internal/export/idna: use nontransitional processing in Go 1.18

Updates golang/go#46001
Updates golang/go#47510

Change-Id: I1e978a3c6230abfd0b1aaab0c7343b33dda1ba64
Reviewed-on: https://go-review.googlesource.com/c/text/+/359634
Trust: Damien Neil <dneil@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Timothy Gu <timothygu99@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

internal/export/idna/example_test.go

@@ -13,27 +13,26 @@ import (
 func ExampleProfile() {
 	// Raw Punycode has no restrictions and does no mappings.
 	fmt.Println(idna.ToASCII(""))
-	fmt.Println(idna.ToASCII("*.faß.com"))
-	fmt.Println(idna.Punycode.ToASCII("*.faß.com"))
+	fmt.Println(idna.ToASCII("*.GÖPHER.com"))
+	fmt.Println(idna.Punycode.ToASCII("*.GÖPHER.com"))
 
-	// Rewrite IDN for lookup. This (currently) uses transitional mappings to
-	// find a balance between IDNA2003 and IDNA2008 compatibility.
+	// Rewrite IDN for lookup.
 	fmt.Println(idna.Lookup.ToASCII(""))
-	fmt.Println(idna.Lookup.ToASCII("www.faß.com"))
+	fmt.Println(idna.Lookup.ToASCII("www.GÖPHER.com"))
 
-	// Convert an IDN to ASCII for registration purposes. This changes the
-	// encoding, but reports an error if the input was illformed.
-	fmt.Println(idna.Registration.ToASCII(""))
-	fmt.Println(idna.Registration.ToASCII("www.faß.com"))
+	// Convert an IDN to ASCII for registration purposes.
+	// This reports an error if the input was illformed.
+	fmt.Println(idna.Registration.ToASCII("www.GÖPHER.com"))
+	fmt.Println(idna.Registration.ToASCII("www.göpher.com"))
 
 	// Output:
 	//  <nil>
-	// *.xn--fa-hia.com <nil>
-	// *.xn--fa-hia.com <nil>
+	// *.xn--GPHER-1oa.com <nil>
+	// *.xn--GPHER-1oa.com <nil>
 	//  <nil>
-	// www.fass.com <nil>
-	//  idna: invalid label ""
-	// www.xn--fa-hia.com <nil>
+	// www.xn--gpher-jua.com <nil>
+	// www.xn--GPHER-1oa.com idna: disallowed rune U+0047
+	// www.xn--gpher-jua.com <nil>
 }
 
 func ExampleNew() {

internal/export/idna/go118.go

@@ -0,0 +1,12 @@
+// Copyright 2021 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 go1.18
+// +build go1.18
+
+package idna
+
+// Transitional processing is disabled by default in Go 1.18.
+// https://golang.org/issue/47510
+const transitionalLookup = false

internal/export/idna/idna10.0.0.go

@@ -284,7 +284,7 @@ var (
 
 	punycode = &Profile{}
 	lookup   = &Profile{options{
-		transitional: true,
+		transitional: transitionalLookup,
 		useSTD3Rules: true,
 		checkHyphens: true,
 		checkJoiners: true,

internal/export/idna/idna10.0.0_test.go

@@ -102,7 +102,7 @@ func TestLabelErrors(t *testing.T) {
 		// Chrome, modern Firefox, Safari, and IE.
 		{resolve, "lab⒐be", "xn--labbe-zh9b", "P1"}, // encode("lab⒐be")
 		{display, "lab⒐be", "lab⒐be", "P1"},
-		{resolve, "plan⒐faß.de", "xn--planfass-c31e.de", "P1"}, // encode("plan⒐fass") + ".de"
+		{transitional, "plan⒐faß.de", "xn--planfass-c31e.de", "P1"}, // encode("plan⒐fass") + ".de"
 		{display, "Plan⒐faß.de", "plan⒐faß.de", "P1"},
 
 		// Transitional vs Nontransitional processing
@@ -115,10 +115,10 @@ func TestLabelErrors(t *testing.T) {
 		// punycode on the result using transitional mapping.
 		// Firefox 49.0.1 goes haywire on this string and prints a bunch of what
 		// seems to be nested punycode encodings.
-		{resolve, "日本⒈co.ßßß.de", "xn--co-wuw5954azlb.ssssss.de", "P1"},
+		{transitional, "日本⒈co.ßßß.de", "xn--co-wuw5954azlb.ssssss.de", "P1"},
 		{display, "日本⒈co.ßßß.de", "日本⒈co.ßßß.de", "P1"},
 
-		{resolve, "a\u200Cb", "ab", ""},
+		{transitional, "a\u200Cb", "ab", ""},
 		{display, "a\u200Cb", "a\u200Cb", "C"},
 
 		{resolve, encode("a\u200Cb"), encode("a\u200Cb"), "C"},
@@ -153,3 +153,11 @@ func TestLabelErrors(t *testing.T) {
 		doTest(t, tc.f, tc.name, tc.input, tc.want, tc.wantErr)
 	}
 }
+
+func TestTransitionalDefault(t *testing.T) {
+	want := "xn--strae-oqa.de"
+	if transitionalLookup {
+		want = "strasse.de"
+	}
+	doTest(t, Lookup.ToASCII, "Lookup", "straße.de", want, "")
+}

internal/export/idna/idna_test.go

@@ -45,7 +45,7 @@ func TestProfiles(t *testing.T) {
 			VerifyDNSLength(true),
 			BidiRule(),
 		)},
-		{"Lookup", lookup, New(MapForLookup(), BidiRule(), Transitional(true))},
+		{"Lookup", lookup, New(MapForLookup(), BidiRule(), Transitional(transitionalLookup))},
 		{"Display", display, New(MapForLookup(), BidiRule())},
 	}
 	for _, tc := range testCases {

internal/export/idna/pre_go118.go

@@ -0,0 +1,10 @@
+// Copyright 2021 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 !go1.18
+// +build !go1.18
+
+package idna
+
+const transitionalLookup = true