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   1 /**
   2  * @fileoverview Rule to flag use constant conditions
   3  * @author Christian Schulz <http://rndm.de>
   4  * @copyright 2014 Christian Schulz. All rights reserved.
   5  */
   6
   7 "use strict";
   8
   9 //------------------------------------------------------------------------------
  10 // Rule Definition
  11 //------------------------------------------------------------------------------
  12
  13 module.exports = function(context) {
  14
  15     //--------------------------------------------------------------------------
  16     // Helpers
  17     //--------------------------------------------------------------------------
  18
  19     /**
  20      * Checks if a node has a constant truthiness value.
  21      * @param {ASTNode} node The AST node to check.
  22      * @returns {Bool} true when node's truthiness is constant
  23      * @private
  24      */
  25     function isConstant(node) {
  26         switch (node.type) {
  27             case "Literal":
  28             case "ArrowFunctionExpression":
  29             case "FunctionExpression":
  30             case "ObjectExpression":
  31             case "ArrayExpression":
  32                 return true;
  33             case "UnaryExpression":
  34                 return isConstant(node.argument);
  35             case "BinaryExpression":
  36             case "LogicalExpression":
  37                 return isConstant(node.left) && isConstant(node.right);
  38             case "AssignmentExpression":
  39                 return (node.operator === "=") && isConstant(node.right);
  40             case "SequenceExpression":
  41                 return isConstant(node.expressions[node.expressions.length - 1]);
  42             // no default
  43         }
  44         return false;
  45     }
  46
  47     /**
  48      * Reports when the given node contains a constant condition.
  49      * @param {ASTNode} node The AST node to check.
  50      * @returns {void}
  51      * @private
  52      */
  53     function checkConstantCondition(node) {
  54         if (node.test && isConstant(node.test)) {
  55             context.report(node, "Unexpected constant condition.");
  56         }
  57     }
  58
  59     //--------------------------------------------------------------------------
  60     // Public
  61     //--------------------------------------------------------------------------
  62
  63     return {
  64         "ConditionalExpression": checkConstantCondition,
  65         "IfStatement": checkConstantCondition,
  66         "WhileStatement": checkConstantCondition,
  67         "DoWhileStatement": checkConstantCondition,
  68         "ForStatement": checkConstantCondition
  69     };
  70
  71 };