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Allow #[must_use] on associated types to warn on unused values in generic contexts #142590

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Allow #[must_use] on associated types to warn on unused values in generic contexts #142590

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a2fb8e7
Allow must_use on associated types
compiler-errors Jun 16, 2025
bb19361
Fix some unused fields in AST visitor
compiler-errors Jun 16, 2025
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1 change: 1 addition & 0 deletions compiler/rustc_ast/src/mut_visit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,7 @@ mod sealed {

/// This is for compatibility with the regular `Visitor`.
pub trait MutVisitorResult {
#[cfg_attr(not(bootstrap), must_use)]
type Result: VisitorResult;
}

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7 changes: 4 additions & 3 deletions compiler/rustc_ast/src/visit.rs
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Expand Up @@ -130,6 +130,7 @@ pub enum LifetimeCtxt {
pub trait Visitor<'ast>: Sized {
/// The result type of the `visit_*` methods. Can be either `()`,
/// or `ControlFlow<T>`.
#[cfg_attr(not(bootstrap), must_use)]
type Result: VisitorResult = ();

fn visit_ident(&mut self, _ident: &'ast Ident) -> Self::Result {
Expand Down Expand Up @@ -884,7 +885,7 @@ macro_rules! common_visitor_and_walkers {
TyKind::BareFn(function_declaration) => {
let BareFnTy { safety, ext: _, generic_params, decl, decl_span } =
&$($mut)? **function_declaration;
visit_safety(vis, safety);
try_visit!(visit_safety(vis, safety));
try_visit!(visit_generic_params(vis, generic_params));
try_visit!(vis.visit_fn_decl(decl));
try_visit!(visit_span(vis, decl_span));
Expand Down Expand Up @@ -1235,7 +1236,7 @@ macro_rules! common_visitor_and_walkers {
bounds,
bound_generic_params,
}) => {
visit_generic_params(vis, bound_generic_params);
try_visit!(visit_generic_params(vis, bound_generic_params));
try_visit!(vis.visit_ty(bounded_ty));
walk_list!(vis, visit_param_bound, bounds, BoundKind::Bound);
}
Expand Down Expand Up @@ -1420,7 +1421,7 @@ macro_rules! common_visitor_and_walkers {
let StructExpr { qself, path, fields, rest } = &$($mut)?**se;
try_visit!(vis.visit_qself(qself));
try_visit!(vis.visit_path(path));
visit_expr_fields(vis, fields);
try_visit!(visit_expr_fields(vis, fields));
match rest {
StructRest::Base(expr) => try_visit!(vis.visit_expr(expr)),
StructRest::Rest(_span) => {}
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1 change: 1 addition & 0 deletions compiler/rustc_hir/src/intravisit.rs
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Expand Up @@ -224,6 +224,7 @@ pub trait Visitor<'v>: Sized {

/// The result type of the `visit_*` methods. Can be either `()`,
/// or `ControlFlow<T>`.
#[cfg_attr(not(bootstrap), must_use)]
type Result: VisitorResult = ();

/// If `type NestedFilter` is set to visit nested items, this method
Expand Down
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