Rollup merge of rust-lang#157351 - xmakro:fix/parallel-collect-jobs-warn, r=petrochenkov

Avoid leaking the query-job collection warning into the panic query stack

Part of rust-lang#154314.

When the compiler panics it prints the active query stack. That collection runs with `CollectActiveJobsKind::PartialAllowed`, which deliberately skips any query state shard whose lock it cannot take without waiting, since a complete job map is not needed just to print a stack.

Under the parallel front-end another thread can still hold a shard lock while the panic is being reported, so a shard is skipped nondeterministically and a `warn!("Failed to collect active jobs ...")` was printed. Because warnings are shown by default (the default `RUSTC_LOG` filter is `WARN`), this leaked an extra line into the diagnostics of panicking compilations and made their output differ run to run. The panicking thread's own query chain is always collectible (a query does not hold its shard lock while it runs), so the printed stack itself is unaffected; only the spurious warning varied.

A skipped shard is expected and tolerated on this path, so `warn!` was the wrong level for it to begin with. This lowers the message to `debug!` so it stays available with `RUSTC_LOG` but no longer pollutes the default output, and re-enables the one ui test that was disabled because of it.

Author: jhpratt

compiler/rustc_query_impl/src/execution.rs

@@ -14,7 +14,7 @@ use rustc_middle::query::{
 use rustc_middle::ty::TyCtxt;
 use rustc_middle::verify_ich::incremental_verify_ich;
 use rustc_span::{DUMMY_SP, Span};
-use tracing::warn;
+use tracing::debug;
 
 use crate::dep_graph::{DepNode, DepNodeIndex};
 use crate::handle_cycle_error;
@@ -100,7 +100,12 @@ fn collect_active_query_jobs_inner<'tcx, C>(
             for shard in query.state.active.try_lock_shards() {
                 match shard {
                     Some(shard) => collect_shard_jobs(&shard),
-                    None => warn!("Failed to collect active jobs for query `{}`!", query.name),
+                    // This collection is best-effort (it is only used to print the query
+                    // stack on panic), so a contended shard is expected and fine to skip.
+                    // Emitting this at `warn!` would leak nondeterministically into the
+                    // panic output under the parallel front-end, where another thread may
+                    // still hold a shard lock, so keep it at `debug!`.
+                    None => debug!("Failed to collect active jobs for query `{}`!", query.name),
                 }
             }
         }

tests/ui/resolve/proc_macro_generated_packed.rs

@@ -1,6 +1,6 @@
 //! This test ICEs because the `repr(packed)` attribute
 //! was generated by a proc macro, so `#[derive]` didn't see it.
-//@ ignore-parallel-frontend failed to collect active jobs
+
 //@proc-macro: proc_macro_generate_packed.rs
 //@known-bug: #120873
 //@ failure-status: 101