Avoid double binding of subdiagnostics inside #[derive(SessionDiagnostic)]

compiler/rustc_macros/src/diagnostics/diagnostic.rs

@@ -71,31 +71,46 @@ impl<'a> SessionDiagnosticDerive<'a> {
                     }
                 };
 
+                // Keep track of which fields are subdiagnostics
+                let mut subdiagnostics = std::collections::HashSet::new();
+
                 // Generates calls to `span_label` and similar functions based on the attributes
                 // on fields. Code for suggestions uses formatting machinery and the value of
                 // other fields - because any given field can be referenced multiple times, it
                 // should be accessed through a borrow. When passing fields to `set_arg` (which
                 // happens below) for Fluent, we want to move the data, so that has to happen
                 // in a separate pass over the fields.
-                let attrs = structure.each(|field_binding| {
-                    let field = field_binding.ast();
-                    let result = field.attrs.iter().map(|attr| {
-                        builder
-                            .generate_field_attr_code(
-                                attr,
-                                FieldInfo {
-                                    vis: &field.vis,
-                                    binding: field_binding,
-                                    ty: &field.ty,
-                                    span: &field.span(),
-                                },
-                            )
-                            .unwrap_or_else(|v| v.to_compile_error())
+                let attrs = structure
+                    .clone()
+                    // Remove the fields that have a `subdiagnostic` attribute.
+                    .filter(|field_binding| {
+                        field_binding.ast().attrs.iter().all(|attr| {
+                            "subdiagnostic" != attr.path.segments.last().unwrap().ident.to_string()
+                                || {
+                                    subdiagnostics.insert(field_binding.binding.clone());
+                                    false
+                                }
+                        })
+                    })
+                    .each(|field_binding| {
+                        let field = field_binding.ast();
+                        let result = field.attrs.iter().map(|attr| {
+                            builder
+                                .generate_field_attr_code(
+                                    attr,
+                                    FieldInfo {
+                                        vis: &field.vis,
+                                        binding: field_binding,
+                                        ty: &field.ty,
+                                        span: &field.span(),
+                                    },
+                                )
+                                .unwrap_or_else(|v| v.to_compile_error())
+                        });
+
+                        quote! { #(#result);* }
                     });
 
-                    quote! { #(#result);* }
-                });
-
                 // When generating `set_arg` calls, move data rather than borrow it to avoid
                 // requiring clones - this must therefore be the last use of each field (for
                 // example, any formatting machinery that might refer to a field should be
@@ -107,7 +122,7 @@ impl<'a> SessionDiagnosticDerive<'a> {
                     // need to be passed as an argument to the diagnostic. But when a field has no
                     // attributes then it must be passed as an argument to the diagnostic so that
                     // it can be referred to by Fluent messages.
-                    if field.attrs.is_empty() {
+                    let tokens = if field.attrs.is_empty() {
                         let diag = &builder.diag;
                         let ident = field_binding.ast().ident.as_ref().unwrap();
                         quote! {
@@ -118,6 +133,27 @@ impl<'a> SessionDiagnosticDerive<'a> {
                         }
                     } else {
                         quote! {}
+                    };
+                    // If this field had a subdiagnostic attribute, we generate the code here to
+                    // avoid binding it twice.
+                    if subdiagnostics.contains(&field_binding.binding) {
+                        let result = field.attrs.iter().map(|attr| {
+                            builder
+                                .generate_field_attr_code(
+                                    attr,
+                                    FieldInfo {
+                                        vis: &field.vis,
+                                        binding: field_binding,
+                                        ty: &field.ty,
+                                        span: &field.span(),
+                                    },
+                                )
+                                .unwrap_or_else(|v| v.to_compile_error())
+                        });
+
+                        quote! { #(#result);* #tokens }
+                    } else {
+                        tokens
                     }
                 });
 
@@ -359,6 +395,8 @@ impl SessionDiagnosticDeriveBuilder {
         let (binding, needs_destructure) = match (name.as_str(), &inner_ty) {
             // `primary_span` can accept a `Vec<Span>` so don't destructure that.
             ("primary_span", FieldInnerTy::Vec(_)) => (quote! { #field_binding.clone() }, false),
+            // `subdiagnostics` are not derefed because they are bound by value.
+            ("subdiagnostic", _) => (quote! { #field_binding }, true),
             _ => (quote! { *#field_binding }, true),
         };
 

compiler/rustc_parse/src/parser/diagnostics.rs

@@ -254,23 +254,23 @@ struct AmbiguousPlus {
 
 #[derive(SessionDiagnostic)]
 #[error(code = "E0178", slug = "parser-maybe-recover-from-bad-type-plus")]
-struct BadTypePlus<'a> {
+struct BadTypePlus {
     pub ty: String,
     #[primary_span]
     pub span: Span,
     #[subdiagnostic]
-    pub sub: BadTypePlusSub<'a>,
+    pub sub: BadTypePlusSub,
 }
 
-#[derive(SessionSubdiagnostic, Clone, Copy)]
-pub enum BadTypePlusSub<'a> {
+#[derive(SessionSubdiagnostic)]
+pub enum BadTypePlusSub {
     #[suggestion(
         slug = "parser-add-paren",
         code = "{sum_with_parens}",
         applicability = "machine-applicable"
     )]
     AddParen {
-        sum_with_parens: &'a str,
+        sum_with_parens: String,
         #[primary_span]
         span: Span,
     },
@@ -1289,11 +1289,9 @@ impl<'a> Parser<'a> {
         let bounds = self.parse_generic_bounds(None)?;
         let sum_span = ty.span.to(self.prev_token.span);
 
-        let sum_with_parens: String;
-
         let sub = match ty.kind {
             TyKind::Rptr(ref lifetime, ref mut_ty) => {
-                sum_with_parens = pprust::to_string(|s| {
+                let sum_with_parens = pprust::to_string(|s| {
                     s.s.word("&");
                     s.print_opt_lifetime(lifetime);
                     s.print_mutability(mut_ty.mutbl, false);
@@ -1303,7 +1301,7 @@ impl<'a> Parser<'a> {
                     s.pclose()
                 });
 
-                BadTypePlusSub::AddParen { sum_with_parens: &sum_with_parens, span: sum_span }
+                BadTypePlusSub::AddParen { sum_with_parens, span: sum_span }
             }
             TyKind::Ptr(..) | TyKind::BareFn(..) => BadTypePlusSub::ForgotParen { span: sum_span },
             _ => BadTypePlusSub::ExpectPath { span: sum_span },