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Cyclic dependencies are mostly forbidden: if A imports B (directly or indirectly) then B is not allowed to import A. However, there are cases when cyclic dependencies would be beneficial. For these cases, another form of import between projects exists: the `limited with'. A project A that imports a project B with a straight `with' may also be imported, directly or indirectly, by B through a limited with.
The difference between straight `with' and limited with is that the name of a project imported with a limited with cannot be used in the project importing it. In particular, its packages cannot be renamed and its variables cannot be referred to.
with "b.gpr";
with "c.gpr";
project A is
for Exec_Dir use B'Exec_Dir; -- ok
end A;
limited with "a.gpr"; -- Cyclic dependency: A -> B -> A
project B is
for Exec_Dir use A'Exec_Dir; -- not ok
end B;
with "d.gpr";
project C is
end C;
limited with "a.gpr"; -- Cyclic dependency: A -> C -> D -> A
project D is
for Exec_Dir use A'Exec_Dir; -- not ok
end D;