Fix WRFDA build failure caused by duplicate da_residual.inc

[the-1000th-summer]

TYPE: bug fix

KEYWORDS: WRFDA, build, symbolic link, duplicate filename, da_residual.inc

SOURCE: Deng Hao (Sun Yat-sen University)

DESCRIPTION OF CHANGES:

Problem:

The WRFDA source tree contains two files with the same basename:

• var/da/da_minimisation/da_residual.inc
• var/da/da_tools/da_residual.inc

The file under da_minimisation is empty, while the file under
da_tools contains the implementation used by da_tools.f90.

During the legacy WRFDA build process, files from the different
var/da/da_* directories are linked into the common var/build
directory. Both source files therefore map to:

var/build/da_residual.inc

With GNU ln, this causes the link-generation step to fail with:

ln: will not overwrite just-created './da_residual.inc'

The current da_minimisation.f90 uses
da_calculate_residual.inc and does not appear to use the empty
da_minimisation/da_residual.inc file.

Solution:

Removed the unused empty file:

var/da/da_minimisation/da_residual.inc

The implementation in var/da/da_tools/da_residual.inc is unchanged.

ISSUE:

Fixes #2364

LIST OF MODIFIED FILES:

D var/da/da_minimisation/da_residual.inc

TESTS CONDUCTED:

1. Reproduced the duplicate-link failure before the change when
   compiling WRFDA 4D-Var.

2. Removed the empty duplicate file, cleaned the source tree,
   reconfigured WRFDA, and rebuilt it using:

   ./clean -a
   ./configure wrfda
   ./compile all_wrfvar

3. The duplicate da_residual.inc link error no longer occurred,
   and the WRFDA build completed successfully.

Test environment:

• Operating system: Ubuntu Linux under WSL2
• C compiler: GCC 15.2.0
• Fortran compiler: GNU Fortran 15.2.0
• Component: WRFDA / 4D-Var
• Base branch: develop

The official Jenkins regression tests were not run locally.

RELEASE NOTE:

Removed an unused empty WRFDA include file that caused a duplicate
filename conflict during the legacy WRFDA build link-generation stage.

[weiwangncar]

The regression test results:

Test Type              | Expected  | Received |  Failed
= = = = = = = = = = = = = = = = = = = = = = = =  = = = =
Number of Tests        : 23           24
Number of Builds       : 60           57
Number of Simulations  : 158           150        0
Number of Comparisons  : 95           86        0

Failed Simulations are: 
None
Which comparisons are not bit-for-bit: 
None