crypto/x509: revert SystemCertPool implementation for Windows

Updates #18609

Change-Id: I8306135660f52cf625bed4c7f53f632e527617de
Reviewed-on: https://go-review.googlesource.com/35265
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-by: Quentin Smith <quentin@golang.org>

doc/go1.8.html

@@ -809,11 +809,6 @@ Optimizations and minor bug fixes are not listed.
 
 <dl id="crypto_x509"><dt><a href="/pkg/crypto/x509/">crypto/x509</a></dt>
   <dd>
-    <p> <!-- CL 30578 -->
-      <a href="/pkg/crypto/x509/#SystemCertPool"><code>SystemCertPool</code></a>
-      is now implemented on Windows.
-    </p>
-
     <p> <!-- CL 24743 -->
       PSS signatures are now supported.
     </p>

src/crypto/x509/cert_pool.go

@@ -4,7 +4,11 @@
 
 package x509
 
-import "encoding/pem"
+import (
+	"encoding/pem"
+	"errors"
+	"runtime"
+)
 
 // CertPool is a set of certificates.
 type CertPool struct {
@@ -26,6 +30,11 @@ func NewCertPool() *CertPool {
 // Any mutations to the returned pool are not written to disk and do
 // not affect any other pool.
 func SystemCertPool() (*CertPool, error) {
+	if runtime.GOOS == "windows" {
+		// Issue 16736, 18609:
+		return nil, errors.New("crypto/x509: system root pool is not available on Windows")
+	}
+
 	return loadSystemRoots()
 }
 

src/crypto/x509/root_windows.go

@@ -226,6 +226,11 @@ func (c *Certificate) systemVerify(opts *VerifyOptions) (chains [][]*Certificate
 }
 
 func loadSystemRoots() (*CertPool, error) {
+	// TODO: restore this functionality on Windows. We tried to do
+	// it in Go 1.8 but had to revert it. See Issue 18609.
+	// Returning (nil, nil) was the old behavior, prior to CL 30578.
+	return nil, nil
+
 	const CRYPT_E_NOT_FOUND = 0x80092004
 
 	store, err := syscall.CertOpenSystemStore(0, syscall.StringToUTF16Ptr("ROOT"))

src/crypto/x509/x509_test.go

@@ -24,6 +24,7 @@ import (
 	"net"
 	"os/exec"
 	"reflect"
+	"runtime"
 	"strings"
 	"testing"
 	"time"
@@ -1477,6 +1478,9 @@ func TestMultipleRDN(t *testing.T) {
 }
 
 func TestSystemCertPool(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("not implemented on Windows; Issue 16736, 18609")
+	}
 	_, err := SystemCertPool()
 	if err != nil {
 		t.Fatal(err)