gtk-sharp3-gapi software package provides C source parser and C# code generator for GObject based APIs, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gtk-sharp3-gapi
gtk-sharp3-gapi is installed in your system.
Make ensure the gtk-sharp3-gapi package were installed using the commands given below,
$ sudo dpkg-query -l | grep gtk-sharp3-gapi *
You will get with gtk-sharp3-gapi package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | Mono/CLI |
| Package | gtk-sharp3-gapi |
| Version | 2.99.3-2+b1 [s390x], 2.99.3-2 |
| Description | C source parser and C# code generator for GObject based APIs |
| Sub Section | Cli-mono |