quic: add go1.21 build constraint

This package will add on crypto/tls features added in Go 1.21,
so use a build constraint to restrict ourselves to that version.

Unlocks the ability to use other features from Go versions more recent
than what's in x/net's go.mod file.

For golang/go#58547

Change-Id: I14011c7506b047e389d9b3e995c0bafcd5e74d44
Reviewed-on: https://go-review.googlesource.com/c/net/+/499283
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Damien Neil <dneil@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

internal/quic/errors.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/files_test.go

@@ -0,0 +1,51 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build go1.21
+
+package quic
+
+import (
+	"bytes"
+	"os"
+	"strings"
+	"testing"
+)
+
+// TestFiles checks that every file in this package has a build constraint on Go 1.21.
+//
+// The QUIC implementation depends on crypto/tls features added in Go 1.21,
+// so there's no point in trying to build on anything older.
+//
+// Drop this test when the x/net go.mod depends on 1.21 or newer.
+func TestFiles(t *testing.T) {
+	f, err := os.Open(".")
+	if err != nil {
+		t.Fatal(err)
+	}
+	names, err := f.Readdirnames(-1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, name := range names {
+		if !strings.HasSuffix(name, ".go") {
+			continue
+		}
+		b, err := os.ReadFile(name)
+		if err != nil {
+			t.Fatal(err)
+		}
+		// Check for copyright header while we're in here.
+		if !bytes.Contains(b, []byte("The Go Authors.")) {
+			t.Errorf("%v: missing copyright", name)
+		}
+		// doc.go doesn't need a build constraint.
+		if name == "doc.go" {
+			continue
+		}
+		if !bytes.Contains(b, []byte("//go:build go1.21")) {
+			t.Errorf("%v: missing constraint on go1.21", name)
+		}
+	}
+}

internal/quic/frame_debug.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/packet.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 // packetType is a QUIC packet type.

internal/quic/packet_codec_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/packet_number.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 // A packetNumber is a QUIC packet number.

internal/quic/packet_number_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/packet_parser.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/packet_protection.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/packet_protection_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/packet_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/packet_writer.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/quic.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/rangeset.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 // A rangeset is a set of int64s, stored as an ordered list of non-overlapping,

internal/quic/rangeset_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (

internal/quic/sent_packet.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (
@@ -32,7 +34,7 @@ type sentPacket struct {
 }
 
 var sentPool = sync.Pool{
-	New: func() interface{} {
+	New: func() any {
 		return &sentPacket{}
 	},
 }

internal/quic/sent_packet_test.go

@@ -2,12 +2,14 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import "testing"
 
 func TestSentPacket(t *testing.T) {
-	frames := []interface{}{
+	frames := []any{
 		byte(frameTypePing),
 		byte(frameTypeStreamBase),
 		uint64(1),

internal/quic/sent_val.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 // A sentVal tracks sending some piece of information to the peer.

internal/quic/sent_val_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import "testing"

internal/quic/wire.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import "encoding/binary"

internal/quic/wire_test.go

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+//go:build go1.21
+
 package quic
 
 import (