Move handling of internal lints to `build.rs`

src/bootstrap/bin/rustc.rs

@@ -101,13 +101,6 @@ fn main() {
         cmd.arg(format!("-Cdebuginfo={}", debuginfo_level));
     }
 
-    if env::var_os("RUSTC_EXTERNAL_TOOL").is_none() {
-        if use_internal_lints(crate_name) {
-            cmd.arg("-Zunstable-options");
-            cmd.arg("-Wrustc::internal");
-        }
-    }
-
     if let Some(target) = target {
         // The stage0 compiler has a special sysroot distinct from what we
         // actually downloaded, so we just always pass the `--sysroot` option,
@@ -261,14 +254,6 @@ fn main() {
     std::process::exit(code);
 }
 
-// Rustc crates for which internal lints are in effect.
-fn use_internal_lints(crate_name: Option<&str>) -> bool {
-    crate_name.map_or(false, |crate_name| {
-        crate_name.starts_with("rustc") || crate_name.starts_with("syntax") ||
-        ["arena", "fmt_macros"].contains(&crate_name)
-    })
-}
-
 #[cfg(unix)]
 fn exec_cmd(cmd: &mut Command) -> io::Result<i32> {
     use std::os::unix::process::CommandExt;

src/bootstrap/builder.rs

@@ -1067,6 +1067,14 @@ impl<'a> Builder<'a> {
             }
         }
 
+        match mode {
+            Mode::Rustc | Mode::Codegen => {
+                rustflags.arg("-Zunstable-options");
+                rustflags.arg("-Wrustc::internal");
+            }
+            _ => {}
+        }
+
         // Throughout the build Cargo can execute a number of build scripts
         // compiling C/C++ code and we need to pass compilers, archivers, flags, etc
         // obtained previously to those build scripts.

src/libserialize/lib.rs

@@ -15,6 +15,7 @@ Core encoding and decoding interfaces.
 #![feature(nll)]
 #![feature(associated_type_bounds)]
 #![cfg_attr(test, feature(test))]
+#![allow(rustc::internal)]
 
 pub use self::serialize::{Decoder, Encoder, Decodable, Encodable};