Appveyor CI jobs have been failing in the last 24 hours due to a seemingly corrupted cache, see #19440.
It’s possible that the appveyor cache issue is related to the recent update of the Visual Studio 2019 image
PR #19431 changes the “save cache or error” to false in an attempt to avoid a failing CI job from potentially corrupting the cache. In theory the only way a PR could affect the cache is if the vcpkg install list changed. That happens very rarely and did not happen in the last 24 hours and so was not the cause of the current cache problems.
I have done some testing with appveyor build jobs on my own fork and found that installing the vcpkg dependencies from scratch and doing a full build can now be done in just under 60 minutes. This is the first time in over 5 months I have been able to build Bitcoin Core on appveyor. Either the new Visual Studio 2019 image has dramatically reduced the build time or appveyor images have had their CPU increased.
This PR removes all use of dependency caching from the appveyor CI config. The trade-off is the 15 minutes saved on each build from having the dependencies cached versus the hours maintainers need to spend investigating when the CI jobs start failing.
