errors: AddToDiagnostic::add_to_diagnostic_with

`AddToDiagnostic::add_to_diagnostic_with` is similar to the previous
`AddToDiagnostic::add_to_diagnostic` but takes a function that can be
used by the caller to modify diagnostic messages originating from the
subdiagnostic (such as performing translation eagerly).

`add_to_diagnostic` now just calls `add_to_diagnostic_with` with an
empty closure.

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

compiler/rustc_ast_lowering/src/errors.rs

@@ -1,4 +1,7 @@
-use rustc_errors::{fluent, AddToDiagnostic, Applicability, Diagnostic, DiagnosticArgFromDisplay};
+use rustc_errors::{
+    fluent, AddToDiagnostic, Applicability, Diagnostic, DiagnosticArgFromDisplay,
+    SubdiagnosticMessage,
+};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{symbol::Ident, Span, Symbol};
 
@@ -19,7 +22,10 @@ pub struct UseAngleBrackets {
 }
 
 impl AddToDiagnostic for UseAngleBrackets {
-    fn add_to_diagnostic(self, diag: &mut Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         diag.multipart_suggestion(
             fluent::ast_lowering::use_angle_brackets,
             vec![(self.open_param, String::from("<")), (self.close_param, String::from(">"))],
@@ -69,7 +75,10 @@ pub enum AssocTyParenthesesSub {
 }
 
 impl AddToDiagnostic for AssocTyParenthesesSub {
-    fn add_to_diagnostic(self, diag: &mut Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         match self {
             Self::Empty { parentheses_span } => diag.multipart_suggestion(
                 fluent::ast_lowering::remove_parentheses,

compiler/rustc_ast_passes/src/errors.rs

@@ -1,6 +1,6 @@
 //! Errors emitted by ast_passes.
 
-use rustc_errors::{fluent, AddToDiagnostic, Applicability, Diagnostic};
+use rustc_errors::{fluent, AddToDiagnostic, Applicability, Diagnostic, SubdiagnosticMessage};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::{Span, Symbol};
 
@@ -17,7 +17,10 @@ pub struct ForbiddenLet {
 }
 
 impl AddToDiagnostic for ForbiddenLetReason {
-    fn add_to_diagnostic(self, diag: &mut Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         match self {
             Self::GenericForbidden => {}
             Self::NotSupportedOr(span) => {
@@ -228,7 +231,10 @@ pub struct ExternBlockSuggestion {
 }
 
 impl AddToDiagnostic for ExternBlockSuggestion {
-    fn add_to_diagnostic(self, diag: &mut Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         let start_suggestion = if let Some(abi) = self.abi {
             format!("extern \"{}\" {{", abi)
         } else {

compiler/rustc_errors/src/diagnostic.rs

@@ -203,9 +203,20 @@ impl IntoDiagnosticArg for ast::token::TokenKind {
 /// `#[derive(Subdiagnostic)]` -- see [rustc_macros::Subdiagnostic].
 #[cfg_attr(bootstrap, rustc_diagnostic_item = "AddSubdiagnostic")]
 #[cfg_attr(not(bootstrap), rustc_diagnostic_item = "AddToDiagnostic")]
-pub trait AddToDiagnostic {
+pub trait AddToDiagnostic
+where
+    Self: Sized,
+{
     /// Add a subdiagnostic to an existing diagnostic.
-    fn add_to_diagnostic(self, diag: &mut Diagnostic);
+    fn add_to_diagnostic(self, diag: &mut Diagnostic) {
+        self.add_to_diagnostic_with(diag, |_, m| m);
+    }
+
+    /// Add a subdiagnostic to an existing diagnostic where `f` is invoked on every message used
+    /// (to optionally perform eager translation).
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, f: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage;
 }
 
 /// Trait implemented by lint types. This should not be implemented manually. Instead, use
@@ -921,8 +932,8 @@ impl Diagnostic {
         self
     }
 
-    /// Add a subdiagnostic from a type that implements `Subdiagnostic` - see
-    /// [rustc_macros::Subdiagnostic].
+    /// Add a subdiagnostic from a type that implements `Subdiagnostic` (see
+    /// [rustc_macros::Subdiagnostic]).
     pub fn subdiagnostic(&mut self, subdiagnostic: impl AddToDiagnostic) -> &mut Self {
         subdiagnostic.add_to_diagnostic(self);
         self

compiler/rustc_infer/src/errors/mod.rs

@@ -1,6 +1,7 @@
 use hir::GenericParamKind;
 use rustc_errors::{
-    fluent, AddToDiagnostic, Applicability, DiagnosticMessage, DiagnosticStyledString, MultiSpan,
+    fluent, AddToDiagnostic, Applicability, Diagnostic, DiagnosticMessage, DiagnosticStyledString,
+    MultiSpan, SubdiagnosticMessage,
 };
 use rustc_hir as hir;
 use rustc_hir::{FnRetTy, Ty};
@@ -229,7 +230,10 @@ pub enum RegionOriginNote<'a> {
 }
 
 impl AddToDiagnostic for RegionOriginNote<'_> {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         let mut label_or_note = |span, msg: DiagnosticMessage| {
             let sub_count = diag.children.iter().filter(|d| d.span.is_dummy()).count();
             let expanded_sub_count = diag.children.iter().filter(|d| !d.span.is_dummy()).count();
@@ -290,7 +294,10 @@ pub enum LifetimeMismatchLabels {
 }
 
 impl AddToDiagnostic for LifetimeMismatchLabels {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         match self {
             LifetimeMismatchLabels::InRet { param_span, ret_span, span, label_var1 } => {
                 diag.span_label(param_span, fluent::infer::declared_different);
@@ -340,7 +347,10 @@ pub struct AddLifetimeParamsSuggestion<'a> {
 }
 
 impl AddToDiagnostic for AddLifetimeParamsSuggestion<'_> {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         let mut mk_suggestion = || {
             let (
                 hir::Ty { kind: hir::TyKind::Rptr(lifetime_sub, _), .. },
@@ -439,7 +449,10 @@ pub struct IntroducesStaticBecauseUnmetLifetimeReq {
 }
 
 impl AddToDiagnostic for IntroducesStaticBecauseUnmetLifetimeReq {
-    fn add_to_diagnostic(mut self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(mut self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         self.unmet_requirements
             .push_span_label(self.binding_span, fluent::infer::msl_introduces_static);
         diag.span_note(self.unmet_requirements, fluent::infer::msl_unmet_req);
@@ -451,7 +464,10 @@ pub struct ImplNote {
 }
 
 impl AddToDiagnostic for ImplNote {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         match self.impl_span {
             Some(span) => diag.span_note(span, fluent::infer::msl_impl_note),
             None => diag.note(fluent::infer::msl_impl_note),
@@ -466,7 +482,10 @@ pub enum TraitSubdiag {
 
 // FIXME(#100717) used in `Vec<TraitSubdiag>` so requires eager translation/list support
 impl AddToDiagnostic for TraitSubdiag {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         match self {
             TraitSubdiag::Note { span } => {
                 diag.span_note(span, "this has an implicit `'static` lifetime requirement");

compiler/rustc_infer/src/errors/note_and_explain.rs

@@ -1,5 +1,7 @@
 use crate::infer::error_reporting::nice_region_error::find_anon_type;
-use rustc_errors::{self, fluent, AddToDiagnostic, IntoDiagnosticArg};
+use rustc_errors::{
+    self, fluent, AddToDiagnostic, Diagnostic, IntoDiagnosticArg, SubdiagnosticMessage,
+};
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::{symbol::kw, Span};
 
@@ -159,7 +161,10 @@ impl RegionExplanation<'_> {
 }
 
 impl AddToDiagnostic for RegionExplanation<'_> {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         if let Some(span) = self.desc.span {
             diag.span_note(span, fluent::infer::region_explanation);
         } else {

compiler/rustc_lint/src/errors.rs

@@ -1,4 +1,7 @@
-use rustc_errors::{fluent, AddToDiagnostic, ErrorGuaranteed, Handler, IntoDiagnostic};
+use rustc_errors::{
+    fluent, AddToDiagnostic, Diagnostic, ErrorGuaranteed, Handler, IntoDiagnostic,
+    SubdiagnosticMessage,
+};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::lint::Level;
 use rustc_span::{Span, Symbol};
@@ -23,7 +26,10 @@ pub enum OverruledAttributeSub {
 }
 
 impl AddToDiagnostic for OverruledAttributeSub {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         match self {
             OverruledAttributeSub::DefaultSource { id } => {
                 diag.note(fluent::lint::default_source);
@@ -88,7 +94,10 @@ pub struct RequestedLevel {
 }
 
 impl AddToDiagnostic for RequestedLevel {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         diag.note(fluent::lint::requested_level);
         diag.set_arg(
             "level",

compiler/rustc_macros/src/diagnostics/mod.rs

@@ -9,7 +9,7 @@ use diagnostic::{DiagnosticDerive, LintDiagnosticDerive};
 pub(crate) use fluent::fluent_messages;
 use proc_macro2::TokenStream;
 use quote::format_ident;
-use subdiagnostic::SubdiagnosticDerive;
+use subdiagnostic::SubdiagnosticDeriveBuilder;
 use synstructure::Structure;
 
 /// Implements `#[derive(Diagnostic)]`, which allows for errors to be specified as a struct,
@@ -155,5 +155,5 @@ pub fn lint_diagnostic_derive(s: Structure<'_>) -> TokenStream {
 /// diag.subdiagnostic(RawIdentifierSuggestion { span, applicability, ident });
 /// ```
 pub fn session_subdiagnostic_derive(s: Structure<'_>) -> TokenStream {
-    SubdiagnosticDerive::new(s).into_tokens()
+    SubdiagnosticDeriveBuilder::new().into_tokens(s)
 }

compiler/rustc_macros/src/diagnostics/subdiagnostic.rs

@@ -15,19 +15,19 @@ use syn::{spanned::Spanned, Attribute, Meta, MetaList, MetaNameValue, NestedMeta
 use synstructure::{BindingInfo, Structure, VariantInfo};
 
 /// The central struct for constructing the `add_to_diagnostic` method from an annotated struct.
-pub(crate) struct SubdiagnosticDerive<'a> {
-    structure: Structure<'a>,
+pub(crate) struct SubdiagnosticDeriveBuilder {
     diag: syn::Ident,
+    f: syn::Ident,
 }
 
-impl<'a> SubdiagnosticDerive<'a> {
-    pub(crate) fn new(structure: Structure<'a>) -> Self {
+impl SubdiagnosticDeriveBuilder {
+    pub(crate) fn new() -> Self {
         let diag = format_ident!("diag");
-        Self { structure, diag }
+        let f = format_ident!("f");
+        Self { diag, f }
     }
 
-    pub(crate) fn into_tokens(self) -> TokenStream {
-        let SubdiagnosticDerive { mut structure, diag } = self;
+    pub(crate) fn into_tokens<'a>(self, mut structure: Structure<'a>) -> TokenStream {
         let implementation = {
             let ast = structure.ast();
             let span = ast.span().unwrap();
@@ -53,8 +53,8 @@ impl<'a> SubdiagnosticDerive<'a> {
 
             structure.bind_with(|_| synstructure::BindStyle::Move);
             let variants_ = structure.each_variant(|variant| {
-                let mut builder = SubdiagnosticDeriveBuilder {
-                    diag: &diag,
+                let mut builder = SubdiagnosticDeriveVariantBuilder {
+                    parent: &self,
                     variant,
                     span,
                     fields: build_field_mapping(variant),
@@ -72,9 +72,17 @@ impl<'a> SubdiagnosticDerive<'a> {
             }
         };
 
+        let diag = &self.diag;
+        let f = &self.f;
         let ret = structure.gen_impl(quote! {
             gen impl rustc_errors::AddToDiagnostic for @Self {
-                fn add_to_diagnostic(self, #diag: &mut rustc_errors::Diagnostic) {
+                fn add_to_diagnostic_with<__F>(self, #diag: &mut rustc_errors::Diagnostic, #f: __F)
+                where
+                    __F: Fn(
+                        &mut rustc_errors::Diagnostic,
+                        rustc_errors::SubdiagnosticMessage
+                    ) -> rustc_errors::SubdiagnosticMessage,
+                {
                     use rustc_errors::{Applicability, IntoDiagnosticArg};
                     #implementation
                 }
@@ -88,9 +96,9 @@ impl<'a> SubdiagnosticDerive<'a> {
 /// for the final generated method. This is a separate struct to `SubdiagnosticDerive`
 /// only to be able to destructure and split `self.builder` and the `self.structure` up to avoid a
 /// double mut borrow later on.
-struct SubdiagnosticDeriveBuilder<'a> {
+struct SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
     /// The identifier to use for the generated `DiagnosticBuilder` instance.
-    diag: &'a syn::Ident,
+    parent: &'parent SubdiagnosticDeriveBuilder,
 
     /// Info for the current variant (or the type if not an enum).
     variant: &'a VariantInfo<'a>,
@@ -112,7 +120,7 @@ struct SubdiagnosticDeriveBuilder<'a> {
     has_suggestion_parts: bool,
 }
 
-impl<'a> HasFieldMap for SubdiagnosticDeriveBuilder<'a> {
+impl<'parent, 'a> HasFieldMap for SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
     fn get_field_binding(&self, field: &String) -> Option<&TokenStream> {
         self.fields.get(field)
     }
@@ -156,7 +164,7 @@ impl<'a> FromIterator<&'a SubdiagnosticKind> for KindsStatistics {
     }
 }
 
-impl<'a> SubdiagnosticDeriveBuilder<'a> {
+impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
     fn identify_kind(&mut self) -> Result<Vec<(SubdiagnosticKind, Path)>, DiagnosticDeriveError> {
         let mut kind_slugs = vec![];
 
@@ -187,7 +195,7 @@ impl<'a> SubdiagnosticDeriveBuilder<'a> {
         let ast = binding.ast();
         assert_eq!(ast.attrs.len(), 0, "field with attribute used as diagnostic arg");
 
-        let diag = &self.diag;
+        let diag = &self.parent.diag;
         let ident = ast.ident.as_ref().unwrap();
         // strip `r#` prefix, if present
         let ident = format_ident!("{}", ident);
@@ -442,11 +450,14 @@ impl<'a> SubdiagnosticDeriveBuilder<'a> {
 
         let span_field = self.span_field.value_ref();
 
-        let diag = &self.diag;
+        let diag = &self.parent.diag;
+        let f = &self.parent.f;
         let mut calls = TokenStream::new();
         for (kind, slug) in kind_slugs {
+            let message = format_ident!("__message");
+            calls.extend(quote! { let #message = #f(#diag, rustc_errors::fluent::#slug.into()); });
+
             let name = format_ident!("{}{}", if span_field.is_some() { "span_" } else { "" }, kind);
-            let message = quote! { rustc_errors::fluent::#slug };
             let call = match kind {
                 SubdiagnosticKind::Suggestion { suggestion_kind, applicability, code } => {
                     let applicability = applicability

compiler/rustc_query_system/src/error.rs

@@ -1,4 +1,4 @@
-use rustc_errors::AddToDiagnostic;
+use rustc_errors::{AddToDiagnostic, Diagnostic, SubdiagnosticMessage};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_session::Limit;
 use rustc_span::{Span, Symbol};
@@ -9,7 +9,10 @@ pub struct CycleStack {
 }
 
 impl AddToDiagnostic for CycleStack {
-    fn add_to_diagnostic(self, diag: &mut rustc_errors::Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         diag.span_note(self.span, &format!("...which requires {}...", self.desc));
     }
 }

src/test/ui-fulldeps/internal-lints/diagnostics.rs

@@ -13,7 +13,7 @@ extern crate rustc_span;
 
 use rustc_errors::{
     AddToDiagnostic, IntoDiagnostic, Diagnostic, DiagnosticBuilder,
-    ErrorGuaranteed, Handler, fluent
+    ErrorGuaranteed, Handler, fluent, SubdiagnosticMessage,
 };
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_span::Span;
@@ -52,7 +52,10 @@ impl<'a> IntoDiagnostic<'a, ErrorGuaranteed> for TranslatableInIntoDiagnostic {
 pub struct UntranslatableInAddToDiagnostic;
 
 impl AddToDiagnostic for UntranslatableInAddToDiagnostic {
-    fn add_to_diagnostic(self, diag: &mut Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         diag.note("untranslatable diagnostic");
         //~^ ERROR diagnostics should be created using translatable messages
     }
@@ -61,7 +64,10 @@ impl AddToDiagnostic for UntranslatableInAddToDiagnostic {
 pub struct TranslatableInAddToDiagnostic;
 
 impl AddToDiagnostic for TranslatableInAddToDiagnostic {
-    fn add_to_diagnostic(self, diag: &mut Diagnostic) {
+    fn add_to_diagnostic_with<F>(self, diag: &mut Diagnostic, _: F)
+    where
+        F: Fn(&mut Diagnostic, SubdiagnosticMessage) -> SubdiagnosticMessage,
+    {
         diag.note(fluent::compiletest::note);
     }
 }

src/test/ui-fulldeps/internal-lints/diagnostics.stderr

@@ -11,13 +11,13 @@ LL | #![deny(rustc::untranslatable_diagnostic)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: diagnostics should be created using translatable messages
-  --> $DIR/diagnostics.rs:56:14
+  --> $DIR/diagnostics.rs:59:14
    |
 LL |         diag.note("untranslatable diagnostic");
    |              ^^^^
 
 error: diagnostics should only be created in `IntoDiagnostic`/`AddToDiagnostic` impls
-  --> $DIR/diagnostics.rs:70:25
+  --> $DIR/diagnostics.rs:76:25
    |
 LL |     let _diag = handler.struct_err(fluent::compiletest::example);
    |                         ^^^^^^^^^^
@@ -29,13 +29,13 @@ LL | #![deny(rustc::diagnostic_outside_of_impl)]
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: diagnostics should only be created in `IntoDiagnostic`/`AddToDiagnostic` impls
-  --> $DIR/diagnostics.rs:73:25
+  --> $DIR/diagnostics.rs:79:25
    |
 LL |     let _diag = handler.struct_err("untranslatable diagnostic");
    |                         ^^^^^^^^^^
 
 error: diagnostics should be created using translatable messages
-  --> $DIR/diagnostics.rs:73:25
+  --> $DIR/diagnostics.rs:79:25
    |
 LL |     let _diag = handler.struct_err("untranslatable diagnostic");
    |                         ^^^^^^^^^^