Selectively ignore CS-only keywords in ES imports and exports (jashkenas#4347)

Author: GabrielRatener

lib/coffee-script/lexer.js

@@ -45,6 +45,7 @@ exports.Lexer = class Lexer
     @seenFor    = no             # Used to recognize FORIN and FOROF tokens.
     @seenImport = no             # Used to recognize IMPORT FROM? AS? tokens.
     @seenExport = no             # Used to recognize EXPORT FROM? AS? tokens.
+    @exportSpecifierList = no    # Used to identify when in an EXPORT {...} FROM? ...
 
     @chunkLine =
       opts.line or 0         # The start line for the current @chunk.
@@ -115,10 +116,14 @@ exports.Lexer = class Lexer
     if id is 'from' and @tag() is 'YIELD'
       @token 'FROM', id
       return id.length
-    if id is 'as' and @seenImport and (@tag() is 'IDENTIFIER' or @value() is '*')
-      @tokens[@tokens.length - 1][0] = 'IMPORT_ALL' if @value() is '*'
-      @token 'AS', id
-      return id.length
+    if id is 'as' and @seenImport
+      if @value() is '*'
+        @tokens[@tokens.length - 1][0] = 'IMPORT_ALL'
+      else if @value() in COFFEE_KEYWORDS
+        @tokens[@tokens.length - 1][0] = 'IDENTIFIER'
+      if @tag() in ['IMPORT_ALL', 'IDENTIFIER']
+        @token 'AS', id
+        return id.length
     if id is 'as' and @seenExport and @tag() is 'IDENTIFIER'
       @token 'AS', id
       return id.length
@@ -136,7 +141,8 @@ exports.Lexer = class Lexer
       else
         'IDENTIFIER'
 
-    if tag is 'IDENTIFIER' and (id in JS_KEYWORDS or id in COFFEE_KEYWORDS)
+    if tag is 'IDENTIFIER' and (id in JS_KEYWORDS or id in COFFEE_KEYWORDS) and
+       not (@exportSpecifierList and id in COFFEE_KEYWORDS)
       tag = id.toUpperCase()
       if tag is 'WHEN' and @tag() in LINE_BREAK
         tag = 'LEADING_WHEN'
@@ -456,6 +462,11 @@ exports.Lexer = class Lexer
         @error message, origin[2] if message
       return value.length if skipToken
 
+    if value is '{' and prev?[0] is 'EXPORT'
+      @exportSpecifierList = yes
+    else if @exportSpecifierList and value is '}'
+      @exportSpecifierList = no
+
     if value is ';'
       @seenFor = @seenImport = @seenExport = no
       tag = 'TERMINATOR'

src/lexer.coffee

@@ -1154,3 +1154,23 @@ test "imported members cannot be reassigned", ->
     export foo = 'bar'
            ^^^
   '''
+
+test "CS only keywords can't be used as unaliased names in import lists", ->
+  assertErrorFormat """
+    import { unless, baz as bar } from 'lib'
+    bar.barMethod()
+  """, '''
+    [stdin]:1:10: error: unexpected unless
+    import { unless, baz as bar } from 'lib'
+             ^^^^^^
+  '''
+
+test "CS only keywords can't be used as local names in import list aliases", ->
+  assertErrorFormat """
+    import { bar as unless, baz as bar } from 'lib'
+    bar.barMethod()
+  """, '''
+    [stdin]:1:17: error: unexpected unless
+    import { bar as unless, baz as bar } from 'lib'
+                    ^^^^^^
+  '''

test/error_messages.coffee

@@ -510,6 +510,23 @@ test "export as aliases members imported from another module", ->
     } from 'lib';"""
   eq toJS(input), output
 
+test "export list can contain CS only keywords", ->
+  input = "export { unless } from 'lib'"
+  output = """
+    export {
+      unless
+    } from 'lib';"""
+  eq toJS(input), output
+
+test "export list can contain CS only keywords when aliasing", ->
+  input = "export { when as bar, baz as unless } from 'lib'"
+  output = """
+    export {
+      when as bar,
+      baz as unless
+    } from 'lib';"""
+  eq toJS(input), output
+
 
 # Edge cases
 
@@ -608,6 +625,18 @@ test "`as` can be used as an alias name", ->
     } from 'lib';"""
   eq toJS(input), output
 
+test "CS only keywords can be used as imported names in import lists", ->
+  input = """
+    import { unless as bar } from 'lib'
+    bar.barMethod()"""
+  output = """
+    import {
+      unless as bar
+    } from 'lib';
+
+    bar.barMethod();"""
+  eq toJS(input), output
+
 test "`*` can be used in an expression on the same line as an export keyword", ->
   input = "export foo = (x) -> x * x"
   output = """