Unable to compile and run simple Ada application - macos

Question

Very new to Ada and have started to learn by doing a Hello World tutorial in GNAT GPS. I'm having a hard time figuring out an error when I compile my code. The error looks like a source file dir issue. But I'm highly unfamiliar with the error output in this type of IDE.
Here is the code I'm trying to compile and run (file: main.adb):
with Ada.Text_IO;
procedure Main is
begin
Ada.text_IO.Put_Line("Hello world!");
null;
end Main;
Image of code and GPS IDE
Here's the build error I'm receiving:
gprbuild -d -P/Users/myname/Desktop/Test/default.gpr /Users/myname/Desktop/Test/src/main.adb
Compile
[Ada] main.adb
Bind
[gprbind] main.bexch
[Ada] main.ali
Link
[link] main.adb
ld: library not found for -lSystem
collect2: error: ld returned 1 exit status
gprbuild: link of main.adb failed
gprbuild: failed command was: /users/myname/opt/gnat/2019/bin/gcc main.o b__main.o -L/Users/myname/Desktop/Test/obj/ -L/Users/myname/Desktop/Test/obj/ -L/users/myname/opt/gnat/2019/lib/gcc/x86_64-apple-darwin17.7.0/8.3.1/adalib/ /users/myname/opt/gnat/2019/lib/gcc/x86_64-apple-darwin17.7.0/8.3.1/adalib/libgnat.a -Wl,-rpath,#executable_path/ -Wl,-rpath,#executable_path/../../..//opt/gnat/2019/lib/gcc/x86_64-apple-darwin17.7.0/8.3.1/adalib -o main
[2019-10-19 11:34:54] process exited with status 4, elapsed time: 01.95s
I'm assuming I installed Ada incorrectly and or GPS. Any suggestions or thoughts? Thank you.
Update/Additional thoughts:
One other thing I'm assuming is that the project is unable to find the Ada source code since the project is saved on the /desktop?

Answer 1

I see you’re running on macOS and using GNAT CE 2019. You need to install Xcode (from the app store, under Develop).
I wrote it up here, but to summarise,
In future, Apple won’t provide includes in /usr/include but instead in the SDK,
clang knows about this but GCC doesn’t,
AdaCore’s response has been to generate their compiler with the system root inside the Xcode SDK,
the system root affects libraries as well as headers,
so no Xcode means no system libraries (in spite of the libraries being in /usr/lib as always!)