Allow Windows Docker containers to map volumes (#13584)

* fix regex for windows path

* Fix escaping

* move validate function out and create test

builtin/providers/docker/resource_docker_container.go

@@ -187,14 +187,7 @@ func resourceDockerContainer() *schema.Resource {
 							Type:         schema.TypeString,
 							Optional:     true,
 							ForceNew:     true,
-							ValidateFunc: func(v interface{}, k string) (ws []string, es []error) {
-								value := v.(string)
-								if !regexp.MustCompile(`^/`).MatchString(value) {
-									es = append(es, fmt.Errorf(
-										"%q must be an absolute path", k))
-								}
-								return
-							},
+							ValidateFunc: validateDockerContainerPath,
 						},
 
 						"volume_name": &schema.Schema{
@@ -515,3 +508,13 @@ func resourceDockerUploadHash(v interface{}) int {
 
 	return hashcode.String(buf.String())
 }
+
+func validateDockerContainerPath(v interface{}, k string) (ws []string, errors []error) {
+
+	value := v.(string)
+	if !regexp.MustCompile(`^[a-zA-Z]:\\|^/`).MatchString(value) {
+		errors = append(errors, fmt.Errorf("%q must be an absolute path", k))
+	}
+
+	return
+}

builtin/providers/docker/resource_docker_container_test.go

@@ -27,6 +27,29 @@ func TestAccDockerContainer_basic(t *testing.T) {
 	})
 }
 
+func TestAccDockerContainerPath_validation(t *testing.T) {
+	cases := []struct {
+		Value    string
+		ErrCount int
+	}{
+		{Value: "/var/log", ErrCount: 0},
+		{Value: "/tmp", ErrCount: 0},
+		{Value: "C:\\Windows\\System32", ErrCount: 0},
+		{Value: "C:\\Program Files\\MSBuild", ErrCount: 0},
+		{Value: "test", ErrCount: 1},
+		{Value: "C:Test", ErrCount: 1},
+		{Value: "", ErrCount: 1},
+	}
+
+	for _, tc := range cases {
+		_, errors := validateDockerContainerPath(tc.Value, "docker_container")
+
+		if len(errors) != tc.ErrCount {
+			t.Fatalf("Expected the Docker Container Path to trigger a validation error")
+		}
+	}
+}
+
 func TestAccDockerContainer_volume(t *testing.T) {
 	var c dc.Container