[flang-commits] [flang] [flang][Semantics] Break recursion on illegal recursive type in I/O check (PR #194284)

[Eugene Epshteyn via flang-commits]

================
@@ -74,3 +74,81 @@ subroutine test4(u)
   end subroutine
 end module
 
+! Regression test: an illegal recursive derived-type component used to cause
+! infinite recursion in FindUnsafeIoDirectComponent when the object appeared
+! in an I/O list (issue #192387).
+subroutine test_recursive_io
+  type t1
+    !ERROR: Recursive use of the derived type requires POINTER or ALLOCATABLE
+    type(t1) :: b
+  end type t1
+  type(t1) :: obj
+  print *, obj
+end subroutine
+
+! Same regression covering the FindInaccessibleComponent walk: the type
+! must be defined in a module and used in I/O outside that module so the
+! recursive component traversal in FindInaccessibleComponent is reached.
+module m_recursive
+  type t2
+    !ERROR: Recursive use of the derived type requires POINTER or ALLOCATABLE
+    type(t2) :: b
----------------
eugeneepshteyn wrote:

I tried to come up with a mutually recursive type test that triggers this error, but the issue is that I can't trigger this code path with it, it errors out (correctly) elsewhere. If I break one of the links, it's no longer a problem, for example:
```
    type :: t2
      type(t1), pointer :: link => null()
      integer :: y
    end type
    type :: t1
      type(t2) :: nested
      integer :: x
    end type
```

https://github.com/llvm/llvm-project/pull/194284