Magic cookies no more

Do not use magic values to forbid the use of unstable values.

WIP to fix rust-lang#21230

Author: nagisa

configure

@@ -603,18 +603,6 @@ then
 fi
 putvar CFG_RELEASE_CHANNEL
 
-# A magic value that allows the compiler to use unstable features
-# during the bootstrap even when doing so would normally be an error
-# because of feature staging or because the build turns on
-# warnings-as-errors and unstable features default to warnings.  The
-# build has to match this key in an env var. Meant to be a mild
-# deterrent from users just turning on unstable features on the stable
-# channel.
-# Basing CFG_BOOTSTRAP_KEY on CFG_BOOTSTRAP_KEY lets it get picked up
-# during a Makefile reconfig.
-CFG_BOOTSTRAP_KEY="${CFG_BOOTSTRAP_KEY-`date +%N`}"
-putvar CFG_BOOTSTRAP_KEY
-
 step_msg "looking for build programs"
 
 probe_need CFG_PERL        perl

mk/main.mk

@@ -157,8 +157,9 @@ endif
 # that the snapshot will be generated with a statically linked rustc so we only
 # have to worry about the distribution of one file (with its native dynamic
 # dependencies)
-RUSTFLAGS_STAGE0 += -C prefer-dynamic
-RUSTFLAGS_STAGE1 += -C prefer-dynamic
+RUSTFLAGS_STAGE0 += -C prefer-dynamic --cfg allow_unstable
+RUSTFLAGS_STAGE1 += -C prefer-dynamic --cfg allow_unstable
+RUSTFLAGS_STAGE2 += --cfg allow_unstable
 RUST_LIB_FLAGS_ST2 += -C prefer-dynamic
 RUST_LIB_FLAGS_ST3 += -C prefer-dynamic
 
@@ -331,9 +332,6 @@ CFG_INFO := $(info cfg: disabling unstable features (CFG_DISABLE_UNSTABLE_FEATUR
 # Turn on feature-staging
 export CFG_DISABLE_UNSTABLE_FEATURES
 endif
-# Subvert unstable feature lints to do the self-build
-export CFG_BOOTSTRAP_KEY
-export RUSTC_BOOTSTRAP_KEY:=$(CFG_BOOTSTRAP_KEY)
 
 ######################################################################
 # Per-stage targets and runner

src/driver/driver.rs

@@ -14,4 +14,9 @@ extern crate "rustdoc" as this;
 #[cfg(rustc)]
 extern crate "rustc_driver" as this;
 
-fn main() { this::main() }
+use std::sync::atomic::Ordering;
+
+fn main() {
+    this::ALLOW_UNSTABLE.store(cfg!(allow_unstable), Ordering::Relaxed);
+    this::main()
+}

src/librustc_driver/lib.rs

@@ -67,6 +67,7 @@ use std::io;
 use std::iter::repeat;
 use std::os;
 use std::sync::mpsc::channel;
+use std::sync::atomic;
 use std::thread;
 
 use rustc::session::early_error;
@@ -87,6 +88,8 @@ pub fn run(args: Vec<String>) -> int {
     0
 }
 
+pub static ALLOW_UNSTABLE: atomic::AtomicBool = atomic::ATOMIC_BOOL_INIT;
+
 static BUG_REPORT_URL: &'static str =
     "http://doc.rust-lang.org/complement-bugreport.html";
 
@@ -235,15 +238,10 @@ fn build_controller<'a>(sess: &Session) -> CompileController<'a> {
 pub fn get_unstable_features_setting() -> 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 = os::getenv("RUSTC_BOOTSTRAP_KEY");
-    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::Default
+    match (disable_unstable_features, ALLOW_UNSTABLE.load(atomic::Ordering::Relaxed)) {
+        (_, true) => UnstableFeatures::Cheat,
+        (true, _) => UnstableFeatures::Disallow,
+        (false, _) => UnstableFeatures::Default
     }
 }
 

src/librustdoc/lib.rs

@@ -47,6 +47,8 @@ use rustc::session::search_paths::SearchPaths;
 
 // reexported from `clean` so it can be easily updated with the mod itself
 pub use clean::SCHEMA_VERSION;
+// reexported since driver/driver.rs needs it
+pub use rustc_driver::ALLOW_UNSTABLE;
 
 #[macro_use]
 pub mod externalfiles;