Fix Mix.Dep.Lock.write/2 ignoring :file option when comparing changes

lib/mix/lib/mix/dep/lock.ex

@@ -42,7 +42,7 @@ defmodule Mix.Dep.Lock do
   def write(map, opts \\ []) do
     lockfile = opts[:file] || lockfile()
 
-    if map != read() do
+    if map != read(lockfile) do
       if Keyword.get(opts, :check_locked, false) do
         Mix.raise(
           "Your #{lockfile} is out of date and must be updated without the --check-locked flag"

lib/mix/test/mix/dep/lock_test.exs

@@ -46,6 +46,17 @@ defmodule Mix.Dep.LockTest do
     end)
   end
 
+  test "does not raise with check_locked when custom lockfile is unchanged", context do
+    in_tmp(context.test, fn ->
+      custom_lockfile = Path.expand("custom.lock")
+
+      Mix.Dep.Lock.write(%{foo: :bar})
+      Mix.Dep.Lock.write(%{bar: :baz}, file: custom_lockfile)
+
+      Mix.Dep.Lock.write(%{bar: :baz}, file: custom_lockfile, check_locked: true)
+    end)
+  end
+
   test "raises a proper error if check_locked opt is true and there are changes", context do
     in_tmp(context.test, fn ->
       Mix.Dep.Lock.write(%{foo: :bar})