config: validate type of default to string or mapping for var

config/config.go

@@ -108,8 +108,13 @@ func (c *Config) Validate() error {
 		varMap[v.Name] = v
 	}
 
-	// TODO(mitchellh): Validate that variable defaults are only a string
-	// or mapping of strings.
+	for _, v := range c.Variables {
+		if v.Type() == VariableTypeUnknown {
+			errs = append(errs, fmt.Errorf(
+				"Variable '%s': must be string or mapping",
+				v.Name))
+		}
+	}
 
 	// Check for references to user variables that do not actually
 	// exist and record those errors.

config/config_test.go

@@ -73,10 +73,6 @@ func TestConfigValidate_varDefault(t *testing.T) {
 }
 
 func TestConfigValidate_varDefaultBadType(t *testing.T) {
-	t.Skip()
-
-	// TODO(mitchellh): FIX
-
 	c := testConfig(t, "validate-var-default-bad-type")
 	if err := c.Validate(); err == nil {
 		t.Fatal("should not be valid")