test: fix miri failure due to tracing deps (#280)

This adds a Cargo patch for the `once_cell` crate to pick up an upstream
branch that fixes an int-to-pointer cast that Miri rejects.

The patch can be removed once matklad/once_cell#185 has merged.

Cargo.toml

@@ -90,6 +90,11 @@ tracing-core = { git = "https://github.com/tokio-rs/tracing" }
 # https://github.com/rust-osdev/volatile/pull/25 merges upstream. this is
 # necessary to build with unstable features on recent nightlies.
 volatile = { git = "https://github.com/hawkw/volatile", branch = "eliza/update-features" }
+# patch `once_cell` to use https://github.com/matklad/once_cell/pull/185 so that
+# Miri doesn't reject `tracing`'s use of `once_cell`.
+#
+# remove this patch once once_cell#185 is merged.
+once_cell = { git = "https://github.com/hawkw/once_cell", branch = "eliza/saethlin/provenance" }
 
 # Custom profile for Loom tests: enable release optimizations so that the loom
 # tests are less slow, but don't disable debug assertions.

cordyceps/src/list/tests.rs

@@ -117,7 +117,7 @@ fn const_new() {
     const _: List<Entry> = List::new();
 }
 
-fn trace_init() -> tracing::dispatcher::DefaultGuard {
+fn trace_init() -> impl Drop {
     use tracing_subscriber::prelude::*;
     tracing_subscriber::fmt()
         .with_test_writer()