diff --git a/compiler/rustc_error_messages/src/lib.rs b/compiler/rustc_error_messages/src/lib.rs
index 7211c0543269..8d5ab1a45173 100644
--- a/compiler/rustc_error_messages/src/lib.rs
+++ b/compiler/rustc_error_messages/src/lib.rs
@@ -347,6 +347,27 @@ impl<S: Into<String>> From<S> for DiagnosticMessage {
     }
 }
 
+/// Translating *into* a subdiagnostic message from a diagnostic message is a little strange - but
+/// the subdiagnostic functions (e.g. `span_label`) take a `SubdiagnosticMessage` and the
+/// subdiagnostic derive refers to typed identifiers that are `DiagnosticMessage`s, so need to be
+/// able to convert between these, as much as they'll be converted back into `DiagnosticMessage`
+/// using `with_subdiagnostic_message` eventually. Don't use this other than for the derive.
+impl Into<SubdiagnosticMessage> for DiagnosticMessage {
+    fn into(self) -> SubdiagnosticMessage {
+        match self {
+            DiagnosticMessage::Str(s) => SubdiagnosticMessage::Str(s),
+            DiagnosticMessage::FluentIdentifier(id, None) => {
+                SubdiagnosticMessage::FluentIdentifier(id)
+            }
+            // There isn't really a sensible behaviour for this because it loses information but
+            // this is the most sensible of the behaviours.
+            DiagnosticMessage::FluentIdentifier(_, Some(attr)) => {
+                SubdiagnosticMessage::FluentAttr(attr)
+            }
+        }
+    }
+}
+
 /// A span together with some additional data.
 #[derive(Clone, Debug)]
 pub struct SpanLabel {
diff --git a/compiler/rustc_macros/src/diagnostics/mod.rs b/compiler/rustc_macros/src/diagnostics/mod.rs
index 88182ed5a122..2eee4bfb5dd4 100644
--- a/compiler/rustc_macros/src/diagnostics/mod.rs
+++ b/compiler/rustc_macros/src/diagnostics/mod.rs
@@ -72,12 +72,12 @@ pub fn session_diagnostic_derive(s: Structure<'_>) -> TokenStream {
 /// ```ignore (rust)
 /// #[derive(SessionSubdiagnostic)]
 /// pub enum ExpectedIdentifierLabel<'tcx> {
-///     #[label(slug = "parser-expected-identifier")]
+///     #[label(parser::expected_identifier)]
 ///     WithoutFound {
 ///         #[primary_span]
 ///         span: Span,
 ///     }
-///     #[label(slug = "parser-expected-identifier-found")]
+///     #[label(parser::expected_identifier_found)]
 ///     WithFound {
 ///         #[primary_span]
 ///         span: Span,
@@ -86,7 +86,7 @@ pub fn session_diagnostic_derive(s: Structure<'_>) -> TokenStream {
 /// }
 ///
 /// #[derive(SessionSubdiagnostic)]
-/// #[suggestion_verbose(slug = "parser-raw-identifier")]
+/// #[suggestion_verbose(parser::raw_identifier)]
 /// pub struct RawIdentifierSuggestion<'tcx> {
 ///     #[primary_span]
 ///     span: Span,
diff --git a/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs b/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
index 9aeb484bfd52..eab954a9c1bf 100644
--- a/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
+++ b/compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
@@ -13,7 +13,7 @@ use quote::{format_ident, quote};
 use std::collections::HashMap;
 use std::fmt;
 use std::str::FromStr;
-use syn::{spanned::Spanned, Meta, MetaList, MetaNameValue};
+use syn::{parse_quote, spanned::Spanned, Meta, MetaList, MetaNameValue, NestedMeta, Path};
 use synstructure::{BindingInfo, Structure, VariantInfo};
 
 /// Which kind of suggestion is being created?
@@ -194,8 +194,8 @@ struct SessionSubdiagnosticDeriveBuilder<'a> {
     kind: Option<(SubdiagnosticKind, proc_macro::Span)>,
 
     /// Slug of the subdiagnostic - corresponds to the Fluent identifier for the message - from the
-    /// `#[kind(slug = "...")]` attribute on the type or variant.
-    slug: Option<(String, proc_macro::Span)>,
+    /// `#[kind(slug)]` attribute on the type or variant.
+    slug: Option<(Path, proc_macro::Span)>,
     /// If a suggestion, the code to suggest as a replacement - from the `#[kind(code = "...")]`
     /// attribute on the type or variant.
     code: Option<(TokenStream, proc_macro::Span)>,
@@ -224,9 +224,34 @@ impl<'a> SessionSubdiagnosticDeriveBuilder<'a> {
             let meta = attr.parse_meta()?;
             let kind = match meta {
                 Meta::List(MetaList { ref nested, .. }) => {
-                    for nested_attr in nested {
+                    let mut nested_iter = nested.into_iter();
+                    if let Some(nested_attr) = nested_iter.next() {
+                        match nested_attr {
+                            NestedMeta::Meta(Meta::Path(path)) => {
+                                self.slug.set_once((path.clone(), span));
+                            }
+                            NestedMeta::Meta(meta @ Meta::NameValue(_))
+                                if matches!(
+                                    meta.path().segments.last().unwrap().ident.to_string().as_str(),
+                                    "code" | "applicability"
+                                ) =>
+                            {
+                                // don't error for valid follow-up attributes
+                            }
+                            nested_attr => {
+                                throw_invalid_nested_attr!(attr, &nested_attr, |diag| {
+                                    diag.help(
+                                        "first argument of the attribute should be the diagnostic \
+                                         slug",
+                                    )
+                                })
+                            }
+                        };
+                    }
+
+                    for nested_attr in nested_iter {
                         let meta = match nested_attr {
-                            syn::NestedMeta::Meta(ref meta) => meta,
+                            NestedMeta::Meta(ref meta) => meta,
                             _ => throw_invalid_nested_attr!(attr, &nested_attr),
                         };
 
@@ -241,7 +266,6 @@ impl<'a> SessionSubdiagnosticDeriveBuilder<'a> {
                                         let formatted_str = self.build_format(&s.value(), s.span());
                                         self.code.set_once((formatted_str, span));
                                     }
-                                    "slug" => self.slug.set_once((s.value(), span)),
                                     "applicability" => {
                                         let value = match Applicability::from_str(&s.value()) {
                                             Ok(v) => v,
@@ -253,11 +277,23 @@ impl<'a> SessionSubdiagnosticDeriveBuilder<'a> {
                                         self.applicability.set_once((quote! { #value }, span));
                                     }
                                     _ => throw_invalid_nested_attr!(attr, &nested_attr, |diag| {
-                                        diag.help("only `code`, `slug` and `applicability` are valid nested attributes")
+                                        diag.help(
+                                            "only `code` and `applicability` are valid nested \
+                                             attributes",
+                                        )
                                     }),
                                 }
                             }
-                            _ => throw_invalid_nested_attr!(attr, &nested_attr),
+                            _ => throw_invalid_nested_attr!(attr, &nested_attr, |diag| {
+                                if matches!(meta, Meta::Path(_)) {
+                                    diag.help(
+                                        "a diagnostic slug must be the first argument to the \
+                                         attribute",
+                                    )
+                                } else {
+                                    diag
+                                }
+                            }),
                         }
                     }
 
@@ -281,10 +317,27 @@ impl<'a> SessionSubdiagnosticDeriveBuilder<'a> {
                 );
             }
 
+            if matches!(
+                kind,
+                SubdiagnosticKind::Label | SubdiagnosticKind::Help | SubdiagnosticKind::Note
+            ) && self.applicability.is_some()
+            {
+                throw_span_err!(
+                    span,
+                    &format!(
+                        "`applicability` is not a valid nested attribute of a `{}` attribute",
+                        name
+                    )
+                );
+            }
+
             if self.slug.is_none() {
                 throw_span_err!(
                     span,
-                    &format!("`slug` must be set in a `#[{}(...)]` attribute", name)
+                    &format!(
+                        "diagnostic slug must be first argument of a `#[{}(...)]` attribute",
+                        name
+                    )
                 );
             }
 
@@ -335,7 +388,10 @@ impl<'a> SessionSubdiagnosticDeriveBuilder<'a> {
                         return Ok(quote! {});
                     }
                     _ => throw_invalid_attr!(attr, &meta, |diag| {
-                        diag.help("only `primary_span`, `applicability` and `skip_arg` are valid field attributes")
+                        diag.help(
+                            "only `primary_span`, `applicability` and `skip_arg` are valid field \
+                             attributes",
+                        )
                     }),
                 },
                 _ => throw_invalid_attr!(attr, &meta),
@@ -375,7 +431,11 @@ impl<'a> SessionSubdiagnosticDeriveBuilder<'a> {
         }
 
         // Missing slug errors will already have been reported.
-        let slug = self.slug.as_ref().map(|(slug, _)| &**slug).unwrap_or("missing-slug");
+        let slug = self
+            .slug
+            .as_ref()
+            .map(|(slug, _)| slug.clone())
+            .unwrap_or_else(|| parse_quote! { you::need::to::specify::a::slug });
         let code = match self.code.as_ref() {
             Some((code, _)) => Some(quote! { #code }),
             None if is_suggestion => {
@@ -397,7 +457,7 @@ impl<'a> SessionSubdiagnosticDeriveBuilder<'a> {
 
         let diag = &self.diag;
         let name = format_ident!("{}{}", if span_field.is_some() { "span_" } else { "" }, kind);
-        let message = quote! { rustc_errors::SubdiagnosticMessage::message(#slug) };
+        let message = quote! { rustc_errors::fluent::#slug };
         let call = if matches!(kind, SubdiagnosticKind::Suggestion(..)) {
             if let Some(span) = span_field {
                 quote! { #diag.#name(#span, #message, #code, #applicability); }
diff --git a/compiler/rustc_parse/src/parser/diagnostics.rs b/compiler/rustc_parse/src/parser/diagnostics.rs
index 30869f055f5f..58d5d43cfbfa 100644
--- a/compiler/rustc_parse/src/parser/diagnostics.rs
+++ b/compiler/rustc_parse/src/parser/diagnostics.rs
@@ -265,7 +265,7 @@ struct BadTypePlus {
 #[derive(SessionSubdiagnostic)]
 pub enum BadTypePlusSub {
     #[suggestion(
-        slug = "parser-add-paren",
+        parser::add_paren,
         code = "{sum_with_parens}",
         applicability = "machine-applicable"
     )]
@@ -274,12 +274,12 @@ pub enum BadTypePlusSub {
         #[primary_span]
         span: Span,
     },
-    #[label(slug = "parser-forgot-paren")]
+    #[label(parser::forgot_paren)]
     ForgotParen {
         #[primary_span]
         span: Span,
     },
-    #[label(slug = "parser-expect-path")]
+    #[label(parser::expect_path)]
     ExpectPath {
         #[primary_span]
         span: Span,
diff --git a/compiler/rustc_typeck/src/errors.rs b/compiler/rustc_typeck/src/errors.rs
index 758108e5d717..4cdec615d829 100644
--- a/compiler/rustc_typeck/src/errors.rs
+++ b/compiler/rustc_typeck/src/errors.rs
@@ -197,7 +197,7 @@ pub struct AddressOfTemporaryTaken {
 #[derive(SessionSubdiagnostic)]
 pub enum AddReturnTypeSuggestion<'tcx> {
     #[suggestion(
-        slug = "typeck-add-return-type-add",
+        typeck::add_return_type_add,
         code = "-> {found} ",
         applicability = "machine-applicable"
     )]
@@ -207,7 +207,7 @@ pub enum AddReturnTypeSuggestion<'tcx> {
         found: Ty<'tcx>,
     },
     #[suggestion(
-        slug = "typeck-add-return-type-missing-here",
+        typeck::add_return_type_missing_here,
         code = "-> _ ",
         applicability = "has-placeholders"
     )]
@@ -219,12 +219,12 @@ pub enum AddReturnTypeSuggestion<'tcx> {
 
 #[derive(SessionSubdiagnostic)]
 pub enum ExpectedReturnTypeLabel<'tcx> {
-    #[label(slug = "typeck-expected-default-return-type")]
+    #[label(typeck::expected_default_return_type)]
     Unit {
         #[primary_span]
         span: Span,
     },
-    #[label(slug = "typeck-expected-return-type")]
+    #[label(typeck::expected_return_type)]
     Other {
         #[primary_span]
         span: Span,
diff --git a/src/test/ui-fulldeps/internal-lints/diagnostics.rs b/src/test/ui-fulldeps/internal-lints/diagnostics.rs
index 3e349ab02586..d6f63d44ba6a 100644
--- a/src/test/ui-fulldeps/internal-lints/diagnostics.rs
+++ b/src/test/ui-fulldeps/internal-lints/diagnostics.rs
@@ -23,7 +23,7 @@ struct DeriveSessionDiagnostic {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[note(slug = "note")]
+#[note(parser::add_paren)]
 struct Note {
     #[primary_span]
     span: Span,
diff --git a/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs b/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
index 8cbee4c6d924..7bec1897fa53 100644
--- a/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
+++ b/src/test/ui-fulldeps/session-diagnostic/diagnostic-derive.rs
@@ -470,7 +470,7 @@ struct NoApplicability {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[note(slug = "note")]
+#[note(parser::add_paren)]
 struct Note;
 
 #[derive(SessionDiagnostic)]
diff --git a/src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.rs b/src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.rs
index bb406c35c0ee..6f4b6105b3e4 100644
--- a/src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.rs
+++ b/src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.rs
@@ -20,7 +20,7 @@ use rustc_span::Span;
 use rustc_macros::SessionSubdiagnostic;
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "label-a")]
+#[label(parser::add_paren)]
 struct A {
     #[primary_span]
     span: Span,
@@ -29,13 +29,13 @@ struct A {
 
 #[derive(SessionSubdiagnostic)]
 enum B {
-    #[label(slug = "label-b-a")]
+    #[label(parser::add_paren)]
     A {
         #[primary_span]
         span: Span,
         var: String,
     },
-    #[label(slug = "label-b-b")]
+    #[label(parser::add_paren)]
     B {
         #[primary_span]
         span: Span,
@@ -44,7 +44,7 @@ enum B {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "label-c")]
+#[label(parser::add_paren)]
 //~^ ERROR label without `#[primary_span]` field
 struct C {
     var: String,
@@ -116,7 +116,8 @@ struct K {
 
 #[derive(SessionSubdiagnostic)]
 #[label(slug)]
-//~^ ERROR `#[label(slug)]` is not a valid attribute
+//~^ ERROR cannot find value `slug` in module `rustc_errors::fluent`
+//~^^ NOTE not found in `rustc_errors::fluent`
 struct L {
     #[primary_span]
     span: Span,
@@ -125,7 +126,7 @@ struct L {
 
 #[derive(SessionSubdiagnostic)]
 #[label()]
-//~^ ERROR `slug` must be set in a `#[label(...)]` attribute
+//~^ ERROR diagnostic slug must be first argument of a `#[label(...)]` attribute
 struct M {
     #[primary_span]
     span: Span,
@@ -133,7 +134,7 @@ struct M {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(code = "...")]
+#[label(parser::add_paren, code = "...")]
 //~^ ERROR `code` is not a valid nested attribute of a `label` attribute
 struct N {
     #[primary_span]
@@ -141,12 +142,21 @@ struct N {
     var: String,
 }
 
+#[derive(SessionSubdiagnostic)]
+#[label(parser::add_paren, applicability = "machine-applicable")]
+//~^ ERROR `applicability` is not a valid nested attribute of a `label` attribute
+struct O {
+    #[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 = "...")]
+enum P {
+    #[label(parser::add_paren)]
     A {
         #[primary_span]
         span: Span,
@@ -155,7 +165,7 @@ enum O {
 }
 
 #[derive(SessionSubdiagnostic)]
-enum P {
+enum Q {
     #[bar]
 //~^ ERROR `#[bar]` is not a valid attribute
 //~^^ ERROR cannot find attribute `bar` in this scope
@@ -166,21 +176,9 @@ enum P {
     }
 }
 
-#[derive(SessionSubdiagnostic)]
-enum Q {
-    #[bar = "..."]
-//~^ ERROR `#[bar = ...]` is not a valid attribute
-//~^^ ERROR cannot find attribute `bar` in this scope
-    A {
-        #[primary_span]
-        span: Span,
-        var: String,
-    }
-}
-
 #[derive(SessionSubdiagnostic)]
 enum R {
-    #[bar = 4]
+    #[bar = "..."]
 //~^ ERROR `#[bar = ...]` is not a valid attribute
 //~^^ ERROR cannot find attribute `bar` in this scope
     A {
@@ -192,6 +190,18 @@ enum R {
 
 #[derive(SessionSubdiagnostic)]
 enum S {
+    #[bar = 4]
+//~^ ERROR `#[bar = ...]` is not a valid attribute
+//~^^ ERROR cannot find attribute `bar` in this scope
+    A {
+        #[primary_span]
+        span: Span,
+        var: String,
+    }
+}
+
+#[derive(SessionSubdiagnostic)]
+enum T {
     #[bar("...")]
 //~^ ERROR `#[bar("...")]` is not a valid attribute
 //~^^ ERROR cannot find attribute `bar` in this scope
@@ -203,9 +213,9 @@ enum S {
 }
 
 #[derive(SessionSubdiagnostic)]
-enum T {
+enum U {
     #[label(code = "...")]
-//~^ ERROR `code` is not a valid nested attribute of a `label`
+//~^ ERROR diagnostic slug must be first argument of a `#[label(...)]` attribute
     A {
         #[primary_span]
         span: Span,
@@ -214,8 +224,8 @@ enum T {
 }
 
 #[derive(SessionSubdiagnostic)]
-enum U {
-    #[label(slug = "label-u")]
+enum V {
+    #[label(parser::add_paren)]
     A {
         #[primary_span]
         span: Span,
@@ -230,17 +240,17 @@ enum U {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "...")]
+#[label(parser::add_paren)]
 //~^ ERROR label without `#[primary_span]` field
-struct V {
+struct W {
     #[primary_span]
     //~^ ERROR the `#[primary_span]` attribute can only be applied to fields of type `Span`
     span: String,
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "...")]
-struct W {
+#[label(parser::add_paren)]
+struct X {
     #[primary_span]
     span: Span,
     #[applicability]
@@ -249,8 +259,8 @@ struct W {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "...")]
-struct X {
+#[label(parser::add_paren)]
+struct Y {
     #[primary_span]
     span: Span,
     #[bar]
@@ -260,8 +270,8 @@ struct X {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "...")]
-struct Y {
+#[label(parser::add_paren)]
+struct Z {
     #[primary_span]
     span: Span,
     #[bar = "..."]
@@ -271,8 +281,8 @@ struct Y {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "...")]
-struct Z {
+#[label(parser::add_paren)]
+struct AA {
     #[primary_span]
     span: Span,
     #[bar("...")]
@@ -282,8 +292,8 @@ struct Z {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "label-aa")]
-struct AA {
+#[label(parser::add_paren)]
+struct AB {
     #[primary_span]
     span: Span,
     #[skip_arg]
@@ -291,37 +301,36 @@ struct AA {
 }
 
 #[derive(SessionSubdiagnostic)]
-union AB {
+union AC {
 //~^ ERROR unexpected unsupported untagged union
     span: u32,
     b: u64
 }
 
 #[derive(SessionSubdiagnostic)]
-#[label(slug = "label-ac-1")]
+#[label(parser::add_paren)]
 //~^ NOTE previously specified here
 //~^^ NOTE previously specified here
-#[label(slug = "label-ac-2")]
+#[label(parser::add_paren)]
 //~^ 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")]
+#[label(parser::add_paren, parser::add_paren)]
+//~^ ERROR `#[label(parser::add_paren)]` is not a valid attribute
 struct AE {
     #[primary_span]
+    span: Span,
+}
+
+#[derive(SessionSubdiagnostic)]
+#[label(parser::add_paren)]
+struct AF {
+    #[primary_span]
 //~^ NOTE previously specified here
     span_a: Span,
     #[primary_span]
@@ -330,15 +339,15 @@ struct AE {
 }
 
 #[derive(SessionSubdiagnostic)]
-struct AF {
+struct AG {
 //~^ ERROR subdiagnostic kind not specified
     #[primary_span]
     span: Span,
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "suggestion-af", code = "...")]
-struct AG {
+#[suggestion(parser::add_paren, code = "...")]
+struct AH {
     #[primary_span]
     span: Span,
     #[applicability]
@@ -347,8 +356,8 @@ struct AG {
 }
 
 #[derive(SessionSubdiagnostic)]
-enum AH {
-    #[suggestion(slug = "suggestion-ag-a", code = "...")]
+enum AI {
+    #[suggestion(parser::add_paren, code = "...")]
     A {
         #[primary_span]
         span: Span,
@@ -356,7 +365,7 @@ enum AH {
         applicability: Applicability,
         var: String,
     },
-    #[suggestion(slug = "suggestion-ag-b", code = "...")]
+    #[suggestion(parser::add_paren, code = "...")]
     B {
         #[primary_span]
         span: Span,
@@ -367,10 +376,10 @@ enum AH {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code = "...", code = "...")]
+#[suggestion(parser::add_paren, code = "...", code = "...")]
 //~^ ERROR specified multiple times
 //~^^ NOTE previously specified here
-struct AI {
+struct AJ {
     #[primary_span]
     span: Span,
     #[applicability]
@@ -378,8 +387,8 @@ struct AI {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code = "...")]
-struct AJ {
+#[suggestion(parser::add_paren, code = "...")]
+struct AK {
     #[primary_span]
     span: Span,
     #[applicability]
@@ -391,9 +400,9 @@ struct AJ {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code = "...")]
+#[suggestion(parser::add_paren, code = "...")]
 //~^ ERROR suggestion without `applicability`
-struct AK {
+struct AL {
     #[primary_span]
     span: Span,
     #[applicability]
@@ -402,17 +411,17 @@ struct AK {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code = "...")]
+#[suggestion(parser::add_paren, code = "...")]
 //~^ ERROR suggestion without `applicability`
-struct AL {
+struct AM {
     #[primary_span]
     span: Span,
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...")]
+#[suggestion(parser::add_paren)]
 //~^ ERROR suggestion without `code = "..."`
-struct AM {
+struct AN {
     #[primary_span]
     span: Span,
     #[applicability]
@@ -420,34 +429,34 @@ struct AM {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code ="...", applicability = "foo")]
+#[suggestion(parser::add_paren, code ="...", applicability = "foo")]
 //~^ ERROR invalid applicability
-struct AN {
+struct AO {
     #[primary_span]
     span: Span,
 }
 
 #[derive(SessionSubdiagnostic)]
-#[help(slug = "label-am")]
-struct AO {
+#[help(parser::add_paren)]
+struct AP {
     var: String
 }
 
 #[derive(SessionSubdiagnostic)]
-#[note(slug = "label-an")]
-struct AP;
+#[note(parser::add_paren)]
+struct AQ;
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code = "...")]
+#[suggestion(parser::add_paren, code = "...")]
 //~^ ERROR suggestion without `applicability`
 //~^^ ERROR suggestion without `#[primary_span]` field
-struct AQ {
+struct AR {
     var: String,
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code ="...", applicability = "machine-applicable")]
-struct AR {
+#[suggestion(parser::add_paren, code ="...", applicability = "machine-applicable")]
+struct AS {
     #[primary_span]
     span: Span,
 }
@@ -455,8 +464,8 @@ struct AR {
 #[derive(SessionSubdiagnostic)]
 #[label]
 //~^ ERROR unsupported type attribute for subdiagnostic enum
-enum AS {
-    #[label(slug = "...")]
+enum AT {
+    #[label(parser::add_paren)]
     A {
         #[primary_span]
         span: Span,
@@ -465,24 +474,24 @@ enum AS {
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
-struct AT {
+#[suggestion(parser::add_paren, code ="{var}", applicability = "machine-applicable")]
+struct AU {
     #[primary_span]
     span: Span,
     var: String,
 }
 
 #[derive(SessionSubdiagnostic)]
-#[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+#[suggestion(parser::add_paren, code ="{var}", applicability = "machine-applicable")]
 //~^ ERROR `var` doesn't refer to a field on this type
-struct AU {
+struct AV {
     #[primary_span]
     span: Span,
 }
 
 #[derive(SessionSubdiagnostic)]
-enum AV {
-    #[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+enum AW {
+    #[suggestion(parser::add_paren, code ="{var}", applicability = "machine-applicable")]
     A {
         #[primary_span]
         span: Span,
@@ -491,8 +500,8 @@ enum AV {
 }
 
 #[derive(SessionSubdiagnostic)]
-enum AW {
-    #[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
+enum AX {
+    #[suggestion(parser::add_paren, code ="{var}", applicability = "machine-applicable")]
 //~^ ERROR `var` doesn't refer to a field on this type
     A {
         #[primary_span]
diff --git a/src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.stderr b/src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.stderr
index 4984cc4b3186..f833bd210f7f 100644
--- a/src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.stderr
+++ b/src/test/ui-fulldeps/session-diagnostic/subdiagnostic-derive.stderr
@@ -1,7 +1,7 @@
 error: label without `#[primary_span]` field
   --> $DIR/subdiagnostic-derive.rs:47:1
    |
-LL | / #[label(slug = "label-c")]
+LL | / #[label(parser::add_paren)]
 LL | |
 LL | | struct C {
 LL | |     var: String,
@@ -32,98 +32,106 @@ error: `#[label(bug = ...)]` is not a valid attribute
 LL | #[label(bug = "...")]
    |         ^^^^^^^^^^^
    |
-   = help: only `code`, `slug` and `applicability` are valid nested attributes
+   = help: first argument of the attribute should be the diagnostic slug
 
 error: `#[label("...")]` is not a valid attribute
   --> $DIR/subdiagnostic-derive.rs:91:9
    |
 LL | #[label("...")]
    |         ^^^^^
+   |
+   = help: first argument of the attribute should be the diagnostic slug
 
 error: `#[label(slug = ...)]` is not a valid attribute
   --> $DIR/subdiagnostic-derive.rs:100:9
    |
 LL | #[label(slug = 4)]
    |         ^^^^^^^^
+   |
+   = help: first argument of the attribute should be the diagnostic slug
 
 error: `#[label(slug(...))]` is not a valid attribute
   --> $DIR/subdiagnostic-derive.rs:109:9
    |
 LL | #[label(slug("..."))]
    |         ^^^^^^^^^^^
-
-error: `#[label(slug)]` is not a valid attribute
-  --> $DIR/subdiagnostic-derive.rs:118:9
    |
-LL | #[label(slug)]
-   |         ^^^^
+   = help: first argument of the attribute should be the diagnostic slug
 
-error: `slug` must be set in a `#[label(...)]` attribute
-  --> $DIR/subdiagnostic-derive.rs:127:1
+error: diagnostic slug must be first argument of a `#[label(...)]` attribute
+  --> $DIR/subdiagnostic-derive.rs:128:1
    |
 LL | #[label()]
    | ^^^^^^^^^^
 
 error: `code` is not a valid nested attribute of a `label` attribute
-  --> $DIR/subdiagnostic-derive.rs:136:1
+  --> $DIR/subdiagnostic-derive.rs:137:1
    |
-LL | #[label(code = "...")]
-   | ^^^^^^^^^^^^^^^^^^^^^^
+LL | #[label(parser::add_paren, code = "...")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `applicability` is not a valid nested attribute of a `label` attribute
+  --> $DIR/subdiagnostic-derive.rs:146:1
+   |
+LL | #[label(parser::add_paren, applicability = "machine-applicable")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: unsupported type attribute for subdiagnostic enum
-  --> $DIR/subdiagnostic-derive.rs:145:1
+  --> $DIR/subdiagnostic-derive.rs:155:1
    |
 LL | #[foo]
    | ^^^^^^
 
 error: `#[bar]` is not a valid attribute
-  --> $DIR/subdiagnostic-derive.rs:159:5
+  --> $DIR/subdiagnostic-derive.rs:169:5
    |
 LL |     #[bar]
    |     ^^^^^^
 
 error: `#[bar = ...]` is not a valid attribute
-  --> $DIR/subdiagnostic-derive.rs:171:5
+  --> $DIR/subdiagnostic-derive.rs:181:5
    |
 LL |     #[bar = "..."]
    |     ^^^^^^^^^^^^^^
 
 error: `#[bar = ...]` is not a valid attribute
-  --> $DIR/subdiagnostic-derive.rs:183:5
+  --> $DIR/subdiagnostic-derive.rs:193:5
    |
 LL |     #[bar = 4]
    |     ^^^^^^^^^^
 
 error: `#[bar("...")]` is not a valid attribute
-  --> $DIR/subdiagnostic-derive.rs:195:11
+  --> $DIR/subdiagnostic-derive.rs:205:11
    |
 LL |     #[bar("...")]
    |           ^^^^^
+   |
+   = help: first argument of the attribute should be the diagnostic slug
 
-error: `code` is not a valid nested attribute of a `label` attribute
-  --> $DIR/subdiagnostic-derive.rs:207:5
+error: diagnostic slug must be first argument of a `#[label(...)]` attribute
+  --> $DIR/subdiagnostic-derive.rs:217:5
    |
 LL |     #[label(code = "...")]
    |     ^^^^^^^^^^^^^^^^^^^^^^
 
 error: subdiagnostic kind not specified
-  --> $DIR/subdiagnostic-derive.rs:224:5
+  --> $DIR/subdiagnostic-derive.rs:234:5
    |
 LL |     B {
    |     ^
 
 error: the `#[primary_span]` attribute can only be applied to fields of type `Span`
-  --> $DIR/subdiagnostic-derive.rs:236:5
+  --> $DIR/subdiagnostic-derive.rs:246:5
    |
 LL |     #[primary_span]
    |     ^^^^^^^^^^^^^^^
 
 error: label without `#[primary_span]` field
-  --> $DIR/subdiagnostic-derive.rs:233:1
+  --> $DIR/subdiagnostic-derive.rs:243:1
    |
-LL | / #[label(slug = "...")]
+LL | / #[label(parser::add_paren)]
 LL | |
-LL | | struct V {
+LL | | struct W {
 LL | |     #[primary_span]
 LL | |
 LL | |     span: String,
@@ -131,13 +139,13 @@ LL | | }
    | |_^
 
 error: `#[applicability]` is only valid on suggestions
-  --> $DIR/subdiagnostic-derive.rs:246:5
+  --> $DIR/subdiagnostic-derive.rs:256:5
    |
 LL |     #[applicability]
    |     ^^^^^^^^^^^^^^^^
 
 error: `#[bar]` is not a valid attribute
-  --> $DIR/subdiagnostic-derive.rs:256:5
+  --> $DIR/subdiagnostic-derive.rs:266:5
    |
 LL |     #[bar]
    |     ^^^^^^
@@ -145,21 +153,21 @@ LL |     #[bar]
    = help: only `primary_span`, `applicability` and `skip_arg` are valid field attributes
 
 error: `#[bar = ...]` is not a valid attribute
-  --> $DIR/subdiagnostic-derive.rs:267:5
+  --> $DIR/subdiagnostic-derive.rs:277:5
    |
 LL |     #[bar = "..."]
    |     ^^^^^^^^^^^^^^
 
 error: `#[bar(...)]` is not a valid attribute
-  --> $DIR/subdiagnostic-derive.rs:278:5
+  --> $DIR/subdiagnostic-derive.rs:288:5
    |
 LL |     #[bar("...")]
    |     ^^^^^^^^^^^^^
 
 error: unexpected unsupported untagged union
-  --> $DIR/subdiagnostic-derive.rs:294:1
+  --> $DIR/subdiagnostic-derive.rs:304:1
    |
-LL | / union AB {
+LL | / union AC {
 LL | |
 LL | |     span: u32,
 LL | |     b: u64
@@ -167,95 +175,91 @@ LL | | }
    | |_^
 
 error: specified multiple times
-  --> $DIR/subdiagnostic-derive.rs:304:9
+  --> $DIR/subdiagnostic-derive.rs:314:1
    |
-LL | #[label(slug = "label-ac-2")]
-   |         ^^^^^^^^^^^^^^^^^^^
+LL | #[label(parser::add_paren)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: previously specified here
-  --> $DIR/subdiagnostic-derive.rs:301:9
+  --> $DIR/subdiagnostic-derive.rs:311:1
    |
-LL | #[label(slug = "label-ac-1")]
-   |         ^^^^^^^^^^^^^^^^^^^
+LL | #[label(parser::add_paren)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: specified multiple times
-  --> $DIR/subdiagnostic-derive.rs:304:1
+  --> $DIR/subdiagnostic-derive.rs:314:1
    |
-LL | #[label(slug = "label-ac-2")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[label(parser::add_paren)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: previously specified here
-  --> $DIR/subdiagnostic-derive.rs:301:1
+  --> $DIR/subdiagnostic-derive.rs:311:1
    |
-LL | #[label(slug = "label-ac-1")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[label(parser::add_paren)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: `#[label(parser::add_paren)]` is not a valid attribute
+  --> $DIR/subdiagnostic-derive.rs:323:28
+   |
+LL | #[label(parser::add_paren, parser::add_paren)]
+   |                            ^^^^^^^^^^^^^^^^^
+   |
+   = help: a diagnostic slug must be the first argument to the attribute
 
 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
+  --> $DIR/subdiagnostic-derive.rs:336:5
    |
 LL |     #[primary_span]
    |     ^^^^^^^^^^^^^^^
    |
 note: previously specified here
-  --> $DIR/subdiagnostic-derive.rs:324:5
+  --> $DIR/subdiagnostic-derive.rs:333:5
    |
 LL |     #[primary_span]
    |     ^^^^^^^^^^^^^^^
 
 error: subdiagnostic kind not specified
-  --> $DIR/subdiagnostic-derive.rs:333:8
+  --> $DIR/subdiagnostic-derive.rs:342:8
    |
-LL | struct AF {
+LL | struct AG {
    |        ^^
 
 error: specified multiple times
-  --> $DIR/subdiagnostic-derive.rs:370:42
+  --> $DIR/subdiagnostic-derive.rs:379:47
    |
-LL | #[suggestion(slug = "...", code = "...", code = "...")]
-   |                                          ^^^^^^^^^^^^
+LL | #[suggestion(parser::add_paren, code = "...", code = "...")]
+   |                                               ^^^^^^^^^^^^
    |
 note: previously specified here
-  --> $DIR/subdiagnostic-derive.rs:370:28
+  --> $DIR/subdiagnostic-derive.rs:379:33
    |
-LL | #[suggestion(slug = "...", code = "...", code = "...")]
-   |                            ^^^^^^^^^^^^
+LL | #[suggestion(parser::add_paren, code = "...", code = "...")]
+   |                                 ^^^^^^^^^^^^
 
 error: specified multiple times
-  --> $DIR/subdiagnostic-derive.rs:388:5
+  --> $DIR/subdiagnostic-derive.rs:397:5
    |
 LL |     #[applicability]
    |     ^^^^^^^^^^^^^^^^
    |
 note: previously specified here
-  --> $DIR/subdiagnostic-derive.rs:385:5
+  --> $DIR/subdiagnostic-derive.rs:394:5
    |
 LL |     #[applicability]
    |     ^^^^^^^^^^^^^^^^
 
 error: the `#[applicability]` attribute can only be applied to fields of type `Applicability`
-  --> $DIR/subdiagnostic-derive.rs:399:5
+  --> $DIR/subdiagnostic-derive.rs:408:5
    |
 LL |     #[applicability]
    |     ^^^^^^^^^^^^^^^^
 
 error: suggestion without `applicability`
-  --> $DIR/subdiagnostic-derive.rs:394:1
+  --> $DIR/subdiagnostic-derive.rs:403:1
    |
-LL | / #[suggestion(slug = "...", code = "...")]
+LL | / #[suggestion(parser::add_paren, code = "...")]
 LL | |
-LL | | struct AK {
+LL | | struct AL {
 LL | |     #[primary_span]
 ...  |
 LL | |     applicability: Span,
@@ -263,22 +267,22 @@ LL | | }
    | |_^
 
 error: suggestion without `applicability`
-  --> $DIR/subdiagnostic-derive.rs:405:1
+  --> $DIR/subdiagnostic-derive.rs:414:1
    |
-LL | / #[suggestion(slug = "...", code = "...")]
+LL | / #[suggestion(parser::add_paren, code = "...")]
 LL | |
-LL | | struct AL {
+LL | | struct AM {
 LL | |     #[primary_span]
 LL | |     span: Span,
 LL | | }
    | |_^
 
 error: suggestion without `code = "..."`
-  --> $DIR/subdiagnostic-derive.rs:413:1
+  --> $DIR/subdiagnostic-derive.rs:422:1
    |
-LL | / #[suggestion(slug = "...")]
+LL | / #[suggestion(parser::add_paren)]
 LL | |
-LL | | struct AM {
+LL | | struct AN {
 LL | |     #[primary_span]
 ...  |
 LL | |     applicability: Applicability,
@@ -286,50 +290,50 @@ LL | | }
    | |_^
 
 error: invalid applicability
-  --> $DIR/subdiagnostic-derive.rs:423:41
+  --> $DIR/subdiagnostic-derive.rs:432:46
    |
-LL | #[suggestion(slug = "...", code ="...", applicability = "foo")]
-   |                                         ^^^^^^^^^^^^^^^^^^^^^
+LL | #[suggestion(parser::add_paren, code ="...", applicability = "foo")]
+   |                                              ^^^^^^^^^^^^^^^^^^^^^
 
 error: suggestion without `applicability`
-  --> $DIR/subdiagnostic-derive.rs:441:1
+  --> $DIR/subdiagnostic-derive.rs:450:1
    |
-LL | / #[suggestion(slug = "...", code = "...")]
+LL | / #[suggestion(parser::add_paren, code = "...")]
 LL | |
 LL | |
-LL | | struct AQ {
+LL | | struct AR {
 LL | |     var: String,
 LL | | }
    | |_^
 
 error: suggestion without `#[primary_span]` field
-  --> $DIR/subdiagnostic-derive.rs:441:1
+  --> $DIR/subdiagnostic-derive.rs:450:1
    |
-LL | / #[suggestion(slug = "...", code = "...")]
+LL | / #[suggestion(parser::add_paren, code = "...")]
 LL | |
 LL | |
-LL | | struct AQ {
+LL | | struct AR {
 LL | |     var: String,
 LL | | }
    | |_^
 
 error: unsupported type attribute for subdiagnostic enum
-  --> $DIR/subdiagnostic-derive.rs:456:1
+  --> $DIR/subdiagnostic-derive.rs:465:1
    |
 LL | #[label]
    | ^^^^^^^^
 
 error: `var` doesn't refer to a field on this type
-  --> $DIR/subdiagnostic-derive.rs:476:34
+  --> $DIR/subdiagnostic-derive.rs:485:39
    |
-LL | #[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
-   |                                  ^^^^^^^
+LL | #[suggestion(parser::add_paren, code ="{var}", applicability = "machine-applicable")]
+   |                                       ^^^^^^^
 
 error: `var` doesn't refer to a field on this type
-  --> $DIR/subdiagnostic-derive.rs:495:38
+  --> $DIR/subdiagnostic-derive.rs:504:43
    |
-LL |     #[suggestion(slug = "...", code ="{var}", applicability = "machine-applicable")]
-   |                                      ^^^^^^^
+LL |     #[suggestion(parser::add_paren, code ="{var}", applicability = "machine-applicable")]
+   |                                           ^^^^^^^
 
 error: cannot find attribute `foo` in this scope
   --> $DIR/subdiagnostic-derive.rs:63:3
@@ -338,52 +342,59 @@ LL | #[foo]
    |   ^^^
 
 error: cannot find attribute `foo` in this scope
-  --> $DIR/subdiagnostic-derive.rs:145:3
+  --> $DIR/subdiagnostic-derive.rs:155:3
    |
 LL | #[foo]
    |   ^^^
 
 error: cannot find attribute `bar` in this scope
-  --> $DIR/subdiagnostic-derive.rs:159:7
+  --> $DIR/subdiagnostic-derive.rs:169:7
    |
 LL |     #[bar]
    |       ^^^
 
 error: cannot find attribute `bar` in this scope
-  --> $DIR/subdiagnostic-derive.rs:171:7
+  --> $DIR/subdiagnostic-derive.rs:181:7
    |
 LL |     #[bar = "..."]
    |       ^^^
 
 error: cannot find attribute `bar` in this scope
-  --> $DIR/subdiagnostic-derive.rs:183:7
+  --> $DIR/subdiagnostic-derive.rs:193:7
    |
 LL |     #[bar = 4]
    |       ^^^
 
 error: cannot find attribute `bar` in this scope
-  --> $DIR/subdiagnostic-derive.rs:195:7
+  --> $DIR/subdiagnostic-derive.rs:205:7
    |
 LL |     #[bar("...")]
    |       ^^^
 
 error: cannot find attribute `bar` in this scope
-  --> $DIR/subdiagnostic-derive.rs:256:7
+  --> $DIR/subdiagnostic-derive.rs:266:7
    |
 LL |     #[bar]
    |       ^^^
 
 error: cannot find attribute `bar` in this scope
-  --> $DIR/subdiagnostic-derive.rs:267:7
+  --> $DIR/subdiagnostic-derive.rs:277:7
    |
 LL |     #[bar = "..."]
    |       ^^^
 
 error: cannot find attribute `bar` in this scope
-  --> $DIR/subdiagnostic-derive.rs:278:7
+  --> $DIR/subdiagnostic-derive.rs:288:7
    |
 LL |     #[bar("...")]
    |       ^^^
 
-error: aborting due to 51 previous errors
+error[E0425]: cannot find value `slug` in module `rustc_errors::fluent`
+  --> $DIR/subdiagnostic-derive.rs:118:9
+   |
+LL | #[label(slug)]
+   |         ^^^^ not found in `rustc_errors::fluent`
 
+error: aborting due to 52 previous errors
+
+For more information about this error, try `rustc --explain E0425`.