Add a for .. from .. loop for generators, see #3832

src/grammar.coffee

@@ -534,6 +534,8 @@ grammar =
     o 'FORIN Expression BY Expression',                 -> source: $2, step:  $4
     o 'FORIN Expression WHEN Expression BY Expression', -> source: $2, guard: $4, step: $6
     o 'FORIN Expression BY Expression WHEN Expression', -> source: $2, step:  $4, guard: $6
+    o 'FORFROM Expression',                             -> source: $2, from: yes
+    o 'FORFROM Expression WHEN Expression',               -> source: $2, guard: $4, from: yes
   ]
 
   Switch: [
@@ -643,7 +645,7 @@ operators = [
   ['nonassoc',  'INDENT', 'OUTDENT']
   ['right',     'YIELD']
   ['right',     '=', ':', 'COMPOUND_ASSIGN', 'RETURN', 'THROW', 'EXTENDS']
-  ['right',     'FORIN', 'FOROF', 'BY', 'WHEN']
+  ['right',     'FORIN', 'FOROF', 'FORFROM', 'BY', 'WHEN']
   ['right',     'IF', 'ELSE', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'SUPER', 'CLASS']
   ['left',      'POST_IF']
 ]

src/lexer.coffee

@@ -42,7 +42,7 @@ exports.Lexer = class Lexer
     @indents    = []             # The stack of all current indentation levels.
     @ends       = []             # The stack for pairing up tokens.
     @tokens     = []             # Stream of parsed tokens in the form `['TYPE', value, location data]`.
-    @seenFor    = no             # Used to recognize FORIN and FOROF tokens.
+    @seenFor    = no             # Used to recognize FORIN, FOROF and FORFROM tokens.
 
     @chunkLine =
       opts.line or 0         # The start line for the current @chunk.
@@ -121,7 +121,11 @@ exports.Lexer = class Lexer
         'PROPERTY'
       else
         'IDENTIFIER'
-
+
+    if tag is 'IDENTIFIER' and @seenFor and id is 'from'
+      tag = 'FORFROM'
+      @seenFor = no
+
     if tag is 'IDENTIFIER' and (id in JS_KEYWORDS or id in COFFEE_KEYWORDS)
       tag = id.toUpperCase()
       if tag is 'WHEN' and @tag() in LINE_BREAK

src/nodes.coffee

@@ -2095,13 +2095,15 @@ exports.For = class For extends While
     @body    = Block.wrap [body]
     @own     = !!source.own
     @object  = !!source.object
-    [@name, @index] = [@index, @name] if @object
+    @from    = !!source.from
+    [@name, @index] = [@index, @name] if @object or @from
     @index.error 'index cannot be a pattern matching expression' if @index instanceof Value
     @range   = @source instanceof Value and @source.base instanceof Range and not @source.properties.length
     @pattern = @name instanceof Value
     @index.error 'indexes do not apply to range loops' if @range and @index
     @name.error 'cannot pattern match over range loops' if @range and @pattern
     @name.error 'cannot use own with for-in' if @own and not @object
+    @name.error 'cannot use index with for-from' if @from and @name
     @returns = false
 
   children: ['body', 'source', 'guard', 'step']
@@ -2121,7 +2123,7 @@ exports.For = class For extends While
     scope.find(name)  if name and not @pattern
     scope.find(index) if index
     rvar        = scope.freeVariable 'results' if @returns
-    ivar        = (@object and index) or scope.freeVariable 'i', single: true
+    ivar        = ((@object or @from) and index) or scope.freeVariable 'i', single: true
     kvar        = (@range and name) or index or ivar
     kvarAssign  = if kvar isnt ivar then "#{kvar} = " else ""
     if @step and not @range
@@ -2142,7 +2144,7 @@ exports.For = class For extends While
         svar       = ref
       if name and not @pattern
         namePart   = "#{name} = #{svar}[#{kvar}]"
-      if not @object
+      if not (@object or @from)
         defPart += "#{@tab}#{step};\n" if step isnt stepVar
         down = stepNum < 0
         lvar = scope.freeVariable 'len' unless @step and stepNum? and down
@@ -2178,6 +2180,9 @@ exports.For = class For extends While
     if @object
       forPartFragments   = [@makeCode("#{kvar} in #{svar}")]
       guardPart = "\n#{idt1}if (!#{utility 'hasProp', o}.call(#{svar}, #{kvar})) continue;" if @own
+    if @from
+      forPartFragments   = [@makeCode("#{kvar} of #{svar}")]
+      guardPart = "\n"
     bodyFragments = body.compileToFragments merge(o, indent: idt1), LEVEL_TOP
     if bodyFragments and (bodyFragments.length > 0)
       bodyFragments = [].concat @makeCode("\n"), bodyFragments, @makeCode("\n")

test/arrays.coffee

@@ -107,3 +107,21 @@ test "regex interpolation in array", ->
   eq 2, arr.length
   eq 'ab', arr[0].source
   eq 'value', arr[1].key
+
+
+test "for-from loops over Array", ->
+  array1 = [50, 30, 70, 20]
+  array2 = []
+  for x from array1
+    array2.push(x)
+  arrayEq array1, array2
+
+
+test "for-from comprehensions over Array", ->
+
+  array1 = (x + 10 for x from [10, 20, 30])
+  ok array1.join(' ') is '20 30 40'
+
+  array2 = (x for x from [30, 41, 57] when x %% 3 == 0)
+  ok array2.join(' ') is '30 57'
+

test/compilation.coffee

@@ -123,3 +123,10 @@ test "#3001: `own` shouldn't be allowed in a `for`-`in` loop", ->
 
 test "#2994: single-line `if` requires `then`", ->
   cantCompile "if b else x"
+
+test "indexes are not supported in for-from loops", ->
+  cantCompile "x for x, i from [1, 2, 3]"
+
+test "own is not supported in for-from loops", ->
+  cantCompile "x for own x from [1, 2, 3]"
+

test/generators.coffee

@@ -250,3 +250,41 @@ test "yield handles 'this' correctly", ->
   ok z.done is false
 
   throws -> y.next new Error "boom"
+
+
+test "for-from comprehensions over generators", ->
+  array1 = [50, 30, 70, 20]
+  gen = -> yield from array1
+
+  array2 = []
+  array3 = []
+  array4 = []
+
+  iterator = gen()
+  for x from iterator
+    array2.push(x)
+    break if x is 30
+
+  for x from iterator
+    array3.push(x)
+
+  for x from iterator
+    array4.push(x)
+
+  arrayEq array2, [50, 30]
+  arrayEq array3, [70, 20]
+  arrayEq array4, []
+
+
+test "for-from comprehensions over generators", ->
+
+  gen = ->
+    yield from [30, 41, 51, 60]
+
+  iterator = gen()
+  array1 = (x for x from iterator when x %% 2 == 1)
+  array2 = (x for x from iterator)
+
+  ok array1.join(' ') is '41 51'
+  ok array2.length is 0
+