UPDATE (Edit 3)

The issue has been fixed on Xcode 11, from beta 3:

• Xcode uses response files by default to pass input files to the Swift compiler. To turn this behavior off, set USE_SWIFT_RESPONSE_FILE to NO.

• You can use an unlimited number of Swift files in a target. (35879960)

Old answer

I've only seen this error arising when the total of files (notice all their respective absolute paths count) exceed the command line length limit (looks like it's imposed by the OS, currently 262144 bytes on my rMBP). It's a known issue.

To fix this (AFAIK), you have 2 options:

• Fast (short term): Put your project on a shorter path on the server (like moving the project from /Users/mrjimoy_05_server/myprojects/mycoolproject/ to /p/mycoolproject)

• Better (long term): While the first solution might work, for now, you'll probably reach the same point where you're now in the near future. So a better solution is to modularize your app (separate it into frameworks/projects). Since every module will get built separately, it'll be much harder to reach the limit and get this error again.

I hope it helps.

PD: Looks like the error thrown by the New Build System is:

unable to spawn process (File exists)

Edit 1

The error thrown by the New Build System on Xcode 10 now is:

unable to spawn process (Argument list too long)

Edit 2

The Swift team have solved this issue, but it also needs some work from the Xcode team, which hasn't been done yet on the latest released Xcode version (10.2)