
         'meteor/blaze-consistent-eventmap-params': 2,
+        'meteor/prefer-session-equals': 0,
       },
     },
   },

lib/rules/prefer-session-equals.js

@@ -0,0 +1,68 @@
+/**
+ * @fileoverview Prefer Session.equals in conditions
+ * @author Dominik Ferber
+ * @copyright 2016 Dominik Ferber. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+
+
+const isSessionGetCallExpression = node => (
+  node.type === 'CallExpression' &&
+  node.callee.type === 'MemberExpression' &&
+  (
+    node.callee.type === 'MemberExpression' &&
+    node.callee.object.type === 'Identifier' && node.callee.object.name === 'Session' &&
+    (
+      (
+        !node.callee.computed &&
+        node.callee.property.type === 'Identifier' &&
+        node.callee.property.name === 'get'
+      ) ||
+      (
+        node.callee.computed &&
+        node.callee.property.type === 'Literal' &&
+        node.callee.property.value === 'get'
+      )
+    )
+  )
+)
+
+
+// -----------------------------------------------------------------------------
+// Rule Definition
+// -----------------------------------------------------------------------------
+module.exports = context => {
+  // ---------------------------------------------------------------------------
+  // Helpers
+  // ---------------------------------------------------------------------------
+  const errorMessage = 'Use "Session.equals" instead'
+
+  const checkTest = (node) => {
+    switch (node.type) {
+      case 'BinaryExpression':
+      case 'LogicalExpression':
+        checkTest(node.left)
+        checkTest(node.right)
+        break
+      case 'CallExpression':
+        if (isSessionGetCallExpression(node)) {
+          context.report(node.callee, errorMessage)
+        }
+        break
+      default:
+        return
+    }
+  }
+
+  // ---------------------------------------------------------------------------
+  // Public
+  // ---------------------------------------------------------------------------
+  return {
+    ConditionalExpression: node => {
+      checkTest(node.test)
+    },
+    IfStatement: node => checkTest(node.test),
+  }
+}
+
+module.exports.schema = []

tests/lib/rules/prefer-session-equals.js

@@ -0,0 +1,84 @@
+/**
+ * @fileoverview Prefer Session.equals in conditions
+ * @author Dominik Ferber
+ * @copyright 2016 Dominik Ferber. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+
+// -----------------------------------------------------------------------------
+// Requirements
+// -----------------------------------------------------------------------------
+
+const rule = require('../../../dist/rules/prefer-session-equals')
+const RuleTester = require('eslint').RuleTester
+const ruleTester = new RuleTester()
+
+ruleTester.run('prefer-session-equals', rule, {
+  valid: [
+    'if (Session.equals("foo", true)) {}',
+    'if (Session.equals("foo", false)) {}',
+    'if (Session.equals("foo", 1)) {}',
+    'if (Session.equals("foo", "hello")) {}',
+    'if (!Session.equals("foo", "hello")) {}',
+    'if (_.isEqual(Session.get("foo"), otherValue)) {}',
+    'Session.equals("foo", true) ? true : false',
+    'if (Session.set("foo")) {}',
+  ],
+
+  invalid: [
+    {
+      code: 'if (Session.get("foo")) {}',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+    {
+      code: 'if (Session.get("foo") == 3) {}',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+    {
+      code: 'if (Session.get("foo") === 3) {}',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+    {
+      code: 'if (Session.get("foo") === bar) {}',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+    {
+      code: 'if (Session.get("foo") !== bar) {}',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+    {
+      code: 'Session.get("foo") ? true : false',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+    {
+      code: 'Session.get("foo") && false ? true : false',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+    {
+      code: 'Session.get("foo") === 2 ? true : false',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+    {
+      code: 'true || Session.get("foo") === 2 ? true : false',
+      errors: [
+        { message: 'Use "Session.equals" instead', type: 'MemberExpression' },
+      ],
+    },
+  ],
+})