2 files changed, 86 insertions, 6 deletions

diff --git a/src/cmd/internal/pkgpath/pkgpath.go b/src/cmd/internal/pkgpath/pkgpath.go
index 0b24468be6..72e3bdb631 100644
--- a/src/cmd/internal/pkgpath/pkgpath.go
+++ b/src/cmd/internal/pkgpath/pkgpath.go
@@ -10,9 +10,9 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	exec "internal/execabs"
 	"io/ioutil"
 	"os"
-	"os/exec"
 	"strings"
 )
 
@@ -50,9 +50,12 @@ func ToSymbolFunc(cmd, tmpdir string) (func(string) string, error) {
 		return nil, err
 	}
 
-	// New mangling: expect go.l..u00e4ufer.Run
-	// Old mangling: expect go.l__ufer.Run
-	if bytes.Contains(buf, []byte("go.l..u00e4ufer.Run")) {
+	// Original mangling: go.l__ufer.Run
+	// Mangling v2: go.l..u00e4ufer.Run
+	// Mangling v3: go_0l_u00e4ufer.Run
+	if bytes.Contains(buf, []byte("go_0l_u00e4ufer.Run")) {
+		return toSymbolV3, nil
+	} else if bytes.Contains(buf, []byte("go.l..u00e4ufer.Run")) {
 		return toSymbolV2, nil
 	} else if bytes.Contains(buf, []byte("go.l__ufer.Run")) {
 		return toSymbolV1, nil
@@ -82,7 +85,7 @@ func toSymbolV1(ppath string) string {
 	return strings.Map(clean, ppath)
 }
 
-// toSymbolV2 converts a package path using the newer mangling scheme.
+// toSymbolV2 converts a package path using the second mangling scheme.
 func toSymbolV2(ppath string) string {
 	// This has to build at boostrap time, so it has to build
 	// with Go 1.4, so we don't use strings.Builder.
@@ -112,3 +115,60 @@ func toSymbolV2(ppath string) string {
 	}
 	return string(bsl)
 }
+
+// v3UnderscoreCodes maps from a character that supports an underscore
+// encoding to the underscore encoding character.
+var v3UnderscoreCodes = map[byte]byte{
+	'_': '_',
+	'.': '0',
+	'/': '1',
+	'*': '2',
+	',': '3',
+	'{': '4',
+	'}': '5',
+	'[': '6',
+	']': '7',
+	'(': '8',
+	')': '9',
+	'"': 'a',
+	' ': 'b',
+	';': 'c',
+}
+
+// toSymbolV3 converts a package path using the third mangling scheme.
+func toSymbolV3(ppath string) string {
+	// This has to build at boostrap time, so it has to build
+	// with Go 1.4, so we don't use strings.Builder.
+	bsl := make([]byte, 0, len(ppath))
+	changed := false
+	for _, c := range ppath {
+		if ('A' <= c && c <= 'Z') || ('a' <= c && c <= 'z') || ('0' <= c && c <= '9') {
+			bsl = append(bsl, byte(c))
+			continue
+		}
+
+		if c < 0x80 {
+			if u, ok := v3UnderscoreCodes[byte(c)]; ok {
+				bsl = append(bsl, '_', u)
+				changed = true
+				continue
+			}
+		}
+
+		var enc string
+		switch {
+		case c < 0x80:
+			enc = fmt.Sprintf("_x%02x", c)
+		case c < 0x10000:
+			enc = fmt.Sprintf("_u%04x", c)
+		default:
+			enc = fmt.Sprintf("_U%08x", c)
+		}
+		bsl = append(bsl, enc...)
+		changed = true
+	}
+	if !changed {
+		return ppath
+	}
+	return string(bsl)
+}
diff --git a/src/cmd/internal/pkgpath/pkgpath_test.go b/src/cmd/internal/pkgpath/pkgpath_test.go
index 7355f81bae..232e803a60 100644
--- a/src/cmd/internal/pkgpath/pkgpath_test.go
+++ b/src/cmd/internal/pkgpath/pkgpath_test.go
@@ -24,6 +24,9 @@ func init() {
 	case "v2":
 		os.Stdout.WriteString(`.string	"go.l..u00e4ufer.Run"`)
 		os.Exit(0)
+	case "v3":
+		os.Stdout.WriteString(`.string	"go_0l_u00e4ufer.Run"`)
+		os.Exit(0)
 	case "error":
 		os.Stdout.WriteString(`unknown string`)
 		os.Exit(0)
@@ -46,6 +49,10 @@ func TestToSymbolFunc(t *testing.T) {
 			mangled: "p..u00e4..u4e16..U0001f703",
 		},
 		{
+			env:     "v3",
+			mangled: "p_u00e4_u4e16_U0001f703",
+		},
+		{
 			env:  "error",
 			fail: true,
 		},
@@ -75,32 +82,37 @@ func TestToSymbolFunc(t *testing.T) {
 }
 
 var symbolTests = []struct {
-	input, v1, v2 string
+	input, v1, v2, v3 string
 }{
 	{
 		"",
 		"",
 		"",
+		"",
 	},
 	{
 		"bytes",
 		"bytes",
 		"bytes",
+		"bytes",
 	},
 	{
 		"net/http",
 		"net_http",
 		"net..z2fhttp",
+		"net_1http",
 	},
 	{
 		"golang.org/x/net/http",
 		"golang_org_x_net_http",
 		"golang.x2eorg..z2fx..z2fnet..z2fhttp",
+		"golang_0org_1x_1net_1http",
 	},
 	{
 		"pä世.🜃",
 		"p____",
 		"p..u00e4..u4e16.x2e..U0001f703",
+		"p_u00e4_u4e16_0_U0001f703",
 	},
 }
 
@@ -119,3 +131,11 @@ func TestV2(t *testing.T) {
 		}
 	}
 }
+
+func TestV3(t *testing.T) {
+	for _, test := range symbolTests {
+		if got, want := toSymbolV3(test.input), test.v3; got != want {
+			t.Errorf("toSymbolV3(%q) = %q, want %q", test.input, got, want)
+		}
+	}
+}