error_info_fallback needs to convert empty message #711
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The OS version of RoOriginateLanguageException converts empty messages into an error message produced by FormatMessage. Our fallback Win7 version does not have this feature, which causes errors to be produced with no message. This defect had been present since inception but was exposed by a correctness fix to `hstring.c_str()` so that it returned an empty string (instead of nullptr) for the null hstring. Prior to the hstring fix, the implementation of `error_info_fallback::GetErrorDetails` would happily pass `nullptr` to `SysAllocString`, which failed with an invalid parameter. This error was propagated (mistakenly as `error_bad_alloc`), and that caused `hresult_error.message()` to fall back to `FormatMessage`. With the hstring fix, the implementation of `error_info_fallback::GetErrorDetails` now passes a non-null empty string, which `SysAllocString` dutifully allocates and returns. We fix `error_info_fallback` by having it autogenerate a message if no message was provided, bringing it into alignment with the `RoOriginateLanguageException` function it was intended to emulate.
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The OS version of RoOriginateLanguageException converts empty messages into an error message produced by FormatMessage. Our fallback Win7 version does not have this feature, which causes errors to be produced with no message.
This defect had been present since inception but was exposed by a correctness fix to
hstring.c_str()so that it returned an empty string (instead of nullptr) for the null hstring.Prior to the hstring fix, the implementation of
error_info_fallback::GetErrorDetailswould happily passnullptrtoSysAllocString, which failed with an invalid parameter. This error was propagated (mistakenly aserror_bad_alloc), and that causedhresult_error.message()to fall back toFormatMessage.With the hstring fix, the implementation of
error_info_fallback::GetErrorDetailsnow passes a non-null empty string, whichSysAllocStringdutifully allocates and returns.We fix
error_info_fallbackby having it autogenerate a message if no message was provided, bringing it into alignment with theRoOriginateLanguageExceptionfunction it was intended to emulate.Fixes #623