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Merged
rust-bors merged 1 commit into from
Mar 3, 2026
Merged

Implement AST -> HIR generics propagation in delegation #151864

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147 changes: 124 additions & 23 deletions compiler/rustc_ast_lowering/src/delegation.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,7 +46,6 @@ use rustc_ast::*;
use rustc_attr_parsing::{AttributeParser, ShouldEmit};
use rustc_data_structures::fx::FxHashSet;
use rustc_errors::ErrorGuaranteed;
use rustc_hir::Target;
use rustc_hir::attrs::{AttributeKind, InlineAttr};
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_middle::span_bug;
Expand All @@ -56,9 +55,14 @@ use rustc_span::{DUMMY_SP, Ident, Span, Symbol};
use smallvec::SmallVec;
use {rustc_ast as ast, rustc_hir as hir};

use super::{GenericArgsMode, ImplTraitContext, LoweringContext, ParamMode};
use crate::delegation::generics::{GenericsGenerationResult, GenericsGenerationResults};
use crate::errors::{CycleInDelegationSignatureResolution, UnresolvedDelegationCallee};
use crate::{AllowReturnTypeNotation, ImplTraitPosition, ResolverAstLoweringExt};
use crate::{
AllowReturnTypeNotation, GenericArgsMode, ImplTraitContext, ImplTraitPosition, LoweringContext,
ParamMode, ResolverAstLoweringExt,
};

mod generics;

pub(crate) struct DelegationResults<'hir> {
pub body_id: hir::BodyId,
Expand Down Expand Up @@ -184,18 +188,48 @@ impl<'hir> LoweringContext<'_, 'hir> {
// we need a function to extract this information
let (param_count, c_variadic) = self.param_count(root_function_id);

let mut generics = self.lower_delegation_generics(
delegation,
ids.root_function_id(),
item_id,
span,
);

let body_id = self.lower_delegation_body(
delegation,
item_id,
is_method,
param_count,
&mut generics,
span,
);

// Here we use `delegee_id`, as this id will then be used to calculate parent for generics
// inheritance, and we want this id to point on a delegee, not on the original
// function (see https://github.com/rust-lang/rust/issues/150152#issuecomment-3674834654)
let decl = self.lower_delegation_decl(delegee_id, param_count, c_variadic, span);
let decl = self.lower_delegation_decl(
delegee_id,
param_count,
c_variadic,
span,
&generics,
);

// Here we pass `root_function_id` as we want to inherit signature (including consts, async)
// from the root function that started delegation
let sig = self.lower_delegation_sig(root_function_id, decl, span);

let body_id = self.lower_delegation_body(delegation, is_method, param_count, span);
let ident = self.lower_ident(delegation.ident);
let generics = self.lower_delegation_generics(span);

let generics = self.arena.alloc(hir::Generics {
has_where_clause_predicates: false,
params: self.arena.alloc_from_iter(generics.all_params(item_id, span, self)),
predicates: self
.arena
.alloc_from_iter(generics.all_predicates(item_id, span, self)),
span,
where_clause_span: span,
});

DelegationResults { body_id, sig, ident, generics }
}
Err(err) => self.generate_delegation_error(err, span, delegation),
Expand Down Expand Up @@ -295,7 +329,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
self.tcx.sess,
attrs,
None,
Target::Fn,
hir::Target::Fn,
DUMMY_SP,
DUMMY_NODE_ID,
Some(self.tcx.features()),
Expand Down Expand Up @@ -364,16 +398,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
self.resolver.get_partial_res(node_id).and_then(|r| r.expect_full_res().opt_def_id())
}

fn lower_delegation_generics(&mut self, span: Span) -> &'hir hir::Generics<'hir> {
self.arena.alloc(hir::Generics {
params: &[],
predicates: &[],
has_where_clause_predicates: false,
where_clause_span: span,
span,
})
}

// Function parameter count, including C variadic `...` if present.
fn param_count(&self, def_id: DefId) -> (usize, bool /*c_variadic*/) {
if let Some(local_sig_id) = def_id.as_local() {
Expand All @@ -393,6 +417,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
param_count: usize,
c_variadic: bool,
span: Span,
generics: &GenericsGenerationResults<'hir>,
) -> &'hir hir::FnDecl<'hir> {
// The last parameter in C variadic functions is skipped in the signature,
// like during regular lowering.
Expand All @@ -405,7 +430,13 @@ impl<'hir> LoweringContext<'_, 'hir> {

let output = self.arena.alloc(hir::Ty {
hir_id: self.next_id(),
kind: hir::TyKind::InferDelegation(sig_id, hir::InferDelegationKind::Output),
kind: hir::TyKind::InferDelegation(
sig_id,
hir::InferDelegationKind::Output(self.arena.alloc(hir::DelegationGenerics {
child_args_segment_id: generics.child.args_segment_id,
parent_args_segment_id: generics.parent.args_segment_id,
})),
),
span,
});

Expand Down Expand Up @@ -460,6 +491,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
abi: sig.abi,
}
};

hir::FnSig { decl, header, span }
}

Expand Down Expand Up @@ -501,6 +533,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
} else {
Symbol::intern(&format!("arg{idx}"))
};

let segments = self.arena.alloc_from_iter(iter::once(hir::PathSegment {
ident: Ident::with_dummy_span(name),
hir_id: self.next_id(),
Expand All @@ -516,8 +549,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
fn lower_delegation_body(
&mut self,
delegation: &Delegation,
item_id: NodeId,
is_method: bool,
param_count: usize,
generics: &mut GenericsGenerationResults<'hir>,
span: Span,
) -> BodyId {
let block = delegation.body.as_deref();
Expand Down Expand Up @@ -548,7 +583,8 @@ impl<'hir> LoweringContext<'_, 'hir> {
args.push(arg);
}

let final_expr = this.finalize_body_lowering(delegation, args, span);
let final_expr = this.finalize_body_lowering(delegation, item_id, args, generics, span);

(this.arena.alloc_from_iter(parameters), final_expr)
})
}
Expand Down Expand Up @@ -584,7 +620,9 @@ impl<'hir> LoweringContext<'_, 'hir> {
fn finalize_body_lowering(
&mut self,
delegation: &Delegation,
item_id: NodeId,
args: Vec<hir::Expr<'hir>>,
generics: &mut GenericsGenerationResults<'hir>,
span: Span,
) -> hir::Expr<'hir> {
let args = self.arena.alloc_from_iter(args);
Expand All @@ -609,6 +647,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
ImplTraitContext::Disallowed(ImplTraitPosition::Path),
None,
);

// FIXME(fn_delegation): proper support for parent generics propagation
// in method call scenario.
let segment = self.process_segment(item_id, span, &segment, &mut generics.child, false);
let segment = self.arena.alloc(segment);

self.arena.alloc(hir::Expr {
Expand All @@ -627,9 +669,41 @@ impl<'hir> LoweringContext<'_, 'hir> {
None,
);

let callee_path = self.arena.alloc(self.mk_expr(hir::ExprKind::Path(path), span));
let new_path = match path {
hir::QPath::Resolved(ty, path) => {
let mut new_path = path.clone();
let len = new_path.segments.len();

new_path.segments = self.arena.alloc_from_iter(
new_path.segments.iter().enumerate().map(|(idx, segment)| {
let mut process_segment = |result, add_lifetimes| {
self.process_segment(item_id, span, segment, result, add_lifetimes)
};

if idx + 2 == len {
process_segment(&mut generics.parent, true)
} else if idx + 1 == len {
process_segment(&mut generics.child, false)
} else {
segment.clone()
}
}),
);

hir::QPath::Resolved(ty, self.arena.alloc(new_path))
}
hir::QPath::TypeRelative(ty, segment) => {
let segment =
self.process_segment(item_id, span, segment, &mut generics.child, false);

hir::QPath::TypeRelative(ty, self.arena.alloc(segment))
}
};

let callee_path = self.arena.alloc(self.mk_expr(hir::ExprKind::Path(new_path), span));
self.arena.alloc(self.mk_expr(hir::ExprKind::Call(callee_path, args), span))
};

let block = self.arena.alloc(hir::Block {
stmts: &[],
expr: Some(call),
Expand All @@ -642,14 +716,40 @@ impl<'hir> LoweringContext<'_, 'hir> {
self.mk_expr(hir::ExprKind::Block(block, None), span)
}

fn process_segment(
&mut self,
item_id: NodeId,
span: Span,
segment: &hir::PathSegment<'hir>,
result: &mut GenericsGenerationResult<'hir>,
add_lifetimes: bool,
) -> hir::PathSegment<'hir> {
// The first condition is needed when there is SelfAndUserSpecified case,
// we don't want to propagate generics params in this situation.
let segment = if !result.generics.is_user_specified()
&& let Some(args) = result
.generics
.into_hir_generics(self, item_id, span)
.into_generic_args(self, add_lifetimes, span)
{
hir::PathSegment { args: Some(args), ..segment.clone() }
} else {
segment.clone()
};

if result.generics.is_user_specified() {
result.args_segment_id = Some(segment.hir_id);
}

segment
}

fn generate_delegation_error(
&mut self,
err: ErrorGuaranteed,
span: Span,
delegation: &Delegation,
) -> DelegationResults<'hir> {
let generics = self.lower_delegation_generics(span);

let decl = self.arena.alloc(hir::FnDecl {
inputs: &[],
output: hir::FnRetTy::DefaultReturn(span),
Expand Down Expand Up @@ -696,6 +796,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
(&[], this.mk_expr(body_expr, span))
});

let generics = hir::Generics::empty();
DelegationResults { ident, generics, body_id, sig }
}

Expand Down
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