Add more options for xerces-c recipe

[FMeinicke]

Specify library name and version: xerces-c/3.2.3

As specified in http://xerces.apache.org/xerces-c/build-3.html#CMake
there are a number of project specific options for configuring xerces-c.
Currently, only the XMLCh type could be configured through a conan
option. This commit adds corresponding conan options for all of the
other options (i.e. network accessor, transcoder, message loader and
mutex manager) that were previously hardcoded. Since not every value of
these options is valid on every platform this commit also adds proper
validation of the user input to detect invalid configurations. Setting
the default value for the conan options is a bit more complicated
because for some options this value is not the same for all platforms.
Therefore, the default_options have been dropped in favor of setting
the options manually from within config_options() if not set by the
user.

---

• I've read the guidelines for contributing.
• I've followed the PEP8 style guides for Python code in the recipes.
• I've used the latest Conan client version.
• I've tried at least one configuration locally with the
  conan-center hook activated.

[CLAassistant]

All committers have signed the CLA.

[jgsogo]

As far as it is possible, we try to keep compatibility with Python2, which is also supported by Conan v1.x. So, please, avoid those f-strings and type hints.

(I would love to use them everywhere, but it will only be possible when we migrate definitively away from some Conan v1.x constraints)

Thanks!

[jgsogo]

There are also some general comments about the changes themselves:

• Try not to assign different option values for different settings. It is better to raise if some option values are incompatible and force the user to provide different (and explicit) input.
• If some option is not supported in some OS, it's better to remove it (typically inside config_options()). Conan should take care of the error message. Then you can use self.options.get_safe('xxxxx', <default>) to retrieve the value of the option (no need to check if it exists first).

[FMeinicke]

• Try not to assign different option values for different settings. It is better to raise if some option values are incompatible and force the user to provide different (and explicit) input.

The problem is that depending on the OS the default value of certain options is different. I could set the network_accessor to socket by default but then a simple conan install would fail on Windows as socket is not supported there.
My goal was that a user would get the best default experience from a conan install without any options regardless of which OS their using. But if it's more conan-like to be explicit then I'm happy to change the default values to be all the same on all OSes and raise if the value is not valid.

• If some option is not supported in some OS, it's better to remove it (typically inside config_options()). Conan should take care of the error message. Then you can use self.options.get_safe('xxxxx', <default>) to retrieve the value of the option (no need to check if it exists first).

That's not really the case here, I think. All options are supported on all OSes but the values an option can have depend on the OS.

[prince-chrismc]

The problem is that depending on the OS the default value of certain options is different.

There are other examples of this in CCI and we usually put a value in the default and then change it in config_options

examples off the top of my head

conan-center-index/recipes/libcurl/all/conanfile.py

Line 116 in 2f74ab3

self.options.with_ssl = "darwinssl" if tools.is_apple_os(self.settings.os) else "openssl"

conan-center-index/recipes/cpr/all/conanfile.py

Line 88 in 2f74ab3

def config_options(self):

[jgsogo]

I think we can simplify that if condition if we use always tuples.

[prince-chrismc]

Please consider FMeinicke#1

[SpaceIm]

Please reopen this review (don't close review when there is no consensus): #6959 (comment)

[madebr]

@jgsogo
prince-chrismc/conan-center-index-pending-review#1 tells me you're blocking this pr.

[conan-center-bot]

All green in build 9 (2eb723e2ed15717ea212c27c4d709be2ebeb09f2):

• xerces-c/3.2.2@:
  All packages built successfully! (All logs)

• xerces-c/3.2.3@:
  All packages built successfully! (All logs)

[uilianries]

@jgsogo ping