[SR-6326] File to small (length = 0) error

[keith]

Previous ID	SR-6326
Radar	rdar://problem/19945961
Original Reporter	@keith
Type	Bug

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 80323f2b7fb37f60938f5895a1fc1d6d

Issue Description:

Sometimes when compiling a Swift app, the linking phase fails with this error:

ld: file too small (length=0) file 'path/to/foo.o' for architecture x86_64

It's hard to tell exactly what the problem is here, although it might happen when a previous build is cancelled during compilation.

In this case we can easily resolve this by removing all `.o` files of size 0 from derived data. I've previously filed a related radar (31521765) about the fact that Xcode doesn't parse this error, but the actual cause seems to be related to Swift and not Xcode.

This isn't a new issue but I haven't been able to find a report for this so I wanted to add one to track any info known about this issue already.

[belkadan]

Yep, known issue. This can happen if the compiler process is killed at the wrong time. We should clearly be cleaning up those empty files, but right now we're not.

I'm not sure how much work this would be to clean up. Last time I looked, Clang's support for "atomic writes" (write to a side file and then rename into place) wasn't so easily reusable by Swift, but things may have changed since then.

[NachoSoto]

FYI 3 years later and this is still an issue that happens pretty regularly.