Disallow multiple definitions of a key.

README.md

@@ -200,6 +200,9 @@ override your defaults. This is simply done by:
 itkconfig.LoadConfig("filename.conf", cfg)
 ```
 
+Non-slice keys can only be defined once per config file. Multiple 
+definitions will produce an error.
+
 ## Authors
 
 * Trygve Aaberge ([trygveaa@samfundet.no](mailto:trygveaa@samfundet.no))

config.go

@@ -165,6 +165,10 @@ func LoadConfig(filename string, config interface{}) error {
 
 			field.Set(reflect.Append(field, v))
 		default:
+			if lastUpdate[*key] != 0 {
+				return syntaxError(fmt.Sprintf("key '%s' was defined multiple times, initially on line %d (did you mean to define a slice?)", *key, lastUpdate[*key]))
+			}
+
 			v, err := parseField(*key, *value, field.Type())
 			if err != nil {
 				return syntaxError(err.Error())

config_test.go

@@ -462,3 +462,17 @@ Could not parse config with multiple quotes correctly.
 	got:      %#v`, want, config)
 	}
 }
+
+func TestMultipleDefinitions(t *testing.T) {
+	type Config struct {
+		Foo string
+	}
+
+	config := Config{
+		Foo: "",
+	}
+	err := LoadConfig("test_configs/multipledefinitions.cfg", &config)
+	if err == nil {
+		t.Fatalf("Should not be allowed to redefine a key.")
+	}
+}

test_configs/multipledefinitions.cfg

@@ -0,0 +1,2 @@
+Foo = "bar"
+Foo = "baz"