rustbuild: Use -Z force-unstable-if-unmarked

Author: alexcrichton

src/bootstrap/bin/rustc.rs

@@ -194,6 +194,8 @@ fn main() {
                 // do that we pass a weird flag to the compiler to get it to do
                 // so. Note that this is definitely a hack, and we should likely
                 // flesh out rpath support more fully in the future.
+                //
+                // FIXME: remove condition after next stage0
                 if stage != "0" {
                     cmd.arg("-Z").arg("osx-rpath-install-name");
                 }
@@ -218,6 +220,17 @@ fn main() {
             cmd.arg("-Z").arg("unstable-options");
             cmd.arg("-C").arg("target-feature=+crt-static");
         }
+
+        // Force all crates compiled by this compiler to (a) be unstable and (b)
+        // allow the `rustc_private` feature to link to other unstable crates
+        // also in the sysroot.
+        //
+        // FIXME: remove condition after next stage0
+        if env::var_os("RUSTC_FORCE_UNSTABLE").is_some() {
+            if stage != "0" {
+                cmd.arg("-Z").arg("force-unstable-if-unmarked");
+            }
+        }
     }
 
     if verbose > 1 {

src/bootstrap/lib.rs

@@ -479,7 +479,8 @@ impl Build {
         // compiled with debuginfo.
         if mode != Mode::Tool {
              cargo.env("RUSTC_DEBUGINFO", self.config.rust_debuginfo.to_string())
-                  .env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string());
+                  .env("RUSTC_DEBUGINFO_LINES", self.config.rust_debuginfo_lines.to_string())
+                  .env("RUSTC_FORCE_UNSTABLE", "1");
         }
 
         // Enable usage of unstable features
@@ -524,7 +525,9 @@ impl Build {
         // the comipiler, libs, and tests are stable and we don't want to make
         // their deps unstable (since this would break the first invariant
         // above).
-        if mode != Mode::Tool {
+        //
+        // FIXME: remove this after next stage0
+        if mode != Mode::Tool && stage == 0 {
             cargo.env("RUSTBUILD_UNSTABLE", "1");
         }