To: J3                                                     J3/21-102
From: R. Bader
Subject: CFI_setpointer interpretation request
Date: 2021-January-23

Reference: 18-007r1

1. Description of the issue
~~~~~~~~~~~~~~~~~~~~~~~~~~~

Section 18.5.5.9 "The CFI_setpointer function" states in para 2 that

"If source is not a null pointer, the corresponding values of the elem_len,
rank, and type members shall be the same in the C descriptors with the
addresses source and result."

The function can therefore not work correctly if the "result" parameter is
a descriptor address for a deferred-length character entity coming in from
Fortran, because the elem_len values will typically mismatch. Manual
updates to result->elem_len are prohibited by 18.6 para 1. Since within
Fortran

CHARACTER(len=4), TARGET :: source
CHARACTER(len=:), POINTER :: result
result => source

will work just fine, this surely is a defect in the current specification.

2. Suggested resolution
~~~~~~~~~~~~~~~~~~~~~~~

For the case of a character result pointer in a call to CFI_setpointer,

- permit result->elem_len having a different value than source->elem
- enforce overwriting result->elem_len with source->elem_len

It is not necessary to explicitly refer to "deferred-length" since this
is enforced by [478:21] in the critical case, and there should be no
problem for such descriptors created inside C.

3. Suggested edits against 18-007r1
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In 18.5.5.9 The CFI_setpointer function

- [491:27] delete "elem_len, ".

- [491:28+] add new sentence
  "If source is not a null pointer and the C descriptor with the address
  result does not describe a character pointer, the corresponding values
  of the elem_len member shall be the same in the C descriptors with
  the addresses source and result."

- [491:31] replace "base_addr and dim" by "base_addr, dim and possibly
  elem_len"

- [491:38+] add new sentence
  "If the C descriptor with the address result describes a character
   pointer, the value of its elem_len member is set to source->elem_len".