1 files changed, 107 insertions, 0 deletions
diff --git a/src/crypto/tls/link_test.go b/src/crypto/tls/link_test.go
new file mode 100644
index 0000000..8c392ff
--- /dev/null
+++ b/src/crypto/tls/link_test.go
@@ -0,0 +1,107 @@
+// Copyright 2020 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.
+
+package tls
+
+import (
+	"bytes"
+	"internal/testenv"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"testing"
+)
+
+// Tests that the linker is able to remove references to the Client or Server if unused.
+func TestLinkerGC(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping in short mode")
+	}
+	t.Parallel()
+	goBin := testenv.GoToolPath(t)
+	testenv.MustHaveGoBuild(t)
+
+	tests := []struct {
+		name    string
+		program string
+		want    []string
+		bad     []string
+	}{
+		{
+			name: "empty_import",
+			program: `package main
+import _ "crypto/tls"
+func main() {}
+`,
+			bad: []string{
+				"tls.(*Conn)",
+				"type.crypto/tls.clientHandshakeState",
+				"type.crypto/tls.serverHandshakeState",
+			},
+		},
+		{
+			name: "client_and_server",
+			program: `package main
+import "crypto/tls"
+func main() {
+  tls.Dial("", "", nil)
+  tls.Server(nil, nil)
+}
+`,
+			want: []string{
+				"crypto/tls.(*Conn).clientHandshake",
+				"crypto/tls.(*Conn).serverHandshake",
+			},
+		},
+		{
+			name: "only_client",
+			program: `package main
+import "crypto/tls"
+func main() { tls.Dial("", "", nil) }
+`,
+			want: []string{
+				"crypto/tls.(*Conn).clientHandshake",
+			},
+			bad: []string{
+				"crypto/tls.(*Conn).serverHandshake",
+			},
+		},
+		// TODO: add only_server like func main() { tls.Server(nil, nil) }
+		// That currently brings in the client via Conn.handleRenegotiation.
+
+	}
+	tmpDir := t.TempDir()
+	goFile := filepath.Join(tmpDir, "x.go")
+	exeFile := filepath.Join(tmpDir, "x.exe")
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if err := os.WriteFile(goFile, []byte(tt.program), 0644); err != nil {
+				t.Fatal(err)
+			}
+			os.Remove(exeFile)
+			cmd := exec.Command(goBin, "build", "-o", "x.exe", "x.go")
+			cmd.Dir = tmpDir
+			if out, err := cmd.CombinedOutput(); err != nil {
+				t.Fatalf("compile: %v, %s", err, out)
+			}
+
+			cmd = exec.Command(goBin, "tool", "nm", "x.exe")
+			cmd.Dir = tmpDir
+			nm, err := cmd.CombinedOutput()
+			if err != nil {
+				t.Fatalf("nm: %v, %s", err, nm)
+			}
+			for _, sym := range tt.want {
+				if !bytes.Contains(nm, []byte(sym)) {
+					t.Errorf("expected symbol %q not found", sym)
+				}
+			}
+			for _, sym := range tt.bad {
+				if bytes.Contains(nm, []byte(sym)) {
+					t.Errorf("unexpected symbol %q found", sym)
+				}
+			}
+		})
+	}
+}