Plugin system: improve error handling

[jaimergp]

Checklist

• I added a descriptive title
• I searched open requests and couldn't find a duplicate

What is the idea?

Add a new configuration option for subcommand plugins:

  @conda.plugins.hookimpl
  def conda_subcommands():
      yield conda.plugins.CondaSubcommand(
          name="build",
          summary="Build conda packages from a conda recipe.",
          action=build,
+         base_exception_class=CondaBuildError,
      )

This is then exposed by the plugin manager to conda's exception handling logic to consider them "expected exceptions" instead of unexpected. The kwarg name can also be expected_exception_type and so on.

Why is this needed?

Subcommands plugins will run their code under conda's exception handler. If the exceptions raised are not covered by this logic:

conda/conda/exception_handler.py

Lines 49 to 75 in bfc82e1

	def handle_exception(self, exc_val, exc_tb):
	from errno import ENOSPC
	from .exceptions import (
	CondaError,
	CondaMemoryError,
	NoSpaceLeftError,
	)
	if isinstance(exc_val, CondaError):
	if exc_val.reportable:
	return self.handle_reportable_application_exception(exc_val, exc_tb)
	else:
	return self.handle_application_exception(exc_val, exc_tb)
	if isinstance(exc_val, EnvironmentError):
	if getattr(exc_val, "errno", None) == ENOSPC:
	return self.handle_application_exception(
	NoSpaceLeftError(exc_val), exc_tb
	)
	if isinstance(exc_val, MemoryError):
	return self.handle_application_exception(CondaMemoryError(exc_val), exc_tb)
	if isinstance(exc_val, KeyboardInterrupt):
	self._print_conda_exception(CondaError("KeyboardInterrupt"), exc_tb)
	return 1
	if isinstance(exc_val, SystemExit):
	return exc_val.code
	return self.handle_unexpected_exception(exc_val, exc_tb)

Then conda will create an error report with added verbosity.

This is creating UX issues in conda-build, where it is normal to raise CalledProcessError for a failed build script. See conda/conda-build#5263.

What should happen?

If a subcommand plugin registers an expected exception type, then conda will not create an error report. The full traceback will be available in --debug and -vvv modes, as usual.

Some documentation on how to use this feature should be added too.

Additional Context

Comes from conda/conda-build#5263. For this to benefit conda-build, conda-build will also need to change the types of their expected exceptions.

[jaimergp]

An alternative proposed by @jezdez would be to instead have a general "expected_exception_type" plugin hook so any plugin can register their known exception types.

I guess we shouldn't allow generic builtins there, but that can be discussed in the eventual PR.

[jaimergp]

Another alternative that is floating is that all plugins that wish to have special treatment by the exception handler subclass conda.CondaError. Maybe we just need to document this "requirement" / API.

[jezdez]

Another alternative that is floating is that all plugins that wish to have special treatment by the exception handler subclass conda.CondaError. Maybe we just need to document this "requirement" / API.

That seems like the best course of action TBH.

[jaimergp]

Let's document that then. I'll open a PR.