Turn SystemError.from_errno into a macro
#15874
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straight-shoota
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The actual method that resolves #15496 is |
HertzDevil
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Jun 4, 2025
ysbaddaden
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Jun 5, 2025
straight-shoota
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This ensures we capture `Errno.value` right away and it cannot be influenced by other code producing the arguments.
Co-authored-by: Quinton Miller <[email protected]>
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src/system_error.cr
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| # The system message corresponding to the OS error value amends the *message*. | ||
| # Additional keyword arguments are forwarded to the exception initializer `.new_from_os_error`. | ||
| macro from_errno(message, **opts) | ||
| # This is a macro in order to retrieve `Errno.value` first before evaluating `message` and `opts`. |
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Polish: maybe move this comment outside of the macro, and be more general:
The following are macros so we can get the errno or winerror before
evaluating message and opts that may change the errno or winerror value.
ysbaddaden
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SystemError.from_errnocallsErrno.valueto retrieve the system error value from the last lib call.But this happens in the body of the method which only executes after its arguments are evaluated (for example building the error message). This can lead to a change in
Errno.valuewhich.from_errnowould then mistake for the original error.In order to fix this, we must query
Errno.valueimmediately after the lib call.Changing
.from_errnointo a macro achieves that because it expands into a call toErrno.valuebefore constructing the actual error object and its arguments.We need to change the deprecated
from_errnomethod which receives anErrnovalue as well because the macro would shadow the method.One downside of the macro approach is that it won't work with file-private error types (#15496 (comment)). But this is probably not a very relevant use case.
If this is accepted, I'll do the same change to
SystemError.from_winerrorandSystemError.from_wsa_error.Resolves #15496