hongbo/helpful oserror

[bobzhang]

• filter target to make output more stable
• add extra payload to make OSError more helpful when possible

[coveralls]

Pull Request Test Coverage Report for Build 696

Details

• 28 of 40 (70.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.5%) to 78.065%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/internal/event_loop/network.mbt	3	4	75.0%
src/internal/event_loop/fs.mbt	25	36	69.44%

Totals
Change from base Build 693:	-0.5%
Covered Lines:	1178
Relevant Lines:	1509

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💛 - Coveralls

[tonyfettes]

LGTM

[Guest0x0]

The idea lgtm, I'll simplify the implementation a bit (directly in this PR).

[Guest0x0]

• merge the extra info directly in the context field, so that we don't have to change the representation of @os_error.OSError (otherwise it would technically be a breaking change. The layout of OSError is also simpler this way)
• instead of adding the extra payload everywhere, let the relevant primtives (open, getaddrinfo) append the file name/path to context directly via catch. This way there is no need for (internal) API change