From 9fc7eca935a00f06c3e47b29a4bb8e313eb47e7a Mon Sep 17 00:00:00 2001
From: clubby789 <jamie@hill-daniel.co.uk>
Date: Mon, 27 Mar 2023 17:11:58 +0100
Subject: [PATCH] Always set `RUSTC_BOOTSTRAP` with `x doc`

---
 src/bootstrap/doc.rs | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/bootstrap/doc.rs b/src/bootstrap/doc.rs
index 36fdd4abf4ffc..be43affa404e9 100644
--- a/src/bootstrap/doc.rs
+++ b/src/bootstrap/doc.rs
@@ -1027,10 +1027,11 @@ impl Step for RustcBook {
         if self.validate {
             cmd.arg("--validate");
         }
-        if !builder.unstable_features() {
-            // We need to validate nightly features, even on the stable channel.
-            cmd.env("RUSTC_BOOTSTRAP", "1");
-        }
+        // We need to validate nightly features, even on the stable channel.
+        // Set this unconditionally as the stage0 compiler may be being used to
+        // document.
+        cmd.env("RUSTC_BOOTSTRAP", "1");
+
         // If the lib directories are in an unusual location (changed in
         // config.toml), then this needs to explicitly update the dylib search
         // path.