From 9c574cbde61433fbdf9bad168b5ddd78984bf1d8 Mon Sep 17 00:00:00 2001
From: Akshay Shah <akshay@akshayshah.org>
Date: Sat, 5 Feb 2022 00:01:35 -0800
Subject: [PATCH] Make assert package more type-safe

Use generics to make the assert package more type-safe (and drop some
unfortunate reflection). Asserting that two values of different types
are equal is now a compile-time type error rather than a head-scratcher
of a diff!
---
 internal/assert/assert.go      | 29 +++++++++--------------------
 internal/assert/assert_test.go |  3 ++-
 2 files changed, 11 insertions(+), 21 deletions(-)

diff --git a/internal/assert/assert.go b/internal/assert/assert.go
index 724398a9..a9b927f5 100644
--- a/internal/assert/assert.go
+++ b/internal/assert/assert.go
@@ -73,7 +73,7 @@ func Diff() Option {
 }
 
 // Equal asserts that two values are equal.
-func Equal(t testing.TB, got, want any, msg string, opts ...Option) bool {
+func Equal[T any](t testing.TB, got, want T, msg string, opts ...Option) bool {
 	t.Helper()
 	params := newParams(got, want, msg, opts...)
 	if cmp.Equal(got, want, params.cmpOpts...) {
@@ -84,7 +84,7 @@ func Equal(t testing.TB, got, want any, msg string, opts ...Option) bool {
 }
 
 // NotEqual asserts that two values aren't equal.
-func NotEqual(t testing.TB, got, want any, msg string, opts ...Option) bool {
+func NotEqual[T any](t testing.TB, got, want T, msg string, opts ...Option) bool {
 	t.Helper()
 	params := newParams(got, want, msg, opts...)
 	if !cmp.Equal(got, want, params.cmpOpts...) {
@@ -117,12 +117,9 @@ func NotNil(t testing.TB, got any, msg string, opts ...Option) bool {
 }
 
 // Zero asserts that the value is its type's zero value.
-func Zero(t testing.TB, got any, msg string, opts ...Option) bool {
+func Zero[T any](t testing.TB, got T, msg string, opts ...Option) bool {
 	t.Helper()
-	if got == nil {
-		return true
-	}
-	want := makeZero(got)
+	var want T
 	params := newParams(got, want, msg, opts...)
 	if cmp.Equal(got, want, params.cmpOpts...) {
 		return true
@@ -132,16 +129,13 @@ func Zero(t testing.TB, got any, msg string, opts ...Option) bool {
 }
 
 // NotZero asserts that the value is non-zero.
-func NotZero(t testing.TB, got any, msg string, opts ...Option) bool {
+func NotZero[T any](t testing.TB, got T, msg string, opts ...Option) bool {
 	t.Helper()
-	if got != nil {
-		want := makeZero(got)
-		params := newParams(got, want, msg, opts...)
-		if !cmp.Equal(got, want, params.cmpOpts...) {
-			return true
-		}
+	var want T
+	params := newParams(got, want, msg, opts...)
+	if !cmp.Equal(got, want, params.cmpOpts...) {
+		return true
 	}
-	params := newParams(got, nil, msg, opts...)
 	report(t, params, fmt.Sprintf("assert.NotZero (type %T)", got), false /* showWant */)
 	return false
 }
@@ -243,8 +237,3 @@ func isNil(got any) bool {
 		return false
 	}
 }
-
-func makeZero(i any) any {
-	typ := reflect.TypeOf(i)
-	return reflect.Zero(typ).Interface()
-}
diff --git a/internal/assert/assert_test.go b/internal/assert/assert_test.go
index 7a5b3cfb..06a6fb3e 100644
--- a/internal/assert/assert_test.go
+++ b/internal/assert/assert_test.go
@@ -38,7 +38,8 @@ func TestAssertions(t *testing.T) {
 	})
 
 	t.Run("zero", func(t *testing.T) {
-		Zero(t, nil, "")
+		var n *int
+		Zero(t, n, "")
 		var pair Pair
 		Zero(t, pair, "")
 		var null *Pair