Improve error message when discovery plugin is not available - #3032
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You'll need to rebase to fix merge conflcits.
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When VIRTUALENV_DISCOVERY is set via environment variable to a plugin that isn't installed, the previous behavior was a raw KeyError which was confusing and unhelpful. Now raises a RuntimeError with a clear message showing the requested plugin name, available discovery methods, and a hint to check if the plugin is installed. Fixes pypa#2896
The test_invalid_discovery_method_via_env test was expecting a ValueError with the old error format from PR pypa#3031, but our changes raise a RuntimeError with improved messaging. Update the test assertions to match. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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When
VIRTUALENV_DISCOVERYis set via environment variable to a plugin that isn't installed, the previous behavior was a rawKeyError:This was confusing, especially for users running virtualenv through tox where the full traceback made it hard to understand the actual problem.
Now it raises a clear
RuntimeErrorwith a helpful message:Note that when
--discoveryis passed as a CLI argument, argparse already validates the choice and gives a reasonable error. This fix covers the env var (and ini config) code path where the value bypasses argparse's choice validation since it's set as a default.Fixes #2896