Argument Clinic: Better internal implementation for `@getter` and `@setter`

[corona10]

Even though we successed to provide @getter and @setter features from #112205
The current internal implementation is full of hacky workaround.

We need to improve the internal implementation for better generated C codes and maintenance.
@erlend-aasland wrote some ideas for this: #112205 (comment)

Linked PRs

• gh-113318: Fix @getter and @setter in Argument Clinic #155778
• [3.15] gh-113318: Fix @getter and @setter in Argument Clinic (GH-155778) #156010
• [3.14] gh-113318: Fix @getter and @setter in Argument Clinic (GH-155778) #156011
• [3.13] gh-113318: Fix @getter and @setter in Argument Clinic (GH-155778) #156012
• gh-113318: Better implementation of @getter and @setter in Argument Clinic #156066

[corona10]

See also: #113160 (comment)

[erlend-aasland]

Thanks for creating this issue, Donghee. See #112205 (comment) for more info.

[serhiy-storchaka]

Not only internal implementation needs improvement, but the interface too.

• Getter should support return converter.
• Setter should support converter for the single parameter (for example, ssl.SSLContext.options would benefit from this).
• Support deleter.

[skirpichev]

My 2c:

1. aliases aren't supported properly

2. "ifdef trick" doesn't work with get/setters. Trying to create a getter/setter in #ifdef block, I get following error from the clinic.py:

Traceback (most recent call last):
  File "/home/sk/src/cpython/Tools/clinic/clinic.py", line 11, in <module>
    main()
    ~~~~^^
  File "/home/sk/src/cpython/Tools/clinic/libclinic/cli.py", line 226, in main
    run_clinic(parser, args)
    ~~~~~~~~~~^^^^^^^^^^^^^^
  File "/home/sk/src/cpython/Tools/clinic/libclinic/cli.py", line 218, in run_clinic
    parse_file(filename, output=ns.output,
    ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^
               verify=not ns.force, limited_capi=ns.limited_capi)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/sk/src/cpython/Tools/clinic/libclinic/cli.py", line 84, in parse_file
    cooked = clinic.parse(raw)
  File "/home/sk/src/cpython/Tools/clinic/libclinic/app.py", line 193, in parse
    parser.parse(block)
    ~~~~~~~~~~~~^^^^^^^
  File "/home/sk/src/cpython/Tools/clinic/libclinic/dsl_parser.py", line 492, in parse
    block.output.extend(self.clinic.language.render(self.clinic, block.signatures))
                        ~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/sk/src/cpython/Tools/clinic/libclinic/clanguage.py", line 83, in render
    return self.render_function(clinic, function)
           ~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/home/sk/src/cpython/Tools/clinic/libclinic/clanguage.py", line 521, in render_function
    s = template.format_map(template_dict)
KeyError: 'methoddef_name'

[serhiy-storchaka]

#155778 fixes several bugs. A larger feature PR will follow.