builder/docker: default container dir to "c:/packer-files" on windows

builder/docker/config.go

@@ -3,6 +3,7 @@ package docker
 import (
 	"fmt"
 	"os"
+	"runtime"
 
 	"github.com/hashicorp/packer/common"
 	"github.com/hashicorp/packer/helper/communicator"
@@ -124,7 +125,11 @@ func NewConfig(raws ...interface{}) (*Config, []string, error) {
 	}
 
 	if c.ContainerDir == "" {
-		c.ContainerDir = "/packer-files"
+		if runtime.GOOS == "windows" {
+			c.ContainerDir = "c:/packer-files"
+		} else {
+			c.ContainerDir = "/packer-files"
+		}
 	}
 
 	if c.EcrLogin && c.LoginServer == "" {

website/source/docs/builders/docker.html.md

@@ -232,8 +232,8 @@ You must specify (only) one of `commit`, `discard`, or `export_path`.
 
 -   `container_dir` (string) - The directory inside container to mount temp
     directory from host server for work [file
-    provisioner](/docs/provisioners/file.html). By default this is set to
-    `/packer-files`.
+    provisioner](/docs/provisioners/file.html). This defaults to
+    `c:/packer-files` on windows and `/packer-files` on other systems.
 
 -   `fix_upload_owner` (boolean) - If true, files uploaded to the container
     will be owned by the user the container is running as. If false, the owner