macros: use typed identifiers in subdiag derive

As in the diagnostic derive, using typed identifiers in the
subdiagnostic derive improves the diagnostics of using the subdiagnostic
derive as Fluent messages will be confirmed to exist at compile-time.

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

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 {

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,

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); }

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,

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,

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,

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)]