Dynamic import

src/grammar.coffee

@@ -240,6 +240,7 @@ grammar =
     o 'Super'
     o 'This'
     o 'SUPER Arguments',               -> new SuperCall LOC(1)(new Super), $2, no, $1
+    o 'DYNAMIC_IMPORT Arguments',      -> new DynamicImportCall LOC(1)(new DynamicImport), $2
     o 'SimpleObjAssignable Arguments', -> new Call (new Value $1), $2
     o 'ObjSpreadExpr Arguments',       -> new Call $1, $2
   ]
@@ -485,6 +486,7 @@ grammar =
     o 'Value OptFuncExist String',              -> new TaggedTemplateCall $1, $3, $2
     o 'Value OptFuncExist Arguments',           -> new Call $1, $3, $2
     o 'SUPER OptFuncExist Arguments',           -> new SuperCall LOC(1)(new Super), $3, $2, $1
+    o 'DYNAMIC_IMPORT Arguments',               -> new DynamicImportCall LOC(1)(new DynamicImport), $2
   ]
 
   # An optional existence check on a function.
@@ -891,7 +893,7 @@ operators = [
   ['right',     'YIELD']
   ['right',     '=', ':', 'COMPOUND_ASSIGN', 'RETURN', 'THROW', 'EXTENDS']
   ['right',     'FORIN', 'FOROF', 'FORFROM', 'BY', 'WHEN']
-  ['right',     'IF', 'ELSE', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'SUPER', 'CLASS', 'IMPORT', 'EXPORT']
+  ['right',     'IF', 'ELSE', 'FOR', 'WHILE', 'UNTIL', 'LOOP', 'SUPER', 'CLASS', 'IMPORT', 'EXPORT', 'DYNAMIC_IMPORT']
   ['left',      'POST_IF']
 ]
 

src/lexer.coffee

@@ -667,6 +667,9 @@ exports.Lexer = class Lexer
         @error message, origin[2] if message
       return value.length if skipToken
 
+    if value is '(' and prev?[0] is 'IMPORT'
+      prev[0] = 'DYNAMIC_IMPORT'
+
     if value is '{' and @seenImport
       @importSpecifierList = yes
     else if @importSpecifierList and value is '}'
@@ -1356,7 +1359,7 @@ BOOL = ['TRUE', 'FALSE']
 # Tokens which could legitimately be invoked or indexed. An opening
 # parentheses or bracket following these tokens will be recorded as the start
 # of a function invocation or indexing operation.
-CALLABLE  = ['IDENTIFIER', 'PROPERTY', ')', ']', '?', '@', 'THIS', 'SUPER']
+CALLABLE  = ['IDENTIFIER', 'PROPERTY', ')', ']', '?', '@', 'THIS', 'SUPER', 'DYNAMIC_IMPORT']
 INDEXABLE = CALLABLE.concat [
   'NUMBER', 'INFINITY', 'NAN', 'STRING', 'STRING_END', 'REGEX', 'REGEX_END'
   'BOOL', 'NULL', 'UNDEFINED', '}', '::'

src/nodes.coffee

@@ -2172,6 +2172,16 @@ exports.ExportSpecifier = class ExportSpecifier extends ModuleSpecifier
   constructor: (local, exported) ->
     super local, exported, 'export'
 
+exports.DynamicImport = class DynamicImport extends Base
+  compileNode: ->
+    [@makeCode 'import']
+
+exports.DynamicImportCall = class DynamicImportCall extends Call
+  compileNode: (o) ->
+    unless @args.length is 1
+      @error 'import() requires exactly one argument'
+    super o
+
 #### Assign
 
 # The **Assign** is used to assign a local variable to value, or to set the

test/error_messages.coffee

@@ -1925,3 +1925,29 @@ test "`new.target` is only allowed meta property", ->
     -> new.something
        ^^^^^^^^^^^^^
   '''
+
+test "#4834: dynamic import requires exactly one argument", ->
+  assertErrorFormat '''
+    import()
+  ''', '''
+    [stdin]:1:1: error: import() requires exactly one argument
+    import()
+    ^^^^^^^^
+  '''
+
+  assertErrorFormat '''
+    import('x', {})
+  ''', '''
+    [stdin]:1:1: error: import() requires exactly one argument
+    import('x', {})
+    ^^^^^^^^^^^^^^^
+  '''
+
+test "#4834: dynamic import requires explicit call parentheses", ->
+  assertErrorFormat '''
+    promise = import 'foo'
+  ''', '''
+    [stdin]:1:23: error: unexpected end of input
+    promise = import 'foo'
+                          ^
+  '''

test/modules.coffee

@@ -920,3 +920,24 @@ test "#4874: backslash `export`", ->
       min
     } from 'underscore';
     """
+
+test "#4834: dynamic import", ->
+  eqJS """
+    import('module').then ->
+  """,
+  """
+    import('module').then(function() {});
+  """
+
+  eqJS """
+    foo = ->
+      bar = await import('bar')
+  """,
+  """
+    var foo;
+
+    foo = async function() {
+      var bar;
+      return bar = (await import('bar'));
+    };
+  """

test/object_rest_spread.coffee

@@ -418,3 +418,13 @@ test "#4673: complex destructured object spread variables", ->
   g = ({@y...}) ->
     eq @y.b, 1
   g b: 1
+
+test "#4834: dynamic import can technically be object spread", ->
+  eqJS """
+    x = {...import('module')}
+  """,
+  """
+    var x;
+
+    x = {...import('module')};
+  """