Rollup merge of #37265 - brson:bootstrap, r=alexcrichton

Allow bootstrapping without a key. Fixes #36548

This will make it easier for packagers to bootstrap rustc when they happen
to have a bootstrap compiler with a slightly different version number.

It's not ok for anything other than the build system to set this environment variable.

r? @alexcrichton

1 files changed, 6 insertions, 9 deletions

diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 9e5dfdc30c8..954fe330b54 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -1330,15 +1330,12 @@ impl UnstableFeatures {
     pub fn from_environment() -> UnstableFeatures {
         // Whether this is a feature-staged build, i.e. on the beta or stable channel
         let disable_unstable_features = option_env!("CFG_DISABLE_UNSTABLE_FEATURES").is_some();
-        // The secret key needed to get through the rustc build itself by
-        // subverting the unstable features lints
-        let bootstrap_secret_key = option_env!("CFG_BOOTSTRAP_KEY");
-        // The matching key to the above, only known by the build system
-        let bootstrap_provided_key = env::var("RUSTC_BOOTSTRAP_KEY").ok();
-        match (disable_unstable_features, bootstrap_secret_key, bootstrap_provided_key) {
-            (_, Some(ref s), Some(ref p)) if s == p => UnstableFeatures::Cheat,
-            (true, _, _) => UnstableFeatures::Disallow,
-            (false, _, _) => UnstableFeatures::Allow
+        // Whether we should enable unstable features for bootstrapping
+        let bootstrap = env::var("RUSTC_BOOTSTRAP").is_ok();
+        match (disable_unstable_features, bootstrap) {
+            (_, true) => UnstableFeatures::Cheat,
+            (true, _) => UnstableFeatures::Disallow,
+            (false, _) => UnstableFeatures::Allow
         }
     }