Do not delay execution nor bind over values in json_map, closes #94 (#95)

Author: josevalim

lib/helpers.ex

@@ -30,12 +30,20 @@ defmodule Jason.Helpers do
 
   """
   defmacro json_map(kv) do
+    kv_values = Macro.expand(kv, __CALLER__)
+    kv_vars = Enum.map(kv_values, fn {key, _} -> {key, generated_var(key, Codegen)} end)
+
+    values = Enum.map(kv_values, &elem(&1, 1))
+    vars = Enum.map(kv_vars, &elem(&1, 1))
+
     escape = quote(do: escape)
     encode_map = quote(do: encode_map)
     encode_args = [escape, encode_map]
-    kv_iodata = Codegen.build_kv_iodata(Macro.expand(kv, __CALLER__), encode_args)
+    kv_iodata = Codegen.build_kv_iodata(kv_vars, encode_args)
 
     quote do
+      {unquote_splicing(vars)} = {unquote_splicing(values)}
+
       %Fragment{
         encode: fn {unquote(escape), unquote(encode_map)} ->
           unquote(kv_iodata)

test/helpers_test.exs

@@ -7,6 +7,14 @@ defmodule Jason.HelpersTest do
   doctest Helpers
 
   describe "json_map/2" do
+    test "does not delay execution" do
+      %Fragment{} = json_map(
+        foo: Process.put(:json, :bar)
+      )
+
+      assert Process.get(:json) == :bar
+    end
+
     test "produces same output as regular encoding" do
       assert %Fragment{} = helper = json_map(bar: 2, baz: 3, foo: 1)
       assert Jason.encode!(helper) == Jason.encode!(%{bar: 2, baz: 3, foo: 1})