Issue #943 -- splices with expressions.

Author: jashkenas

Cakefile

@@ -165,8 +165,8 @@ runTests = (CoffeeScript) ->
     try
       fn()
     catch e
-      e.message = description if description?
-      e.source  = fn.toString() if fn.toString?
+      e.description = description if description?
+      e.source      = fn.toString() if fn.toString?
       failures.push file: currentFile, error: e
 
   # A recursive functional equivalence helper; uses egal for testing equivalence.
@@ -197,7 +197,8 @@ runTests = (CoffeeScript) ->
       jsFile             = file.replace(/\.coffee$/,'.js')
       match              = error.stack?.match(new RegExp(fail.file+":(\\d+):(\\d+)"))
       [match, line, col] = match if match
-      log "\n  #{error.message}", red if error.message
+      log "\n  #{error.toString()}", red
+      log "  #{error.description}", red if error.description
       log "  #{jsFile}: line #{line or 'unknown'}, column #{col or 'unknown'}", red
       console.log "  #{error.source}" if error.source
 

lib/nodes.js

@@ -969,17 +969,20 @@ exports.Assign = class Assign extends Base
     {range} = @variable.properties.pop()
     name    = @variable.compile o
     excl    = range.exclusive
-    from    = if range.from then range.from.compile(o) else '0'
     to      = "#{name}.length" unless range.to
+    if range.from
+      [fromDecl, fromRef] = range.from.cache o, LEVEL_OP
+    else
+      [fromDecl, fromRef] = ['0', '0']
     unless to
       if range.from and range.from.isSimpleNumber() and range.to.isSimpleNumber()
-        to = +range.to.compile(o) - +from
+        to = +range.to.compile(o) - +fromRef
         to += 1 unless excl
       else
-        to = range.to.compile(o) + ' - ' + from
+        to = range.to.compile(o) + ' - ' + fromRef
         to += ' + 1' unless excl
     val = @value.compile(o)
-    "[].splice.apply(#{name}, [#{from}, #{to}].concat(#{val}))"
+    "[].splice.apply(#{name}, [#{fromDecl}, #{to}].concat(#{val}))"
 
 #### Code
 
@@ -1193,6 +1196,8 @@ exports.Op = class Op extends Base
 
   children: ['first', 'second']
 
+  isSimpleNumber: NO
+
   isUnary: ->
     not @second
 

src/nodes.coffee

@@ -153,10 +153,9 @@ test "splicing with variables as endpoints", ->
   ary[a...b] = [5]
   arrayEq [0, 5, 8, 9], ary
 
-# currently broken:
-# test "splicing with expressions as endpoints", ->
-#   [a, b] = [1, 3]
-# 
-#   ary = [0..9]
-#   ary[ a+1 .. 2*b+1 ] = [4]
-#   arrayEq [0, 1, 4, 7, 8, 9], ary
+test "splicing with expressions as endpoints", ->
+  [a, b] = [1, 3]
+
+  ary = [0..9]
+  ary[ a+1 .. 2*b+1 ] = [4]
+  arrayEq [0, 1, 4, 8, 9], ary