| Issue |
63844
|
| Summary |
[flang][Preprocessor] Unexpected error mesage due to unusual macro usage
|
| Labels |
new issue
|
| Assignees |
|
| Reporter |
rofirrim
|
The following input (simplified from a real occurence in an in-house application of ours):
```fortran
! input.F90
subroutine foo(a, d)
implicit none
integer :: a
integer :: d
#ifdef SOME_CASE
#define MY_MACRO )
#else
#define MY_MACRO ,d)
#endif
call foo2(a MY_MACRO
a = 3*a
end subroutine foo
```
fails to parse.
```
$ flang-new -c input.F90
error: Could not parse input.F90
./input.F90:14:3: error: expected end of statement
a = 3*a
^
./input.F90:13:3: in the context: execution part construct
call foo2(a MY_MACRO
^
./input.F90:13:3: in the context: execution part
call foo2(a MY_MACRO
^
./input.F90:2:1: in the context: SUBROUTINE subprogram
subroutine foo(a, d)
^
error: end of file
./input.F90:2:1: in the context: SUBROUTINE subprogram
subroutine foo(a, d)
^
error: expected end of line
```
At some point in the scanner, before preprocessing, we have the following token formed:
```
call foo2(a MY_MACRO a = 3*aend subroutine foo
```
After preprocessing this gets expanded into
```
call foo2(a ,d) a = 3*aend subroutine foo
```
The reason for the token to span to the next line in the file seems to be caused by the scanner allowing implicit continuations as described in https://flang.llvm.org/docs/Preprocessing.html but this seems to interact badly in this case.
If you remove the macro definition, then the scanner diagnoses an error much earlier because the lack of expansion of `MY_MACRO` means the parentheses are not well-balanced, so the parser never gets to see the statement.
gfortran and ifort/ifx accept this input.
### Workaround
We can avoid this issue if we factor out the closing parenthesis (`)`) out of the macro and move it to the macro use.
```fortran
! workaround.F90
subroutine foo(a, d)
implicit none
integer :: a
integer :: d
#ifdef SOME_CASE
#define MY_MACRO
#else
#define MY_MACRO ,d
#endif
call foo2(a MY_MACRO )
a = 3*a
end subroutine foo
```
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