As of #6246, rust-analyzer follows symlinks. This can introduce an
infinite loop if symlinks point to parent directories.
Considering that #6246 was added in 2020 without many bug reports,
this is clearly a rare occurrence. However, I am observing
rust-analyzer hang on projects that have symlinks of the form:
```
test/a_symlink -> ../../
```
Ignore symlinks that only point to the parent directories, as this is
more robust but still allows typical symlink usage patterns.
This code replaces the thread pool implementation we were using
previously (from the `threadpool` crate). By making the thread pool
aware of QoS, each job spawned on the thread pool can have a different
QoS class.
This commit also replaces every QoS class used previously with Default
as a temporary measure so that each usage can be chosen deliberately.
When r-a starts up, it starts switching the workspace before all vfs
events have been processed which causes us to switch workspace multiple
times until all vfs changes have been processed. This scales with the
size of the project and its dependencies. If workspace files from
dependencies as well as the sysroot get loaded, we shouldn't switch
the workspace as those have no impact on the project workspace.
The thread name is shown in debugger as well as panic messages and this
patch makes it easier to follow a thread instead of looking through
full backtrace, by naming all spawned threads according to their
functioning.
In some situations we reloaded the workspace in the tests after having reported
to be ready. There's two fixes here:
1. Add a version to the VFS config and include that version in progress reports,
so that we don't think we're done prematurely;
2. Delay status transitions until after changes are applied. Otherwise the last
change during loading can potentially trigger a workspace reload, if it contains
interesting changes.
