Provide structured suggestion for #![feature(..)] in more cases

compiler/rustc_const_eval/messages.ftl

@@ -421,7 +421,7 @@ const_eval_unstable_in_stable_exposed =
     .bypass_sugg = otherwise, as a last resort `#[rustc_allow_const_fn_unstable]` can be used to bypass stability checks (this requires team approval)
 
 const_eval_unstable_intrinsic = `{$name}` is not yet stable as a const intrinsic
-    .help = add `#![feature({$feature})]` to the crate attributes to enable
+const_eval_unstable_intrinsic_suggestion = add `#![feature({$feature})]` to the crate attributes to enable
 
 const_eval_unterminated_c_string =
     reading a null-terminated string starting at {$pointer} with no null found before end of allocation

compiler/rustc_const_eval/src/check_consts/check.rs

@@ -457,6 +457,12 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
             err_span,
         );
     }
+
+    fn crate_inject_span(&self) -> Option<Span> {
+        self.tcx.hir_crate_items(()).definitions().next().and_then(|id| {
+            self.tcx.crate_level_attribute_injection_span(self.tcx.local_def_id_to_hir_id(id))
+        })
+    }
 }
 
 impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
@@ -803,6 +809,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                                 name: intrinsic.name,
                                 feature,
                                 const_stable_indirect: is_const_stable,
+                                suggestion: self.crate_inject_span(),
                             });
                         }
                         Some(ConstStability { level: StabilityLevel::Stable { .. }, .. }) => {
@@ -891,7 +898,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                                 // regular stability.
                                 feature == sym::rustc_private
                                     && issue == NonZero::new(27812)
-                                    && self.tcx.sess.opts.unstable_opts.force_unstable_if_unmarked
+                                    && tcx.sess.opts.unstable_opts.force_unstable_if_unmarked
                             };
                         // Even if the feature is enabled, we still need check_op to double-check
                         // this if the callee is not safe to expose on stable.
@@ -901,6 +908,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                                 feature,
                                 feature_enabled,
                                 safe_to_expose_on_stable: callee_safe_to_expose_on_stable,
+                                suggestion_span: self.crate_inject_span(),
                             });
                         }
                     }

compiler/rustc_const_eval/src/check_consts/ops.rs

@@ -1,8 +1,8 @@
 //! Concrete error types for all operations which may be invalid in a certain const context.
 
 use hir::{ConstContext, LangItem};
-use rustc_errors::Diag;
 use rustc_errors::codes::*;
+use rustc_errors::{Applicability, Diag};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::TyCtxtInferExt;
@@ -335,6 +335,7 @@ pub(crate) struct FnCallUnstable {
     /// expose on stable.
     pub feature_enabled: bool,
     pub safe_to_expose_on_stable: bool,
+    pub suggestion_span: Option<Span>,
 }
 
 impl<'tcx> NonConstOp<'tcx> for FnCallUnstable {
@@ -354,8 +355,18 @@ impl<'tcx> NonConstOp<'tcx> for FnCallUnstable {
             def_path: ccx.tcx.def_path_str(self.def_id),
         });
         // FIXME: make this translatable
+        let msg = format!("add `#![feature({})]` to the crate attributes to enable", self.feature);
         #[allow(rustc::untranslatable_diagnostic)]
-        err.help(format!("add `#![feature({})]` to the crate attributes to enable", self.feature));
+        if let Some(span) = self.suggestion_span {
+            err.span_suggestion_verbose(
+                span,
+                msg,
+                format!("#![feature({})]\n", self.feature),
+                Applicability::MachineApplicable,
+            );
+        } else {
+            err.help(msg);
+        }
 
         err
     }
@@ -383,6 +394,7 @@ pub(crate) struct IntrinsicUnstable {
     pub name: Symbol,
     pub feature: Symbol,
     pub const_stable_indirect: bool,
+    pub suggestion: Option<Span>,
 }
 
 impl<'tcx> NonConstOp<'tcx> for IntrinsicUnstable {
@@ -402,6 +414,8 @@ impl<'tcx> NonConstOp<'tcx> for IntrinsicUnstable {
             span,
             name: self.name,
             feature: self.feature,
+            suggestion: self.suggestion,
+            help: self.suggestion.is_none(),
         })
     }
 }

compiler/rustc_const_eval/src/errors.rs

@@ -123,12 +123,19 @@ pub(crate) struct UnstableConstFn {
 
 #[derive(Diagnostic)]
 #[diag(const_eval_unstable_intrinsic)]
-#[help]
 pub(crate) struct UnstableIntrinsic {
     #[primary_span]
     pub span: Span,
     pub name: Symbol,
     pub feature: Symbol,
+    #[suggestion(
+        const_eval_unstable_intrinsic_suggestion,
+        code = "#![feature(\"{feature}\")]\n",
+        applicability = "machine-applicable"
+    )]
+    pub suggestion: Option<Span>,
+    #[help(const_eval_unstable_intrinsic_suggestion)]
+    pub help: bool,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_hir_typeck/src/errors.rs

@@ -19,8 +19,15 @@ use crate::fluent_generated as fluent;
 pub(crate) struct BaseExpressionDoubleDot {
     #[primary_span]
     pub span: Span,
+    #[suggestion(
+        hir_typeck_base_expression_double_dot_enable_default_field_values,
+        code = "#![feature(default_field_values)]\n",
+        applicability = "machine-applicable",
+        style = "verbose"
+    )]
+    pub default_field_values_suggestion: Option<Span>,
     #[subdiagnostic]
-    pub default_field_values: Option<BaseExpressionDoubleDotEnableDefaultFieldValues>,
+    pub default_field_values_help: Option<BaseExpressionDoubleDotEnableDefaultFieldValues>,
     #[subdiagnostic]
     pub add_expr: Option<BaseExpressionDoubleDotAddExpr>,
     #[subdiagnostic]

compiler/rustc_hir_typeck/src/expr.rs

@@ -2152,13 +2152,24 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
             }
             if !self.tcx.features().default_field_values() {
+                let sugg = self.tcx.crate_level_attribute_injection_span(expr.hir_id);
                 self.dcx().emit_err(BaseExpressionDoubleDot {
                     span: span.shrink_to_hi(),
                     // We only mention enabling the feature if this is a nightly rustc *and* the
                     // expression would make sense with the feature enabled.
-                    default_field_values: if self.tcx.sess.is_nightly_build()
+                    default_field_values_suggestion: if self.tcx.sess.is_nightly_build()
                         && missing_mandatory_fields.is_empty()
                         && !missing_optional_fields.is_empty()
+                        && sugg.is_some()
+                    {
+                        sugg
+                    } else {
+                        None
+                    },
+                    default_field_values_help: if self.tcx.sess.is_nightly_build()
+                        && missing_mandatory_fields.is_empty()
+                        && !missing_optional_fields.is_empty()
+                        && sugg.is_none()
                     {
                         Some(BaseExpressionDoubleDotEnableDefaultFieldValues)
                     } else {

tests/ui/consts/const-unstable-intrinsic.stderr

@@ -24,15 +24,21 @@ error: `size_of_val` is not yet stable as a const intrinsic
 LL |         unstable_intrinsic::size_of_val(&x);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: add `#![feature(unstable)]` to the crate attributes to enable
+help: add `#![feature(unstable)]` to the crate attributes to enable
+   |
+LL + #![feature("unstable")]
+   |
 
 error: `min_align_of_val` is not yet stable as a const intrinsic
   --> $DIR/const-unstable-intrinsic.rs:20:9
    |
 LL |         unstable_intrinsic::min_align_of_val(&x);
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = help: add `#![feature(unstable)]` to the crate attributes to enable
+help: add `#![feature(unstable)]` to the crate attributes to enable
+   |
+LL + #![feature("unstable")]
+   |
 
 error: const function that might be (indirectly) exposed to stable cannot use `#[feature(local)]`
   --> $DIR/const-unstable-intrinsic.rs:24:9

tests/ui/feature-gates/feature-gate-default-field-values.stderr

@@ -130,7 +130,10 @@ error[E0797]: base expression required after `..`
 LL |     let x = Foo { .. };
    |                     ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     let x = Foo { ../* expr */ };
@@ -142,7 +145,10 @@ error[E0797]: base expression required after `..`
 LL |     let z = Foo { baz: 1, .. };
    |                             ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     let z = Foo { baz: 1, ../* expr */ };
@@ -154,7 +160,10 @@ error[E0797]: base expression required after `..`
 LL |     let x = Bar::Foo { .. };
    |                          ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     let x = Bar::Foo { ../* expr */ };
@@ -166,7 +175,10 @@ error[E0797]: base expression required after `..`
 LL |     let z = Bar::Foo { baz: 1, .. };
    |                                  ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     let z = Bar::Foo { baz: 1, ../* expr */ };
@@ -178,7 +190,10 @@ error[E0797]: base expression required after `..`
 LL |     let x = Qux::<i32, 4> { .. };
    |                               ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     let x = Qux::<i32, 4> { ../* expr */ };
@@ -190,7 +205,10 @@ error[E0797]: base expression required after `..`
 LL |     assert!(matches!(Qux::<i32, 4> { bar: S, baz: 42, bat: 2, bay: 4, .. }, x));
    |                                                                         ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     assert!(matches!(Qux::<i32, 4> { bar: S, baz: 42, bat: 2, bay: 4, ../* expr */ }, x));
@@ -202,7 +220,10 @@ error[E0797]: base expression required after `..`
 LL |     let y = Opt { mandatory: None, .. };
    |                                      ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     let y = Opt { mandatory: None, ../* expr */ };
@@ -214,7 +235,10 @@ error[E0797]: base expression required after `..`
 LL |     assert!(matches!(Opt { mandatory: None, .. }, z));
    |                                               ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     assert!(matches!(Opt { mandatory: None, ../* expr */ }, z));
@@ -260,7 +284,10 @@ error[E0797]: base expression required after `..`
 LL |     let y = OptEnum::Variant { mandatory: None, .. };
    |                                                   ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     let y = OptEnum::Variant { mandatory: None, ../* expr */ };
@@ -272,7 +299,10 @@ error[E0797]: base expression required after `..`
 LL |     assert!(matches!(OptEnum::Variant { mandatory: None, .. }, z));
    |                                                            ^
    |
-   = help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+help: add `#![feature(default_field_values)]` to the crate attributes to enable default values on `struct` fields
+   |
+LL + #![feature(default_field_values)]
+   |
 help: add a base expression here
    |
 LL |     assert!(matches!(OptEnum::Variant { mandatory: None, ../* expr */ }, z));

tests/ui/stability-attribute/const-stability-attribute-implies-no-feature.stderr

@@ -4,7 +4,10 @@ error: `foobar` is not yet stable as a const fn
 LL |     foobar();
    |     ^^^^^^^^
    |
-   = help: add `#![feature(const_foobar)]` to the crate attributes to enable
+help: add `#![feature(const_foobar)]` to the crate attributes to enable
+   |
+LL + #![feature(const_foobar)]
+   |
 
 error: aborting due to 1 previous error