Move windows-specific path shortening to separate file

go/tools/builders/BUILD.bazel

@@ -142,7 +142,10 @@ go_tool_binary(
         "flags.go",
         "replicate.go",
         "stdlib.go",
-    ],
+    ] + select({
+        "@bazel_tools//src/conditions:windows": ["path_windows.go"],
+        "//conditions:default": ["path.go"],
+    }),
     visibility = ["//visibility:public"],
 )
 

go/tools/builders/path.go

@@ -0,0 +1,7 @@
+// +build !windows
+
+package main
+
+func processPath(path string) (string, error) {
+	return path, nil
+}

go/tools/builders/path_windows.go

@@ -0,0 +1,25 @@
+// +build windows
+
+package main
+
+import (
+	"runtime"
+	"syscall"
+)
+
+func processPath(path string) (string, error) {
+	if runtime.GOOS != "windows" {
+		return path, nil
+	}
+
+	var buf [258]uint16
+	up, err := syscall.UTF16PtrFromString(path)
+	if err != nil {
+		return path, err
+	}
+	_, err = syscall.GetShortPathName(up, &buf[0], 258)
+	if err != nil {
+		return path, err
+	}
+	return syscall.UTF16ToString(buf[:]), nil
+}

go/tools/builders/stdlib.go

@@ -22,9 +22,7 @@ import (
 	"log"
 	"os"
 	"path/filepath"
-	"runtime"
 	"strings"
-	"syscall"
 )
 
 func run(args []string) error {
@@ -57,17 +55,9 @@ func run(args []string) error {
 		return err
 	}
 
-	if runtime.GOOS == "windows" {
-		var buf [258]uint16
-		up, err := syscall.UTF16PtrFromString(output)
-		if err != nil {
-			return err
-		}
-		_, err = syscall.GetShortPathName(up, &buf[0], 258)
-		if err != nil {
-			return err
-		}
-		output = syscall.UTF16ToString(buf[:])
+	output, err := processPath(output)
+	if err != nil {
+		return err
 	}
 
 	// Now switch to the newly created GOROOT