enable rust_2018_idioms for doctests

Signed-off-by: ozkanonur <work@onurozkan.dev>

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -31,7 +31,7 @@ pub enum TypeAnnotationNeeded {
     /// ```
     E0282,
     /// An implementation cannot be chosen unambiguously because of lack of information.
-    /// ```compile_fail,E0283
+    /// ```compile_fail,E0790
     /// let _ = Default::default();
     /// ```
     E0283,

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/different_lifetimes.rs

@@ -21,7 +21,7 @@ impl<'a, 'tcx> NiceRegionError<'a, 'tcx> {
     ///
     /// Consider a case where we have
     ///
-    /// ```compile_fail,E0623
+    /// ```compile_fail
     /// fn foo(x: &mut Vec<&u8>, y: &u8) {
     ///     x.push(y);
     /// }

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/find_anon_type.rs

@@ -14,7 +14,7 @@ use rustc_middle::ty::{self, Region, TyCtxt};
 /// br - the bound region corresponding to the above region which is of type `BrAnon(_)`
 ///
 /// # Example
-/// ```compile_fail,E0623
+/// ```compile_fail
 /// fn foo(x: &mut Vec<&u8>, y: &u8)
 ///    { x.push(y); }
 /// ```

compiler/rustc_infer/src/infer/outlives/test_type_match.rs

@@ -13,9 +13,11 @@ use crate::infer::region_constraints::VerifyIfEq;
 
 /// Given a "verify-if-eq" type test like:
 ///
-///     exists<'a...> {
-///         verify_if_eq(some_type, bound_region)
-///     }
+/// ```rust,ignore (pseudo-Rust)
+/// exists<'a...> {
+///     verify_if_eq(some_type, bound_region)
+/// }
+/// ```
 ///
 /// and the type `test_ty` that the type test is being tested against,
 /// returns:

compiler/rustc_infer/src/infer/outlives/verify.rs

@@ -277,7 +277,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     ///
     /// It will not, however, work for higher-ranked bounds like:
     ///
-    /// ```compile_fail,E0311
+    /// ```ignore(this does compile today, previously was marked as `compile_fail,E0311`)
     /// trait Foo<'a, 'b>
     /// where for<'x> <Self as Foo<'x, 'b>>::Bar: 'x
     /// {

compiler/rustc_infer/src/infer/region_constraints/mod.rs

@@ -217,7 +217,7 @@ pub enum VerifyBound<'tcx> {
 /// and supplies a bound if it ended up being relevant. It's used in situations
 /// like this:
 ///
-/// ```rust
+/// ```rust,ignore (pseudo-Rust)
 /// fn foo<'a, 'b, T: SomeTrait<'a>>
 /// where
 ///    <T as SomeTrait<'a>>::Item: 'b
@@ -232,7 +232,7 @@ pub enum VerifyBound<'tcx> {
 /// In the [`VerifyBound`], this struct is enclosed in `Binder` to account
 /// for cases like
 ///
-/// ```rust
+/// ```rust,ignore (pseudo-Rust)
 /// where for<'a> <T as SomeTrait<'a>::Item: 'a
 /// ```
 ///