v.clip: do not fail when clip map has no table connected

[landam]

In GRASS 8.4 v.clip fails when clip map has no table connected. Steps to reproduce in NC location:

v.extract input=boundary_county cat=1 output=aoi
v.db.connect aoi -d
v.clip input=geology clip=aoi output=geology_clip --o

v.clip currently fails with:

ERROR: Database connection for map <aoi> is not defined in DB file
Traceback (most recent call last):
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/scripts/v.dissolve", line 686, in <module>
    main()
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/scripts/v.dissolve", line 566, in main
    aggregate_columns_exist_or_fatal(input_vector, layer, columns_to_aggregate)
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/scripts/v.dissolve", line 265, in aggregate_columns_exist_or_fatal
    column_names = gs.vector_columns(vector, layer).keys()
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/etc/python/grass/script/vector.py", line 128, in vector_columns
    s = read_command(
        ^^^^^^^^^^^^^
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/etc/python/grass/script/core.py", line 532, in read_command
    return handle_errors(returncode, stdout, args, kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/etc/python/grass/script/core.py", line 344, in handle_errors
    raise CalledModuleError(module=module, code=code, returncode=returncode)
grass.exceptions.CalledModuleError: Module run `v.info --q -c map=aoi layer=1` ended with an error.
The subprocess ended with a non-zero return code: 1. See errors above the traceback or in the error output.
Traceback (most recent call last):
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/scripts/v.clip", line 226, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/scripts/v.clip", line 150, in main
    grass.run_command("v.dissolve", input=clip_map, output=temp_clip_map)
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/etc/python/grass/script/core.py", line 465, in run_command
    return handle_errors(returncode, result=None, args=args, kwargs=kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/martin/src/grass/dist.x86_64-pc-linux-gnu/etc/python/grass/script/core.py", line 344, in handle_errors
    raise CalledModuleError(module=module, code=code, returncode=returncode)
grass.exceptions.CalledModuleError: Module run `v.dissolve input=aoi output=temp_20535` ended with an error.
The subprocess ended with a non-zero return code: 1. See errors above the traceback or in the error output.

It is regression, in GRASS 8.3 v.clip module works as expected.

[landam]

See related #2388

[wenzeslaus]

Thanks. That should work.

It does seems that the whole code should behave better for this case, like fail nicely when user provides the names, but the table is missing.

Clearly, neither v.dissolve nor v.clip cover the case without a table in their tests.