https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126478
Bug ID: 126478
Summary: Bogus error for coarray ALLOCATE with MOLD= or SOURCE=
specifier
Product: gcc
Version: 16.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: fortran
Assignee: unassigned at gcc dot gnu.org
Reporter: dobonachea at lbl dot gov
CC: damian at archaeologic dot codes
Target Milestone: ---
Created attachment 65164
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=65164&action=edit
ALLOCATE statement for an allocatable array coarray with a SOURCE= specifier
The ALLOCATE statement for an allocatable array coarray is not correctly parsed
with a MOLD= or SOURCE= specifier by GFortran 16.1.0.
The two demonstration programs below both compile and execute correctly with
NAG Fortran 7.2:
---------------------------------------------------------
cgpu$ cat coarrays_31.f90
program coarrays_31
implicit none
! Declare an allocatable array coarray
integer, allocatable, save :: arr_coarray(:)[:]
integer :: i
! Allocate the coarray using a SOURCE= specifier.
! The array dimensions and values are taken from the array constructor.
! The explicit [*] defines the co-dimensions.
allocate(arr_coarray[*], source=[(i * 10, i = 1, 5)])
! Verify the allocation state
if (.not. allocated(arr_coarray)) then
error stop "Error: arr_coarray was not allocated."
end if
! Verify the inherited size and values
if (size(arr_coarray) /= 5) then
error stop "Error: array size does not match SOURCE."
end if
if (any(arr_coarray /= [10, 20, 30, 40, 50])) then
error stop "Error: array values do not match SOURCE."
end if
end program coarrays_31
cgpu$ gfortran -fcoarray=lib -c coarrays_31.f90
coarrays_31.f90:11:25:
11 | allocate(arr_coarray[*], source=[(i * 10, i = 1, 5)])
| 1
Error: Array section designator, e.g. '(:)', is required besides the coarray
designator '[...]' at (1)
cgpu$ cat coarrays_32.f90
program coarrays_32
implicit none
real, allocatable :: prototype(:,:)
real, allocatable :: target_arr(:,:)[:]
allocate(prototype(10:12, 20:23))
allocate(target_arr[*], mold=prototype)
if (.not. allocated(target_arr)) error stop "Allocation failed"
deallocate(target_arr)
deallocate(prototype)
end program coarrays_32
cgpu$ gfortran -fcoarray=lib -c coarrays_32.f90
coarrays_32.f90:9:24:
9 | allocate(target_arr[*], mold=prototype)
| 1
Error: Array section designator, e.g. '(:)', is required besides the coarray
designator '[...]' at (1)
cgpu$ gfortran --version
GNU Fortran (GCC) 16.1.0
Copyright (C) 2026 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
---------------------------------------------------------
The error messages asking for an "Array section designator" (grammatically, an
allocate-shape-spec-list) are incorrect. Redundantly providing the *optional*
explicit array bounds is an effective workaround to the defect, but that is
*not* required by Fortran specification.
The relevant specification text from Fortran 2023, subclause 9.7.1.1: (where
R933 is corrected as per J3/25-167)
R929 allocate-stmt is ALLOCATE ( [ type-spec :: ] allocation-list \
[ , alloc-opt-list ] )
R930 alloc-opt is ERRMSG = errmsg-variable
or MOLD = source-expr
or SOURCE = source-expr
or STAT = stat-variable
R933 allocation is allocate-object [ ( allocate-shape-spec-list ) ] \
[ lbracket allocate-coarray-spec rbracket ]
or allocate-object ( [ lower-bounds-expr : ] upper-bounds-expr ) \
[ lbracket allocate-coarray-spec rbracket ]
C943 (R929) If an allocate-object is an array, either allocate-shape-spec-list
or upper-bounds-expr shall appear in its allocation,
or source-expr shall appear in the ALLOCATE statement and
have the same rank as the allocate-object.
The final clause of C943 specifies that neither allocate-shape-spec-list nor
upper-bounds-expr is required when the SOURCE= or MOLD= specifiers are
provided. That is, in fact, the sole purpose of the MOLD= specifier.
