[CS2] Destructuring object spreads (#4493)

* Don’t confuse the syntax highlighter

* Comment Assign::compilePatternMatch a bit

* Assignment expressions in conditionals are a bad practice

* Rename `wrapInBraces` to `wrapInParentheses`, to set the stage for future `wrapInBraces` that uses `{` and `wrapInBrackets` that uses `[`

* Correct comment

* object destructuring

* Allow custom position of the rest element.

* Output simple array destructuring assignments to ES2015

* Output simple object destructured assignments to ES2015

* Compile shorthand object properties to ES2015 shorthand properties

This dramatically improves the appearance of destructured imports.

* Don’t confuse the syntax highlighter

* Comment Assign::compilePatternMatch a bit

* Assignment expressions in conditionals are a bad practice

* Rename `wrapInBraces` to `wrapInParentheses`, to set the stage for future `wrapInBraces` that uses `{` and `wrapInBrackets` that uses `[`

* object destructuring

* Allow custom position of the rest element.

* rest element in object destructuring

* rest element in object destructuring

* fix string interpolation

* merging

* fixing splats in object literal

* Rest element in parameter destructuring

* merging with CS2

* merged with CS2

* Add support for the object spread initializer. https://github.com/tc39/proposal-object-rest-spread/blob/master/Spread.md

* Fix misspellings, trailing whitespace, other minor details

* merging with beta2

* refactor object spread properties

* small fix

* - Fixed object spread function parameters.
- Clean up "Assign" and moved all logic for object rest properties in single method (compileObjectDestruct).
- Add helper function "objectWithoutKeys" to the "UTILITIES" for use with object rest properties,
  e.g. {a, b, r...} = obj => {a, b} = obj, r = objectWithoutKeys(...)
- Clean up "Obj" and moved all logic for object spread properties in single method (compileSpread).
- Clean up "Code".
- Add method "hasSplat" to "Obj" and "Value" for checking if Obj contains the splat.
- Enable placing spread syntax triple dots on either right or left, per #85 (https://github.com/coffeescript6/discuss/issues/85)

* Fixed typos

* Remove unused code

* Removed dots (e.g. splat) on the left side from the grammar

* Initial release for deep spread properties, e.g. obj2 = {obj.b..., a: 1} or {obj[b][c]..., d: 7}
Tests need to be prepared!

* 1. Object literal spread properties

Object literals:
- obj = { {b:{c:{d:1}}}..., a:1 }

Parenthetical:
- obj = { ( body ), a:1 }
- obj = { ( body )..., a:1 }

Invocation:
- obj = { ( (args) -> ... )(params), a:1 }
- obj = { ( (args) -> ... )(params)..., a:1 }
- obj = { foo(), a:1 }
- obj = { foo()..., a:1 }

2. Refactor, cleanup & other optimizations.

* Merged with 2.0

* Cleanup

* Some more cleanup.

* Fixed error with freeVariable and object destructuring.

* Fixed errors with object spread properties.

* Improvements, fixed errors.

* Minor improvement.

* Minor improvements.

* Typo.

* Remove unnecessary whitespace.

* Remove unnecessary whitespace.

* Changed few "assertErrorFormat" tests since parentheses are now allowed in the Obj.

* Whitespace cleanup

* Comments cleanup

* fix destructured obj param declarations

* refine fix; add test

* Refactor function args ({a, b...})

* Additional tests for object destructuring in function argument.

* Minor improvement for object destructuring variable declaration.

* refactor function args ({a, b...}) and ({a, b...} = {}); Obj And Param cleanup

* fix comment

* Fix object destructuring variable declaration.

* more tests with default values

* fix typo

* Fixed default values in object destructuring.

* small fix

* Babel’s tests for object rest spread

* Style: spaces after colons in object declarations

* Cleanup comments

* Simplify Babel tests

* Fix comments

* Fix destructuring with splats in multiple objects

* Add test for default values in detsructuring assignment with splats

* Handle default values when assigning to object splats

* Rewrite traverseRest to fix handling of dynamic keys

* Fix double parens around destructuring with splats

* Update compileObjectDestruct comments

* Improve formatting of top-level destructures with splats and tidy parens

* Added a bigger destructuring-with-defaults test and fixed a bug

* Refactor destructuring grammar to allow additional forms

* Add a missing case to ObjSpreadExpr

* These tests shouldn’t run in the browser

* Fix test.html

.gitignore

@@ -8,3 +8,4 @@ test/*.js
 parser.output
 /node_modules
 npm-debug.log*
+yarn.lock

documentation/test.html

@@ -39,6 +39,7 @@
 <script type="text/coffeescript">
 @testingBrowser = yes
 @global = window
+bold = red = green = reset = ''
 stdout = document.getElementById 'stdout'
 start = new Date
 @currentFile = ''

lib/coffeescript/grammar.js

@@ -123,7 +123,7 @@
     AssignObj: [
       o('ObjAssignable', function() {
         return new Value($1);
-      }), o('ObjAssignable : Expression', function() {
+      }), o('ObjRestValue'), o('ObjAssignable : Expression', function() {
         return new Assign(LOC(1)(new Value($1)), $3, 'object', {
           operatorToken: LOC(2)(new Literal($2))
         });
@@ -143,6 +143,29 @@
     ],
     SimpleObjAssignable: [o('Identifier'), o('Property'), o('ThisProperty')],
     ObjAssignable: [o('SimpleObjAssignable'), o('AlphaNumeric')],
+    ObjRestValue: [
+      o('SimpleObjAssignable ...', function() {
+        return new Splat(new Value($1));
+      }), o('ObjSpreadExpr ...', function() {
+        return new Splat($1);
+      })
+    ],
+    ObjSpreadExpr: [
+      o('ObjSpreadIdentifier'), o('Object'), o('Parenthetical'), o('Super'), o('This'), o('SUPER Arguments', function() {
+        return new SuperCall(LOC(1)(new Super), $2);
+      }), o('SimpleObjAssignable Arguments', function() {
+        return new Call(new Value($1), $2);
+      }), o('ObjSpreadExpr Arguments', function() {
+        return new Call($1, $2);
+      })
+    ],
+    ObjSpreadIdentifier: [
+      o('SimpleObjAssignable . Property', function() {
+        return (new Value($1)).add(new Access($3));
+      }), o('SimpleObjAssignable INDEX_START IndexValue INDEX_END', function() {
+        return (new Value($1)).add($3);
+      })
+    ],
     Return: [
       o('RETURN Expression', function() {
         return new Return($2);

lib/coffeescript/nodes.js

@@ -1543,8 +1543,20 @@
         return !this.isAssignable();
       }
 
+      hasSplat() {
+        var j, len1, prop, ref1, splat;
+        ref1 = this.properties;
+        for (j = 0, len1 = ref1.length; j < len1; j++) {
+          prop = ref1[j];
+          if (prop instanceof Splat) {
+            splat = true;
+          }
+        }
+        return splat != null ? splat : false;
+      }
+
       compileNode(o) {
-        var answer, i, idt, indent, isCompact, j, join, k, key, l, lastNoncom, len1, len2, len3, len4, node, p, prop, props, ref1, unwrappedVal, value;
+        var answer, i, idt, indent, isCompact, j, join, k, key, l, lastNoncom, len1, len2, len3, len4, node, prop, props, q, ref1, unwrappedVal, value;
         props = this.properties;
         if (this.generated) {
           for (j = 0, len1 = props.length; j < len1; j++) {
@@ -1554,6 +1566,9 @@
             }
           }
         }
+        if (this.hasSplat()) {
+          return this.compileSpread(o);
+        }
         idt = o.indent += TAB;
         lastNoncom = this.lastNonComment(this.properties);
         if (this.lhs) {
@@ -1581,7 +1596,7 @@
         }
         answer = [];
         answer.push(this.makeCode(isCompact ? '' : '\n'));
-        for (i = p = 0, len4 = props.length; p < len4; i = ++p) {
+        for (i = q = 0, len4 = props.length; q < len4; i = ++q) {
           prop = props[i];
           join = i === props.length - 1 ? '' : isCompact && this.csx ? ' ' : isCompact ? ', ' : prop === lastNoncom || prop instanceof Comment || this.csx ? '\n' : ',\n';
           indent = isCompact || prop instanceof Comment ? '' : idt;
@@ -1660,6 +1675,38 @@
         return results;
       }
 
+      compileSpread(o) {
+        var addSlice, j, len1, prop, propSlices, props, slices, splatSlice;
+        props = this.properties;
+        splatSlice = [];
+        propSlices = [];
+        slices = [];
+        addSlice = function() {
+          if (propSlices.length) {
+            slices.push(new Obj(propSlices));
+          }
+          if (splatSlice.length) {
+            slices.push(...splatSlice);
+          }
+          splatSlice = [];
+          return propSlices = [];
+        };
+        for (j = 0, len1 = props.length; j < len1; j++) {
+          prop = props[j];
+          if (prop instanceof Splat) {
+            splatSlice.push(new Value(prop.name));
+            addSlice();
+          } else {
+            propSlices.push(prop);
+          }
+        }
+        addSlice();
+        if (!(slices[0] instanceof Obj)) {
+          slices.unshift(new Obj);
+        }
+        return (new Call(new Literal('Object.assign'), slices)).compileToFragments(o);
+      }
+
     };
 
     Obj.prototype.children = ['properties'];
@@ -2445,6 +2492,11 @@
             if (!this.variable.isAssignable()) {
               return this.compileDestructuring(o);
             }
+            if (this.variable.isObject() && this.variable.contains(function(node) {
+              return node instanceof Obj && node.hasSplat();
+            })) {
+              return this.compileObjectDestruct(o);
+            }
           }
           if (this.variable.isSplice()) {
             return this.compileSplice(o);
@@ -2501,13 +2553,117 @@
           return compiledName.concat(this.makeCode(this.csx ? '=' : ': '), val);
         }
         answer = compiledName.concat(this.makeCode(` ${this.context || '='} `), val);
-        if (o.level > LEVEL_LIST || (isValue && this.variable.base instanceof Obj && !this.nestedLhs && !this.param)) {
+        if (o.level > LEVEL_LIST || (o.level === LEVEL_TOP && isValue && this.variable.base instanceof Obj && !this.nestedLhs && !this.param)) {
           return this.wrapInParentheses(answer);
         } else {
           return answer;
         }
       }
 
+      compileObjectDestruct(o) {
+        var fragments, getPropKey, getPropName, j, len1, restElement, restElements, result, setScopeVar, traverseRest, value, valueRef;
+        setScopeVar = function(prop) {
+          var newVar;
+          newVar = false;
+          if (prop instanceof Assign && prop.value.base instanceof Obj) {
+            return;
+          }
+          if (prop instanceof Assign) {
+            if (prop.value.base instanceof IdentifierLiteral) {
+              newVar = prop.value.base.compile(o);
+            } else {
+              newVar = prop.variable.base.compile(o);
+            }
+          } else {
+            newVar = prop.compile(o);
+          }
+          if (newVar) {
+            return o.scope.add(newVar, 'var', true);
+          }
+        };
+        getPropKey = function(prop) {
+          var key;
+          if (prop instanceof Assign) {
+            [prop.variable, key] = prop.variable.cache(o);
+            return key;
+          } else {
+            return prop;
+          }
+        };
+        getPropName = function(prop) {
+          var cached, key;
+          key = getPropKey(prop);
+          cached = prop instanceof Assign && prop.variable !== key;
+          if (cached || !key.isAssignable()) {
+            return key;
+          } else {
+            return new Literal(`'${key.compile(o)}'`);
+          }
+        };
+        traverseRest = (properties, source) => {
+          var base1, index, j, len1, nestedProperties, nestedSource, nestedSourceDefault, p, prop, restElements, restIndex;
+          restElements = [];
+          restIndex = void 0;
+          for (index = j = 0, len1 = properties.length; j < len1; index = ++j) {
+            prop = properties[index];
+            setScopeVar(prop.unwrap());
+            if (prop instanceof Assign) {
+              if (typeof (base1 = prop.value).isObject === "function" ? base1.isObject() : void 0) {
+                nestedProperties = prop.value.base.properties;
+              } else if (prop.value instanceof Assign && prop.value.variable.isObject()) {
+                nestedProperties = prop.value.variable.base.properties;
+                [prop.value.value, nestedSourceDefault] = prop.value.value.cache(o);
+              }
+              if (nestedProperties) {
+                nestedSource = new Value(source.base, source.properties.concat([new Access(getPropKey(prop))]));
+                if (nestedSourceDefault) {
+                  nestedSource = new Value(new Op('?', nestedSource, nestedSourceDefault));
+                }
+                restElements = restElements.concat(traverseRest(nestedProperties, nestedSource));
+              }
+            } else if (prop instanceof Splat) {
+              if (restIndex != null) {
+                prop.error("multiple rest elements are disallowed in object destructuring");
+              }
+              restIndex = index;
+              restElements.push({
+                name: prop.name.unwrapAll(),
+                source,
+                excludeProps: new Arr((function() {
+                  var k, len2, results;
+                  results = [];
+                  for (k = 0, len2 = properties.length; k < len2; k++) {
+                    p = properties[k];
+                    if (p !== prop) {
+                      results.push(getPropName(p));
+                    }
+                  }
+                  return results;
+                })())
+              });
+            }
+          }
+          if (restIndex != null) {
+            properties.splice(restIndex, 1);
+          }
+          return restElements;
+        };
+        [this.value, valueRef] = this.value.cache(o);
+        restElements = traverseRest(this.variable.base.properties, valueRef);
+        result = new Block([this]);
+        for (j = 0, len1 = restElements.length; j < len1; j++) {
+          restElement = restElements[j];
+          value = new Call(new Value(new Literal(utility('objectWithoutKeys', o))), [restElement.source, restElement.excludeProps]);
+          result.push(new Assign(restElement.name, value));
+        }
+        fragments = result.compileToFragments(o);
+        if (o.level === LEVEL_TOP) {
+          fragments.shift();
+          fragments.pop();
+        }
+        return fragments;
+      }
+
       compileDestructuring(o) {
         var acc, assigns, code, defaultValue, expandedIdx, fragments, i, idx, isObject, ivar, j, len1, message, name, obj, objects, olen, ref, rest, top, val, value, vvar, vvarText;
         top = o.level === LEVEL_TOP;
@@ -2825,17 +2981,13 @@
               if (param.name instanceof Arr) {
                 splatParamName = o.scope.freeVariable('arg');
                 params.push(ref = new Value(new IdentifierLiteral(splatParamName)));
-                exprs.push(new Assign(new Value(param.name), ref, null, {
+                exprs.push(new Assign(new Value(param.name), ref));
-                  param: true
-                }));
               } else {
                 params.push(ref = param.asReference(o));
                 splatParamName = fragmentsToText(ref.compileNode(o));
               }
               if (param.shouldCache()) {
-                exprs.push(new Assign(new Value(param.name), ref, null, {
+                exprs.push(new Assign(new Value(param.name), ref));
-                  param: true
-                }));
               }
             } else {
               splatParamName = o.scope.freeVariable('args');
@@ -2848,14 +3000,10 @@
               haveBodyParam = true;
               if (param.value != null) {
                 condition = new Op('===', param, new UndefinedLiteral);
-                ifTrue = new Assign(new Value(param.name), param.value, null, {
+                ifTrue = new Assign(new Value(param.name), param.value);
-                  param: true
-                });
                 exprs.push(new If(condition, ifTrue));
               } else {
-                exprs.push(new Assign(new Value(param.name), param.asReference(o), null, {
+                exprs.push(new Assign(new Value(param.name), param.asReference(o)));
-                  param: true
-                }));
               }
             }
             if (!haveSplatParam) {
@@ -2875,6 +3023,17 @@
                 param.name.eachName(function(prop) {
                   return o.scope.parameter(prop.value);
                 });
+                if (param.name instanceof Obj && param.name.hasSplat()) {
+                  splatParamName = o.scope.freeVariable('arg');
+                  o.scope.parameter(splatParamName);
+                  ref = new Value(new IdentifierLiteral(splatParamName));
+                  exprs.push(new Assign(new Value(param.name), ref));
+                  if ((param.value != null) && !param.assignedInBody) {
+                    ref = new Assign(ref, param.value, null, {
+                      param: true
+                    });
+                  }
+                }
               } else {
                 o.scope.parameter(fragmentsToText((param.value != null ? param : ref).compileToFragments(o)));
               }
@@ -3060,12 +3219,12 @@
 
   exports.Param = Param = (function() {
     class Param extends Base {
-      constructor(name1, value1, splat) {
+      constructor(name1, value1, splat1) {
         var message, token;
         super();
         this.name = name1;
         this.value = value1;
-        this.splat = splat;
+        this.splat = splat1;
         message = isUnassignable(this.name.unwrapAll().value);
         if (message) {
           this.name.error(message);
@@ -4296,6 +4455,9 @@
     modulo: function() {
       return 'function(a, b) { return (+a % (b = +b) + b) % b; }';
     },
+    objectWithoutKeys: function() {
+      return "function(o, ks) { var res = {}; for (var k in o) ([].indexOf.call(ks, k) < 0 && {}.hasOwnProperty.call(o, k)) && (res[k] = o[k]); return res; }";
+    },
     boundMethodCheck: function() {
       return "function(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new Error('Bound instance method accessed before binding'); } }";
     },

src/grammar.coffee

@@ -190,6 +190,7 @@ grammar =
   # the ordinary **Assign** is that these allow numbers and strings as keys.
   AssignObj: [
     o 'ObjAssignable',                          -> new Value $1
+    o 'ObjRestValue'
     o 'ObjAssignable : Expression',             -> new Assign LOC(1)(new Value $1), $3, 'object',
                                                               operatorToken: LOC(2)(new Literal $2)
     o 'ObjAssignable :
@@ -214,6 +215,28 @@ grammar =
     o 'AlphaNumeric'
   ]
 
+  # Object literal spread properties.
+  ObjRestValue: [
+    o 'SimpleObjAssignable ...', -> new Splat new Value $1
+    o 'ObjSpreadExpr ...',       -> new Splat $1
+  ]
+
+  ObjSpreadExpr: [
+    o 'ObjSpreadIdentifier'
+    o 'Object'
+    o 'Parenthetical'
+    o 'Super'
+    o 'This'
+    o 'SUPER Arguments',               -> new SuperCall LOC(1)(new Super), $2
+    o 'SimpleObjAssignable Arguments', -> new Call (new Value $1), $2
+    o 'ObjSpreadExpr Arguments',       -> new Call $1, $2
+  ]
+
+  ObjSpreadIdentifier: [
+    o 'SimpleObjAssignable . Property',                             -> (new Value $1).add(new Access $3)
+    o 'SimpleObjAssignable INDEX_START IndexValue INDEX_END',       -> (new Value $1).add($3)
+  ]
+
   # A return statement from a function body.
   Return: [
     o 'RETURN Expression',                      -> new Return $2
@@ -701,7 +724,6 @@ grammar =
        Expression',                             -> new Assign $1, $4, $2
   ]
 
-
 # Precedence
 # ----------
 

src/nodes.coffee

@@ -1157,11 +1157,20 @@ exports.Obj = class Obj extends Base
   shouldCache: ->
     not @isAssignable()
 
+  # Check if object contains splat.
+  hasSplat: ->
+    splat = yes for prop in @properties when prop instanceof Splat
+    splat ? no
+
   compileNode: (o) ->
     props = @properties
     if @generated
       for node in props when node instanceof Value
         node.error 'cannot have an implicit value in an implicit object'
+
+    # Object spread properties. https://github.com/tc39/proposal-object-rest-spread/blob/master/Spread.md
+    return @compileSpread o if @hasSplat()
+
     idt        = o.indent += TAB
     lastNoncom = @lastNonComment @properties
 
@@ -1203,12 +1212,10 @@ exports.Obj = class Obj extends Base
         prop.variable
       else if prop not instanceof Comment
         prop
-
       if key instanceof Value and key.hasProperties()
         key.error 'invalid object key' if prop.context is 'object' or not key.this
         key  = key.properties[0].name
         prop = new Assign key, prop, 'object'
-
       if key is prop
         if prop.shouldCache()
           [key, value] = prop.base.cache o
@@ -1216,7 +1223,6 @@ exports.Obj = class Obj extends Base
           prop = new Assign key, value, 'object'
         else if not prop.bareLiteral?(IdentifierLiteral)
           prop = new Assign prop, prop, 'object'
-
       if indent then answer.push @makeCode indent
       prop.csx = yes if @csx
       answer.push @makeCode ' ' if @csx and i is 0
@@ -1236,6 +1242,29 @@ exports.Obj = class Obj extends Base
       prop = prop.unwrapAll()
       prop.eachName iterator if prop.eachName?
 
+  # Object spread properties. https://github.com/tc39/proposal-object-rest-spread/blob/master/Spread.md
+  # `obj2 = {a: 1, obj..., c: 3, d: 4}` → `obj2 = Object.assign({}, {a: 1}, obj, {c: 3, d: 4})`
+  compileSpread: (o) ->
+    props = @properties
+    # Store object spreads.
+    splatSlice = []
+    propSlices = []
+    slices = []
+    addSlice = ->
+      slices.push new Obj propSlices if propSlices.length
+      slices.push splatSlice... if splatSlice.length
+      splatSlice = []
+      propSlices = []
+    for prop in props
+      if prop instanceof Splat
+        splatSlice.push new Value prop.name
+        addSlice()
+      else
+        propSlices.push prop
+    addSlice()
+    slices.unshift new Obj unless slices[0] instanceof Obj
+    (new Call new Literal('Object.assign'), slices).compileToFragments o
+
 #### Arr
 
 # An array literal.
@@ -1796,6 +1825,9 @@ exports.Assign = class Assign extends Base
         # destructured variables.
         @variable.base.lhs = yes
         return @compileDestructuring o unless @variable.isAssignable()
+        # Object destructuring. Can be removed once ES proposal hits Stage 4.
+        return @compileObjectDestruct(o) if @variable.isObject() and @variable.contains (node) ->
+          node instanceof Obj and node.hasSplat()
 
       return @compileSplice       o if @variable.isSplice()
       return @compileConditional  o if @context in ['||=', '&&=', '?=']
@@ -1839,11 +1871,105 @@ exports.Assign = class Assign extends Base
     answer = compiledName.concat @makeCode(" #{ @context or '=' } "), val
     # Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment#Assignment_without_declaration,
     # if we’re destructuring without declaring, the destructuring assignment must be wrapped in parentheses.
-    if o.level > LEVEL_LIST or (isValue and @variable.base instanceof Obj and not @nestedLhs and not @param)
+    if o.level > LEVEL_LIST or (o.level is LEVEL_TOP and isValue and @variable.base instanceof Obj and not @nestedLhs and not @param)
       @wrapInParentheses answer
     else
       answer
 
+  # Check object destructuring variable for rest elements;
+  # can be removed once ES proposal hits Stage 4.
+  compileObjectDestruct: (o) ->
+    # Per https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment#Assignment_without_declaration,
+    # if we’re destructuring without declaring, the destructuring assignment
+    # must be wrapped in parentheses: `({a, b} = obj)`. Helper function
+    # `setScopeVar()` declares variables `a` and `b` at the top of the
+    # current scope.
+    setScopeVar = (prop) ->
+      newVar = false
+      return if prop instanceof Assign and prop.value.base instanceof Obj
+      if prop instanceof Assign
+        if prop.value.base instanceof IdentifierLiteral
+          newVar = prop.value.base.compile o
+        else
+          newVar = prop.variable.base.compile o
+      else
+        newVar = prop.compile o
+      o.scope.add(newVar, 'var', true) if newVar
+
+    # Returns a safe (cached) reference to the key for a given property
+    getPropKey = (prop) ->
+      if prop instanceof Assign
+        [prop.variable, key] = prop.variable.cache o
+        key
+      else
+        prop
+
+    # Returns the name of a given property for use with excludeProps
+    # Property names are quoted (e.g. `a: b` -> 'a'), and everything else uses the key reference
+    # (e.g. `'a': b -> 'a'`, `"#{a}": b` -> <cached>`)
+    getPropName = (prop) ->
+      key = getPropKey prop
+      cached = prop instanceof Assign and prop.variable != key
+      if cached or not key.isAssignable()
+        key
+      else
+        new Literal "'#{key.compile o}'"
+
+    # Recursive function for searching and storing rest elements in objects.
+    # e.g. `{[properties...]} = source`.
+    traverseRest = (properties, source) =>
+      restElements = []
+      restIndex = undefined
+
+      for prop, index in properties
+        setScopeVar prop.unwrap()
+        if prop instanceof Assign
+          # prop is `k: expr`, we need to check `expr` for nested splats
+          if prop.value.isObject?()
+            # prop is `k: {...}`
+            nestedProperties = prop.value.base.properties
+          else if prop.value instanceof Assign and prop.value.variable.isObject()
+            # prop is `k: {...} = default`
+            nestedProperties = prop.value.variable.base.properties
+            [prop.value.value, nestedSourceDefault] = prop.value.value.cache o
+          if nestedProperties
+            nestedSource = new Value source.base, source.properties.concat [new Access getPropKey prop]
+            nestedSource = new Value new Op '?', nestedSource, nestedSourceDefault if nestedSourceDefault
+            restElements = restElements.concat traverseRest nestedProperties, nestedSource
+        else if prop instanceof Splat
+          prop.error "multiple rest elements are disallowed in object destructuring" if restIndex?
+          restIndex = index
+          restElements.push {
+            name: prop.name.unwrapAll()
+            source
+            excludeProps: new Arr (getPropName p for p in properties when p isnt prop)
+          }
+
+      if restIndex?
+        # Remove rest element from the properties after iteration
+        properties.splice restIndex, 1
+
+      restElements
+
+    # Cache the value for reuse with rest elements
+    [@value, valueRef] = @value.cache o
+
+    # Find all rest elements.
+    restElements = traverseRest @variable.base.properties, valueRef
+
+    result = new Block [@]
+    for restElement in restElements
+      value = new Call new Value(new Literal utility 'objectWithoutKeys', o), [restElement.source, restElement.excludeProps]
+      result.push new Assign restElement.name, value
+
+    fragments = result.compileToFragments o
+    if o.level is LEVEL_TOP
+      # Remove leading tab and trailing semicolon
+      fragments.shift()
+      fragments.pop()
+
+    fragments
+
   # Brief implementation of recursive pattern matching, when assigning array or
   # object literals to a value. Peeks at their properties to assign inner names.
   compileDestructuring: (o) ->
@@ -1907,7 +2033,7 @@ exports.Assign = class Assign extends Base
 
     # At this point, there are several things to destructure. So the `fn()` in
     # `{a, b} = fn()` must be cached, for example. Make vvar into a simple
-    # variable if it isn't already.
+    # variable if it isn’t already.
     if value.unwrap() not instanceof IdentifierLiteral or @variable.assigns(vvarText)
       ref = o.scope.freeVariable 'ref'
       assigns.push [@makeCode(ref + ' = '), vvar...]
@@ -2098,7 +2224,6 @@ exports.Code = class Code extends Base
     @eachParamName (name, node, param) ->
       node.error "multiple parameters named '#{name}'" if name in paramNames
       paramNames.push name
-
       if node.this
         name   = node.properties[0].name.value
         name   = "_#{name}" if name in JS_FORBIDDEN
@@ -2123,7 +2248,6 @@ exports.Code = class Code extends Base
           param.error 'only one splat or expansion parameter is allowed per function definition'
         else if param instanceof Expansion and @params.length is 1
           param.error 'an expansion parameter cannot be the only parameter in a function definition'
-
         haveSplatParam = yes
         if param.splat
           if param.name instanceof Arr
@@ -2132,12 +2256,12 @@ exports.Code = class Code extends Base
             # function parameter list, and if so, how?
             splatParamName = o.scope.freeVariable 'arg'
             params.push ref = new Value new IdentifierLiteral splatParamName
-            exprs.push new Assign new Value(param.name), ref, null, param: yes
+            exprs.push new Assign new Value(param.name), ref
           else
             params.push ref = param.asReference o
             splatParamName = fragmentsToText ref.compileNode o
           if param.shouldCache()
-            exprs.push new Assign new Value(param.name), ref, null, param: yes
+            exprs.push new Assign new Value(param.name), ref
         else # `param` is an Expansion
           splatParamName = o.scope.freeVariable 'args'
           params.push new Value new IdentifierLiteral splatParamName
@@ -2157,10 +2281,10 @@ exports.Code = class Code extends Base
           # `(arg) => { var a = arg.a; }`, with a default value if it has one.
           if param.value?
             condition = new Op '===', param, new UndefinedLiteral
-            ifTrue = new Assign new Value(param.name), param.value, null, param: yes
+            ifTrue = new Assign new Value(param.name), param.value
             exprs.push new If condition, ifTrue
           else
-            exprs.push new Assign new Value(param.name), param.asReference(o), null, param: yes
+            exprs.push new Assign new Value(param.name), param.asReference(o)
 
         # If this parameter comes before the splat or expansion, it will go
         # in the function definition parameter list.
@@ -2182,6 +2306,16 @@ exports.Code = class Code extends Base
             param.name.lhs = yes
             param.name.eachName (prop) ->
               o.scope.parameter prop.value
+            # Compile `foo({a, b...}) ->` to `foo(arg) -> {a, b...} = arg`.
+            # Can be removed once ES proposal hits Stage 4.
+            if param.name instanceof Obj and param.name.hasSplat()
+              splatParamName = o.scope.freeVariable 'arg'
+              o.scope.parameter splatParamName
+              ref = new Value new IdentifierLiteral splatParamName
+              exprs.push new Assign new Value(param.name), ref
+              # Compile `foo({a, b...} = {}) ->` to `foo(arg = {}) -> {a, b...} = arg`.
+              if param.value?  and not param.assignedInBody
+                ref = new Assign ref, param.value, null, param: yes
           else
             o.scope.parameter fragmentsToText (if param.value? then param else ref).compileToFragments o
           params.push ref
@@ -2194,7 +2328,8 @@ exports.Code = class Code extends Base
             condition = new Op '===', param, new UndefinedLiteral
             ifTrue = new Assign new Value(param.name), param.value
             exprs.push new If condition, ifTrue
-          # Add this parameter to the scope, since it wouldn’t have been added yet since it was skipped earlier.
+          # Add this parameter to the scope, since it wouldn’t have been added
+          # yet since it was skipped earlier.
           o.scope.add param.name.value, 'var', yes if param.name?.value?
 
     # If there were parameters after the splat or expansion parameter, those
@@ -3181,6 +3316,13 @@ exports.If = class If extends Base
 
 UTILITIES =
   modulo: -> 'function(a, b) { return (+a % (b = +b) + b) % b; }'
+  objectWithoutKeys: -> "
+      function(o, ks) {
+        var res = {};
+        for (var k in o) ([].indexOf.call(ks, k) < 0 && {}.hasOwnProperty.call(o, k)) && (res[k] = o[k]);
+        return res;
+      }
+    "
   boundMethodCheck: -> "
     function(instance, Constructor) {
       if (!(instance instanceof Constructor)) {

test/argument-parsing.coffee

@@ -1,4 +1,5 @@
 return unless require?
+
 {buildCSOptionParser} = require '../lib/coffeescript/command'
 
 optionParser = buildCSOptionParser()

test/assignment.coffee

@@ -235,6 +235,154 @@ test "destructuring assignment against an expression", ->
   eq a, y
   eq b, z
 
+test "destructuring assignment with objects and splats: ES2015", ->
+  obj = {a: 1, b: 2, c: 3, d: 4, e: 5}
+  throws (-> CoffeeScript.compile "{a, r..., s...} = x"), null, "multiple rest elements are disallowed"
+  throws (-> CoffeeScript.compile "{a, r..., s..., b} = x"), null, "multiple rest elements are disallowed"
+  prop = "b"
+  {a, b, r...} = obj
+  eq a, 1
+  eq b, 2
+  eq r.e, obj.e
+  eq r.a, undefined
+  {d, c: x, r...} = obj
+  eq x, 3
+  eq d, 4
+  eq r.c, undefined
+  eq r.b, 2
+  {a, 'b': z, g = 9, r...} = obj
+  eq g, 9
+  eq z, 2
+  eq r.b, undefined
+
+test "destructuring assignment with splats and default values", ->
+  obj = {}
+  c = {b: 1}
+  { a: {b} = c, d...} = obj
+
+  eq b, 1
+  deepEqual d, {}
+
+test "destructuring assignment with splat with default value", ->
+  obj = {}
+  c = {val: 1}
+  { a: {b...} = c } = obj
+
+  deepEqual b, val: 1
+
+test "destructuring assignment with multiple splats in different objects", ->
+  obj = { a: {val: 1}, b: {val: 2} }
+  { a: {a...}, b: {b...} } = obj
+  deepEqual a, val: 1
+  deepEqual b, val: 2
+
+test "destructuring assignment with dynamic keys and splats", ->
+  i = 0
+  foo = -> ++i
+
+  obj = {1: 'a', 2: 'b'}
+  { "#{foo()}": a, b... } = obj
+
+  eq a, 'a'
+  eq i, 1
+  deepEqual b, 2: 'b'
+
+# Tests from https://babeljs.io/docs/plugins/transform-object-rest-spread/.
+test "destructuring assignment with objects and splats: Babel tests", ->
+  # What Babel calls “rest properties:”
+  { x, y, z... } = { x: 1, y: 2, a: 3, b: 4 }
+  eq x, 1
+  eq y, 2
+  deepEqual z, { a: 3, b: 4 }
+
+  # What Babel calls “spread properties:”
+  n = { x, y, z... }
+  deepEqual n, { x: 1, y: 2, a: 3, b: 4 }
+
+test "deep destructuring assignment with objects: ES2015", ->
+  a1={}; b1={}; c1={}; d1={}
+  obj = {
+    a: a1
+    b: {
+      'c': {
+        d: {
+          b1
+          e: c1
+          f: d1
+        }
+      }
+    }
+    b2: {b1, c1}
+  }
+  {a: w, b: {c: {d: {b1: bb, r1...}}}, r2...} = obj
+  eq r1.e, c1
+  eq r2.b, undefined
+  eq bb, b1
+  eq r2.b2, obj.b2
+
+test "deep destructuring assignment with defaults: ES2015", ->
+  obj =
+    b: { c: 1, baz: 'qux' }
+    foo: 'bar'
+  j =
+    f: 'world'
+  i =
+    some: 'prop'
+  {
+    a...
+    b: { c, d... }
+    e: {
+      f: hello
+      g: { h... } = i
+    } = j
+  } = obj
+
+  deepEqual a, foo: 'bar'
+  eq c, 1
+  deepEqual d, baz: 'qux'
+  eq hello, 'world'
+  deepEqual h, some: 'prop'
+
+test "object spread properties: ES2015", ->
+  obj = {a: 1, b: 2, c: 3, d: 4, e: 5}
+  obj2 = {obj..., c:9}
+  eq obj2.c, 9
+  eq obj.a, obj2.a
+
+  obj2 = {obj..., a: 8, c: 9, obj...}
+  eq obj2.c, 3
+  eq obj.a, obj2.a
+
+  obj3 = {obj..., b: 7, g: {obj2..., c: 1}}
+  eq obj3.g.c, 1
+  eq obj3.b, 7
+  deepEqual obj3.g, {obj..., c: 1}
+
+  (({a, b, r...}) ->
+    eq 1, a
+    deepEqual r, {c: 3, d: 44, e: 55}
+  ) {obj2..., d: 44, e: 55}
+
+  obj = {a: 1, b: 2, c: {d: 3, e: 4, f: {g: 5}}}
+  obj4 = {a: 10, obj.c...}
+  eq obj4.a, 10
+  eq obj4.d, 3
+  eq obj4.f.g, 5
+  deepEqual obj4.f, obj.c.f
+
+  obj5 = {obj..., ((k) -> {b: k})(99)...}
+  eq obj5.b, 99
+  deepEqual obj5.c, obj.c
+
+  fn = -> {c: {d: 33, e: 44, f: {g: 55}}}
+  obj6 = {obj..., fn()...}
+  eq obj6.c.d, 33
+  deepEqual obj6.c, {d: 33, e: 44, f: {g: 55}}
+
+  obj7 = {obj..., fn()..., {c: {d: 55, e: 66, f: {77}}}...}
+  eq obj7.c.d, 55
+  deepEqual obj6.c, {d: 33, e: 44, f: {g: 55}}
+
 test "bracket insertion when necessary", ->
   [a] = [0] ? [1]
   eq a, 0

test/error_messages.coffee

@@ -804,26 +804,27 @@ test "unexpected object keys", ->
     [[]]: 1
     ^
   '''
+
   assertErrorFormat '''
     {(a + "b")}
   ''', '''
-    [stdin]:1:2: error: unexpected (
+    [stdin]:1:11: error: unexpected }
     {(a + "b")}
-     ^
+              ^
   '''
   assertErrorFormat '''
     {(a + "b"): 1}
   ''', '''
-    [stdin]:1:2: error: unexpected (
+    [stdin]:1:11: error: unexpected :
     {(a + "b"): 1}
-     ^
+              ^
   '''
   assertErrorFormat '''
     (a + "b"): 1
   ''', '''
-    [stdin]:1:1: error: unexpected (
+    [stdin]:1:10: error: unexpected :
     (a + "b"): 1
-    ^
+             ^
   '''
   assertErrorFormat '''
     a: 1, [[]]: 2

test/functions.coffee

@@ -183,6 +183,69 @@ test "destructuring in function definition", ->
     url: '/home', async: true, beforeSend: fn, cache: true, method: 'post', data: {}
   }
 
+test "rest element destructuring in function definition", ->
+  obj = {a: 1, b: 2, c: 3, d: 4, e: 5}
+
+  (({a, b, r...}) ->
+    eq 1, a
+    eq 2, b,
+    deepEqual r, {c: 3, d: 4, e: 5}
+  ) obj
+
+  (({a: p, b, r...}, q) ->
+    eq p, 1
+    eq q, 9
+    deepEqual r, {c: 3, d: 4, e: 5}
+  ) {a:1, b:2, c:3, d:4, e:5}, 9
+
+  a1={}; b1={}; c1={}; d1={}
+  obj1 = {
+    a: a1
+    b: {
+      'c': {
+        d: {
+          b1
+          e: c1
+          f: d1
+        }
+      }
+    }
+    b2: {b1, c1}
+  }
+
+  (({a: w, b: {c: {d: {b1: bb, r1...}}}, r2...}) ->
+    eq a1, w
+    eq bb, b1
+    eq r2.b, undefined
+    deepEqual r1, {e: c1, f: d1}
+    deepEqual r2.b2, {b1, c1}
+  ) obj1
+
+  b = 3
+  f = ({a, b...}) ->
+  f {}
+  eq 3, b
+
+  (({a, r...} = {}) ->
+    eq a, undefined
+    deepEqual r, {}
+  )()
+
+  (({a, r...} = {}) ->
+    eq a, 1
+    deepEqual r, {b: 2, c: 3}
+  ) {a: 1, b: 2, c: 3}
+
+  f = ({a, r...} = {}) -> [a, r]
+  deepEqual [undefined, {}], f()
+  deepEqual [1, {b: 2}], f {a: 1, b: 2}
+  deepEqual [1, {}], f {a: 1}
+
+  f = ({a, r...} = {a: 1, b: 2}) -> [a, r]
+  deepEqual [1, {b:2}], f()
+  deepEqual [2, {}], f {a:2}
+  deepEqual [3, {c:5}], f {a:3, c:5}
+
 test "#4005: `([a = {}]..., b) ->` weirdness", ->
   fn = ([a = {}]..., b) -> [a, b]
   deepEqual fn(5), [{}, 5]