feat(rules): add 'no-shadowing' rule

README.md

@@ -35,6 +35,7 @@ Rule                         | Default       | Options
 ----                         | -------       | -------
 [missing-perform][]          | 2             |
 [no-browser-pause][]         | 2             |
+[no-shadowing][]             | 2             |
 [missing-wait-message][]     | 1             |
 [no-browser-sleep][]         | 1             |
 [no-by-xpath][]              | 1             |
@@ -61,6 +62,7 @@ See [configuring rules][] for more information.
 
 [missing-perform]: docs/rules/missing-perform.md
 [no-browser-pause]: docs/rules/no-browser-pause.md
+[no-shadowing]: docs/rules/no-shadowing.md
 [missing-wait-message]: docs/rules/missing-wait-message.md
 [no-browser-sleep]: docs/rules/no-browser-sleep.md
 [no-by-xpath]: docs/rules/no-by-xpath.md

docs/rules/no-shadowing.md

@@ -0,0 +1,41 @@
+# Don't allow to shadow the built-in Protractor globals
+
+The rule is to prevent shadowing the built-in Protractor globals, like `element` or `by`.
+
+## Rule details
+
+Here is the list of global variables checked for not to be shadowed:
+
+ * `browser`
+ * `protractor`
+ * `element`
+ * `by`
+ * `$`
+ * `$$`
+
+The following patterns are considered warnings: 
+
+```js
+var element = "something";
+function test (browser) {};
+var protractor;
+function by () {};
+var $ = 1;
+var a = 2, $$ = 3;
+for (var by = 0; by < 10; ++by) {}
+try { json = JSON.parse(input) } catch (browser) {}
+switch (element) { case 1: break; default: break; }
+```
+
+The following patterns are not warnings:
+
+```js
+var element2 = "something";
+element(by.id("test"));
+var EC = protractor.ExpectedConditions;
+var elm = $(".myclass");
+var elements = $$(".myclass");
+for (var i = 0; i < 10; ++i) {}
+try { json = JSON.parse(input) } catch (e) {}
+switch (a) { case 1: break; default: break; }
+```

index.js

@@ -4,6 +4,7 @@ module.exports = {
   rules: {
     'missing-perform': require('./lib/rules/missing-perform'),
     'no-browser-pause': require('./lib/rules/no-browser-pause'),
+    'no-shadowing': require('./lib/rules/no-shadowing'),
     'missing-wait-message': require('./lib/rules/missing-wait-message'),
     'no-browser-sleep': require('./lib/rules/no-browser-sleep'),
     'no-by-xpath': require('./lib/rules/no-by-xpath'),
@@ -18,6 +19,7 @@ module.exports = {
       rules: {
         'protractor/missing-perform': 2,
         'protractor/no-browser-pause': 2,
+        'protractor/no-shadowing': 2,
         'protractor/missing-wait-message': 1,
         'protractor/no-browser-sleep': 1,
         'protractor/no-by-xpath': 1,

lib/rules/no-shadowing.js

@@ -0,0 +1,41 @@
+'use strict'
+
+/**
+ * @fileoverview Don't allow to shadow the built-in Protractor globals
+ * @author Alexander Afanasyev
+ */
+
+module.exports = function (context) {
+  var protractorGlobals = [
+    'browser',
+    'protractor',
+    'element',
+    'by',
+    '$',
+    '$$'
+  ]
+
+  function checkVariables (node) {
+    var variables = context.getDeclaredVariables(node)
+    for (var i = 0; i < variables.length; ++i) {
+      if (protractorGlobals.indexOf(variables[i].name) !== -1) {
+        context.report(node, 'Unexpected Protractor built-in global variable shadowing')
+      }
+    }
+
+    // handling switch manually - getDeclaredVariables() does not return the switch discriminant
+    if (node.type === 'SwitchStatement' && node.discriminant) {
+      if (protractorGlobals.indexOf(node.discriminant.name) !== -1) {
+        context.report(node, 'Unexpected Protractor built-in global variable shadowing')
+      }
+    }
+  }
+
+  return {
+    'VariableDeclaration': checkVariables,
+    'FunctionDeclaration': checkVariables,
+    'FunctionExpression': checkVariables,
+    'CatchClause': checkVariables,
+    'SwitchStatement': checkVariables
+  }
+}

test/rules/no-shadowing.js

@@ -0,0 +1,94 @@
+'use strict'
+
+var rule = require('../../lib/rules/no-shadowing')
+var RuleTester = require('eslint').RuleTester
+
+var eslintTester = new RuleTester()
+
+eslintTester.run('no-shadowing', rule, {
+  valid: [
+    'var element2 = "something";',
+    'element(by.id("test"));',
+    'var EC = protractor.ExpectedConditions;',
+    'var elm = $(".myclass");',
+    'var elements = $$(".myclass");',
+    'for (var i = 0; i < variables.length; ++i) {}',
+    'try { json = JSON.parse(input) } catch (e) {}',
+    'switch (a) { case 1: break; default: break; }'
+  ],
+
+  invalid: [
+    {
+      code: 'var element = "something";',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    },
+    {
+      code: 'function test (browser) {};',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    },
+    {
+      code: 'var protractor;',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    },
+    {
+      code: 'function by () {};',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    },
+    {
+      code: 'var $ = 1;',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    },
+    {
+      code: 'var a = 2, $$ = 3;',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    },
+    {
+      code: 'for (var by = 0; by < 10; ++by) {}',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    },
+    {
+      code: 'try { json = JSON.parse(input) } catch (browser) {}',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    },
+    {
+      code: 'switch (element) { case 1: break; default: break; }',
+      errors: [
+        {
+          message: 'Unexpected Protractor built-in global variable shadowing'
+        }
+      ]
+    }
+  ]
+})