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   1 /**
   2  * @fileoverview Rule to flag unnecessary strict directives.
   3  * @author Ian Christian Myers
   4  * @copyright 2014 Ian Christian Myers. All rights reserved.
   5  */
   6 "use strict";
   7
   8 //------------------------------------------------------------------------------
   9 // Rule Definition
  10 //------------------------------------------------------------------------------
  11
  12 module.exports = function(context) {
  13
  14     function directives(block) {
  15         var ds = [], body = block.body, e, i, l;
  16
  17         if (body) {
  18             for (i = 0, l = body.length; i < l; ++i) {
  19                 e = body[i];
  20
  21                 if (
  22                     e.type === "ExpressionStatement" &&
  23                     e.expression.type === "Literal" &&
  24                     typeof e.expression.value === "string"
  25                 ) {
  26                     ds.push(e.expression);
  27                 } else {
  28                     break;
  29                 }
  30             }
  31         }
  32
  33         return ds;
  34     }
  35
  36     function isStrict(directive) {
  37         return directive.value === "use strict";
  38     }
  39
  40     function checkForUnnecessaryUseStrict(node) {
  41         var useStrictDirectives = directives(node).filter(isStrict),
  42             scope,
  43             upper;
  44
  45         switch (useStrictDirectives.length) {
  46             case 0:
  47                 break;
  48
  49             case 1:
  50                 scope = context.getScope();
  51                 upper = scope.upper;
  52
  53                 if (upper && upper.functionExpressionScope) {
  54                     upper = upper.upper;
  55                 }
  56
  57                 if (upper && upper.isStrict) {
  58                     context.report(useStrictDirectives[0], "Unnecessary 'use strict'.");
  59                 }
  60                 break;
  61
  62             default:
  63                 context.report(useStrictDirectives[1], "Multiple 'use strict' directives.");
  64         }
  65     }
  66
  67     return {
  68
  69         "Program": checkForUnnecessaryUseStrict,
  70
  71         "ArrowFunctionExpression": function(node) {
  72             checkForUnnecessaryUseStrict(node.body);
  73         },
  74
  75         "FunctionExpression": function(node) {
  76             checkForUnnecessaryUseStrict(node.body);
  77         },
  78
  79         "FunctionDeclaration": function(node) {
  80             checkForUnnecessaryUseStrict(node.body);
  81         }
  82     };
  83
  84 };