1 files changed, 60 insertions, 0 deletions
diff --git a/src/librustdoc/json/mod.rs b/src/librustdoc/json/mod.rs
index ba27eed7c11..131a12ce228 100644
--- a/src/librustdoc/json/mod.rs
+++ b/src/librustdoc/json/mod.rs
@@ -14,6 +14,7 @@ use std::io::{BufWriter, Write, stdout};
 use std::path::PathBuf;
 use std::rc::Rc;
 
+use rustc_data_structures::fx::FxHashSet;
 use rustc_hir::def_id::{DefId, DefIdSet};
 use rustc_middle::ty::TyCtxt;
 use rustc_session::Session;
@@ -123,6 +124,58 @@ impl<'tcx> JsonRenderer<'tcx> {
     }
 }
 
+fn target(sess: &rustc_session::Session) -> types::Target {
+    // Build a set of which features are enabled on this target
+    let globally_enabled_features: FxHashSet<&str> =
+        sess.unstable_target_features.iter().map(|name| name.as_str()).collect();
+
+    // Build a map of target feature stability by feature name
+    use rustc_target::target_features::Stability;
+    let feature_stability: FxHashMap<&str, Stability> = sess
+        .target
+        .rust_target_features()
+        .into_iter()
+        .copied()
+        .map(|(name, stability, _)| (name, stability))
+        .collect();
+
+    types::Target {
+        triple: sess.opts.target_triple.tuple().into(),
+        target_features: sess
+            .target
+            .rust_target_features()
+            .into_iter()
+            .copied()
+            .filter(|(_, stability, _)| {
+                // Describe only target features which the user can toggle
+                stability.toggle_allowed().is_ok()
+            })
+            .map(|(name, stability, implied_features)| {
+                types::TargetFeature {
+                    name: name.into(),
+                    unstable_feature_gate: match stability {
+                        Stability::Unstable(feature_gate) => Some(feature_gate.as_str().into()),
+                        _ => None,
+                    },
+                    implies_features: implied_features
+                        .into_iter()
+                        .copied()
+                        .filter(|name| {
+                            // Imply only target features which the user can toggle
+                            feature_stability
+                                .get(name)
+                                .map(|stability| stability.toggle_allowed().is_ok())
+                                .unwrap_or(false)
+                        })
+                        .map(String::from)
+                        .collect(),
+                    globally_enabled: globally_enabled_features.contains(name),
+                }
+            })
+            .collect(),
+    }
+}
+
 impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
     fn descr() -> &'static str {
         "json"
@@ -248,6 +301,12 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
         let e = ExternalCrate { crate_num: LOCAL_CRATE };
         let index = (*self.index).clone().into_inner();
 
+        // Note that tcx.rust_target_features is inappropriate here because rustdoc tries to run for
+        // multiple targets: https://github.com/rust-lang/rust/pull/137632
+        //
+        // We want to describe a single target, so pass tcx.sess rather than tcx.
+        let target = target(self.tcx.sess);
+
         debug!("Constructing Output");
         let output_crate = types::Crate {
             root: self.id_from_item_default(e.def_id().into()),
@@ -288,6 +347,7 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
                     )
                 })
                 .collect(),
+            target,
             format_version: types::FORMAT_VERSION,
         };
         if let Some(ref out_dir) = self.out_dir {