[Flang][OpenMP] No error checking of a continuation line that does not have a line to be continued in Fixed Source Form Conditional Compilation Sentinel

[ohno-fj]

Version of flang : 21.0.0(c8b40867d144395ad3c306a3cf87f970e0f97f07)/AArch64

The attached program is incorrect.
In Fixed Source Form Conditional Compilation Sentinel, flang does not output an error message during compilation for a continuation line that does not have a line to be continued.

The following are the test program, Flang, Gfortran and ifx compilation/execution result.

err_sngg081g_2.f:

c$   !   0      !

      print *,'pass'
      end

$ export OMP_NUM_THREADS=2; flang -fopenmp err_sngg081g_2.f; ./a.out
flang-20: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
 pass
$

$ export OMP_NUM_THREADS=2; gfortran -fopenmp err_sngg081g_2.f; ./a.out
 pass
$

$ ifx -qopenmp err_sngg081g_2.f
err_sngg081g_2.f(1): error #5118: First statement in file must not be continued
c$   !   0      !
-----^
err_sngg081g_2.f(1): error #5082: Syntax error, found INTEGER_CONSTANT '0' when expecting one of: <LABEL> <END-OF-STATEMENT>
; <IDENTIFIER> TYPE MODULE ELEMENTAL IMPURE NON_RECURSIVE ...
c$   !   0      !
---------^
err_sngg081g_2.f(1): error #6905: A label cannot be zero; it must be an integer in the range 1 through 99999.   [0]
c$   !   0      !
---------^
err_sngg081g_2.f(1): error #6321: An unterminated block exists.
c$   !   0      !
^
err_sngg081g_2.f(1): error #6323: This label is not defined in this scoping unit.   [0]
c$   !   0      !
---------^
compilation aborted for err_sngg081g_2.f (code 1)
$

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: None (ohno-fj)

``` Version of flang : 21.0.0(c8b4086)/AArch64 ```

The attached program is incorrect.
In Fixed Source Form Conditional Compilation Sentinel, flang does not output an error message during compilation for a continuation line that does not have a line to be continued.

The following are the test program, Flang, Gfortran and ifx compilation/execution result.

err_sngg081g_2.f:

c$   !   0      !

      print *,'pass'
      end

$ export OMP_NUM_THREADS=2; flang -fopenmp err_sngg081g_2.f; ./a.out
flang-20: warning: OpenMP support in flang is still experimental [-Wexperimental-option]
 pass
$

$ export OMP_NUM_THREADS=2; gfortran -fopenmp err_sngg081g_2.f; ./a.out
 pass
$

$ ifx -qopenmp err_sngg081g_2.f
err_sngg081g_2.f(1): error #<!-- -->5118: First statement in file must not be continued
c$   !   0      !
-----^
err_sngg081g_2.f(1): error #<!-- -->5082: Syntax error, found INTEGER_CONSTANT '0' when expecting one of: &lt;LABEL&gt; &lt;END-OF-STATEMENT&gt;
; &lt;IDENTIFIER&gt; TYPE MODULE ELEMENTAL IMPURE NON_RECURSIVE ...
c$   !   0      !
---------^
err_sngg081g_2.f(1): error #<!-- -->6905: A label cannot be zero; it must be an integer in the range 1 through 99999.   [0]
c$   !   0      !
---------^
err_sngg081g_2.f(1): error #<!-- -->6321: An unterminated block exists.
c$   !   0      !
^
err_sngg081g_2.f(1): error #<!-- -->6323: This label is not defined in this scoping unit.   [0]
c$   !   0      !
---------^
compilation aborted for err_sngg081g_2.f (code 1)
$