lib/walk.js

// AST walker module for Mozilla Parser API compatible trees

(function(mod) {
  if (typeof exports == "object" && typeof module == "object") return mod(exports); // CommonJS
  if (typeof define == "function" && define.amd) return define(["exports"], mod); // AMD
  mod((this.acorn || (this.acorn = {})).walk = {}); // Plain browser env
})(function(exports) {
  "use strict";

  // A simple walk is one where you simply specify callbacks to be
  // called on specific nodes. The last two arguments are optional. A
  // simple use would be
  //
  //     walk.simple(myTree, {
  //         Expression: function(node) { ... }
  //     });
  //
  // to do something with all expressions. All Parser API node types
  // can be used to identify node types, as well as Expression,
  // Statement, and ScopeBody, which denote categories of nodes.
  //
  // The base argument can be used to pass a custom (recursive)
  // walker, and state can be used to give this walked an initial
  // state.
  exports.simple = function(node, visitors, base, state) {
    if (!base) base = exports.base;
    function c(node, st, override) {
      var type = override || node.type, found = visitors[type];
      base[type](node, st, c);
      if (found) found(node, st);
    }
    c(node, state);
  };

  // An ancestor walk builds up an array of ancestor nodes (including
  // the current node) and passes them to the callback as the state parameter.
  exports.ancestor = function(node, visitors, base, state) {
    if (!base) base = exports.base;
    if (!state) state = [];
    function c(node, st, override) {
      var type = override || node.type, found = visitors[type];
      if (node != st[st.length - 1]) {
        st = st.slice();
        st.push(node);
      }
      base[type](node, st, c);
      if (found) found(node, st);
    }
    c(node, state);
  };

  // A recursive walk is one where your functions override the default
  // walkers. They can modify and replace the state parameter that's
  // threaded through the walk, and can opt how and whether to walk
  // their child nodes (by calling their third argument on these
  // nodes).
  exports.recursive = function(node, state, funcs, base) {
    var visitor = funcs ? exports.make(funcs, base) : base;
    function c(node, st, override) {
      visitor[override || node.type](node, st, c);
    }
    c(node, state);
  };

  function makeTest(test) {
    if (typeof test == "string")
      return function(type) { return type == test; };
    else if (!test)
      return function() { return true; };
    else
      return test;
  }

  function Found(node, state) { this.node = node; this.state = state; }

  // Find a node with a given start, end, and type (all are optional,
  // null can be used as wildcard). Returns a {node, state} object, or
  // undefined when it doesn't find a matching node.
  exports.findNodeAt = function(node, start, end, test, base, state) {
    test = makeTest(test);
    try {
      if (!base) base = exports.base;
      var c = function(node, st, override) {
        var type = override || node.type;
        if ((start == null || node.start <= start) &&
            (end == null || node.end >= end))
          base[type](node, st, c);
        if (test(type, node) &&
            (start == null || node.start == start) &&
            (end == null || node.end == end))
          throw new Found(node, st);
      };
      c(node, state);
    } catch (e) {
      if (e instanceof Found) return e;
      throw e;
    }
  };

  // Find the innermost node of a given type that contains the given
  // position. Interface similar to findNodeAt.
  exports.findNodeAround = function(node, pos, test, base, state) {
    test = makeTest(test);
    try {
      if (!base) base = exports.base;
      var c = function(node, st, override) {
        var type = override || node.type;
        if (node.start > pos || node.end < pos) return;
        base[type](node, st, c);
        if (test(type, node)) throw new Found(node, st);
      };
      c(node, state);
    } catch (e) {
      if (e instanceof Found) return e;
      throw e;
    }
  };

  // Find the outermost matching node after a given position.
  exports.findNodeAfter = function(node, pos, test, base, state) {
    test = makeTest(test);
    try {
      if (!base) base = exports.base;
      var c = function(node, st, override) {
        if (node.end < pos) return;
        var type = override || node.type;
        if (node.start >= pos && test(type, node)) throw new Found(node, st);
        base[type](node, st, c);
      };
      c(node, state);
    } catch (e) {
      if (e instanceof Found) return e;
      throw e;
    }
  };

  // Find the outermost matching node before a given position.
  exports.findNodeBefore = function(node, pos, test, base, state) {
    test = makeTest(test);
    if (!base) base = exports.base;
    var max;
    var c = function(node, st, override) {
      if (node.start > pos) return;
      var type = override || node.type;
      if (node.end <= pos && (!max || max.node.end < node.end) && test(type, node))
        max = new Found(node, st);
      base[type](node, st, c);
    };
    c(node, state);
    return max;
  };

  // Used to create a custom walker. Will fill in all missing node
  // type properties with the defaults.
  exports.make = function(funcs, base) {
    if (!base) base = exports.base;
    var visitor = {};
    for (var type in base) visitor[type] = base[type];
    for (var type in funcs) visitor[type] = funcs[type];
    return visitor;
  };

  function skipThrough(node, st, c) { c(node, st); }
  function ignore(_node, _st, _c) {}

  // Node walkers.

  var base = exports.base = {};
  base.Program = base.BlockStatement = function(node, st, c) {
    for (var i = 0; i < node.body.length; ++i)
      c(node.body[i], st, "Statement");
  };
  base.Statement = skipThrough;
  base.EmptyStatement = ignore;
  base.ExpressionStatement = function(node, st, c) {
    c(node.expression, st, "Expression");
  };
  base.IfStatement = function(node, st, c) {
    c(node.test, st, "Expression");
    c(node.consequent, st, "Statement");
    if (node.alternate) c(node.alternate, st, "Statement");
  };
  base.LabeledStatement = function(node, st, c) {
    c(node.body, st, "Statement");
  };
  base.BreakStatement = base.ContinueStatement = ignore;
  base.WithStatement = function(node, st, c) {
    c(node.object, st, "Expression");
    c(node.body, st, "Statement");
  };
  base.SwitchStatement = function(node, st, c) {
    c(node.discriminant, st, "Expression");
    for (var i = 0; i < node.cases.length; ++i) {
      var cs = node.cases[i];
      if (cs.test) c(cs.test, st, "Expression");
      for (var j = 0; j < cs.consequent.length; ++j)
        c(cs.consequent[j], st, "Statement");
    }
  };
  base.ReturnStatement = function(node, st, c) {
    if (node.argument) c(node.argument, st, "Expression");
  };
  base.ThrowStatement = function(node, st, c) {
    c(node.argument, st, "Expression");
  };
  base.TryStatement = function(node, st, c) {
    c(node.block, st, "Statement");
    if (node.handler) c(node.handler.body, st, "ScopeBody");
    if (node.finalizer) c(node.finalizer, st, "Statement");
  };
  base.WhileStatement = function(node, st, c) {
    c(node.test, st, "Expression");
    c(node.body, st, "Statement");
  };
  base.DoWhileStatement = base.WhileStatement;
  base.ForStatement = function(node, st, c) {
    if (node.init) c(node.init, st, "ForInit");
    if (node.test) c(node.test, st, "Expression");
    if (node.update) c(node.update, st, "Expression");
    c(node.body, st, "Statement");
  };
  base.ForInStatement = function(node, st, c) {
    c(node.left, st, "ForInit");
    c(node.right, st, "Expression");
    c(node.body, st, "Statement");
  };
  base.ForInit = function(node, st, c) {
    if (node.type == "VariableDeclaration") c(node, st);
    else c(node, st, "Expression");
  };
  base.DebuggerStatement = ignore;

  base.FunctionDeclaration = function(node, st, c) {
    c(node, st, "Function");
  };
  base.VariableDeclaration = function(node, st, c) {
    for (var i = 0; i < node.declarations.length; ++i) {
      var decl = node.declarations[i];
      if (decl.init) c(decl.init, st, "Expression");
    }
  };

  base.Function = function(node, st, c) {
    c(node.body, st, "ScopeBody");
  };
  base.ScopeBody = function(node, st, c) {
    c(node, st, "Statement");
  };

  base.Expression = skipThrough;
  base.ThisExpression = ignore;
  base.ArrayExpression = function(node, st, c) {
    for (var i = 0; i < node.elements.length; ++i) {
      var elt = node.elements[i];
      if (elt) c(elt, st, "Expression");
    }
  };
  base.ObjectExpression = function(node, st, c) {
    for (var i = 0; i < node.properties.length; ++i)
      c(node.properties[i].value, st, "Expression");
  };
  base.FunctionExpression = base.FunctionDeclaration;
  base.SequenceExpression = function(node, st, c) {
    for (var i = 0; i < node.expressions.length; ++i)
      c(node.expressions[i], st, "Expression");
  };
  base.UnaryExpression = base.UpdateExpression = function(node, st, c) {
    c(node.argument, st, "Expression");
  };
  base.BinaryExpression = base.AssignmentExpression = base.LogicalExpression = function(node, st, c) {
    c(node.left, st, "Expression");
    c(node.right, st, "Expression");
  };
  base.ConditionalExpression = function(node, st, c) {
    c(node.test, st, "Expression");
    c(node.consequent, st, "Expression");
    c(node.alternate, st, "Expression");
  };
  base.NewExpression = base.CallExpression = function(node, st, c) {
    c(node.callee, st, "Expression");
    if (node.arguments) for (var i = 0; i < node.arguments.length; ++i)
      c(node.arguments[i], st, "Expression");
  };
  base.MemberExpression = function(node, st, c) {
    c(node.object, st, "Expression");
    if (node.computed) c(node.property, st, "Expression");
  };
  base.Identifier = base.Literal = ignore;

  // A custom walker that keeps track of the scope chain and the
  // variables defined in it.
  function makeScope(prev, isCatch) {
    return {vars: Object.create(null), prev: prev, isCatch: isCatch};
  }
  function normalScope(scope) {
    while (scope.isCatch) scope = scope.prev;
    return scope;
  }
  exports.scopeVisitor = exports.make({
    Function: function(node, scope, c) {
      var inner = makeScope(scope);
      for (var i = 0; i < node.params.length; ++i)
        inner.vars[node.params[i].name] = {type: "argument", node: node.params[i]};
      if (node.id) {
        var decl = node.type == "FunctionDeclaration";
        (decl ? normalScope(scope) : inner).vars[node.id.name] =
          {type: decl ? "function" : "function name", node: node.id};
      }
      c(node.body, inner, "ScopeBody");
    },
    TryStatement: function(node, scope, c) {
      c(node.block, scope, "Statement");
      if (node.handler) {
        var inner = makeScope(scope, true);
        inner.vars[node.handler.param.name] = {type: "catch clause", node: node.handler.param};
        c(node.handler.body, inner, "ScopeBody");
      }
      if (node.finalizer) c(node.finalizer, scope, "Statement");
    },
    VariableDeclaration: function(node, scope, c) {
      var target = normalScope(scope);
      for (var i = 0; i < node.declarations.length; ++i) {
        var decl = node.declarations[i];
        target.vars[decl.id.name] = {type: "var", node: decl.id};
        if (decl.init) c(decl.init, scope, "Expression");
      }
    }
  });

});