From a447c21afaa00cc047e70fe4205c33c2dc4aa2cb Mon Sep 17 00:00:00 2001
From: Jonas Schievink <jonasschievink@gmail.com>
Date: Sun, 13 Sep 2020 01:58:17 +0200
Subject: [PATCH] Don't query unstable data when `staged_api` is off

---
 Cargo.lock                                   |  1 +
 compiler/rustc_metadata/Cargo.toml           |  1 +
 compiler/rustc_metadata/src/rmeta/encoder.rs | 20 ++++++++++++++++----
 3 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index b448baf425b..9eab4ec10b4 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3703,6 +3703,7 @@ dependencies = [
  "rustc_data_structures",
  "rustc_errors",
  "rustc_expand",
+ "rustc_feature",
  "rustc_hir",
  "rustc_hir_pretty",
  "rustc_index",
diff --git a/compiler/rustc_metadata/Cargo.toml b/compiler/rustc_metadata/Cargo.toml
index 4b144f94ea7..f1975e78801 100644
--- a/compiler/rustc_metadata/Cargo.toml
+++ b/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" }
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index deca80f590f..8287666d435 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/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(),