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fix: add raise ... from e in all except handlers - #2777
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kiankhooban wants to merge 2 commits into
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Preserves exception chaining so the original traceback is always visible when exceptions are re-raised inside except blocks. Fixes 11 sites across 6 files — follow-up to modelcontextprotocol#2542.
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Pull request overview
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Improve debuggability by preserving original exceptions when re-raising errors across resources, prompts, and client/auth flows.
Changes:
- Add explicit exception chaining (
raise ... from e) to preserve original tracebacks. - Apply the same pattern across resource reading/creation, prompt rendering, tool result validation, and OAuth response parsing.
Reviewed changes
Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.
Show a summary per file
| File | Description |
|---|---|
| src/mcp/server/mcpserver/resources/types.py | Chain underlying exceptions for resource/file/directory read/list errors. |
| src/mcp/server/mcpserver/resources/templates.py | Chain underlying exceptions when template-based resource creation fails. |
| src/mcp/server/mcpserver/resources/resource_manager.py | Chain underlying exceptions when resolving resources via templates fails. |
| src/mcp/server/mcpserver/prompts/base.py | Chain underlying exceptions when prompt rendering fails. |
| src/mcp/client/session.py | Chain schema/validation exceptions when validating tool structured output. |
| src/mcp/client/auth/utils.py | Chain validation exceptions when parsing OAuth registration/token responses fails. |
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| except SchemaError as e: # pragma: no cover | ||
| raise RuntimeError(f"Invalid schema for tool {name}: {e}") # pragma: no cover | ||
| raise RuntimeError(f"Invalid schema for tool {name}: {e}") from e # pragma: no cover |
| return client_info | ||
| except ValidationError as e: # pragma: no cover | ||
| raise OAuthRegistrationError(f"Invalid registration response: {e}") | ||
| raise OAuthRegistrationError(f"Invalid registration response: {e}") from e |
| return token_response | ||
| except ValidationError as e: # pragma: no cover | ||
| raise OAuthTokenError(f"Invalid token response: {e}") | ||
| raise OAuthTokenError(f"Invalid token response: {e}") from e |
- Remove duplicate pragma: no cover from raise line in session.py
- Strip {e} from OAuth error messages to avoid leaking token data;
the chained exception already carries full details for debuggingmaxisbey
commented
Jul 24, 2026
Contributor
Thanks for the PR. Tracking this in #2565 instead. Closing as part of a general backlog cleanup ahead of the v2 release. If this is still relevant against current |
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Follow-up to #2542.
Adds
from eto all remainingraisestatements insideexcept ... as e:blocks that were missing exception chaining. This ensures the original traceback is preserved when exceptions are re-raised, making debugging significantly easier.Files changed (11 sites across 6 files):
src/mcp/client/session.py(2)src/mcp/client/auth/utils.py(2)src/mcp/server/mcpserver/resources/types.py(4)src/mcp/server/mcpserver/resources/resource_manager.py(1)src/mcp/server/mcpserver/resources/templates.py(1)src/mcp/server/mcpserver/prompts/base.py(1)