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Cleanup of #[derive(Diagnostic)] attribute parsers #151657

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9e61014
Convert `parse_nested_meta` to `parse_args_with` for `#[diagnostic]`
JonathanBrouwer Jan 28, 2026
5d21a21
Convert `parse_nested_meta` to `parse_args_with` for `#[subdiagnostic]`
JonathanBrouwer Jan 28, 2026
0bf3f5d
Remove unused `no_span` option
JonathanBrouwer Jan 25, 2026
2e8347a
Remove `HasFieldMap` trait in favour of passing `FieldMap` directly
JonathanBrouwer Jan 28, 2026
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88 changes: 45 additions & 43 deletions compiler/rustc_macros/src/diagnostics/diagnostic_builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@

use proc_macro2::{Ident, Span, TokenStream};
use quote::{format_ident, quote, quote_spanned};
use syn::parse::ParseStream;
use syn::spanned::Spanned;
use syn::{Attribute, Meta, Path, Token, Type, parse_quote};
use synstructure::{BindingInfo, Structure, VariantInfo};
Expand All @@ -11,7 +12,7 @@ use crate::diagnostics::error::{
DiagnosticDeriveError, span_err, throw_invalid_attr, throw_span_err,
};
use crate::diagnostics::utils::{
FieldInfo, FieldInnerTy, FieldMap, HasFieldMap, SetOnce, SpannedOption, SubdiagnosticKind,
FieldInfo, FieldInnerTy, FieldMap, SetOnce, SpannedOption, SubdiagnosticKind,
build_field_mapping, is_doc_comment, report_error_if_not_applied_to_span, report_type_error,
should_generate_arg, type_is_bool, type_is_unit, type_matches_path,
};
Expand Down Expand Up @@ -42,19 +43,13 @@ pub(crate) struct DiagnosticDeriveVariantBuilder {

/// Slug is a mandatory part of the struct attribute as corresponds to the Fluent message that
/// has the actual diagnostic message.
pub slug: SpannedOption<Path>,
pub slug: Option<Path>,

/// Error codes are a optional part of the struct attribute - this is only set to detect
/// multiple specifications.
pub code: SpannedOption<()>,
}

impl HasFieldMap for DiagnosticDeriveVariantBuilder {
fn get_field_binding(&self, field: &String) -> Option<&TokenStream> {
self.field_map.get(field)
}
}

impl DiagnosticDeriveKind {
/// Call `f` for the struct or for each variant of the enum, returning a `TokenStream` with the
/// tokens from `f` wrapped in an `match` expression. Emits errors for use of derive on unions
Expand Down Expand Up @@ -111,7 +106,7 @@ impl DiagnosticDeriveKind {

impl DiagnosticDeriveVariantBuilder {
pub(crate) fn primary_message(&self) -> Option<&Path> {
match self.slug.value_ref() {
match self.slug.as_ref() {
None => {
span_err(self.span, "diagnostic slug not specified")
.help(
Expand Down Expand Up @@ -169,7 +164,7 @@ impl DiagnosticDeriveVariantBuilder {
&self,
attr: &Attribute,
) -> Result<Option<(SubdiagnosticKind, Path, bool)>, DiagnosticDeriveError> {
let Some(subdiag) = SubdiagnosticVariant::from_attr(attr, self)? else {
let Some(subdiag) = SubdiagnosticVariant::from_attr(attr, &self.field_map)? else {
// Some attributes aren't errors - like documentation comments - but also aren't
// subdiagnostics.
return Ok(None);
Expand All @@ -191,7 +186,7 @@ impl DiagnosticDeriveVariantBuilder {
SubdiagnosticKind::MultipartSuggestion { .. } => unreachable!(),
});

Ok(Some((subdiag.kind, slug, subdiag.no_span)))
Ok(Some((subdiag.kind, slug, false)))
}

/// Establishes state in the `DiagnosticDeriveBuilder` resulting from the struct
Expand All @@ -209,47 +204,54 @@ impl DiagnosticDeriveVariantBuilder {
let name = attr.path().segments.last().unwrap().ident.to_string();
let name = name.as_str();

let mut first = true;

if name == "diag" {
let mut tokens = TokenStream::new();
attr.parse_nested_meta(|nested| {
let path = &nested.path;
attr.parse_args_with(|input: ParseStream<'_>| {
let mut input = &*input;
let slug_recovery_point = input.fork();

if first && (nested.input.is_empty() || nested.input.peek(Token![,])) {
self.slug.set_once(path.clone(), path.span().unwrap());
first = false;
return Ok(());
let slug = input.parse::<Path>()?;
if input.is_empty() || input.peek(Token![,]) {
self.slug = Some(slug);
} else {
input = &slug_recovery_point;
}

first = false;

let Ok(nested) = nested.value() else {
span_err(
nested.input.span().unwrap(),
"diagnostic slug must be the first argument",
)
.emit();
return Ok(());
};

if path.is_ident("code") {
self.code.set_once((), path.span().unwrap());

let code = nested.parse::<syn::Expr>()?;
tokens.extend(quote! {
diag.code(#code);
});
} else {
span_err(path.span().unwrap(), "unknown argument")
.note("only the `code` parameter is valid after the slug")
while !input.is_empty() {
input.parse::<Token![,]>()?;
// Allow trailing comma
if input.is_empty() {
break;
}
let arg_name: Path = input.parse::<Path>()?;
if input.peek(Token![,]) {
span_err(
arg_name.span().unwrap(),
"diagnostic slug must be the first argument",
)
.emit();

// consume the buffer so we don't have syntax errors from syn
let _ = nested.parse::<TokenStream>();
continue;
}
let arg_name = arg_name.require_ident()?;
input.parse::<Token![=]>()?;
let arg_value = input.parse::<syn::Expr>()?;
match arg_name.to_string().as_str() {
"code" => {
self.code.set_once((), arg_name.span().unwrap());
tokens.extend(quote! {
diag.code(#arg_value);
});
}
_ => {
span_err(arg_name.span().unwrap(), "unknown argument")
.note("only the `code` parameter is valid after the slug")
.emit();
}
}
}
Ok(())
})?;

return Ok(tokens);
}

Expand Down
90 changes: 44 additions & 46 deletions compiler/rustc_macros/src/diagnostics/subdiagnostic.rs
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Original file line number Diff line number Diff line change
@@ -1,20 +1,21 @@
#![deny(unused_must_use)]

use proc_macro2::TokenStream;
use proc_macro2::{Ident, TokenStream};
use quote::{format_ident, quote};
use syn::parse::ParseStream;
use syn::spanned::Spanned;
use syn::{Attribute, Meta, MetaList, Path};
use syn::{Attribute, Meta, MetaList, Path, Token};
use synstructure::{BindingInfo, Structure, VariantInfo};

use super::utils::SubdiagnosticVariant;
use crate::diagnostics::error::{
DiagnosticDeriveError, invalid_attr, span_err, throw_invalid_attr, throw_span_err,
};
use crate::diagnostics::utils::{
AllowMultipleAlternatives, FieldInfo, FieldInnerTy, FieldMap, HasFieldMap, SetOnce,
SpannedOption, SubdiagnosticKind, build_field_mapping, build_suggestion_code, is_doc_comment,
new_code_ident, report_error_if_not_applied_to_applicability,
report_error_if_not_applied_to_span, should_generate_arg,
AllowMultipleAlternatives, FieldInfo, FieldInnerTy, FieldMap, SetOnce, SpannedOption,
SubdiagnosticKind, build_field_mapping, build_suggestion_code, is_doc_comment, new_code_ident,
report_error_if_not_applied_to_applicability, report_error_if_not_applied_to_span,
should_generate_arg,
};

/// The central struct for constructing the `add_to_diag` method from an annotated struct.
Expand Down Expand Up @@ -142,12 +143,6 @@ struct SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
is_enum: bool,
}

impl<'parent, 'a> HasFieldMap for SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
fn get_field_binding(&self, field: &String) -> Option<&TokenStream> {
self.fields.get(field)
}
}

/// Provides frequently-needed information about the diagnostic kinds being derived for this type.
#[derive(Clone, Copy, Debug)]
struct KindsStatistics {
Expand Down Expand Up @@ -187,14 +182,12 @@ impl<'a> FromIterator<&'a SubdiagnosticKind> for KindsStatistics {
}

impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
fn identify_kind(
&mut self,
) -> Result<Vec<(SubdiagnosticKind, Path, bool)>, DiagnosticDeriveError> {
fn identify_kind(&mut self) -> Result<Vec<(SubdiagnosticKind, Path)>, DiagnosticDeriveError> {
let mut kind_slugs = vec![];

for attr in self.variant.ast().attrs {
let Some(SubdiagnosticVariant { kind, slug, no_span }) =
SubdiagnosticVariant::from_attr(attr, self)?
let Some(SubdiagnosticVariant { kind, slug }) =
SubdiagnosticVariant::from_attr(attr, &self.fields)?
else {
// Some attributes aren't errors - like documentation comments - but also aren't
// subdiagnostics.
Expand All @@ -213,7 +206,7 @@ impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
);
};

kind_slugs.push((kind, slug, no_span));
kind_slugs.push((kind, slug));
}

Ok(kind_slugs)
Expand Down Expand Up @@ -437,23 +430,35 @@ impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {

let mut code = None;

list.parse_nested_meta(|nested| {
if nested.path.is_ident("code") {
let code_field = new_code_ident();
let span = nested.path.span().unwrap();
let formatting_init = build_suggestion_code(
&code_field,
nested,
self,
AllowMultipleAlternatives::No,
);
code.set_once((code_field, formatting_init), span);
} else {
span_err(
nested.path.span().unwrap(),
"`code` is the only valid nested attribute",
)
.emit();
list.parse_args_with(|input: ParseStream<'_>| {
while !input.is_empty() {
let arg_name = input.parse::<Ident>()?;
match arg_name.to_string().as_str() {
"code" => {
let code_field = new_code_ident();
let formatting_init = build_suggestion_code(
&code_field,
input,
&self.fields,
AllowMultipleAlternatives::No,
)?;
code.set_once(
(code_field, formatting_init),
arg_name.span().unwrap(),
);
}
_ => {
span_err(
arg_name.span().unwrap(),
"`code` is the only valid nested attribute",
)
.emit();
}
}
if input.is_empty() {
break;
}
input.parse::<Token![,]>()?;
}
Ok(())
})?;
Expand Down Expand Up @@ -492,8 +497,7 @@ impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
pub(crate) fn into_tokens(&mut self) -> Result<TokenStream, DiagnosticDeriveError> {
let kind_slugs = self.identify_kind()?;

let kind_stats: KindsStatistics =
kind_slugs.iter().map(|(kind, _slug, _no_span)| kind).collect();
let kind_stats: KindsStatistics = kind_slugs.iter().map(|(kind, _slug)| kind).collect();

let init = if kind_stats.has_multipart_suggestion {
quote! { let mut suggestions = Vec::new(); }
Expand Down Expand Up @@ -526,17 +530,13 @@ impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {

let diag = &self.parent.diag;
let mut calls = TokenStream::new();
for (kind, slug, no_span) in kind_slugs {
for (kind, slug) in kind_slugs {
let message = format_ident!("__message");
calls.extend(
quote! { let #message = #diag.eagerly_translate(crate::fluent_generated::#slug); },
);

let name = format_ident!(
"{}{}",
if span_field.is_some() && !no_span { "span_" } else { "" },
kind
);
let name = format_ident!("{}{}", if span_field.is_some() { "span_" } else { "" }, kind);
let call = match kind {
SubdiagnosticKind::Suggestion {
suggestion_kind,
Expand Down Expand Up @@ -588,9 +588,7 @@ impl<'parent, 'a> SubdiagnosticDeriveVariantBuilder<'parent, 'a> {
}
}
_ => {
if let Some(span) = span_field
&& !no_span
{
if let Some(span) = span_field {
quote! { #diag.#name(#span, #message); }
} else {
quote! { #diag.#name(#message); }
Expand Down
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