The nRF Connect for VS Code extension uses build system output to provide the C/C++ extension with a list of paths that should be indexed for its go-to-definition mechanism.
Some include paths would be specified as relative paths by the build system, but the C/C++ extension is not able to relate this to the build directory itself, so in some cases, it would end up indexing the entire workspace folder, which took a lot of time and resources. This would normally manifest itself as a never ending loading indicator on the C language status bar item, and generally poor performance for C/C++ language support.
We have now addressed this by converting all paths passed to the C/C++ extension to absolute paths. The C/C++ extension might take a few seconds to reset itself and purge any unneeded indexing files, but once that initial cleanup is finished, both go-to-definition and other language support mechanisms in C/C++ should be significantly faster.