proc_macro: use crossbeam channels for the proc_macro cross-thread bridge

This is done by having the crossbeam dependency inserted into the
proc_macro server code from the server side, to avoid adding a
dependency to proc_macro.

In addition, this introduces a -Z command-line option which will switch
rustc to run proc-macros using this cross-thread executor. With the
changes to the bridge in #98186, #98187, #98188 and #98189, the
performance of the executor should be much closer to same-thread
execution.

In local testing, the crossbeam executor was substantially more
performant than either of the two existing CrossThread strategies, so
they have been removed to keep things simple.

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 57ce4933a3b..a9fdfa24141 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -11,7 +11,7 @@ use rustc_session::config::{
 };
 use rustc_session::config::{
     BranchProtection, Externs, OomStrategy, OutputType, OutputTypes, PAuthKey, PacRet,
-    SymbolManglingVersion, WasiExecModel,
+    ProcMacroExecutionStrategy, SymbolManglingVersion, WasiExecModel,
 };
 use rustc_session::config::{CFGuard, ExternEntry, LinkerPluginLto, LtoCli, SwitchWithOptPath};
 use rustc_session::lint::Level;
@@ -685,6 +685,7 @@ fn test_unstable_options_tracking_hash() {
     untracked!(print_mono_items, Some(String::from("abc")));
     untracked!(print_type_sizes, true);
     untracked!(proc_macro_backtrace, true);
+    untracked!(proc_macro_execution_strategy, ProcMacroExecutionStrategy::CrossThread);
     untracked!(query_dep_graph, true);
     untracked!(save_analysis, true);
     untracked!(self_profile, SwitchWithOptPath::Enabled(None));