xmakro 51001cf7ef Make the retained dep graph deterministic under the parallel frontend ...

The in-memory dep graph kept for `-Zquery-dep-graph` is built by
`GraphEncoder::record`, which pushed each node using `try_lock` and
silently dropped the node when the lock was contended. Single-threaded
the only contention is a query forced re-entrantly from within
`with_retained_dep_graph`, so dropping was harmless. Under the parallel
frontend several encoder threads record nodes at the same time, so a
contended `try_lock` dropped nodes and edges at random, leaving the
retained graph nondeterministic and making the dep-graph ui tests, which
assert on its contents, fail intermittently.

Remove that reentrancy in `check_paths`: read the graph into owned
results while the lock is held, then emit the diagnostics afterwards.
The only query forced inside the old closure was `def_path_str` (for the
error messages), which can create dep nodes and re-enter the encoder;
doing the emission after the lock is released means `record` never
re-enters while the lock is held. `record` can then block on the lock
unconditionally instead of using `try_lock`, so concurrent encoders
never drop a node or edge.

This only affects compilation with `-Zquery-dep-graph`; with the flag
off the retained graph is absent and nothing changes.

2026-06-04 08:40:28 -07:00

..

src

Make the retained dep graph deterministic under the parallel frontend

2026-06-04 08:40:28 -07:00

Cargo.toml

Auto merge of #155256 - cuviper:hashbrown-0.17, r=Mark-Simulacrum

2026-04-15 11:01:30 +00:00