Restrict inline table to parent table's namespace

Fixes naoina#7.

decode.go

@@ -469,6 +469,30 @@ func (p *toml) SetTable(buf []rune, begin, end int) {
 	p.setTable(p.table, buf, begin, end)
 }
 
+func (p *toml) setInlineTable(t *ast.Table, buf []rune, begin, end int) {
+	name := string(buf[begin:end])
+	if val, exists := t.Fields[name]; exists {
+		switch v := val.(type) {
+		case *ast.Table:
+			p.Error(fmt.Errorf("inline table `%s' is conflict with %v table in line %d", name, v.Type, v.Line))
+		case *ast.KeyValue:
+			p.Error(fmt.Errorf("inline table `%s' is conflict with line %d", name, v.Line))
+		default:
+			p.Error(fmt.Errorf("BUG: inline table `%s' is in conflict but it's unknown type `%T'", name, v))
+		}
+	}
+	tbl := &ast.Table{
+		Line: p.line,
+		Name: name,
+		Type: ast.TableTypeNormal,
+	}
+	p.currentTable = tbl
+	if t.Fields == nil {
+		t.Fields = make(map[string]interface{})
+	}
+	t.Fields[name] = tbl
+}
+
 func (p *toml) setTable(t *ast.Table, buf []rune, begin, end int) {
 	name := string(buf[begin:end])
 	names := splitTableKey(name)
@@ -535,7 +559,7 @@ func (p *toml) StartInlineTable() {
 	p.stack = append(p.stack, &stack{p.key, p.currentTable})
 	buf := []rune(p.key)
 	if p.arr == nil {
-		p.setTable(p.currentTable, buf, 0, len(buf))
+		p.setInlineTable(p.currentTable, buf, 0, len(buf))
 	} else {
 		p.setArrayTable(p.currentTable, buf, 0, len(buf))
 	}