Remove use of '!' type in favor of 'Infallible'.

This removes the use of and dependence on the 'never_type' feature.

contrib/lib/src/lib.rs

@@ -1,5 +1,4 @@
 #![feature(crate_visibility_modifier)]
-#![feature(never_type)]
 #![feature(doc_cfg)]
 
 #![doc(html_root_url = "https://api.rocket.rs/v0.5")]

core/http/src/cookies.rs

@@ -74,7 +74,7 @@ mod key {
 /// [private cookie]: Cookies::add_private()
 ///
 /// ```rust
-/// # #![feature(proc_macro_hygiene, decl_macro, never_type)]
+/// # #![feature(proc_macro_hygiene, decl_macro)]
 /// # #[macro_use] extern crate rocket;
 /// #
 /// use rocket::http::Status;
@@ -85,9 +85,9 @@ mod key {
 /// struct User(usize);
 ///
 /// impl FromRequest<'_, '_> for User {
-///     type Error = !;
+///     type Error = std::convert::Infallible;
 ///
-///     fn from_request(request: &Request<'_>) -> request::Outcome<User, !> {
+///     fn from_request(request: &Request<'_>) -> request::Outcome<Self, Self::Error> {
 ///         request.cookies()
 ///             .get_private("user_id")
 ///             .and_then(|cookie| cookie.value().parse().ok())

core/lib/src/data/from_data.rs

@@ -388,7 +388,7 @@ pub trait FromData<'a>: Sized {
 
 /// The identity implementation of `FromData`. Always returns `Success`.
 impl<'f> FromData<'f> for Data {
-    type Error = !;
+    type Error = std::convert::Infallible;
     type Owned = Data;
     type Borrowed = Data;
 

core/lib/src/lib.rs

@@ -1,7 +1,6 @@
 #![feature(specialization)]
 #![feature(decl_macro)]
 #![feature(try_trait)]
-#![feature(never_type)]
 #![feature(proc_macro_hygiene)]
 #![feature(crate_visibility_modifier)]
 #![feature(label_break_value)]

core/lib/src/request/form/from_form.rs

@@ -111,19 +111,19 @@ pub trait FromForm<'f>: Sized {
 }
 
 impl<'f, T: FromForm<'f>> FromForm<'f> for Option<T> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline]
-    fn from_form(items: &mut FormItems<'f>, strict: bool) -> Result<Option<T>, !> {
+    fn from_form(items: &mut FormItems<'f>, strict: bool) -> Result<Option<T>, Self::Error> {
         Ok(T::from_form(items, strict).ok())
     }
 }
 
 impl<'f, T: FromForm<'f>> FromForm<'f> for Result<T, T::Error> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline]
-    fn from_form(items: &mut FormItems<'f>, strict: bool) -> Result<Self, !> {
+    fn from_form(items: &mut FormItems<'f>, strict: bool) -> Result<Self, Self::Error> {
         Ok(T::from_form(items, strict))
     }
 }

core/lib/src/request/form/from_form_value.rs

@@ -191,7 +191,7 @@ pub trait FromFormValue<'v>: Sized {
 }
 
 impl<'v> FromFormValue<'v> for &'v RawStr {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     // This just gives the raw string.
     #[inline(always)]
@@ -248,7 +248,7 @@ impl_with_fromstr!(
 );
 
 impl<'v, T: FromFormValue<'v>> FromFormValue<'v> for Option<T> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline(always)]
     fn from_form_value(v: &'v RawStr) -> Result<Self, Self::Error> {
@@ -266,7 +266,7 @@ impl<'v, T: FromFormValue<'v>> FromFormValue<'v> for Option<T> {
 
 // // TODO: Add more useful implementations (range, regex, etc.).
 impl<'v, T: FromFormValue<'v>> FromFormValue<'v> for Result<T, T::Error> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline(always)]
     fn from_form_value(v: &'v RawStr) -> Result<Self, Self::Error> {

core/lib/src/request/from_request.rs

@@ -284,7 +284,6 @@ impl<S, E> IntoOutcome<S, (Status, E), ()> for Result<S, E> {
 ///
 /// ```rust
 /// # #![feature(proc_macro_hygiene, decl_macro)]
-/// # #![feature(never_type)]
 /// # #[macro_use] extern crate rocket;
 /// # #[cfg(feature = "private-cookies")] mod inner {
 /// # use rocket::outcome::{IntoOutcome, Outcome};
@@ -306,9 +305,9 @@ impl<S, E> IntoOutcome<S, (Status, E), ()> for Result<S, E> {
 /// # struct Admin<'a> { user: &'a User }
 /// #
 /// impl<'a> FromRequest<'a, '_> for &'a User {
-///     type Error = !;
+///     type Error = std::convert::Infallible;
 ///
-///     fn from_request(request: &'a Request<'_>) -> request::Outcome<&'a User, !> {
+///     fn from_request(request: &'a Request<'_>) -> request::Outcome<Self, Self::Error> {
 ///         // This closure will execute at most once per request, regardless of
 ///         // the number of times the `User` guard is executed.
 ///         let user_result = request.local_cache(|| {
@@ -324,9 +323,9 @@ impl<S, E> IntoOutcome<S, (Status, E), ()> for Result<S, E> {
 /// }
 ///
 /// impl<'a> FromRequest<'a, '_> for Admin<'a> {
-///     type Error = !;
+///     type Error = std::convert::Infallible;
 ///
-///     fn from_request(request: &'a Request<'_>) -> request::Outcome<Admin<'a>, !> {
+///     fn from_request(request: &'a Request<'_>) -> request::Outcome<Self, Self::Error> {
 ///         let user = request.guard::<&User>()?;
 ///
 ///         if user.is_admin {
@@ -358,7 +357,7 @@ pub trait FromRequest<'a, 'r>: Sized {
 }
 
 impl FromRequest<'_, '_> for Method {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &Request<'_>) -> Outcome<Self, Self::Error> {
         Success(request.method())
@@ -366,7 +365,7 @@ impl FromRequest<'_, '_> for Method {
 }
 
 impl<'a> FromRequest<'a, '_> for &'a Origin<'a> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &'a Request<'_>) -> Outcome<Self, Self::Error> {
         Success(request.uri())
@@ -374,7 +373,7 @@ impl<'a> FromRequest<'a, '_> for &'a Origin<'a> {
 }
 
 impl<'r> FromRequest<'_, 'r> for &'r Route {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &Request<'r>) -> Outcome<Self, Self::Error> {
         match request.route() {
@@ -385,7 +384,7 @@ impl<'r> FromRequest<'_, 'r> for &'r Route {
 }
 
 impl<'a> FromRequest<'a, '_> for Cookies<'a> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &'a Request<'_>) -> Outcome<Self, Self::Error> {
         Success(request.cookies())
@@ -393,7 +392,7 @@ impl<'a> FromRequest<'a, '_> for Cookies<'a> {
 }
 
 impl<'a> FromRequest<'a, '_> for &'a Accept {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &'a Request<'_>) -> Outcome<Self, Self::Error> {
         match request.accept() {
@@ -404,7 +403,7 @@ impl<'a> FromRequest<'a, '_> for &'a Accept {
 }
 
 impl<'a> FromRequest<'a, '_> for &'a ContentType {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &'a Request<'_>) -> Outcome<Self, Self::Error> {
         match request.content_type() {
@@ -415,7 +414,7 @@ impl<'a> FromRequest<'a, '_> for &'a ContentType {
 }
 
 impl FromRequest<'_, '_> for SocketAddr {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &Request<'_>) -> Outcome<Self, Self::Error> {
         match request.remote() {
@@ -426,7 +425,7 @@ impl FromRequest<'_, '_> for SocketAddr {
 }
 
 impl<'a, 'r, T: FromRequest<'a, 'r>> FromRequest<'a, 'r> for Result<T, T::Error> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &'a Request<'r>) -> Outcome<Self, Self::Error> {
         match T::from_request(request) {
@@ -438,7 +437,7 @@ impl<'a, 'r, T: FromRequest<'a, 'r>> FromRequest<'a, 'r> for Result<T, T::Error>
 }
 
 impl<'a, 'r, T: FromRequest<'a, 'r>> FromRequest<'a, 'r> for Option<T> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     fn from_request(request: &'a Request<'r>) -> Outcome<Self, Self::Error> {
         match T::from_request(request) {

core/lib/src/request/param.rs

@@ -205,7 +205,7 @@ pub trait FromParam<'a>: Sized {
 }
 
 impl<'a> FromParam<'a> for &'a RawStr {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline(always)]
     fn from_param(param: &'a RawStr) -> Result<&'a RawStr, Self::Error> {
@@ -258,7 +258,7 @@ impl_with_fromstr! {
 }
 
 impl<'a, T: FromParam<'a>> FromParam<'a> for Result<T, T::Error> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline]
     fn from_param(param: &'a RawStr) -> Result<Self, Self::Error> {
@@ -270,7 +270,7 @@ impl<'a, T: FromParam<'a>> FromParam<'a> for Result<T, T::Error> {
 }
 
 impl<'a, T: FromParam<'a>> FromParam<'a> for Option<T> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline]
     fn from_param(param: &'a RawStr) -> Result<Self, Self::Error> {
@@ -309,7 +309,7 @@ pub trait FromSegments<'a>: Sized {
 }
 
 impl<'a> FromSegments<'a> for Segments<'a> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline(always)]
     fn from_segments(segments: Segments<'a>) -> Result<Segments<'a>, Self::Error> {
@@ -342,10 +342,10 @@ impl FromSegments<'_> for PathBuf {
 }
 
 impl<'a, T: FromSegments<'a>> FromSegments<'a> for Result<T, T::Error> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline]
-    fn from_segments(segments: Segments<'a>) -> Result<Result<T, T::Error>, !> {
+    fn from_segments(segments: Segments<'a>) -> Result<Result<T, T::Error>, Self::Error> {
         match T::from_segments(segments) {
             Ok(val) => Ok(Ok(val)),
             Err(e) => Ok(Err(e)),
@@ -354,10 +354,10 @@ impl<'a, T: FromSegments<'a>> FromSegments<'a> for Result<T, T::Error> {
 }
 
 impl<'a, T: FromSegments<'a>> FromSegments<'a> for Option<T> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline]
-    fn from_segments(segments: Segments<'a>) -> Result<Option<T>, !> {
+    fn from_segments(segments: Segments<'a>) -> Result<Option<T>, Self::Error> {
         match T::from_segments(segments) {
             Ok(val) => Ok(Some(val)),
             Err(_) => Ok(None)

core/lib/src/request/query.rs

@@ -219,7 +219,7 @@ impl<'q, T: FromForm<'q>> FromQuery<'q> for LenientForm<T> {
 }
 
 impl<'q, T: FromQuery<'q>> FromQuery<'q> for Option<T> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline]
     fn from_query(q: Query<'q>) -> Result<Self, Self::Error> {
@@ -228,7 +228,7 @@ impl<'q, T: FromQuery<'q>> FromQuery<'q> for Option<T> {
 }
 
 impl<'q, T: FromQuery<'q>> FromQuery<'q> for Result<T, T::Error> {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
     #[inline]
     fn from_query(q: Query<'q>) -> Result<Self, Self::Error> {

examples/request_guard/src/main.rs

@@ -1,4 +1,4 @@
-#![feature(proc_macro_hygiene, decl_macro, never_type)]
+#![feature(proc_macro_hygiene, decl_macro)]
 
 #[macro_use] extern crate rocket;
 
@@ -9,9 +9,9 @@ use rocket::outcome::Outcome::*;
 struct HeaderCount(usize);
 
 impl<'a, 'r> FromRequest<'a, 'r> for HeaderCount {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
-    fn from_request(request: &'a Request<'r>) -> request::Outcome<Self, !> {
+    fn from_request(request: &'a Request<'r>) -> request::Outcome<Self, Self::Error> {
         Success(HeaderCount(request.headers().len()))
     }
 }

examples/session/src/main.rs

@@ -1,4 +1,4 @@
-#![feature(proc_macro_hygiene, decl_macro, never_type)]
+#![feature(proc_macro_hygiene, decl_macro)]
 
 #[macro_use] extern crate rocket;
 
@@ -22,9 +22,9 @@ struct Login {
 struct User(usize);
 
 impl<'a, 'r> FromRequest<'a, 'r> for User {
-    type Error = !;
+    type Error = std::convert::Infallible;
 
-    fn from_request(request: &'a Request<'r>) -> request::Outcome<User, !> {
+    fn from_request(request: &'a Request<'r>) -> request::Outcome<User, Self::Error> {
         request.cookies()
             .get_private("user_id")
             .and_then(|cookie| cookie.value().parse().ok())