Xcode 6 linker error - Undefined symbols for architecture armv7

Question

After upgrading to Xcode 6 beta 7 (and now still with Xcode 6 GM) I am unable to link my Swift app. I receive errors such as:

Undefined symbols for archit

Answer 1

There appears to be a bug in Xcode 6.0.1 that is causing the linker to drop dependencies in existing project files. I have had this same problem across several different projects, new and old, since the 6.0.1 update.

The easy 'fix' is to just trash your entire 'Derrived Data' and all build files (i.e. manually clean the project) and then rebuild after a fresh Xcode restart. Magically, the linker now finds all the missing architectures/symbols.

NOTE: I have had several incompatible v-table crashes caused by this same bug. The C++ linker appears to be generating incomplete linkages, causing absurd errors where there are no real errors to be found. Again, just rebuild from a clean state and .. ta da.. save yourself a LOT of headache and wasted time tracking down a non-issue.