diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index 637323331f582..042e3b55cc994 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -103,7 +103,6 @@
 //! More documentation can be found in each respective module below, and you can
 //! also check out the `src/bootstrap/README.md` file for more information.
 
-#![feature(core_intrinsics)]
 #![feature(drain_filter)]
 
 use std::cell::{Cell, RefCell};
diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index 744ee1a65e154..33552ffb03e6d 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -27,7 +27,6 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
-#![feature(arbitrary_self_types)]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
@@ -39,21 +38,15 @@
 #![feature(overlapping_marker_traits)]
 #![feature(extern_types)]
 #![feature(nll)]
-#![feature(optin_builtin_traits)]
 #![feature(option_expect_none)]
 #![feature(range_is_empty)]
 #![feature(specialization)]
-#![feature(unboxed_closures)]
-#![feature(thread_local)]
-#![feature(trace_macros)]
 #![feature(trusted_len)]
 #![feature(vec_remove_item)]
 #![feature(stmt_expr_attributes)]
-#![feature(integer_atomics)]
 #![feature(test)]
 #![feature(in_band_lifetimes)]
 #![feature(crate_visibility_modifier)]
-#![feature(log_syntax)]
 #![feature(associated_type_bounds)]
 #![feature(rustc_attrs)]
 #![feature(hash_raw_entry)]
diff --git a/src/librustc_codegen_llvm/lib.rs b/src/librustc_codegen_llvm/lib.rs
index 8091a74854070..98a3e695fa079 100644
--- a/src/librustc_codegen_llvm/lib.rs
+++ b/src/librustc_codegen_llvm/lib.rs
@@ -6,18 +6,11 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(bool_to_option)]
-#![feature(box_patterns)]
-#![feature(box_syntax)]
 #![feature(const_cstr_unchecked)]
 #![feature(crate_visibility_modifier)]
 #![feature(extern_types)]
 #![feature(in_band_lifetimes)]
-#![feature(libc)]
 #![feature(nll)]
-#![feature(optin_builtin_traits)]
-#![feature(concat_idents)]
-#![feature(link_args)]
-#![feature(static_nobundle)]
 #![feature(trusted_len)]
 #![recursion_limit = "256"]
 
@@ -196,7 +189,7 @@ unsafe impl Sync for LlvmCodegenBackend {}
 
 impl LlvmCodegenBackend {
     pub fn new() -> Box<dyn CodegenBackend> {
-        box LlvmCodegenBackend(())
+        Box::new(LlvmCodegenBackend(()))
     }
 }
 
@@ -245,7 +238,7 @@ impl CodegenBackend for LlvmCodegenBackend {
     }
 
     fn metadata_loader(&self) -> Box<MetadataLoaderDyn> {
-        box metadata::LlvmMetadataLoader
+        Box::new(metadata::LlvmMetadataLoader)
     }
 
     fn provide(&self, providers: &mut ty::query::Providers<'_>) {
@@ -262,12 +255,12 @@ impl CodegenBackend for LlvmCodegenBackend {
         metadata: EncodedMetadata,
         need_metadata_module: bool,
     ) -> Box<dyn Any> {
-        box rustc_codegen_ssa::base::codegen_crate(
+        Box::new(rustc_codegen_ssa::base::codegen_crate(
             LlvmCodegenBackend(()),
             tcx,
             metadata,
             need_metadata_module,
-        )
+        ))
     }
 
     fn join_codegen(
diff --git a/src/librustc_codegen_llvm/metadata.rs b/src/librustc_codegen_llvm/metadata.rs
index abe34bb148ce5..0f30c2c020de7 100644
--- a/src/librustc_codegen_llvm/metadata.rs
+++ b/src/librustc_codegen_llvm/metadata.rs
@@ -22,10 +22,11 @@ impl MetadataLoader for LlvmMetadataLoader {
         // Use ArchiveRO for speed here, it's backed by LLVM and uses mmap
         // internally to read the file. We also avoid even using a memcpy by
         // just keeping the archive along while the metadata is in use.
-        let archive = ArchiveRO::open(filename).map(|ar| OwningRef::new(box ar)).map_err(|e| {
-            debug!("llvm didn't like `{}`: {}", filename.display(), e);
-            format!("failed to read rlib metadata in '{}': {}", filename.display(), e)
-        })?;
+        let archive =
+            ArchiveRO::open(filename).map(|ar| OwningRef::new(Box::new(ar))).map_err(|e| {
+                debug!("llvm didn't like `{}`: {}", filename.display(), e);
+                format!("failed to read rlib metadata in '{}': {}", filename.display(), e)
+            })?;
         let buf: OwningRef<_, [u8]> = archive.try_map(|ar| {
             ar.iter()
                 .filter_map(|s| s.ok())
@@ -44,9 +45,10 @@ impl MetadataLoader for LlvmMetadataLoader {
             let buf = path_to_c_string(filename);
             let mb = llvm::LLVMRustCreateMemoryBufferWithContentsOfFile(buf.as_ptr())
                 .ok_or_else(|| format!("error reading library: '{}'", filename.display()))?;
-            let of = ObjectFile::new(mb).map(|of| OwningRef::new(box of)).ok_or_else(|| {
-                format!("provided path not an object file: '{}'", filename.display())
-            })?;
+            let of =
+                ObjectFile::new(mb).map(|of| OwningRef::new(Box::new(of))).ok_or_else(|| {
+                    format!("provided path not an object file: '{}'", filename.display())
+                })?;
             let buf = of.try_map(|of| search_meta_section(of, target, filename))?;
             Ok(rustc_erase_owner!(buf))
         }
diff --git a/src/librustc_codegen_ssa/lib.rs b/src/librustc_codegen_ssa/lib.rs
index f39587122c56d..a2bb39b9e4019 100644
--- a/src/librustc_codegen_ssa/lib.rs
+++ b/src/librustc_codegen_ssa/lib.rs
@@ -1,10 +1,6 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
-#![feature(box_syntax)]
-#![feature(core_intrinsics)]
-#![feature(libc)]
-#![feature(stmt_expr_attributes)]
 #![feature(try_blocks)]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
diff --git a/src/librustc_codegen_utils/lib.rs b/src/librustc_codegen_utils/lib.rs
index 6b802bf530e86..38906bbaef810 100644
--- a/src/librustc_codegen_utils/lib.rs
+++ b/src/librustc_codegen_utils/lib.rs
@@ -3,10 +3,6 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
-#![feature(arbitrary_self_types)]
-#![feature(box_patterns)]
-#![feature(box_syntax)]
-#![feature(core_intrinsics)]
 #![feature(never_type)]
 #![feature(nll)]
 #![feature(in_band_lifetimes)]
diff --git a/src/librustc_data_structures/lib.rs b/src/librustc_data_structures/lib.rs
index aaac7fb4460cd..13792a0c890c4 100644
--- a/src/librustc_data_structures/lib.rs
+++ b/src/librustc_data_structures/lib.rs
@@ -12,7 +12,6 @@
 #![feature(generators)]
 #![feature(generator_trait)]
 #![feature(fn_traits)]
-#![feature(unsize)]
 #![feature(specialization)]
 #![feature(optin_builtin_traits)]
 #![feature(nll)]
@@ -20,11 +19,9 @@
 #![feature(hash_raw_entry)]
 #![feature(stmt_expr_attributes)]
 #![feature(core_intrinsics)]
-#![feature(integer_atomics)]
 #![feature(test)]
 #![feature(associated_type_bounds)]
 #![feature(thread_id_value)]
-#![cfg_attr(unix, feature(libc))]
 #![allow(rustc::default_hash_types)]
 
 #[macro_use]
diff --git a/src/librustc_driver/lib.rs b/src/librustc_driver/lib.rs
index 019ff431bcb97..52c6399498534 100644
--- a/src/librustc_driver/lib.rs
+++ b/src/librustc_driver/lib.rs
@@ -5,12 +5,7 @@
 //! This API is completely unstable and subject to change.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
-#![feature(box_syntax)]
-#![cfg_attr(unix, feature(libc))]
 #![feature(nll)]
-#![feature(set_stdio)]
-#![feature(no_debug)]
-#![feature(integer_atomics)]
 #![recursion_limit = "256"]
 
 pub extern crate getopts;
diff --git a/src/librustc_errors/lib.rs b/src/librustc_errors/lib.rs
index 17b293401f89e..109b151e4140b 100644
--- a/src/librustc_errors/lib.rs
+++ b/src/librustc_errors/lib.rs
@@ -4,9 +4,7 @@
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(crate_visibility_modifier)]
-#![cfg_attr(unix, feature(libc))]
 #![feature(nll)]
-#![feature(optin_builtin_traits)]
 
 pub use emitter::ColorConfig;
 
diff --git a/src/librustc_incremental/lib.rs b/src/librustc_incremental/lib.rs
index 7ce4def2886b8..ca824fde7efc1 100644
--- a/src/librustc_incremental/lib.rs
+++ b/src/librustc_incremental/lib.rs
@@ -3,7 +3,6 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
-#![feature(specialization)]
 #![recursion_limit = "256"]
 
 #[macro_use]
diff --git a/src/librustc_interface/lib.rs b/src/librustc_interface/lib.rs
index e4e6849ab8e59..ba1e2216ca805 100644
--- a/src/librustc_interface/lib.rs
+++ b/src/librustc_interface/lib.rs
@@ -2,10 +2,8 @@
 #![feature(box_syntax)]
 #![feature(set_stdio)]
 #![feature(nll)]
-#![feature(arbitrary_self_types)]
 #![feature(generator_trait)]
 #![feature(generators)]
-#![cfg_attr(unix, feature(libc))]
 #![recursion_limit = "256"]
 
 #[cfg(unix)]
diff --git a/src/librustc_lint/lib.rs b/src/librustc_lint/lib.rs
index 78e9d0f14f2de..6e2db65c84005 100644
--- a/src/librustc_lint/lib.rs
+++ b/src/librustc_lint/lib.rs
@@ -28,7 +28,6 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![cfg_attr(test, feature(test))]
 #![feature(bool_to_option)]
-#![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(crate_visibility_modifier)]
 #![feature(never_type)]
diff --git a/src/librustc_metadata/lib.rs b/src/librustc_metadata/lib.rs
index d94f23ff8bc6a..d4cc3c32616ac 100644
--- a/src/librustc_metadata/lib.rs
+++ b/src/librustc_metadata/lib.rs
@@ -1,15 +1,11 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(bool_to_option)]
-#![feature(box_patterns)]
 #![feature(core_intrinsics)]
 #![feature(crate_visibility_modifier)]
 #![feature(drain_filter)]
 #![feature(in_band_lifetimes)]
-#![feature(libc)]
 #![feature(nll)]
 #![feature(proc_macro_internals)]
-#![feature(proc_macro_quote)]
-#![feature(rustc_private)]
 #![feature(specialization)]
 #![feature(stmt_expr_attributes)]
 #![recursion_limit = "256"]
diff --git a/src/librustc_mir/lib.rs b/src/librustc_mir/lib.rs
index f064869d66471..4f1b90e34cf00 100644
--- a/src/librustc_mir/lib.rs
+++ b/src/librustc_mir/lib.rs
@@ -6,21 +6,15 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 
 #![feature(nll)]
 #![feature(in_band_lifetimes)]
-#![feature(inner_deref)]
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(crate_visibility_modifier)]
-#![feature(core_intrinsics)]
-#![feature(decl_macro)]
 #![feature(drain_filter)]
 #![feature(exhaustive_patterns)]
 #![feature(iter_order_by)]
 #![feature(never_type)]
 #![feature(specialization)]
-#![feature(try_trait)]
-#![feature(unicode_internals)]
-#![feature(slice_concat_ext)]
 #![feature(trusted_len)]
 #![feature(try_blocks)]
 #![feature(associated_type_bounds)]
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index af4ba4c0eb20e..2e63c3e170605 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -9,7 +9,6 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![feature(bool_to_option)]
 #![feature(crate_visibility_modifier)]
-#![feature(label_break_value)]
 #![feature(nll)]
 #![recursion_limit = "256"]
 
diff --git a/src/librustc_span/lib.rs b/src/librustc_span/lib.rs
index 413bd77daae24..2e149c96b9123 100644
--- a/src/librustc_span/lib.rs
+++ b/src/librustc_span/lib.rs
@@ -8,9 +8,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(nll)]
 #![feature(optin_builtin_traits)]
-#![feature(rustc_attrs)]
 #![feature(specialization)]
-#![feature(step_trait)]
 
 use rustc_data_structures::AtomicRef;
 use rustc_macros::HashStable_Generic;
diff --git a/src/librustc_target/lib.rs b/src/librustc_target/lib.rs
index a9db0254a7d11..71150e74f70d4 100644
--- a/src/librustc_target/lib.rs
+++ b/src/librustc_target/lib.rs
@@ -8,7 +8,6 @@
 //! LLVM.
 
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
-#![feature(box_syntax)]
 #![feature(bool_to_option)]
 #![feature(nll)]
 
diff --git a/src/librustc_typeck/lib.rs b/src/librustc_typeck/lib.rs
index 05ea9b1ac56dc..474868f0dd6c4 100644
--- a/src/librustc_typeck/lib.rs
+++ b/src/librustc_typeck/lib.rs
@@ -58,10 +58,8 @@ This API is completely unstable and subject to change.
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 #![allow(non_camel_case_types)]
 #![feature(bool_to_option)]
-#![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(crate_visibility_modifier)]
-#![feature(exhaustive_patterns)]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
 #![feature(try_blocks)]
diff --git a/src/librustdoc/lib.rs b/src/librustdoc/lib.rs
index ed3f0f94e0ed8..4e0a2d9427431 100644
--- a/src/librustdoc/lib.rs
+++ b/src/librustdoc/lib.rs
@@ -3,19 +3,15 @@
     html_playground_url = "https://play.rust-lang.org/"
 )]
 #![feature(rustc_private)]
-#![feature(arbitrary_self_types)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 #![feature(in_band_lifetimes)]
 #![feature(nll)]
-#![feature(set_stdio)]
 #![feature(test)]
 #![feature(vec_remove_item)]
 #![feature(ptr_offset_from)]
 #![feature(crate_visibility_modifier)]
-#![feature(drain_filter)]
 #![feature(never_type)]
-#![feature(unicode_internals)]
 #![recursion_limit = "256"]
 
 extern crate env_logger;
diff --git a/src/libserialize/lib.rs b/src/libserialize/lib.rs
index 280fb078f7de4..b990e71bef0dd 100644
--- a/src/libserialize/lib.rs
+++ b/src/libserialize/lib.rs
@@ -10,7 +10,6 @@ Core encoding and decoding interfaces.
     test(attr(allow(unused_variables), deny(warnings)))
 )]
 #![feature(box_syntax)]
-#![feature(core_intrinsics)]
 #![feature(specialization)]
 #![feature(never_type)]
 #![feature(nll)]
diff --git a/src/test/ui/consts/miri_unleashed/mutable_const2.stderr b/src/test/ui/consts/miri_unleashed/mutable_const2.stderr
index a316d8f1698ac..3eb8e0ec18288 100644
--- a/src/test/ui/consts/miri_unleashed/mutable_const2.stderr
+++ b/src/test/ui/consts/miri_unleashed/mutable_const2.stderr
@@ -10,7 +10,7 @@ error: internal compiler error: mutable allocation in constant
 LL | const MUTABLE_BEHIND_RAW: *mut i32 = &UnsafeCell::new(42) as *const _ as *mut _;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:357:17
+thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', src/librustc_errors/lib.rs:355:17
 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
 
 error: internal compiler error: unexpected panic