error[E0463]: can't find crate for `rustc_serialize`
  --> $DIR/feature-gate-rustc_encodable_decodable.rs:4:1
   |
LL | extern crate rustc_serialize;
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't find crate
   |
   = help: maybe you need to install the missing components with: `rustup component add rust-src rustc-dev llvm-tools-preview`

error: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
  --> $DIR/feature-gate-rustc_encodable_decodable.rs:7:5
   |
LL |     RustcEncodable,
   |     ^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
   = note: `#[deny(soft_unstable)]` on by default

warning: use of deprecated macro `RustcEncodable`: rustc-serialize is deprecated and no longer supported
  --> $DIR/feature-gate-rustc_encodable_decodable.rs:7:5
   |
LL |     RustcEncodable,
   |     ^^^^^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

error: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
  --> $DIR/feature-gate-rustc_encodable_decodable.rs:11:5
   |
LL |     RustcDecodable,
   |     ^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>

warning: use of deprecated macro `RustcDecodable`: rustc-serialize is deprecated and no longer supported
  --> $DIR/feature-gate-rustc_encodable_decodable.rs:11:5
   |
LL |     RustcDecodable,
   |     ^^^^^^^^^^^^^^

error: aborting due to 3 previous errors; 2 warnings emitted

For more information about this error, try `rustc --explain E0463`.
Future incompatibility report: Future breakage diagnostic:
error: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
  --> $DIR/feature-gate-rustc_encodable_decodable.rs:7:5
   |
LL |     RustcEncodable,
   |     ^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
   = note: `#[deny(soft_unstable)]` on by default

Future breakage diagnostic:
error: use of unstable library feature 'rustc_encodable_decodable': derive macro for `rustc-serialize`; should not be used in new code
  --> $DIR/feature-gate-rustc_encodable_decodable.rs:11:5
   |
LL |     RustcDecodable,
   |     ^^^^^^^^^^^^^^
   |
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
   = note: `#[deny(soft_unstable)]` on by default