You have been doing a great job with the community. Since you open sourced Swift, we have seen the language evolving a lot, we've been able to follow the progress in the language, let you know about the issues that we found, and contribute directly to the language.
However, we haven't seen a lot of improvements in the tools that we use to build apps using Swift and Objective-C. That has brought some frustration, and we've ended up creating our tools to improve the way we develop, build and test our apps. In some cases, reverse engineering is the only API that we have.
Some issues that we're frequently facing and ideas to address them are:
.xcconfigfile, the rest of the project settings are not very accessible. Introducing changes in the project setup is only possible by using Xcode or parsing the unaccessible project files. A more open configuration would provide developers with more flexibility defining how the projects get built.
XCTestprovided communication APIs it'd, simplify the way we UI test nowadays.
Every WWDC we cross our fingers to see improvements in the tools that we need to create app experiences. Since Xcode and the build tools are not open source, the only option we have is kindly asking you to hear us.
If you are a Xcode developer you can sign the letter here
This open letter idea is inspired in GitHub's one.
Note: You can also approach Apple, and report bugs and requests as radars on https://bugreport.apple.com/