Allow computed class properties (#5206)

* fix broken JS output

* static computed properties

Author: helixbass

lib/coffeescript/grammar.js

@@ -222,6 +222,7 @@ grammar =
   ObjAssignable: [
     o 'SimpleObjAssignable'
     o '[ Expression ]',          -> new Value new ComputedPropertyName $2
+    o '@ [ Expression ]',        -> new Value LOC(1)(new ThisLiteral $1), [LOC(3)(new ComputedPropertyName($3))], 'this'
     o 'AlphaNumeric'
   ]
 

lib/coffeescript/nodes.js

@@ -2007,7 +2007,11 @@ exports.ExecutableClassBody = class ExecutableClassBody extends Base
         # The class scope is not available yet, so return the assignment to update later
         assign = @externalCtor = new Assign new Value, value
       else if not assign.variable.this
-        name      = new (if base.shouldCache() then Index else Access) base
+        name =
+          if base instanceof ComputedPropertyName
+            new Index base.value
+          else
+            new (if base.shouldCache() then Index else Access) base
         prototype = new Access new PropertyName 'prototype'
         variable  = new Value new ThisLiteral(), [ prototype, name ]
 

lib/coffeescript/parser.js

@@ -118,14 +118,21 @@ exports.Rewriter = class Rewriter
   # The lexer has tagged the opening bracket of an indexing operation call.
   # Match it with its paired close.
   closeOpenIndexes: ->
+    startToken = null
     condition = (token, i) ->
       token[0] in [']', 'INDEX_END']
 
     action = (token, i) ->
-      token[0] = 'INDEX_END'
+      if @tokens.length >= i and @tokens[i + 1][0] is ':'
+        startToken[0] = '['
+        token[0] = ']'
+      else
+        token[0] = 'INDEX_END'
 
     @scanTokens (token, i) ->
-      @detectEnd i + 1, condition, action if token[0] is 'INDEX_START'
+      if token[0] is 'INDEX_START'
+        startToken = token
+        @detectEnd i + 1, condition, action
       1
 
   # Match tags in token stream starting at `i` with `pattern`.
@@ -321,7 +328,12 @@ exports.Rewriter = class Rewriter
       if tag is ':'
         # Go back to the (implicit) start of the object.
         s = switch
-          when @tag(i - 1) in EXPRESSION_END then start[1]
+          when @tag(i - 1) in EXPRESSION_END
+            [startTag, startIndex] = start
+            if startTag is '[' and startIndex > 0 and @tag(startIndex - 1) is '@' and not tokens[startIndex - 1].spaced
+              startIndex - 1
+            else
+              startIndex
           when @tag(i - 2) is '@' then i - 2
           else i - 1
 

lib/coffeescript/rewriter.js

@@ -1935,3 +1935,20 @@ test "#5085: Bug: @ reference to class not maintained in do block", ->
 
   eq thisFoo, 'foo assigned in class'
   eq thisBar, 'foo assigned in class'
+
+test "#5204: Computed class property", ->
+  foo = 'bar'
+  class A
+    [foo]: 'baz'
+  a = new A()
+  eq a.bar, 'baz'
+  eq A::bar, 'baz'
+
+test "#5204: Static computed class property", ->
+  foo = 'bar'
+  qux = 'quux'
+  class A
+    @[foo]: 'baz'
+    @[qux]: -> 3
+  eq A.bar, 'baz'
+  eq A.quux(), 3

src/grammar.coffee

@@ -855,6 +855,13 @@ test "invalid object keys", ->
     {a=2}
       ^
   '''
+  assertErrorFormat '''
+    @[a]: 1
+  ''', '''
+    [stdin]:1:1: error: invalid object key
+    @[a]: 1
+    ^^^^
+  '''
 
 test "invalid destructuring default target", ->
   assertErrorFormat '''

src/nodes.coffee

@@ -903,3 +903,6 @@ test "#4579: Postfix for/while/until in first line of implicit object literals",
       baz: 1337
   arrayEq [4, 3, 2, 1, 0], six.foo.bar
   eq 1337, six.foo.baz
+
+test "#5204: not parsed as static property", ->
+  doesNotThrow -> CoffeeScript.compile "@ [b]: 2"