chore: add some `tracing` to project loading
I wanted to see what's happening during project loading and if it could be parallelized. I'm thinking maybe, but it's not this PR :)
Fix crate IDs when multiple workspaces are loaded
Previously, we assumed that the crate numbers in a `rust-project.json` always matched the `CrateId` values in the crate graph. This isn't true when there are multiple workspaces, because the crate graphs are merged and the `CrateId` values in the merged graph are different.
This broke flycheck (see first commit), because we were unable to find the workspace when a file changed, so we every single flycheck, producing duplicate compilation errors.
Instead, use the crate root module path to look up the relevant flycheck. This makes `ProjectWorkspace::Json` consistenet with `ProjectWorkspace::Cargo`.
Also, define a separate JSON crate number type, to prevent bugs like this happening again.
`cargo rustc -- <args>` first builds dependencies then calls `rustc <args>` for the current package. Here, we don't want to build dependencies, we just want to call `rustc --print`. An unstable `cargo rustc` `--print` command bypasses building dependencies first. This speeds up execution of this code path and ensures RA doesn't recompile dependencies with the `RUSTC_BOOTSRAP=1` env var flag set.
Note that we must pass `-Z unstable-options` twice, first to enable the `cargo` unstable `--print` flag, then later to enable the unstable `rustc` `target-spec-json` print request.
Some packages (e.g. thiserror) force a recompile if the value of the `RUSTC_BOOTSTRAP` env var changes. RA sets the variable to 1 in order to enable rustc / cargo unstable options it uses. This causes flapping recompiles when building outside of RA.
As of Cargo 1.75 the `--keep-going` flag is stable. This change uses the flag without `RUSTC_BOOTSTRAP` if the Cargo version is >= 1.75, and drops `--keep-going` otherwise. This fixes build script recompilation.
