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Merged
rust-bors merged 4 commits into from
Apr 3, 2026
Merged

Improve workings of the desc query modifier and custom query cycle handlers #154698

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nnethercote Mar 16, 2026
aebce4c
Process query modifiers in alphabetical order everywhere.
nnethercote Apr 2, 2026
d913766
Remove the `_description_fns` module.
nnethercote Mar 16, 2026
15c6e6e
Add a `handle_cycle_error` query modifier.
nnethercote Apr 1, 2026
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112 changes: 48 additions & 64 deletions compiler/rustc_macros/src/query.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -128,6 +128,7 @@ impl<T: Parse> Parse for List<T> {
}

struct Desc {
// This ident is always `desc` but we need it for its span, for `crate::query::modifiers`.
modifier: Ident,
expr_list: Punctuated<Expr, Token![,]>,
}
Expand All @@ -141,22 +142,26 @@ struct QueryModifiers {
desc: Desc,
eval_always: Option<Ident>,
feedable: Option<Ident>,
handle_cycle_error: Option<Ident>,
no_force: Option<Ident>,
no_hash: Option<Ident>,
separate_provide_extern: Option<Ident>,
// tidy-alphabetical-end
}

fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
// tidy-alphabetical-start
let mut arena_cache = None;
let mut cache_on_disk = None;
let mut depth_limit = None;
let mut desc = None;
let mut eval_always = None;
let mut feedable = None;
let mut handle_cycle_error = None;
let mut no_force = None;
let mut no_hash = None;
let mut eval_always = None;
let mut depth_limit = None;
let mut separate_provide_extern = None;
let mut feedable = None;
// tidy-alphabetical-end

while !input.is_empty() {
let modifier: Ident = input.parse()?;
Expand All @@ -170,29 +175,31 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
};
}

if modifier == "desc" {
if modifier == "arena_cache" {
try_insert!(arena_cache = modifier);
} else if modifier == "cache_on_disk" {
try_insert!(cache_on_disk = modifier);
} else if modifier == "depth_limit" {
try_insert!(depth_limit = modifier);
} else if modifier == "desc" {
// Parse a description modifier like:
// `desc { "foo {}", tcx.item_path(key) }`
let attr_content;
braced!(attr_content in input);
let expr_list = attr_content.parse_terminated(Expr::parse, Token![,])?;
try_insert!(desc = Desc { modifier, expr_list });
} else if modifier == "cache_on_disk" {
try_insert!(cache_on_disk = modifier);
} else if modifier == "arena_cache" {
try_insert!(arena_cache = modifier);
} else if modifier == "eval_always" {
try_insert!(eval_always = modifier);
} else if modifier == "feedable" {
try_insert!(feedable = modifier);
} else if modifier == "handle_cycle_error" {
try_insert!(handle_cycle_error = modifier);
} else if modifier == "no_force" {
try_insert!(no_force = modifier);
} else if modifier == "no_hash" {
try_insert!(no_hash = modifier);
} else if modifier == "eval_always" {
try_insert!(eval_always = modifier);
} else if modifier == "depth_limit" {
try_insert!(depth_limit = modifier);
} else if modifier == "separate_provide_extern" {
try_insert!(separate_provide_extern = modifier);
} else if modifier == "feedable" {
try_insert!(feedable = modifier);
} else {
return Err(Error::new(modifier.span(), "unknown query modifier"));
}
Expand All @@ -201,15 +208,18 @@ fn parse_query_modifiers(input: ParseStream<'_>) -> Result<QueryModifiers> {
return Err(input.error("no description provided"));
};
Ok(QueryModifiers {
// tidy-alphabetical-start
arena_cache,
cache_on_disk,
depth_limit,
desc,
eval_always,
feedable,
handle_cycle_error,
no_force,
no_hash,
eval_always,
depth_limit,
separate_provide_extern,
feedable,
// tidy-alphabetical-end
})
}

Expand Down Expand Up @@ -238,24 +248,40 @@ fn make_modifiers_stream(query: &Query) -> proc_macro2::TokenStream {
arena_cache,
cache_on_disk,
depth_limit,
desc: _,
desc,
eval_always,
feedable,
handle_cycle_error,
no_force,
no_hash,
separate_provide_extern,
// tidy-alphabetical-end
} = &query.modifiers;

// tidy-alphabetical-start
let arena_cache = arena_cache.is_some();
let cache_on_disk = cache_on_disk.is_some();
let depth_limit = depth_limit.is_some();
let desc = {
// Put a description closure in the `desc` modifier.
let key_pat = &query.key_pat;
let key_ty = &query.key_ty;
let desc_expr_list = &desc.expr_list;
quote! {
{
#[allow(unused_variables)]
|tcx: TyCtxt<'tcx>, #key_pat: #key_ty| format!(#desc_expr_list)
}
}
};
let eval_always = eval_always.is_some();
let feedable = feedable.is_some();
let handle_cycle_error = handle_cycle_error.is_some();
let no_force = no_force.is_some();
let no_hash = no_hash.is_some();
let returns_error_guaranteed = returns_error_guaranteed(&query.return_ty);
let separate_provide_extern = separate_provide_extern.is_some();
// tidy-alphabetical-end

// Giving an input span to the modifier names in the modifier list seems
// to give slightly more helpful errors when one of the callback macros
Expand All @@ -268,8 +294,10 @@ fn make_modifiers_stream(query: &Query) -> proc_macro2::TokenStream {
arena_cache: #arena_cache,
cache_on_disk: #cache_on_disk,
depth_limit: #depth_limit,
desc: #desc,
eval_always: #eval_always,
feedable: #feedable,
handle_cycle_error: #handle_cycle_error,
no_force: #no_force,
no_hash: #no_hash,
returns_error_guaranteed: #returns_error_guaranteed,
Expand Down Expand Up @@ -305,37 +333,6 @@ fn doc_comment_from_desc(list: &Punctuated<Expr, token::Comma>) -> Result<Attrib
Ok(parse_quote! { #[doc = #doc_string] })
}

/// Contains token streams that are used to accumulate per-query helper
/// functions, to be used by the final output of `rustc_queries!`.
///
/// Helper items typically have the same name as the query they relate to,
/// and expect to be interpolated into a dedicated module.
#[derive(Default)]
struct HelperTokenStreams {
description_fns_stream: proc_macro2::TokenStream,
}

fn make_helpers_for_query(query: &Query, streams: &mut HelperTokenStreams) {
let Query { name, key_pat, key_ty, modifiers, .. } = &query;

// Replace span for `name` to make rust-analyzer ignore it.
let mut erased_name = name.clone();
erased_name.set_span(Span::call_site());

let Desc { expr_list, .. } = &modifiers.desc;

let desc = quote! {
#[allow(unused_variables)]
pub fn #erased_name<'tcx>(tcx: TyCtxt<'tcx>, #key_pat: #key_ty) -> String {
format!(#expr_list)
}
};

streams.description_fns_stream.extend(quote! {
#desc
});
}

/// Add hints for rust-analyzer
fn add_to_analyzer_stream(query: &Query, analyzer_stream: &mut proc_macro2::TokenStream) {
// Add links to relevant modifiers
Expand Down Expand Up @@ -366,8 +363,10 @@ fn add_to_analyzer_stream(query: &Query, analyzer_stream: &mut proc_macro2::Toke
arena_cache,
cache_on_disk,
depth_limit,
// `desc` is handled above
eval_always,
feedable,
handle_cycle_error,
no_force,
no_hash,
separate_provide_extern,
Expand Down Expand Up @@ -409,7 +408,6 @@ pub(super) fn rustc_queries(input: TokenStream) -> TokenStream {

let mut query_stream = quote! {};
let mut non_query_stream = quote! {};
let mut helpers = HelperTokenStreams::default();
let mut analyzer_stream = quote! {};
let mut errors = quote! {};

Expand Down Expand Up @@ -462,11 +460,8 @@ pub(super) fn rustc_queries(input: TokenStream) -> TokenStream {
}

add_to_analyzer_stream(&query, &mut analyzer_stream);
make_helpers_for_query(&query, &mut helpers);
}

let HelperTokenStreams { description_fns_stream } = helpers;

TokenStream::from(quote! {
/// Higher-order macro that invokes the specified macro with (a) a list of all query
/// signatures (including modifiers), and (b) a list of non-query names. This allows
Expand All @@ -490,17 +485,6 @@ pub(super) fn rustc_queries(input: TokenStream) -> TokenStream {
#analyzer_stream
}

/// Functions that format a human-readable description of each query
/// and its key, as specified by the `desc` query modifier.
///
/// (The leading `_` avoids collisions with actual query names when
/// expanded in `rustc_middle::queries`, and makes this macro-generated
/// module easier to search for.)
pub mod _description_fns {
use super::*;
#description_fns_stream
}

#errors
})
}
5 changes: 5 additions & 0 deletions compiler/rustc_middle/src/queries.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -583,6 +583,7 @@ rustc_queries! {
// messages about cycles that then abort.)
query check_representability(key: LocalDefId) {
desc { "checking if `{}` is representable", tcx.def_path_str(key) }
handle_cycle_error
// We don't want recursive representability calls to be forced with
// incremental compilation because, if a cycle occurs, we need the
// entire cycle to be in memory for diagnostics.
Expand All @@ -593,6 +594,7 @@ rustc_queries! {
/// details, particularly on the modifiers.
query check_representability_adt_ty(key: Ty<'tcx>) {
desc { "checking if `{}` is representable", key }
handle_cycle_error
no_force
}

Expand Down Expand Up @@ -1032,6 +1034,7 @@ rustc_queries! {
query variances_of(def_id: DefId) -> &'tcx [ty::Variance] {
desc { "computing the variances of `{}`", tcx.def_path_str(def_id) }
cache_on_disk
handle_cycle_error
separate_provide_extern
}

Expand Down Expand Up @@ -1164,6 +1167,7 @@ rustc_queries! {
query fn_sig(key: DefId) -> ty::EarlyBinder<'tcx, ty::PolyFnSig<'tcx>> {
desc { "computing function signature of `{}`", tcx.def_path_str(key) }
cache_on_disk
handle_cycle_error
separate_provide_extern
}

Expand Down Expand Up @@ -1756,6 +1760,7 @@ rustc_queries! {
) -> Result<ty::layout::TyAndLayout<'tcx>, &'tcx ty::layout::LayoutError<'tcx>> {
depth_limit
desc { "computing layout of `{}`", key.value }
handle_cycle_error
}

/// Compute a `FnAbi` suitable for indirect calls, i.e. to `fn` pointers.
Expand Down
8 changes: 8 additions & 0 deletions compiler/rustc_middle/src/query/modifiers.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -58,6 +58,14 @@ pub(crate) struct eval_always;
/// Generate a `feed` method to set the query's value from another query.
pub(crate) struct feedable;

/// # `handle_cycle_error` query modifier
///
/// The default behaviour for a query cycle is to emit a cycle error and halt
/// compilation. Queries with this modifier will instead use a custom handler,
/// which must be provided at `rustc_query_impl::handle_cycle_error::$name`,
/// where `$name` is the query name.
pub(crate) struct handle_cycle_error;

/// # `no_force` query modifier
///
/// Dep nodes of queries with this modifier will never be "forced" when trying
Expand Down
5 changes: 3 additions & 2 deletions compiler/rustc_middle/src/query/plumbing.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -301,8 +301,10 @@ macro_rules! define_callbacks {
arena_cache: $arena_cache:literal,
cache_on_disk: $cache_on_disk:literal,
depth_limit: $depth_limit:literal,
desc: $desc:expr,
eval_always: $eval_always:literal,
feedable: $feedable:literal,
handle_cycle_error: $handle_cycle_error:literal,
no_force: $no_force:literal,
no_hash: $no_hash:literal,
returns_error_guaranteed: $returns_error_guaranteed:literal,
Expand Down Expand Up @@ -435,8 +437,7 @@ macro_rules! define_callbacks {
pub fn description(&self, tcx: TyCtxt<'tcx>) -> String {
let (name, description) = ty::print::with_no_queries!(match self {
$(
TaggedQueryKey::$name(key) =>
(stringify!($name), _description_fns::$name(tcx, *key)),
TaggedQueryKey::$name(key) => (stringify!($name), ($desc)(tcx, *key)),
)*
});
if tcx.sess.verbose_internals() {
Expand Down
2 changes: 2 additions & 0 deletions compiler/rustc_query_impl/src/dep_kind_vtables.rs
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Expand Up @@ -135,8 +135,10 @@ macro_rules! define_dep_kind_vtables {
arena_cache: $arena_cache:literal,
cache_on_disk: $cache_on_disk:literal,
depth_limit: $depth_limit:literal,
desc: $desc:expr,
eval_always: $eval_always:literal,
feedable: $feedable:literal,
handle_cycle_error: $handle_cycle_error:literal,
no_force: $no_force:literal,
no_hash: $no_hash:literal,
returns_error_guaranteed: $returns_error_guaranteed:literal,
Expand Down
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