lift expressions from chain indexes on update operator, fixes #185

moonscript/transform/statement.lua

@@ -353,18 +353,85 @@ return Transformer({
     if not op_final then
       error("Unknown op: " .. op)
     end
+    local lifted
+    if ntype(name) == "chain" then
+      lifted = { }
+      local new_chain
+      do
+        local _accum_0 = { }
+        local _len_0 = 1
+        for _index_0 = 3, #name do
+          local part = name[_index_0]
+          if ntype(part) == "index" then
+            local proxy = NameProxy("update")
+            table.insert(lifted, {
+              proxy,
+              part[2]
+            })
+            _accum_0[_len_0] = {
+              "index",
+              proxy
+            }
+          else
+            _accum_0[_len_0] = part
+          end
+          _len_0 = _len_0 + 1
+        end
+        new_chain = _accum_0
+      end
+      if next(lifted) then
+        name = {
+          name[1],
+          name[2],
+          unpack(new_chain)
+        }
+      end
+    end
     if not (value_is_singular(exp)) then
       exp = {
         "parens",
         exp
       }
     end
-    return build.assign_one(name, {
+    local out = build.assign_one(name, {
       "exp",
       name,
       op_final,
       exp
     })
+    if lifted and next(lifted) then
+      local names
+      do
+        local _accum_0 = { }
+        local _len_0 = 1
+        for _index_0 = 1, #lifted do
+          local l = lifted[_index_0]
+          _accum_0[_len_0] = l[1]
+          _len_0 = _len_0 + 1
+        end
+        names = _accum_0
+      end
+      local values
+      do
+        local _accum_0 = { }
+        local _len_0 = 1
+        for _index_0 = 1, #lifted do
+          local l = lifted[_index_0]
+          _accum_0[_len_0] = l[2]
+          _len_0 = _len_0 + 1
+        end
+        values = _accum_0
+      end
+      out = build.group({
+        {
+          "assign",
+          names,
+          values
+        },
+        out
+      })
+    end
+    return out
   end,
   import = function(self, node)
     local names, source = unpack(node, 2)

moonscript/transform/statement.moon

@@ -229,9 +229,37 @@ Transformer {
   update: (node) =>
     name, op, exp = unpack node, 2
     op_final = op\match "^(.+)=$"
+
     error "Unknown op: "..op if not op_final
+
+    local lifted
+
+    if ntype(name) == "chain"
+      lifted = {}
+      new_chain = for part in *name[3,]
+        if ntype(part) == "index"
+          proxy = NameProxy "update"
+          table.insert lifted, { proxy, part[2] }
+          { "index", proxy }
+        else
+          part
+
+      if next lifted
+        name = {name[1], name[2], unpack new_chain}
+
     exp = {"parens", exp} unless value_is_singular exp
-    build.assign_one name, {"exp", name, op_final, exp}
+    out = build.assign_one name, {"exp", name, op_final, exp}
+
+    if lifted and next lifted
+      names = [l[1] for l in *lifted]
+      values = [l[2] for l in *lifted]
+
+      out = build.group {
+        {"assign", names, values}
+        out
+      }
+
+    out
 
   import: (node) =>
     names, source = unpack node, 2

spec/inputs/syntax.moon

@@ -158,6 +158,10 @@ hello ..= "world"
 @@something += 10
 @something += 10
 
+a["hello"] += 10
+a["hello#{tostring ff}"] += 10
+a[four].x += 10
+
 x = 0
 (if ntype(v) == "fndef" then x += 1) for v in *values
 

spec/outputs/syntax.lua

@@ -162,6 +162,12 @@ local m = m % 2
 local hello = hello .. "world"
 self.__class.something = self.__class.something + 10
 self.something = self.something + 10
+local _update_0 = "hello"
+a[_update_0] = a[_update_0] + 10
+local _update_1 = "hello" .. tostring(tostring(ff))
+a[_update_1] = a[_update_1] + 10
+local _update_2 = four
+a[_update_2].x = a[_update_2].x + 10
 x = 0
 local _list_0 = values
 for _index_0 = 1, #_list_0 do