Improve rustc diagnostics

compiler/rustc_resolve/src/diagnostics/impls.rs

@@ -1747,9 +1747,23 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                     }
 
                     if candidates.iter().all(|v: &ImportSuggestion| v.did != did) {
+                        // Add a note about unstable features on nightly Rust.
+                        let note = if !is_stable
+                            && let Some(did) = did
+                            && let Some(stab) = this.tcx.lookup_stability(did)
+                            && let StabilityLevel::Unstable { .. } = stab.level
+                        {
+                            Some(format!(
+                                "'{}' is unstable in nightly Rust \
+                                    and is only available with the \
+                                    `#![feature({})]` attribute",
+                                path_names_to_string(&path),
+                                stab.feature
+                            ))
+                        }
                         // See if we're recommending TryFrom, TryInto, or FromIterator and add
                         // a note about editions
-                        let note = if let Some(did) = did {
+                        else if let Some(did) = did {
                             let requires_note = !did.is_local()
                                 && find_attr!(
                                     this.tcx,

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -952,17 +952,12 @@ impl<'ast, 'ra, 'tcx> LateResolutionVisitor<'_, 'ast, 'ra, 'tcx> {
                 }
             })
             .collect::<Vec<_>>();
-        // Try to filter out intrinsics candidates, as long as we have
-        // some other candidates to suggest.
-        let intrinsic_candidates: Vec<_> = candidates
-            .extract_if(.., |sugg| {
-                let path = path_names_to_string(&sugg.path);
-                path.starts_with("core::intrinsics::") || path.starts_with("std::intrinsics::")
-            })
-            .collect();
-        if candidates.is_empty() {
-            // Put them back if we have no more candidates to suggest...
-            candidates = intrinsic_candidates;
+        // Only suggest intrinsics when the `core_intrinsics` feature is already enabled
+        if !self.r.features.enabled(sym::core_intrinsics) {
+            candidates.retain(|sugg| {
+                let p = path_names_to_string(&sugg.path);
+                !(p.starts_with("core::intrinsics::") || p.starts_with("std::intrinsics::"))
+            });
         }
         let crate_def_id = CRATE_DEF_ID.to_def_id();
         if candidates.is_empty() && is_expected(Res::Def(DefKind::Enum, crate_def_id)) {

compiler/rustc_span/src/symbol.rs

@@ -726,6 +726,7 @@ symbols! {
         copysignf64,
         copysignf128,
         core,
+        core_intrinsics,
         core_panic,
         core_panic_2015_macro,
         core_panic_macro,

tests/ui/annotate-snippet/missing-type.stderr

@@ -4,6 +4,7 @@ error[E0425]: cannot find type `Iter` in this scope
 LL |     let x: Iter;
    |            ^^^^ not found in this scope
    |
+   = note: 'std::sync::mpmc::Iter' is unstable in nightly Rust and is only available with the `#![feature(mpmc_channel)]` attribute
 help: consider importing one of these structs
    |
 LL + use std::collections::binary_heap::Iter;

tests/ui/argument-suggestions/disjoint-spans-issue-151607.stderr

@@ -25,6 +25,8 @@ error[E0425]: cannot find value `E` in this scope
 LL |     foo(B, g, D, E, F, G)
    |                  ^ not found in this scope
    |
+   = note: 'std::f128::consts::E' is unstable in nightly Rust and is only available with the `#![feature(f128)]` attribute
+   = note: 'std::f16::consts::E' is unstable in nightly Rust and is only available with the `#![feature(f16)]` attribute
 help: a local variable with a similar name exists
    |
 LL -     foo(B, g, D, E, F, G)

tests/ui/const-generics/issues/issue-82956.stderr

@@ -4,6 +4,7 @@ error[E0433]: cannot find type `IntoIter` in this scope
 LL |         let mut iter = IntoIter::new(self);
    |                        ^^^^^^^^ use of undeclared type `IntoIter`
    |
+   = note: 'std::sync::mpmc::IntoIter' is unstable in nightly Rust and is only available with the `#![feature(mpmc_channel)]` attribute
 help: consider importing one of these structs
    |
 LL + use std::array::IntoIter;

tests/ui/feature-gates/feature-gate-autodiff.no_support.stderr

@@ -4,6 +4,7 @@ error: cannot find attribute `autodiff_reverse` in this scope
 LL | #[autodiff_reverse(dfoo)]
    |   ^^^^^^^^^^^^^^^^
    |
+   = note: 'std::autodiff::autodiff_reverse' is unstable in nightly Rust and is only available with the `#![feature(autodiff)]` attribute
 help: consider importing this attribute macro
    |
 LL + use std::autodiff::autodiff_reverse;

tests/ui/lint/use_suggestion_json.stderr

@@ -90,6 +90,14 @@ current module, then it must also be declared as public (e.g., `pub fn`).
     }
   ],
   "children": [
+    {
+      "message": "'std::sync::mpmc::Iter' is unstable in nightly Rust and is only available with the `#![feature(mpmc_channel)]` attribute",
+      "code": null,
+      "level": "note",
+      "spans": [],
+      "children": [],
+      "rendered": null
+    },
     {
       "message": "consider importing one of these structs",
       "code": null,
@@ -405,6 +413,7 @@ current module, then it must also be declared as public (e.g., `pub fn`).
 \u001b[1m\u001b[94mLL\u001b[0m \u001b[1m\u001b[94m|\u001b[0m     let x: Iter;
    \u001b[1m\u001b[94m|\u001b[0m            \u001b[1m\u001b[91m^^^^\u001b[0m \u001b[1m\u001b[91mnot found in this scope\u001b[0m
    \u001b[1m\u001b[94m|\u001b[0m
+   \u001b[1m\u001b[94m= \u001b[0m\u001b[1mnote\u001b[0m: 'std::sync::mpmc::Iter' is unstable in nightly Rust and is only available with the `#![feature(mpmc_channel)]` attribute
 \u001b[1m\u001b[96mhelp\u001b[0m: consider importing one of these structs
    \u001b[1m\u001b[94m|\u001b[0m
 \u001b[1m\u001b[94mLL\u001b[0m \u001b[92m+ use std::collections::binary_heap::Iter;\u001b[0m

tests/ui/mir/gvn-nonsensical-coroutine-layout.stderr

@@ -15,6 +15,7 @@ error[E0574]: expected struct, variant or union type, found enum `Request`
 LL |         static instance: Request = Request { bar: 17 };
    |                                    ^^^^^^^ not a struct, variant or union type
    |
+   = note: 'std::error::Request' is unstable in nightly Rust and is only available with the `#![feature(error_generic_member_access)]` attribute
 help: consider importing this struct instead
    |
 LL + use std::error::Request;

tests/ui/resolve/filter-intrinsics.gate_off.stderr

@@ -0,0 +1,20 @@
+error[E0425]: cannot find function `transmute` in this scope
+  --> $DIR/filter-intrinsics.rs:7:13
+   |
+LL |     let _ = transmute::<usize>();
+   |             ^^^^^^^^^ not found in this scope
+   |
+help: consider importing this function
+   |
+LL + use std::mem::transmute;
+   |
+
+error[E0425]: cannot find function `fabs` in this scope
+  --> $DIR/filter-intrinsics.rs:10:13
+   |
+LL |     let _ = fabs(1.0);
+   |             ^^^^ not found in this scope
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0425`.

tests/ui/resolve/filter-intrinsics.stderr → tests/ui/resolve/filter-intrinsics.gate_on.stderr

@@ -1,5 +1,5 @@
 error[E0425]: cannot find function `transmute` in this scope
-  --> $DIR/filter-intrinsics.rs:3:13
+  --> $DIR/filter-intrinsics.rs:7:13
    |
 LL |     let _ = transmute::<usize>();
    |             ^^^^^^^^^ not found in this scope
@@ -10,7 +10,7 @@ LL + use std::mem::transmute;
    |
 
 error[E0425]: cannot find function `fabs` in this scope
-  --> $DIR/filter-intrinsics.rs:8:13
+  --> $DIR/filter-intrinsics.rs:10:13
    |
 LL |     let _ = fabs(1.0);
    |             ^^^^ not found in this scope

tests/ui/resolve/filter-intrinsics.rs

@@ -1,10 +1,12 @@
+//@ revisions: gate_off gate_on
+//@ dont-require-annotations: HELP
+
+#![cfg_attr(gate_on, feature(core_intrinsics))]
 fn main() {
-    // Should suggest only `std::mem::transmute`
+//[gate_on]~^ HELP consider importing this function
     let _ = transmute::<usize>();
-    //~^ ERROR cannot find
+    //~^ ERROR cannot find function `transmute` in this scope
 
-    // Should suggest `std::intrinsics::fabs`,
-    // since there is no non-intrinsic to suggest.
     let _ = fabs(1.0);
-    //~^ ERROR cannot find
+    //~^ ERROR cannot find function `fabs` in this scope
 }

tests/ui/resolve/import-suggestion-unstable-feature-note.gate_off.stderr

@@ -0,0 +1,37 @@
+error[E0425]: cannot find type `BorrowedBuf` in this scope
+  --> $DIR/import-suggestion-unstable-feature-note.rs:9:12
+   |
+LL |     let _: BorrowedBuf;
+   |            ^^^^^^^^^^^ not found in this scope
+   |
+   = note: 'std::io::BorrowedBuf' is unstable in nightly Rust and is only available with the `#![feature(core_io_borrowed_buf)]` attribute
+help: consider importing this struct
+   |
+LL + use std::io::BorrowedBuf;
+   |
+
+error[E0425]: cannot find type `HashMap` in this scope
+  --> $DIR/import-suggestion-unstable-feature-note.rs:13:12
+   |
+LL |     let _: HashMap;
+   |            ^^^^^^^ not found in this scope
+   |
+help: consider importing this struct
+   |
+LL + use std::collections::HashMap;
+   |
+
+error[E0425]: cannot find type `S` in this scope
+  --> $DIR/import-suggestion-unstable-feature-note.rs:16:12
+   |
+LL |     let _: S;
+   |            ^ not found in this scope
+   |
+help: consider importing this struct
+   |
+LL + use extern_prelude::S;
+   |
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0425`.

tests/ui/resolve/import-suggestion-unstable-feature-note.gate_on.stderr

@@ -0,0 +1,36 @@
+error[E0425]: cannot find type `BorrowedBuf` in this scope
+  --> $DIR/import-suggestion-unstable-feature-note.rs:9:12
+   |
+LL |     let _: BorrowedBuf;
+   |            ^^^^^^^^^^^ not found in this scope
+   |
+help: consider importing this struct
+   |
+LL + use std::io::BorrowedBuf;
+   |
+
+error[E0425]: cannot find type `HashMap` in this scope
+  --> $DIR/import-suggestion-unstable-feature-note.rs:13:12
+   |
+LL |     let _: HashMap;
+   |            ^^^^^^^ not found in this scope
+   |
+help: consider importing this struct
+   |
+LL + use std::collections::HashMap;
+   |
+
+error[E0425]: cannot find type `S` in this scope
+  --> $DIR/import-suggestion-unstable-feature-note.rs:16:12
+   |
+LL |     let _: S;
+   |            ^ not found in this scope
+   |
+help: consider importing this struct
+   |
+LL + use extern_prelude::S;
+   |
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0425`.

tests/ui/resolve/import-suggestion-unstable-feature-note.rs

@@ -0,0 +1,18 @@
+//@ revisions: gate_off gate_on
+//@ aux-build:extern-prelude.rs
+//@ dont-require-annotations: NOTE
+#![cfg_attr(gate_on, feature(core_io_borrowed_buf))]
+
+extern crate extern_prelude;
+
+fn main() {
+    let _: BorrowedBuf;
+    //~^ ERROR cannot find type `BorrowedBuf` in this scope
+    //[gate_off]~| NOTE 'std::io::BorrowedBuf' is unstable in nightly Rust and is only available with the `#![feature(core_io_borrowed_buf)]` attribute
+
+    let _: HashMap;
+    //~^ ERROR cannot find type `HashMap` in this scope
+
+    let _: S;
+    //~^ ERROR cannot find type `S` in this scope
+}

tests/ui/resolve/issue-50599.stderr

@@ -4,6 +4,8 @@ error[E0425]: cannot find value `LOG10_2` in module `std::f64`
 LL |     const M: usize = (f64::from(N) * std::f64::LOG10_2) as usize;
    |                                                ^^^^^^^ not found in `std::f64`
    |
+   = note: 'std::f128::consts::LOG10_2' is unstable in nightly Rust and is only available with the `#![feature(f128)]` attribute
+   = note: 'std::f16::consts::LOG10_2' is unstable in nightly Rust and is only available with the `#![feature(f16)]` attribute
 help: consider importing one of these constants
    |
 LL + use std::f128::consts::LOG10_2;

tests/ui/resolve/issue-73427.stderr

@@ -115,6 +115,8 @@ LL | / enum E {
 LL | |     TupleWithFields(()),
 LL | | }
    | |_^
+   = note: 'std::f128::consts::E' is unstable in nightly Rust and is only available with the `#![feature(f128)]` attribute
+   = note: 'std::f16::consts::E' is unstable in nightly Rust and is only available with the `#![feature(f16)]` attribute
 help: the following enum variant is available
    |
 LL -     E.foo();

tests/ui/resolve/privacy-enum-ctor.stderr

@@ -79,6 +79,8 @@ note: similarly named function `f` defined here
    |
 LL |     fn f() {
    |     ^^^^^^
+   = note: 'std::f128::consts::E' is unstable in nightly Rust and is only available with the `#![feature(f128)]` attribute
+   = note: 'std::f16::consts::E' is unstable in nightly Rust and is only available with the `#![feature(f16)]` attribute
 help: you might have meant to use the following enum variant
    |
 LL -     let _: E = m::E;
@@ -128,6 +130,8 @@ LL | |         },
 LL | |         Unit,
 LL | |     }
    | |_____^
+   = note: 'std::f128::consts::E' is unstable in nightly Rust and is only available with the `#![feature(f128)]` attribute
+   = note: 'std::f16::consts::E' is unstable in nightly Rust and is only available with the `#![feature(f16)]` attribute
 help: you might have meant to use the following enum variant
    |
 LL |     let _: E = E::Unit;

tests/ui/resolve/resolve-assoc-suggestions.stderr

@@ -27,6 +27,7 @@ error[E0425]: cannot find type `Type` in this scope
 LL |         let _: Type;
    |                ^^^^
    |
+   = note: 'std::mem::type_info::Type' is unstable in nightly Rust and is only available with the `#![feature(type_info)]` attribute
 help: you might have meant to use the associated type
    |
 LL |         let _: Self::Type;
@@ -42,6 +43,7 @@ error[E0531]: cannot find tuple struct or tuple variant `Type` in this scope
 LL |         let Type(..);
    |             ^^^^ not found in this scope
    |
+   = note: 'std::mem::type_info::Generic::Type' is unstable in nightly Rust and is only available with the `#![feature(type_info)]` attribute
 help: consider importing this tuple variant
    |
 LL + use std::mem::type_info::Generic::Type;
@@ -53,6 +55,7 @@ error[E0425]: cannot find value `Type` in this scope
 LL |         Type;
    |         ^^^^ not found in this scope
    |
+   = note: 'std::mem::type_info::Generic::Type' is unstable in nightly Rust and is only available with the `#![feature(type_info)]` attribute
 help: consider importing this tuple variant
    |
 LL + use std::mem::type_info::Generic::Type;

tests/ui/simd/portable-intrinsics-arent-exposed.stderr

@@ -18,6 +18,7 @@ LL | use std::simd::intrinsics;
    |                |
    |                no `intrinsics` in `simd`
    |
+   = note: 'std::intrinsics' is unstable in nightly Rust and is only available with the `#![feature(core_intrinsics)]` attribute
 help: consider importing this module instead
    |
 LL - use std::simd::intrinsics;

tests/ui/test-attrs/inaccessible-test-modules.stderr

@@ -14,6 +14,7 @@ LL | use test as y;
    |     |
    |     no `test` in the root
    |
+   = note: 'test::test' is unstable in nightly Rust and is only available with the `#![feature(test)]` attribute
 help: consider importing this module instead
    |
 LL | use test::test as y;

tests/ui/traits/ignore-err-impls.stderr

@@ -4,6 +4,7 @@ error[E0425]: cannot find type `Type` in this scope
 LL | impl Generic<Type> for S {}
    |              ^^^^ not found in this scope
    |
+   = note: 'std::mem::type_info::Type' is unstable in nightly Rust and is only available with the `#![feature(type_info)]` attribute
 help: consider importing this struct
    |
 LL + use std::mem::type_info::Type;

tests/ui/unresolved/unresolved-candidates.stderr

@@ -4,6 +4,7 @@ error[E0432]: unresolved import `Trait`
 LL |     use Trait;
    |         ^^^^^ no `Trait` in the root
    |
+   = note: 'std::mem::type_info::Trait' is unstable in nightly Rust and is only available with the `#![feature(type_info)]` attribute
 help: consider importing one of these items instead
    |
 LL |     use std::mem::type_info::Trait;

tests/ui/use/issue-18986.stderr

@@ -4,6 +4,7 @@ error[E0574]: expected struct, variant or union type, found trait `Trait`
 LL |         Trait { x: 42 } => ()
    |         ^^^^^ not a struct, variant or union type
    |
+   = note: 'std::mem::type_info::Trait' is unstable in nightly Rust and is only available with the `#![feature(type_info)]` attribute
 help: consider importing this struct instead
    |
 LL + use std::mem::type_info::Trait;