If vhd or vhdx extension is specified for ISOUrls, we want to use an existing hard drive which means that we don't need to specify hard drive size

Filepath.ext includes the dot

builder/hyperv/common/step_clone_vm.go

@@ -40,7 +40,7 @@ func (s *StepCloneVM) Run(state multistep.StateBag) multistep.StepAction {
 	harddrivePath := ""
 	if harddrivePathRaw, ok := state.GetOk("iso_path"); ok {
 		extension := strings.ToLower(filepath.Ext(harddrivePathRaw.(string)))
-		if extension == "vhd" || extension == "vhdx" {
+		if extension == ".vhd" || extension == ".vhdx" {
 			harddrivePath = harddrivePathRaw.(string)
 		} else {
 			log.Println("No existing virtual harddrive, not attaching.")

builder/hyperv/common/step_create_vm.go

@@ -39,7 +39,7 @@ func (s *StepCreateVM) Run(state multistep.StateBag) multistep.StepAction {
 	harddrivePath := ""
 	if harddrivePathRaw, ok := state.GetOk("iso_path"); ok {
 		extension := strings.ToLower(filepath.Ext(harddrivePathRaw.(string)))
-		if extension == "vhd" || extension == "vhdx" {
+		if extension == ".vhd" || extension == ".vhdx" {
 			harddrivePath = harddrivePathRaw.(string)
 		} else {
 			log.Println("No existing virtual harddrive, not attaching.")

builder/hyperv/iso/builder.go

@@ -118,13 +118,6 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 	warnings = append(warnings, isoWarnings...)
 	errs = packer.MultiErrorAppend(errs, isoErrs...)
 	
-	if len(b.config.ISOConfig.ISOUrls) > 0 {
-		extension := strings.ToLower(filepath.Ext(b.config.ISOConfig.ISOUrls[0]))
-		if extension == "vhd" || extension == "vhdx" {
-			b.config.ISOConfig.TargetExtension = extension
-		}
-	}
-	
 	errs = packer.MultiErrorAppend(errs, b.config.FloppyConfig.Prepare(&b.config.ctx)...)
 	errs = packer.MultiErrorAppend(errs, b.config.HTTPConfig.Prepare(&b.config.ctx)...)
 	errs = packer.MultiErrorAppend(errs, b.config.RunConfig.Prepare(&b.config.ctx)...)
@@ -132,7 +125,7 @@ func (b *Builder) Prepare(raws ...interface{}) ([]string, error) {
 	errs = packer.MultiErrorAppend(errs, b.config.SSHConfig.Prepare(&b.config.ctx)...)
 	errs = packer.MultiErrorAppend(errs, b.config.ShutdownConfig.Prepare(&b.config.ctx)...)
 
-	if b.config.ISOConfig.TargetExtension != "vhd" && b.config.ISOConfig.TargetExtension != "vhdx" {
+	if len(b.config.ISOConfig.ISOUrls) < 1 || (strings.ToLower(filepath.Ext(b.config.ISOConfig.ISOUrls[0])) != ".vhd" && strings.ToLower(filepath.Ext(b.config.ISOConfig.ISOUrls[0])) != ".vhdx")  {
 		//We only create a new hard drive if an existing one to copy from does not exist
 		err = b.checkDiskSize()
 		if err != nil {

builder/hyperv/iso/builder_test.go

@@ -300,6 +300,98 @@ func TestBuilderPrepare_ISOUrl(t *testing.T) {
 	}
 }
 
+func TestBuilderPrepare_SizeNotRequiredWhenUsingExistingHarddrive(t *testing.T) {
+	var b Builder
+	config := testConfig()
+	delete(config, "iso_url")
+	delete(config, "iso_urls")
+	delete(config, "disk_size")
+
+	config["disk_size"] = 1
+
+	// Test just iso_urls set but with vhdx
+	delete(config, "iso_url")
+	config["iso_urls"] = []string{
+		"http://www.packer.io/hdd.vhdx",
+		"http://www.hashicorp.com/dvd.iso",
+	}
+
+	b = Builder{}
+	warns, err := b.Prepare(config)
+	if len(warns) > 0 {
+		t.Fatalf("bad: %#v", warns)
+	}
+	if err != nil {
+		t.Errorf("should not have error: %s", err)
+	}
+
+	expected := []string{
+		"http://www.packer.io/hdd.vhdx",
+		"http://www.hashicorp.com/dvd.iso",
+	}
+	if !reflect.DeepEqual(b.config.ISOUrls, expected) {
+		t.Fatalf("bad: %#v", b.config.ISOUrls)
+	}
+
+	// Test just iso_urls set but with vhd
+	delete(config, "iso_url")
+	config["iso_urls"] = []string{
+		"http://www.packer.io/hdd.vhd",
+		"http://www.hashicorp.com/dvd.iso",
+	}
+
+	b = Builder{}
+	warns, err = b.Prepare(config)
+	if len(warns) > 0 {
+		t.Fatalf("bad: %#v", warns)
+	}
+	if err != nil {
+		t.Errorf("should not have error: %s", err)
+	}
+
+	expected = []string{
+		"http://www.packer.io/hdd.vhd",
+		"http://www.hashicorp.com/dvd.iso",
+	}
+	if !reflect.DeepEqual(b.config.ISOUrls, expected) {
+		t.Fatalf("bad: %#v", b.config.ISOUrls)
+	}
+}
+
+func TestBuilderPrepare_SizeIsRequiredWhenNotUsingExistingHarddrive(t *testing.T) {
+	var b Builder
+	config := testConfig()
+	delete(config, "iso_url")
+	delete(config, "iso_urls")
+	delete(config, "disk_size")
+
+	config["disk_size"] = 1
+
+	// Test just iso_urls set but with vhdx
+	delete(config, "iso_url")
+	config["iso_urls"] = []string{
+		"http://www.packer.io/os.iso",
+		"http://www.hashicorp.com/dvd.iso",
+	}
+
+	b = Builder{}
+	warns, err := b.Prepare(config)
+	if len(warns) > 0 {
+		t.Fatalf("bad: %#v", warns)
+	}
+	if err == nil {
+		t.Errorf("should have error")
+	}
+
+	expected := []string{
+		"http://www.packer.io/os.iso",
+		"http://www.hashicorp.com/dvd.iso",
+	}
+	if !reflect.DeepEqual(b.config.ISOUrls, expected) {
+		t.Fatalf("bad: %#v", b.config.ISOUrls)
+	}
+}
+
 func TestBuilderPrepare_FloppyFiles(t *testing.T) {
 	var b Builder
 	config := testConfig()