macros: subdiagnostic derive

Add a new derive, `#[derive(SessionSubdiagnostic)]`, which enables
deriving structs for labels, notes, helps and suggestions.

Signed-off-by: David Wood <david.wood@huawei.com>

compiler/rustc_error_messages/locales/en-US/typeck.ftl

@@ -82,3 +82,11 @@ typeck-value-of-associated-struct-already-specified =
 
 typeck-address-of-temporary-taken = cannot take address of a temporary
     .label = temporary value
+
+typeck-add-return-type-add = try adding a return type
+
+typeck-add-return-type-missing-here = a return type might be missing here
+
+typeck-expected-default-return-type = expected `()` because of default return type
+
+typeck-expected-return-type = expected `{$expected}` because of return type

compiler/rustc_errors/src/diagnostic.rs

@@ -78,6 +78,13 @@ impl<'source> Into<FluentValue<'source>> for DiagnosticArgValue<'source> {
     }
 }
 
+/// Trait implemented by error types. This should not be implemented manually. Instead, use
+/// `#[derive(SessionSubdiagnostic)]` -- see [rustc_macros::SessionSubdiagnostic].
+pub trait AddSubdiagnostic {
+    /// Add a subdiagnostic to an existing diagnostic.
+    fn add_to_diagnostic(self, diag: &mut Diagnostic);
+}
+
 #[must_use]
 #[derive(Clone, Debug, Encodable, Decodable)]
 pub struct Diagnostic {
@@ -768,6 +775,13 @@ impl Diagnostic {
         self
     }
 
+    /// Add a subdiagnostic from a type that implements `SessionSubdiagnostic` - see
+    /// [rustc_macros::SessionSubdiagnostic].
+    pub fn subdiagnostic(&mut self, subdiagnostic: impl AddSubdiagnostic) -> &mut Self {
+        subdiagnostic.add_to_diagnostic(self);
+        self
+    }
+
     pub fn set_span<S: Into<MultiSpan>>(&mut self, sp: S) -> &mut Self {
         self.span = sp.into();
         if let Some(span) = self.span.primary_span() {

compiler/rustc_errors/src/diagnostic_builder.rs

@@ -530,6 +530,11 @@ impl<'a, G: EmissionGuarantee> DiagnosticBuilder<'a, G> {
         name: impl Into<Cow<'static, str>>,
         arg: DiagnosticArgValue<'static>,
     ) -> &mut Self);
+
+    forward!(pub fn subdiagnostic(
+        &mut self,
+        subdiagnostic: impl crate::AddSubdiagnostic
+    ) -> &mut Self);
 }
 
 impl<G: EmissionGuarantee> Debug for DiagnosticBuilder<'_, G> {

compiler/rustc_errors/src/lib.rs

@@ -370,8 +370,8 @@ impl fmt::Display for ExplicitBug {
 impl error::Error for ExplicitBug {}
 
 pub use diagnostic::{
-    Diagnostic, DiagnosticArg, DiagnosticArgValue, DiagnosticId, DiagnosticStyledString,
-    IntoDiagnosticArg, SubDiagnostic,
+    AddSubdiagnostic, Diagnostic, DiagnosticArg, DiagnosticArgValue, DiagnosticId,
+    DiagnosticStyledString, IntoDiagnosticArg, SubDiagnostic,
 };
 pub use diagnostic_builder::{DiagnosticBuilder, EmissionGuarantee};
 use std::backtrace::Backtrace;

compiler/rustc_macros/src/lib.rs

@@ -1,5 +1,6 @@
-#![feature(proc_macro_diagnostic)]
 #![feature(allow_internal_unstable)]
+#![feature(let_else)]
+#![feature(proc_macro_diagnostic)]
 #![allow(rustc::default_hash_types)]
 #![recursion_limit = "128"]
 
@@ -77,3 +78,18 @@ decl_derive!(
         suggestion_hidden,
         suggestion_verbose)] => session_diagnostic::session_diagnostic_derive
 );
+decl_derive!(
+    [SessionSubdiagnostic, attributes(
+        // struct/variant attributes
+        label,
+        help,
+        note,
+        suggestion,
+        suggestion_short,
+        suggestion_hidden,
+        suggestion_verbose,
+        // field attributes
+        skip_arg,
+        primary_span,
+        applicability)] => session_diagnostic::session_subdiagnostic_derive
+);

compiler/rustc_typeck/src/check/fn_ctxt/suggestions.rs

@@ -1,5 +1,6 @@
 use super::FnCtxt;
 use crate::astconv::AstConv;
+use crate::errors::{AddReturnTypeSuggestion, ExpectedReturnTypeLabel};
 
 use rustc_ast::util::parser::ExprPrecedence;
 use rustc_errors::{Applicability, Diagnostic, MultiSpan};
@@ -527,28 +528,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // haven't set a return type at all (and aren't `fn main()` or an impl).
         match (&fn_decl.output, found.is_suggestable(self.tcx), can_suggest, expected.is_unit()) {
             (&hir::FnRetTy::DefaultReturn(span), true, true, true) => {
-                err.span_suggestion(
-                    span,
-                    "try adding a return type",
-                    format!("-> {} ", found),
-                    Applicability::MachineApplicable,
-                );
+                err.subdiagnostic(AddReturnTypeSuggestion::Add { span, found });
                 true
             }
             (&hir::FnRetTy::DefaultReturn(span), false, true, true) => {
                 // FIXME: if `found` could be `impl Iterator` or `impl Fn*`, we should suggest
                 // that.
-                err.span_suggestion(
-                    span,
-                    "a return type might be missing here",
-                    "-> _ ".to_string(),
-                    Applicability::HasPlaceholders,
-                );
+                err.subdiagnostic(AddReturnTypeSuggestion::MissingHere { span });
                 true
             }
             (&hir::FnRetTy::DefaultReturn(span), _, false, true) => {
                 // `fn main()` must return `()`, do not suggest changing return type
-                err.span_label(span, "expected `()` because of default return type");
+                err.subdiagnostic(ExpectedReturnTypeLabel::Unit { span });
                 true
             }
             // expectation was caused by something else, not the default return
@@ -557,16 +548,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // Only point to return type if the expected type is the return type, as if they
                 // are not, the expectation must have been caused by something else.
                 debug!("suggest_missing_return_type: return type {:?} node {:?}", ty, ty.kind);
-                let sp = ty.span;
+                let span = ty.span;
                 let ty = <dyn AstConv<'_>>::ast_ty_to_ty(self, ty);
                 debug!("suggest_missing_return_type: return type {:?}", ty);
                 debug!("suggest_missing_return_type: expected type {:?}", ty);
                 let bound_vars = self.tcx.late_bound_vars(fn_id);
                 let ty = Binder::bind_with_vars(ty, bound_vars);
-                let ty = self.normalize_associated_types_in(sp, ty);
+                let ty = self.normalize_associated_types_in(span, ty);
                 let ty = self.tcx.erase_late_bound_regions(ty);
                 if self.can_coerce(expected, ty) {
-                    err.span_label(sp, format!("expected `{}` because of return type", expected));
+                    err.subdiagnostic(ExpectedReturnTypeLabel::Other { span, expected });
                     self.try_suggest_return_impl_trait(err, expected, ty, fn_id);
                     return true;
                 }

compiler/rustc_typeck/src/errors.rs

@@ -1,6 +1,6 @@
 //! Errors emitted by typeck.
 use rustc_errors::Applicability;
-use rustc_macros::SessionDiagnostic;
+use rustc_macros::{SessionDiagnostic, SessionSubdiagnostic};
 use rustc_middle::ty::Ty;
 use rustc_span::{symbol::Ident, Span, Symbol};
 
@@ -190,3 +190,41 @@ pub struct AddressOfTemporaryTaken {
     #[label]
     pub span: Span,
 }
+
+#[derive(SessionSubdiagnostic)]
+pub enum AddReturnTypeSuggestion<'tcx> {
+    #[suggestion(
+        slug = "typeck-add-return-type-add",
+        code = "-> {found} ",
+        applicability = "machine-applicable"
+    )]
+    Add {
+        #[primary_span]
+        span: Span,
+        found: Ty<'tcx>,
+    },
+    #[suggestion(
+        slug = "typeck-add-return-type-missing-here",
+        code = "-> _ ",
+        applicability = "has-placeholders"
+    )]
+    MissingHere {
+        #[primary_span]
+        span: Span,
+    },
+}
+
+#[derive(SessionSubdiagnostic)]
+pub enum ExpectedReturnTypeLabel<'tcx> {
+    #[label(slug = "typeck-expected-default-return-type")]
+    Unit {
+        #[primary_span]
+        span: Span,
+    },
+    #[label(slug = "typeck-expected-return-type")]
+    Other {
+        #[primary_span]
+        span: Span,
+        expected: Ty<'tcx>,
+    },
+}

src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.rs

@@ -0,0 +1,501 @@
+// check-fail
+// Tests error conditions for specifying subdiagnostics using #[derive(SessionSubdiagnostic)]
+
+// The proc_macro2 crate handles spans differently when on beta/stable release rather than nightly,
+// changing the output of this test. Since SessionSubdiagnostic is strictly internal to the compiler
+// the test is just ignored on stable and beta:
+// ignore-beta
+// ignore-stable
+
+#![feature(rustc_private)]
+#![crate_type = "lib"]
+
+extern crate rustc_errors;
+extern crate rustc_session;
+extern crate rustc_span;
+extern crate rustc_macros;
+
+use rustc_errors::Applicability;
+use rustc_span::Span;
+use rustc_macros::SessionSubdiagnostic;
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "label-a")]
+struct A {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+enum B {
+    #[label(slug = "label-b-a")]
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    },
+    #[label(slug = "label-b-b")]
+    B {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "label-c")]
+//~^ ERROR label without `#[primary_span]` field
+struct C {
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label]
+//~^ ERROR `#[label]` is not a valid `SessionSubdiagnostic` attribute 
+struct D {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[foo]
+//~^ ERROR `#[foo]` is not a valid `SessionSubdiagnostic` attribute
+//~^^ ERROR cannot find attribute `foo` in this scope
+struct E {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label = "..."]
+//~^ ERROR `#[label = ...]` is not a valid `SessionSubdiagnostic` attribute
+struct F {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(bug = "...")]
+//~^ ERROR `#[label(bug = ...)]` is not a valid `SessionSubdiagnostic` attribute
+struct G {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label("...")]
+//~^ ERROR `#[label("...")]` is not a valid `SessionSubdiagnostic` attribute
+struct H {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = 4)]
+//~^ ERROR `#[label(slug = ...)]` is not a valid `SessionSubdiagnostic` attribute
+struct J {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug("..."))]
+//~^ ERROR `#[label(slug(...))]` is not a valid `SessionSubdiagnostic` attribute
+struct K {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug)]
+//~^ ERROR `#[label(slug)]` is not a valid `SessionSubdiagnostic` attribute
+struct L {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label()]
+//~^ ERROR `slug` must be set in a `#[label(...)]` attribute
+struct M {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(code = "...")]
+//~^ ERROR `code` is not a valid nested attribute of a `label` attribute
+struct N {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[foo]
+//~^ ERROR cannot find attribute `foo` in this scope
+//~^^ ERROR unsupported type attribute for subdiagnostic enum
+enum O {
+    #[label(slug = "...")]
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+enum P {
+    #[bar]
+//~^ ERROR `#[bar]` is not a valid `SessionSubdiagnostic` attribute
+//~^^ ERROR cannot find attribute `bar` in this scope
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+enum Q {
+    #[bar = "..."]
+//~^ ERROR `#[bar = ...]` is not a valid `SessionSubdiagnostic` attribute
+//~^^ ERROR cannot find attribute `bar` in this scope
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+enum R {
+    #[bar = 4]
+//~^ ERROR `#[bar = ...]` is not a valid `SessionSubdiagnostic` attribute
+//~^^ ERROR cannot find attribute `bar` in this scope
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+enum S {
+    #[bar("...")]
+//~^ ERROR `#[bar("...")]` is not a valid `SessionSubdiagnostic` attribute
+//~^^ ERROR cannot find attribute `bar` in this scope
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+enum T {
+    #[label(code = "...")]
+//~^ ERROR `code` is not a valid nested attribute of a `label`
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+enum U {
+    #[label(slug = "label-u")]
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    },
+    B {
+//~^ ERROR subdiagnostic kind not specified
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "...")]
+//~^ ERROR label without `#[primary_span]` field
+struct V {
+    #[primary_span]
+    //~^ ERROR the `#[primary_span]` attribute can only be applied to fields of type `Span`
+    span: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "...")]
+struct W {
+    #[primary_span]
+    span: Span,
+    #[applicability]
+    //~^ ERROR `#[applicability]` is only valid on suggestions
+    applicability: Applicability,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "...")]
+struct X {
+    #[primary_span]
+    span: Span,
+    #[bar]
+    //~^ ERROR `#[bar]` is not a valid `SessionSubdiagnostic` field attribute
+    //~^^ ERROR cannot find attribute `bar` in this scope
+    bar: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "...")]
+struct Y {
+    #[primary_span]
+    span: Span,
+    #[bar = "..."]
+    //~^ ERROR `#[bar = ...]` is not a valid `SessionSubdiagnostic` field attribute
+    //~^^ ERROR cannot find attribute `bar` in this scope
+    bar: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "...")]
+struct Z {
+    #[primary_span]
+    span: Span,
+    #[bar("...")]
+    //~^ ERROR `#[bar(...)]` is not a valid `SessionSubdiagnostic` field attribute
+    //~^^ ERROR cannot find attribute `bar` in this scope
+    bar: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "label-aa")]
+struct AA {
+    #[primary_span]
+    span: Span,
+    #[skip_arg]
+    z: Z
+}
+
+#[derive(SessionSubdiagnostic)]
+union AB {
+//~^ ERROR unexpected unsupported untagged union
+    span: u32,
+    b: u64
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "label-ac-1")]
+//~^ NOTE previously specified here
+//~^^ NOTE previously specified here
+#[label(slug = "label-ac-2")]
+//~^ ERROR specified multiple times
+//~^^ ERROR specified multiple times
+struct AC {
+    #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "label-ad-1", slug = "label-ad-2")]
+//~^ ERROR specified multiple times
+//~^^ NOTE previously specified here
+struct AD {
+    #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(slug = "label-ad-1")]
+struct AE {
+    #[primary_span]
+//~^ NOTE previously specified here
+    span_a: Span,
+    #[primary_span]
+//~^ ERROR specified multiple times
+    span_b: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+struct AF {
+//~^ ERROR subdiagnostic kind not specified
+    #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "suggestion-af", code = "...")]
+struct AG {
+    #[primary_span]
+    span: Span,
+    #[applicability]
+    applicability: Applicability,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+enum AH {
+    #[suggestion(slug = "suggestion-ag-a", code = "...")]
+    A {
+        #[primary_span]
+        span: Span,
+        #[applicability]
+        applicability: Applicability,
+        var: String,
+    },
+    #[suggestion(slug = "suggestion-ag-b", code = "...")]
+    B {
+        #[primary_span]
+        span: Span,
+        #[applicability]
+        applicability: Applicability,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code = "...", code = "...")]
+//~^ ERROR specified multiple times
+//~^^ NOTE previously specified here
+struct AI {
+    #[primary_span]
+    span: Span,
+    #[applicability]
+    applicability: Applicability,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code = "...")]
+struct AJ {
+    #[primary_span]
+    span: Span,
+    #[applicability]
+//~^ NOTE previously specified here
+    applicability_a: Applicability,
+    #[applicability]
+//~^ ERROR specified multiple times
+    applicability_b: Applicability,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code = "...")]
+//~^ ERROR suggestion without `applicability`
+struct AK {
+    #[primary_span]
+    span: Span,
+    #[applicability]
+//~^ ERROR the `#[applicability]` attribute can only be applied to fields of type `Applicability`
+    applicability: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code = "...")]
+//~^ ERROR suggestion without `applicability`
+struct AL {
+    #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...")]
+//~^ ERROR suggestion without `code = "..."`
+struct AM {
+    #[primary_span]
+    span: Span,
+    #[applicability]
+    applicability: Applicability,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code ="...", applicability = "foo")]
+//~^ ERROR invalid applicability
+struct AN {
+    #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[help(slug = "label-am")]
+struct AO {
+    var: String
+}
+
+#[derive(SessionSubdiagnostic)]
+#[note(slug = "label-an")]
+struct AP;
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code = "...")]
+//~^ ERROR suggestion without `applicability`
+//~^^ ERROR suggestion without `#[primary_span]` field
+struct AQ {
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code ="...", applicability = "machine-applicable")]
+struct AR {
+    #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label]
+//~^ ERROR unsupported type attribute for subdiagnostic enum
+enum AS {
+    #[label(slug = "...")]
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+struct AT {
+    #[primary_span]
+    span: Span,
+    var: String,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+//~^ ERROR `var` doesn't refer to a field on this type
+struct AU {
+    #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+enum AV {
+    #[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+enum AW {
+    #[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+//~^ ERROR `var` doesn't refer to a field on this type
+    A {
+        #[primary_span]
+        span: Span,
+    }
+}

src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.stderr

@@ -0,0 +1,387 @@
+error: label without `#[primary_span]` field
+  --> $DIR/subdiagnostic-derive.rs:47:1
+   |
+LL | / #[label(slug = "label-c")]
+LL | |
+LL | | struct C {
+LL | |     var: String,
+LL | | }
+   | |_^
+
+error: `#[label]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:54:1
+   |
+LL | #[label]
+   | ^^^^^^^^
+
+error: `#[foo]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:63:1
+   |
+LL | #[foo]
+   | ^^^^^^
+
+error: `#[label = ...]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:73:1
+   |
+LL | #[label = "..."]
+   | ^^^^^^^^^^^^^^^^
+
+error: `#[label(bug = ...)]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:82:9
+   |
+LL | #[label(bug = "...")]
+   |         ^^^^^^^^^^^
+
+error: `#[label("...")]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:91:1
+   |
+LL | #[label("...")]
+   | ^^^^^^^^^^^^^^^
+
+error: `#[label(slug = ...)]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:100:9
+   |
+LL | #[label(slug = 4)]
+   |         ^^^^^^^^
+   |
+   = help: value must be a string
+
+error: `#[label(slug(...))]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:109:9
+   |
+LL | #[label(slug("..."))]
+   |         ^^^^^^^^^^^
+
+error: `#[label(slug)]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:118:9
+   |
+LL | #[label(slug)]
+   |         ^^^^
+
+error: `slug` must be set in a `#[label(...)]` attribute
+  --> $DIR/subdiagnostic-derive.rs:127:1
+   |
+LL | #[label()]
+   | ^^^^^^^^^^
+
+error: `code` is not a valid nested attribute of a `label` attribute
+  --> $DIR/subdiagnostic-derive.rs:136:1
+   |
+LL | #[label(code = "...")]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error: unsupported type attribute for subdiagnostic enum
+  --> $DIR/subdiagnostic-derive.rs:145:1
+   |
+LL | #[foo]
+   | ^^^^^^
+
+error: `#[bar]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:159:5
+   |
+LL |     #[bar]
+   |     ^^^^^^
+
+error: `#[bar = ...]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:171:5
+   |
+LL |     #[bar = "..."]
+   |     ^^^^^^^^^^^^^^
+
+error: `#[bar = ...]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:183:5
+   |
+LL |     #[bar = 4]
+   |     ^^^^^^^^^^
+
+error: `#[bar("...")]` is not a valid `SessionSubdiagnostic` attribute
+  --> $DIR/subdiagnostic-derive.rs:195:5
+   |
+LL |     #[bar("...")]
+   |     ^^^^^^^^^^^^^
+
+error: `code` is not a valid nested attribute of a `label` attribute
+  --> $DIR/subdiagnostic-derive.rs:207:5
+   |
+LL |     #[label(code = "...")]
+   |     ^^^^^^^^^^^^^^^^^^^^^^
+
+error: subdiagnostic kind not specified
+  --> $DIR/subdiagnostic-derive.rs:224:5
+   |
+LL |     B {
+   |     ^
+
+error: the `#[primary_span]` attribute can only be applied to fields of type `Span`
+  --> $DIR/subdiagnostic-derive.rs:236:5
+   |
+LL |     #[primary_span]
+   |     ^^^^^^^^^^^^^^^
+
+error: label without `#[primary_span]` field
+  --> $DIR/subdiagnostic-derive.rs:233:1
+   |
+LL | / #[label(slug = "...")]
+LL | |
+LL | | struct V {
+LL | |     #[primary_span]
+LL | |
+LL | |     span: String,
+LL | | }
+   | |_^
+
+error: `#[applicability]` is only valid on suggestions
+  --> $DIR/subdiagnostic-derive.rs:246:5
+   |
+LL |     #[applicability]
+   |     ^^^^^^^^^^^^^^^^
+
+error: `#[bar]` is not a valid `SessionSubdiagnostic` field attribute
+  --> $DIR/subdiagnostic-derive.rs:256:5
+   |
+LL |     #[bar]
+   |     ^^^^^^
+
+error: `#[bar = ...]` is not a valid `SessionSubdiagnostic` field attribute
+  --> $DIR/subdiagnostic-derive.rs:267:5
+   |
+LL |     #[bar = "..."]
+   |     ^^^^^^^^^^^^^^
+
+error: `#[bar(...)]` is not a valid `SessionSubdiagnostic` field attribute
+  --> $DIR/subdiagnostic-derive.rs:278:5
+   |
+LL |     #[bar("...")]
+   |     ^^^^^^^^^^^^^
+
+error: unexpected unsupported untagged union
+  --> $DIR/subdiagnostic-derive.rs:294:1
+   |
+LL | / union AB {
+LL | |
+LL | |     span: u32,
+LL | |     b: u64
+LL | | }
+   | |_^
+
+error: specified multiple times
+  --> $DIR/subdiagnostic-derive.rs:304:9
+   |
+LL | #[label(slug = "label-ac-2")]
+   |         ^^^^^^^^^^^^^^^^^^^
+   |
+note: previously specified here
+  --> $DIR/subdiagnostic-derive.rs:301:9
+   |
+LL | #[label(slug = "label-ac-1")]
+   |         ^^^^^^^^^^^^^^^^^^^
+
+error: specified multiple times
+  --> $DIR/subdiagnostic-derive.rs:304:1
+   |
+LL | #[label(slug = "label-ac-2")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: previously specified here
+  --> $DIR/subdiagnostic-derive.rs:301:1
+   |
+LL | #[label(slug = "label-ac-1")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: specified multiple times
+  --> $DIR/subdiagnostic-derive.rs:313:30
+   |
+LL | #[label(slug = "label-ad-1", slug = "label-ad-2")]
+   |                              ^^^^^^^^^^^^^^^^^^^
+   |
+note: previously specified here
+  --> $DIR/subdiagnostic-derive.rs:313:9
+   |
+LL | #[label(slug = "label-ad-1", slug = "label-ad-2")]
+   |         ^^^^^^^^^^^^^^^^^^^
+
+error: specified multiple times
+  --> $DIR/subdiagnostic-derive.rs:327:5
+   |
+LL |     #[primary_span]
+   |     ^^^^^^^^^^^^^^^
+   |
+note: previously specified here
+  --> $DIR/subdiagnostic-derive.rs:324:5
+   |
+LL |     #[primary_span]
+   |     ^^^^^^^^^^^^^^^
+
+error: subdiagnostic kind not specified
+  --> $DIR/subdiagnostic-derive.rs:333:8
+   |
+LL | struct AF {
+   |        ^^
+
+error: specified multiple times
+  --> $DIR/subdiagnostic-derive.rs:370:42
+   |
+LL | #[suggestion(slug = "...", code = "...", code = "...")]
+   |                                          ^^^^^^^^^^^^
+   |
+note: previously specified here
+  --> $DIR/subdiagnostic-derive.rs:370:28
+   |
+LL | #[suggestion(slug = "...", code = "...", code = "...")]
+   |                            ^^^^^^^^^^^^
+
+error: specified multiple times
+  --> $DIR/subdiagnostic-derive.rs:388:5
+   |
+LL |     #[applicability]
+   |     ^^^^^^^^^^^^^^^^
+   |
+note: previously specified here
+  --> $DIR/subdiagnostic-derive.rs:385:5
+   |
+LL |     #[applicability]
+   |     ^^^^^^^^^^^^^^^^
+
+error: the `#[applicability]` attribute can only be applied to fields of type `Applicability`
+  --> $DIR/subdiagnostic-derive.rs:399:5
+   |
+LL |     #[applicability]
+   |     ^^^^^^^^^^^^^^^^
+
+error: suggestion without `applicability`
+  --> $DIR/subdiagnostic-derive.rs:394:1
+   |
+LL | / #[suggestion(slug = "...", code = "...")]
+LL | |
+LL | | struct AK {
+LL | |     #[primary_span]
+...  |
+LL | |     applicability: Span,
+LL | | }
+   | |_^
+
+error: suggestion without `applicability`
+  --> $DIR/subdiagnostic-derive.rs:405:1
+   |
+LL | / #[suggestion(slug = "...", code = "...")]
+LL | |
+LL | | struct AL {
+LL | |     #[primary_span]
+LL | |     span: Span,
+LL | | }
+   | |_^
+
+error: suggestion without `code = "..."`
+  --> $DIR/subdiagnostic-derive.rs:413:1
+   |
+LL | / #[suggestion(slug = "...")]
+LL | |
+LL | | struct AM {
+LL | |     #[primary_span]
+...  |
+LL | |     applicability: Applicability,
+LL | | }
+   | |_^
+
+error: invalid applicability
+  --> $DIR/subdiagnostic-derive.rs:423:41
+   |
+LL | #[suggestion(slug = "...", code ="...", applicability = "foo")]
+   |                                         ^^^^^^^^^^^^^^^^^^^^^
+
+error: suggestion without `applicability`
+  --> $DIR/subdiagnostic-derive.rs:441:1
+   |
+LL | / #[suggestion(slug = "...", code = "...")]
+LL | |
+LL | |
+LL | | struct AQ {
+LL | |     var: String,
+LL | | }
+   | |_^
+
+error: suggestion without `#[primary_span]` field
+  --> $DIR/subdiagnostic-derive.rs:441:1
+   |
+LL | / #[suggestion(slug = "...", code = "...")]
+LL | |
+LL | |
+LL | | struct AQ {
+LL | |     var: String,
+LL | | }
+   | |_^
+
+error: unsupported type attribute for subdiagnostic enum
+  --> $DIR/subdiagnostic-derive.rs:456:1
+   |
+LL | #[label]
+   | ^^^^^^^^
+
+error: `var` doesn't refer to a field on this type
+  --> $DIR/subdiagnostic-derive.rs:476:34
+   |
+LL | #[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+   |                                  ^^^^^^^
+
+error: `var` doesn't refer to a field on this type
+  --> $DIR/subdiagnostic-derive.rs:495:38
+   |
+LL |     #[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+   |                                      ^^^^^^^
+
+error: cannot find attribute `foo` in this scope
+  --> $DIR/subdiagnostic-derive.rs:63:3
+   |
+LL | #[foo]
+   |   ^^^
+
+error: cannot find attribute `foo` in this scope
+  --> $DIR/subdiagnostic-derive.rs:145:3
+   |
+LL | #[foo]
+   |   ^^^
+
+error: cannot find attribute `bar` in this scope
+  --> $DIR/subdiagnostic-derive.rs:159:7
+   |
+LL |     #[bar]
+   |       ^^^
+
+error: cannot find attribute `bar` in this scope
+  --> $DIR/subdiagnostic-derive.rs:171:7
+   |
+LL |     #[bar = "..."]
+   |       ^^^
+
+error: cannot find attribute `bar` in this scope
+  --> $DIR/subdiagnostic-derive.rs:183:7
+   |
+LL |     #[bar = 4]
+   |       ^^^
+
+error: cannot find attribute `bar` in this scope
+  --> $DIR/subdiagnostic-derive.rs:195:7
+   |
+LL |     #[bar("...")]
+   |       ^^^
+
+error: cannot find attribute `bar` in this scope
+  --> $DIR/subdiagnostic-derive.rs:256:7
+   |
+LL |     #[bar]
+   |       ^^^
+
+error: cannot find attribute `bar` in this scope
+  --> $DIR/subdiagnostic-derive.rs:267:7
+   |
+LL |     #[bar = "..."]
+   |       ^^^
+
+error: cannot find attribute `bar` in this scope
+  --> $DIR/subdiagnostic-derive.rs:278:7
+   |
+LL |     #[bar("...")]
+   |       ^^^
+
+error: aborting due to 51 previous errors
+