GPRbuild: File specific compiler switches

Does GPRbuild support a configuration option or any other way to apply special compiler switches only to special files?

That could be useful if -gnatyXYZ switches for strict syntax checks are used for most files in a project but some external / not project specific Ada files are not compliant with the enforced syntax checks.

You can specify both default switches for all Ada files and specific switches for individual files:

package Compiler is
   for Default_Switches ("Ada")
      use ("-O2");
   for Switches ("proc.adb")
      use ("-O0");
end Compiler;

GNAT's documentation gives more info.

EDIT: To address user @Martin's comment to my answer, it does indeed work when you need multiple switches for Default_Switches and only want to change one in Switches. See:

package Compiler is
   for Default_Switches ("Ada")
      use ("-gnata", "-O2");
   for Switches ("proc.adb")
      use ("-gnata", "-O0");
end Compiler;

Here the only switch that changes is the optimization flag. For large lists of switches you can use a variable to hold the ones shared by all files and append the different ones differently for Default_Switches and Switches

Shared_Switches := ("-gnata", "-fstack-check");

package Compiler is
   for Default_Switches ("Ada")
      use Shared_Switches & ("-O2");
   for Switches ("proc.adb")
      use Shared_Switches & ("-O0");
end Compiler;