Note
The official site of Emacs ada-mode is https://savannah.nongnu.org/projects/ada-mode/, where their sources can be found. This "unofficial" GitHub repository has been set up only for having a GitHub action that gets the latest Alire release and builds the binaries with a setup that should work for most of the Linux users. Maybe someone can contribute similar actions for MacOS or other OSes, so it serves more users.
AppImages of the Emacs ada-mode executables can be found in the releases section.
The AppImage acts as ada_mode_wisi_lalr_parse, but all the executables are inside and can be extracted and directly used, since they are mostly statically linked.
chmod +x emacs_ada_mode-8.1.0-x86_64.AppImage
./emacs_ada_mode-8.1.0-x86_64.AppImage --appimage-extract
mv squashfs-root/usr/bin/* ~/.local/bin
Make sure that ~/.local/bin is on the PATH or use any other directory already on it.
The executables are dynamically linked with GNAT 12. Thus, unless you have GNAT 12 libraries already installed, you have to move also the libraries to an appropriate place (e.g. present in LD_LIBRARY_PATH).
mv squashfs-root/usr/lib/* ~/.local/lib
Due to the version requirement on re2c, it was not possible to use the oldest supported Ubuntu LTS release, as recommended by the AppImage project. In order to fix that, I've patched ada-mode in this fork and branch. That repository is cloned by the GitHub action in order to build on Ubuntu 20.04. You can take a look at how the binaries are built and then pushed directly to Releases in .github/workflows/main.yml.