Auto merge of rust-lang#76656 - jonas-schievink:fewer-unstable-metadata-queries, r=lcnr

Don't query stability data when `staged_api` is off

This data only needs to be encoded when `#![feature(staged_api)]` or `-Zforce-unstable-if-unmarked` is on. Running these queries takes measurable time on large crates with many items, so skip it when the unstable flags have not been enabled.

Author: bors

Cargo.lock

@@ -3703,6 +3703,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_errors",
  "rustc_expand",
+ "rustc_feature",
  "rustc_hir",
  "rustc_hir_pretty",
  "rustc_index",

compiler/rustc_metadata/Cargo.toml

@@ -17,6 +17,7 @@ rustc_middle = { path = "../rustc_middle" }
 rustc_attr = { path = "../rustc_attr" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }
+rustc_feature = { path = "../rustc_feature" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }
 rustc_target = { path = "../rustc_target" }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -40,6 +40,7 @@ use tracing::{debug, trace};
 pub(super) struct EncodeContext<'a, 'tcx> {
     opaque: opaque::Encoder,
     tcx: TyCtxt<'tcx>,
+    feat: &'tcx rustc_feature::Features,
 
     tables: TableBuilders<'tcx>,
 
@@ -1132,15 +1133,25 @@ impl EncodeContext<'a, 'tcx> {
 
     fn encode_stability(&mut self, def_id: DefId) {
         debug!("EncodeContext::encode_stability({:?})", def_id);
-        if let Some(stab) = self.tcx.lookup_stability(def_id) {
-            record!(self.tables.stability[def_id] <- stab)
+
+        // The query lookup can take a measurable amount of time in crates with many items. Check if
+        // the stability attributes are even enabled before using their queries.
+        if self.feat.staged_api || self.tcx.sess.opts.debugging_opts.force_unstable_if_unmarked {
+            if let Some(stab) = self.tcx.lookup_stability(def_id) {
+                record!(self.tables.stability[def_id] <- stab)
+            }
         }
     }
 
     fn encode_const_stability(&mut self, def_id: DefId) {
         debug!("EncodeContext::encode_const_stability({:?})", def_id);
-        if let Some(stab) = self.tcx.lookup_const_stability(def_id) {
-            record!(self.tables.const_stability[def_id] <- stab)
+
+        // The query lookup can take a measurable amount of time in crates with many items. Check if
+        // the stability attributes are even enabled before using their queries.
+        if self.feat.staged_api || self.tcx.sess.opts.debugging_opts.force_unstable_if_unmarked {
+            if let Some(stab) = self.tcx.lookup_const_stability(def_id) {
+                record!(self.tables.const_stability[def_id] <- stab)
+            }
         }
     }
 
@@ -1979,6 +1990,7 @@ fn encode_metadata_impl(tcx: TyCtxt<'_>) -> EncodedMetadata {
     let mut ecx = EncodeContext {
         opaque: encoder,
         tcx,
+        feat: tcx.features(),
         tables: Default::default(),
         lazy_state: LazyState::NoNode,
         type_shorthands: Default::default(),