packer: default user var values needn't be strings [GH-456]

CHANGELOG.md

 ## 0.3.9 (unreleased)
 
+BUG FIXES:
 
+* core: default user variable values don't need to be strings. [GH-456]
 
 ## 0.3.8 (September 22, 2013)
 

packer/template.go

@@ -124,18 +124,24 @@ func ParseTemplate(data []byte) (t *Template, err error) {
 	// Gather all the variables
 	for k, v := range rawTpl.Variables {
 		var variable RawVariable
-		variable.Default = ""
 		variable.Required = v == nil
 
-		if v != nil {
-			def, ok := v.(string)
-			if !ok {
-				errors = append(errors,
-					fmt.Errorf("variable '%s': default value must be string or null", k))
-				continue
-			}
+		// Create a new mapstructure decoder in order to decode the default
+		// value since this is the only value in the regular template that
+		// can be weakly typed.
+		decoder, err := mapstructure.NewDecoder(&mapstructure.DecoderConfig{
+			Result:           &variable.Default,
+			WeaklyTypedInput: true,
+		})
+		if err != nil {
+			// This should never happen.
+			panic(err)
+		}
 
-			variable.Default = def
+		err = decoder.Decode(v)
+		if err != nil {
+			errors = append(errors,
+				fmt.Errorf("Error decoding default value for user var '%s': %s", k, err))
 		}
 
 		t.Variables[k] = variable

packer/template_test.go

@@ -391,7 +391,8 @@ func TestParseTemplate_Variables(t *testing.T) {
 	{
 		"variables": {
 			"foo": "bar",
-			"bar": null
+			"bar": null,
+			"baz": 27
 		},
 
 		"builders": [{"type": "something"}]
@@ -403,7 +404,7 @@ func TestParseTemplate_Variables(t *testing.T) {
 		t.Fatalf("err: %s", err)
 	}
 
-	if result.Variables == nil || len(result.Variables) != 2 {
+	if result.Variables == nil || len(result.Variables) != 3 {
 		t.Fatalf("bad vars: %#v", result.Variables)
 	}
 
@@ -422,6 +423,14 @@ func TestParseTemplate_Variables(t *testing.T) {
 	if !result.Variables["bar"].Required {
 		t.Fatal("bar should be required")
 	}
+
+	if result.Variables["baz"].Default != "27" {
+		t.Fatal("default should be empty")
+	}
+
+	if result.Variables["baz"].Required {
+		t.Fatal("baz should not be required")
+	}
 }
 
 func TestParseTemplate_variablesBadDefault(t *testing.T) {