cmd/go: preserve %SYSTEMROOT% in TestScript on Windows

Windows networking doesn't work without this environment variable (#25210).

Re-enable TestScript on Windows, and fix two minor failures.

Fixes #26457.

Change-Id: Id9bea49dfb58403195c29c3d831a532ef0f9a233
Reviewed-on: https://go-review.googlesource.com/124858
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/script_test.go

@@ -42,10 +42,6 @@ func TestScript(t *testing.T) {
 		file := file
 		name := strings.TrimSuffix(filepath.Base(file), ".txt")
 		t.Run(name, func(t *testing.T) {
-			if strings.HasPrefix(name, "mod_") && runtime.GOOS == "windows" {
-				// Windows is very unhappy about the module proxy.
-				t.Skip("golang.org/issue/26457")
-			}
 			t.Parallel()
 			ts := &testScript{t: t, name: name, file: file}
 			ts.setup()
@@ -76,6 +72,10 @@ type testScript struct {
 	start   time.Time         // time phase started
 }
 
+var extraEnvKeys = []string{
+	"SYSTEMROOT", // must be preserved on Windows to find DLLs; golang.org/issue/25210
+}
+
 // setup sets up the test execution temporary directory and environment.
 func (ts *testScript) setup() {
 	StartProxy()
@@ -96,11 +96,18 @@ func (ts *testScript) setup() {
 		tempEnvName() + "=" + filepath.Join(ts.workdir, "tmp"),
 		"devnull=" + os.DevNull,
 	}
+
 	if runtime.GOOS == "windows" {
 		ts.env = append(ts.env, "exe=.exe")
 	} else {
 		ts.env = append(ts.env, "exe=")
 	}
+	for _, key := range extraEnvKeys {
+		if val := os.Getenv(key); val != "" {
+			ts.env = append(ts.env, key+"="+val)
+		}
+	}
+
 	ts.envMap = make(map[string]string)
 	for _, kv := range ts.env {
 		if i := strings.Index(kv, "="); i >= 0 {

src/cmd/go/testdata/script/mod_bad_filenames.txt

@@ -2,10 +2,10 @@ env GO111MODULE=on
 
 ! go get rsc.io/badfile1 rsc.io/badfile2 rsc.io/badfile3 rsc.io/badfile4 rsc.io/badfile5
 ! stderr 'unzip.*badfile1'
-stderr 'unzip.*badfile2/@v/v1.0.0.zip:.*malformed file path "☺.go": invalid char ''☺'''
-stderr 'unzip.*badfile3/@v/v1.0.0.zip: malformed file path "x\?y.go": invalid char ''\?'''
-stderr 'unzip.*badfile4/@v/v1.0.0.zip: case-insensitive file name collision: "x/Y.go" and "x/y.go"'
-stderr 'unzip.*badfile5/@v/v1.0.0.zip: case-insensitive file name collision: "x/y" and "x/Y"'
+stderr 'unzip.*badfile2[\\/]@v[\\/]v1.0.0.zip:.*malformed file path "☺.go": invalid char ''☺'''
+stderr 'unzip.*badfile3[\\/]@v[\\/]v1.0.0.zip: malformed file path "x\?y.go": invalid char ''\?'''
+stderr 'unzip.*badfile4[\\/]@v[\\/]v1.0.0.zip: case-insensitive file name collision: "x/Y.go" and "x/y.go"'
+stderr 'unzip.*badfile5[\\/]@v[\\/]v1.0.0.zip: case-insensitive file name collision: "x/y" and "x/Y"'
 
 -- go.mod --
 module x

src/cmd/go/testdata/script/mod_file_proxy.txt

@@ -10,6 +10,7 @@ go list -getmode=local
 grep v1.5.1 $GOPATH/src/mod/cache/download/rsc.io/quote/@v/list
 
 # Use download cache as file:/// proxy.
+[windows] stop # TODO: file://$WORK puts backslashes in the URL
 env GOPATH=$WORK/gopath2
 env GOPROXY=file:///nonexist
 ! go list -getmode=local