staticcheck: Fix unused fields

The embedded `nocmp` field and other similar fields are unused in tests
and the rest of our code.

We can get the effect of `nocmp` without embedding the fields by using
`_ nocmp` as a field.

bool.go

@@ -28,7 +28,7 @@ import (
 
 // Bool is an atomic type-safe wrapper for bool values.
 type Bool struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v Uint32
 }

duration.go

@@ -29,7 +29,7 @@ import (
 
 // Duration is an atomic type-safe wrapper for time.Duration values.
 type Duration struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v Int64
 }

error.go

@@ -24,7 +24,7 @@ package atomic
 
 // Error is an atomic type-safe wrapper for error values.
 type Error struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v Value
 }

float64.go

@@ -29,7 +29,7 @@ import (
 
 // Float64 is an atomic type-safe wrapper for float64 values.
 type Float64 struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v Uint64
 }

int32.go

@@ -30,7 +30,7 @@ import (
 
 // Int32 is an atomic wrapper around int32.
 type Int32 struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v int32
 }

int64.go

@@ -30,7 +30,7 @@ import (
 
 // Int64 is an atomic wrapper around int64.
 type Int64 struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v int64
 }

internal/gen-atomicint/main.go

@@ -135,7 +135,7 @@ import (
 
 // {{ .Name }} is an atomic wrapper around {{ .Wrapped }}.
 type {{ .Name }} struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v {{ .Wrapped }}
 }

internal/gen-atomicwrapper/main.go

@@ -227,7 +227,7 @@ import (
 
 // {{ .Name }} is an atomic type-safe wrapper for {{ .Type }} values.
 type {{ .Name }} struct{
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v {{ .Wrapped }}
 }

nocmp_test.go

@@ -77,14 +77,13 @@ func TestNocmpComparability(t *testing.T) {
 
 // nocmp must not add to the size of a struct in-memory.
 func TestNocmpSize(t *testing.T) {
-	type x struct{ i int }
+	type x struct{ _ int }
 
 	before := reflect.TypeOf(x{}).Size()
 
 	type y struct {
-		nocmp
-
-		x x
+		_ nocmp
+		_ x
 	}
 
 	after := reflect.TypeOf(y{}).Size()
@@ -100,7 +99,7 @@ func TestNocmpSize(t *testing.T) {
 //   var x atomic.Int32
 //   x = atomic.NewInt32(1)
 func TestNocmpCopy(t *testing.T) {
-	type foo struct{ nocmp }
+	type foo struct{ _ nocmp }
 
 	t.Run("struct copy", func(t *testing.T) {
 		a := foo{}

string.go

@@ -24,7 +24,7 @@ package atomic
 
 // String is an atomic type-safe wrapper for string values.
 type String struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v Value
 }

uint32.go

@@ -30,7 +30,7 @@ import (
 
 // Uint32 is an atomic wrapper around uint32.
 type Uint32 struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v uint32
 }

uint64.go

@@ -30,7 +30,7 @@ import (
 
 // Uint64 is an atomic wrapper around uint64.
 type Uint64 struct {
-	nocmp // disallow non-atomic comparison
+	_ nocmp // disallow non-atomic comparison
 
 	v uint64
 }

value.go

@@ -25,6 +25,7 @@ import "sync/atomic"
 // Value shadows the type of the same name from sync/atomic
 // https://godoc.org/sync/atomic#Value
 type Value struct {
-	nocmp // disallow non-atomic comparison
 	atomic.Value
+
+	_ nocmp // disallow non-atomic comparison
 }