From bd884d8043b9ebd4e2bbae0e31bc4780d2e26c6a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E8=AE=B8=E6=9D=B0=E5=8F=8B=20Jieyou=20Xu=20=28Joe=29?=
 <39484203+jieyouxu@users.noreply.github.com>
Date: Mon, 24 Feb 2025 20:10:49 +0800
Subject: [PATCH] Prevent `rmake.rs` from using any nightly/unstable features

---
 src/tools/compiletest/src/runtest/run_make.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/tools/compiletest/src/runtest/run_make.rs b/src/tools/compiletest/src/runtest/run_make.rs
index 8900752bd4be..073116933bdb 100644
--- a/src/tools/compiletest/src/runtest/run_make.rs
+++ b/src/tools/compiletest/src/runtest/run_make.rs
@@ -105,6 +105,11 @@ impl TestCx<'_> {
             .expect("stage0 rustc is required to run run-make tests");
         let mut rustc = Command::new(&stage0_rustc);
         rustc
+            // `rmake.rs` **must** be buildable by a stable compiler, it may not use *any* unstable
+            // library or compiler features. Here, we force the stage 0 rustc to consider itself as
+            // a stable-channel compiler via `RUSTC_BOOTSTRAP=-1` to prevent *any* unstable
+            // library/compiler usages, even if stage 0 rustc is *actually* a nightly rustc.
+            .env("RUSTC_BOOTSTRAP", "-1")
             .arg("-o")
             .arg(&recipe_bin)
             // Specify library search paths for `run_make_support`.