Tweak rendering of cfg'd out item

```
error[E0433]: failed to resolve: could not find `doesnt_exist` in `inner`
  --> $DIR/diagnostics-cross-crate.rs:18:23
   |
LL |     cfged_out::inner::doesnt_exist::hello();
   |                       ^^^^^^^^^^^^ could not find `doesnt_exist` in `inner`
   |
note: found an item that was configured out
  --> $DIR/auxiliary/cfged_out.rs:6:13
   |
LL |     #[cfg(false)]
   |           ----- the item is gated here
LL |     pub mod doesnt_exist {
   |             ^^^^^^^^^^^^
```

Author: estebank

compiler/rustc_resolve/src/diagnostics.rs

@@ -2841,16 +2841,13 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
                 continue;
             }
 
-            let note = errors::FoundItemConfigureOut { span: ident.span };
-            err.subdiagnostic(note);
-
-            if let CfgEntry::NameValue { value: Some((feature, _)), .. } = cfg.0 {
-                let note = errors::ItemWasBehindFeature { feature, span: cfg.1 };
-                err.subdiagnostic(note);
+            let item_was = if let CfgEntry::NameValue { value: Some((feature, _)), .. } = cfg.0 {
+                errors::ItemWas::BehindFeature { feature, span: cfg.1 }
             } else {
-                let note = errors::ItemWasCfgOut { span: cfg.1 };
-                err.subdiagnostic(note);
-            }
+                errors::ItemWas::CfgOut { span: cfg.1 }
+            };
+            let note = errors::FoundItemConfigureOut { span: ident.span, item_was };
+            err.subdiagnostic(note);
         }
     }
 }

compiler/rustc_resolve/src/errors.rs

@@ -1,10 +1,13 @@
 use rustc_errors::codes::*;
-use rustc_errors::{Applicability, ElidedLifetimeInPathSubdiag, MultiSpan};
+use rustc_errors::{
+    Applicability, Diag, ElidedLifetimeInPathSubdiag, EmissionGuarantee, IntoDiagArg, MultiSpan,
+    Subdiagnostic,
+};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{Ident, Span, Symbol};
 
-use crate::Res;
 use crate::late::PatternSource;
+use crate::{Res, fluent_generated as fluent};
 
 #[derive(Diagnostic)]
 #[diag(resolve_generic_params_from_outer_item, code = E0401)]
@@ -1201,26 +1204,35 @@ pub(crate) struct IdentInScopeButItIsDesc<'a> {
     pub(crate) imported_ident_desc: &'a str,
 }
 
-#[derive(Subdiagnostic)]
-#[note(resolve_found_an_item_configured_out)]
 pub(crate) struct FoundItemConfigureOut {
-    #[primary_span]
-    pub(crate) span: Span,
-}
-
-#[derive(Subdiagnostic)]
-#[note(resolve_item_was_behind_feature)]
-pub(crate) struct ItemWasBehindFeature {
-    pub(crate) feature: Symbol,
-    #[primary_span]
-    pub(crate) span: Span,
-}
-
-#[derive(Subdiagnostic)]
-#[note(resolve_item_was_cfg_out)]
-pub(crate) struct ItemWasCfgOut {
-    #[primary_span]
     pub(crate) span: Span,
+    pub(crate) item_was: ItemWas,
+}
+
+pub(crate) enum ItemWas {
+    BehindFeature { feature: Symbol, span: Span },
+    CfgOut { span: Span },
+}
+
+impl Subdiagnostic for FoundItemConfigureOut {
+    fn add_to_diag<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
+        let mut multispan: MultiSpan = self.span.into();
+        match self.item_was {
+            ItemWas::BehindFeature { feature, span } => {
+                let key = "feature".into();
+                let value = feature.into_diag_arg(&mut None);
+                let msg = diag.dcx.eagerly_translate_to_string(
+                    fluent::resolve_item_was_behind_feature,
+                    [(&key, &value)].into_iter(),
+                );
+                multispan.push_span_label(span, msg);
+            }
+            ItemWas::CfgOut { span } => {
+                multispan.push_span_label(span, fluent::resolve_item_was_cfg_out);
+            }
+        }
+        diag.span_note(multispan, fluent::resolve_found_an_item_configured_out);
+    }
 }
 
 #[derive(Diagnostic)]

tests/ui/cfg/both-true-false.stderr

@@ -7,23 +7,18 @@ LL |     foo();
 note: found an item that was configured out
   --> $DIR/both-true-false.rs:6:4
    |
+LL | #[cfg(false)]
+   |       ----- the item is gated here
+LL | #[cfg(true)]
 LL | fn foo() {}
    |    ^^^
-note: the item is gated here
-  --> $DIR/both-true-false.rs:4:7
-   |
-LL | #[cfg(false)]
-   |       ^^^^^
 note: found an item that was configured out
   --> $DIR/both-true-false.rs:10:4
    |
+LL | #[cfg(false)]
+   |       ----- the item is gated here
 LL | fn foo() {}
    |    ^^^
-note: the item is gated here
-  --> $DIR/both-true-false.rs:9:7
-   |
-LL | #[cfg(false)]
-   |       ^^^^^
 
 error: aborting due to 1 previous error
 

tests/ui/cfg/cfg-version/syntax.stderr

@@ -132,13 +132,11 @@ LL |     key_value_form();
 note: found an item that was configured out
   --> $DIR/syntax.rs:32:4
    |
+LL | #[cfg(version = "1.43")]
+   |       ---------------- the item is gated behind the `1.43` feature
+LL |
 LL | fn key_value_form() {}
    |    ^^^^^^^^^^^^^^
-note: the item is gated behind the `1.43` feature
-  --> $DIR/syntax.rs:30:7
-   |
-LL | #[cfg(version = "1.43")]
-   |       ^^^^^^^^^^^^^^^^
 
 error[E0425]: cannot find function `not_numbers_or_periods` in this scope
   --> $DIR/syntax.rs:143:5
@@ -149,13 +147,11 @@ LL |     not_numbers_or_periods();
 note: found an item that was configured out
   --> $DIR/syntax.rs:53:4
    |
+LL | #[cfg(version("foo"))]
+   |              ------- the item is gated here
+LL |
 LL | fn not_numbers_or_periods() {}
    |    ^^^^^^^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:51:14
-   |
-LL | #[cfg(version("foo"))]
-   |              ^^^^^^^
 
 error[E0425]: cannot find function `complex_semver_with_metadata` in this scope
   --> $DIR/syntax.rs:144:5
@@ -166,13 +162,11 @@ LL |     complex_semver_with_metadata();
 note: found an item that was configured out
   --> $DIR/syntax.rs:57:4
    |
+LL | #[cfg(version("1.20.0-stable"))]
+   |              ----------------- the item is gated here
+LL |
 LL | fn complex_semver_with_metadata() {}
    |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:55:14
-   |
-LL | #[cfg(version("1.20.0-stable"))]
-   |              ^^^^^^^^^^^^^^^^^
 
 error[E0425]: cannot find function `invalid_major_only` in this scope
   --> $DIR/syntax.rs:145:5
@@ -183,13 +177,11 @@ LL |     invalid_major_only();
 note: found an item that was configured out
   --> $DIR/syntax.rs:80:4
    |
+LL | #[cfg(version("1"))]
+   |              ----- the item is gated here
+LL |
 LL | fn invalid_major_only() {}
    |    ^^^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:78:14
-   |
-LL | #[cfg(version("1"))]
-   |              ^^^^^
 
 error[E0425]: cannot find function `invalid_major_only_zero` in this scope
   --> $DIR/syntax.rs:146:5
@@ -200,13 +192,11 @@ LL |     invalid_major_only_zero();
 note: found an item that was configured out
   --> $DIR/syntax.rs:84:4
    |
+LL | #[cfg(version("0"))]
+   |              ----- the item is gated here
+LL |
 LL | fn invalid_major_only_zero() {}
    |    ^^^^^^^^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:82:14
-   |
-LL | #[cfg(version("0"))]
-   |              ^^^^^
 
 error[E0425]: cannot find function `invalid_major_only_negative` in this scope
   --> $DIR/syntax.rs:147:5
@@ -217,13 +207,11 @@ LL |     invalid_major_only_negative();
 note: found an item that was configured out
   --> $DIR/syntax.rs:97:4
    |
+LL | #[cfg(version("-1"))]
+   |              ------ the item is gated here
+LL |
 LL | fn invalid_major_only_negative() {}
    |    ^^^^^^^^^^^^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:95:14
-   |
-LL | #[cfg(version("-1"))]
-   |              ^^^^^^
 
 error[E0425]: cannot find function `exceed_u16_major` in this scope
   --> $DIR/syntax.rs:148:5
@@ -234,13 +222,11 @@ LL |     exceed_u16_major();
 note: found an item that was configured out
   --> $DIR/syntax.rs:103:4
    |
+LL | #[cfg(version("65536"))]
+   |              --------- the item is gated here
+LL |
 LL | fn exceed_u16_major() {}
    |    ^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:101:14
-   |
-LL | #[cfg(version("65536"))]
-   |              ^^^^^^^^^
 
 error[E0425]: cannot find function `exceed_u16_minor` in this scope
   --> $DIR/syntax.rs:149:5
@@ -251,13 +237,11 @@ LL |     exceed_u16_minor();
 note: found an item that was configured out
   --> $DIR/syntax.rs:107:4
    |
+LL | #[cfg(version("1.65536.0"))]
+   |              ------------- the item is gated here
+LL |
 LL | fn exceed_u16_minor() {}
    |    ^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:105:14
-   |
-LL | #[cfg(version("1.65536.0"))]
-   |              ^^^^^^^^^^^^^
 
 error[E0425]: cannot find function `exceed_u16_patch` in this scope
   --> $DIR/syntax.rs:150:5
@@ -268,13 +252,11 @@ LL |     exceed_u16_patch();
 note: found an item that was configured out
   --> $DIR/syntax.rs:111:4
    |
+LL | #[cfg(version("1.0.65536"))]
+   |              ------------- the item is gated here
+LL |
 LL | fn exceed_u16_patch() {}
    |    ^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:109:14
-   |
-LL | #[cfg(version("1.0.65536"))]
-   |              ^^^^^^^^^^^^^
 
 error[E0425]: cannot find function `exceed_u16_mixed` in this scope
   --> $DIR/syntax.rs:151:5
@@ -285,13 +267,11 @@ LL |     exceed_u16_mixed();
 note: found an item that was configured out
   --> $DIR/syntax.rs:115:4
    |
+LL | #[cfg(version("65536.0.65536"))]
+   |              ----------------- the item is gated here
+LL |
 LL | fn exceed_u16_mixed() {}
    |    ^^^^^^^^^^^^^^^^
-note: the item is gated here
-  --> $DIR/syntax.rs:113:14
-   |
-LL | #[cfg(version("65536.0.65536"))]
-   |              ^^^^^^^^^^^^^^^^^
 
 error: aborting due to 14 previous errors; 14 warnings emitted
 

tests/ui/cfg/cmdline-false.stderr

@@ -7,13 +7,10 @@ LL |     foo();
 note: found an item that was configured out
   --> $DIR/cmdline-false.rs:5:4
    |
+LL | #[cfg(false)]
+   |       ----- the item is gated here
 LL | fn foo() {}
    |    ^^^
-note: the item is gated here
-  --> $DIR/cmdline-false.rs:4:7
-   |
-LL | #[cfg(false)]
-   |       ^^^^^
 
 error: aborting due to 1 previous error
 

tests/ui/cfg/diagnostics-cross-crate.rs

@@ -11,24 +11,20 @@ fn main() {
     cfged_out::inner::uwu(); //~ ERROR cannot find function
     //~^ NOTE found an item that was configured out
     //~| NOTE not found in `cfged_out::inner`
-    //~| NOTE the item is gated here
 
     // The module isn't found - we would like to get a diagnostic, but currently don't due to
     // the awkward way the resolver diagnostics are currently implemented.
     cfged_out::inner::doesnt_exist::hello(); //~ ERROR failed to resolve
     //~^ NOTE could not find `doesnt_exist` in `inner`
     //~| NOTE found an item that was configured out
-    //~| NOTE the item is gated here
 
     // It should find the one in the right module, not the wrong one.
     cfged_out::inner::right::meow(); //~ ERROR cannot find function
     //~^ NOTE found an item that was configured out
     //~| NOTE not found in `cfged_out::inner::right
-    //~| NOTE the item is gated behind the `what-a-cool-feature` feature
 
     // Exists in the crate root - diagnostic.
     cfged_out::vanished(); //~ ERROR cannot find function
     //~^ NOTE found an item that was configured out
     //~| NOTE not found in `cfged_out`
-    //~| NOTE the item is gated here
 }