Fix diffing for variable structs, closes #9958

Author: josevalim

lib/ex_unit/lib/ex_unit/diff.ex

@@ -82,17 +82,12 @@ defmodule ExUnit.Diff do
     diff_tuple(Tuple.to_list(left), Tuple.to_list(right), env)
   end
 
-  defp diff_quoted({:%, _, [struct, {:%{}, _, kw}]}, %{} = right, env)
-       when is_atom(struct) and is_list(kw) do
-    diff_quoted_struct([__struct__: struct] ++ kw, struct, right, env)
+  defp diff_quoted({:%, _, [struct, {:%{}, _, kw}]}, %{} = right, env) when is_list(kw) do
+    diff_quoted_struct([__struct__: struct] ++ kw, right, env)
   end
 
-  defp diff_quoted({:%{}, _, items}, %{} = right, env) when is_list(items) do
-    if struct = items[:__struct__] do
-      diff_quoted_struct(items, struct, right, env)
-    else
-      diff_map(items, right, nil, maybe_struct(right), env)
-    end
+  defp diff_quoted({:%{}, _, kw}, %{} = right, env) when is_list(kw) do
+    diff_quoted_struct(kw, right, env)
   end
 
   defp diff_quoted({:<>, _, [literal, _]} = left, right, env)
@@ -628,8 +623,9 @@ defmodule ExUnit.Diff do
 
   # Structs
 
-  defp diff_quoted_struct(kw, struct1, right, env) do
-    left = load_struct(struct1)
+  defp diff_quoted_struct(kw, right, env) do
+    struct1 = kw[:__struct__]
+    left = load_struct(kw[:__struct__])
 
     if left && Enum.all?(kw, fn {k, _} -> Map.has_key?(left, k) end) do
       if Macro.quoted_literal?(kw) do
@@ -676,7 +672,8 @@ defmodule ExUnit.Diff do
   end
 
   defp load_struct(struct) do
-    if Code.ensure_loaded?(struct) and function_exported?(struct, :__struct__, 0) do
+    if is_atom(struct) and struct != nil and
+         Code.ensure_loaded?(struct) and function_exported?(struct, :__struct__, 0) do
       struct.__struct__
     end
   end

lib/ex_unit/test/ex_unit/diff_test.exs

@@ -627,7 +627,7 @@ defmodule ExUnit.DiffTest do
     )
   end
 
-  test "structs with inspect difference" do
+  test "structs with same inspect but different" do
     refute_diff(
       %Opaque{data: 1} = %Opaque{data: 2},
       "%ExUnit.DiffTest.Opaque{data: -1-}",
@@ -641,7 +641,7 @@ defmodule ExUnit.DiffTest do
     )
   end
 
-  test "structs without inspect difference outside match" do
+  test "structs with same inspect but different outside match" do
     refute_diff(
       %Opaque{data: 1} == %Opaque{data: 2},
       "%ExUnit.DiffTest.Opaque{data: -1-}",
@@ -663,6 +663,66 @@ defmodule ExUnit.DiffTest do
     )
   end
 
+  test "structs with matched type" do
+    pins = %{{:type, nil} => User, {:age, nil} => 33}
+
+    # pin on __struct__
+    assert_diff(
+      %{__struct__: ^type, age: ^age, name: "john"} = %User{name: "john", age: 33},
+      [],
+      pins
+    )
+
+    refute_diff(
+      %{__struct__: ^type, age: ^age, name: "john"} = %User{name: "jane", age: 33},
+      "%{__struct__: ^type, age: ^age, name: \"j-oh-n\"}",
+      "%ExUnit.DiffTest.User{age: 33, name: \"j+a+n+e+\"}",
+      pins
+    )
+
+    refute_diff(
+      %{__struct__: ^type, age: ^age, name: "john"} = %User{name: "john", age: 35},
+      "%{__struct__: ^type, age: -^age-, name: \"john\"}",
+      "%ExUnit.DiffTest.User{age: 3+5+, name: \"john\"}",
+      pins
+    )
+
+    refute_diff(
+      %{__struct__: ^type, age: ^age, name: "john"} = ~D[2020-01-01],
+      "%{__struct__: -^type-, -age: ^age-, -name: \"john\"-}",
+      "%+Date+{calendar: Calendar.ISO, day: 1, month: 1, year: 2020}",
+      pins
+    )
+
+    # pin on %
+    assert_diff(
+      %^type{age: ^age, name: "john"} = %User{name: "john", age: 33},
+      [],
+      pins
+    )
+
+    refute_diff(
+      %^type{age: ^age, name: "john"} = %User{name: "jane", age: 33},
+      "%{__struct__: ^type, age: ^age, name: \"j-oh-n\"}",
+      "%ExUnit.DiffTest.User{age: 33, name: \"j+a+n+e+\"}",
+      pins
+    )
+
+    refute_diff(
+      %^type{age: ^age, name: "john"} = %User{name: "john", age: 35},
+      "%{__struct__: ^type, age: -^age-, name: \"john\"}",
+      "%ExUnit.DiffTest.User{age: 3+5+, name: \"john\"}",
+      pins
+    )
+
+    refute_diff(
+      %^type{age: ^age, name: "john"} = ~D[2020-01-01],
+      "%{__struct__: -^type-, -age: ^age-, -name: \"john\"-}",
+      "%+Date+{calendar: Calendar.ISO, day: 1, month: 1, year: 2020}",
+      pins
+    )
+  end
+
   test "invalid structs" do
     refute_diff(
       %{__struct__: Unknown} = %{},