Fixed Issue when Caching of SwiftTemplate Binary Fails

[art-divin]

Context

Currently, whenever Sourcery is done with compiling SwiftTemplate executable binary, it tries to move this binary into a shared cache folder.

However, if Sourcery is executed concurrently, i.e. sourcery binary is launched multiple times with a same .swifttemplate, an error is thrown because one of the sourcery executions was able to move the same file from within a guarding if statement:

Error Domain=NSCocoaErrorDomain Code=516 "“SwiftTemplate” couldn’t be moved to “Equality.swifttemplate” because an item with the same name already exists." UserInfo={NSSourceFilePathErrorKey=/var/folders/90/8tcwdk19055d0rrgfp00h25h0000gn/T/SwiftTemplate/4F2C1EC9-D4B9-44BE-A854-1F6BAAFD5113/Major.Minor.Patch/.build/release/SwiftTemplate, NSUserStringVariant=(
    Move
), NSDestinationFilePath=/Users/art-divin/Library/Caches/Sourcery/Equality.swifttemplate/oSLR1bsrLapzaddnJtSrw7XLwIcd94jZorJD%2BX3XSxA%3D, NSFilePath=/var/folders/90/8tcwdk19055d0rrgfp00h25h0000gn/T/SwiftTemplate/4F2C1EC9-D4B9-44BE-A854-1F6BAAFD5113/Major.Minor.Patch/.build/release/SwiftTemplate, NSUnderlyingError=0x600001928030 {Error Domain=NSPOSIXErrorDomain Code=17 "File exists"}}

Details

To resolve this, the move of the compiled SwiftTemplate binary is now optional, i.e. thrown error is ignored. Essentially, it is irrelevant if the binary was cached or not, since Sourcery's task is to execute SwiftTemplate and not cache SwiftTemplate.

Verification is done using a new unit test.