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refactor(needless_arbitrary_self_type): give suggestions with finer diffs #16005

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84fd155
clean-up
ada4a Nov 1, 2025
b698bc2
give suggestions with finer diffs
ada4a Nov 1, 2025
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108 changes: 48 additions & 60 deletions clippy_lints/src/needless_arbitrary_self_type.rs
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Original file line number Diff line number Diff line change
@@ -1,10 +1,9 @@
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::source::snippet_with_applicability;
use rustc_ast::ast::{BindingMode, ByRef, Lifetime, Mutability, Param, PatKind, Path, TyKind};
use rustc_ast::ast::{BindingMode, ByRef, Lifetime, Param, PatKind, TyKind};
use rustc_errors::Applicability;
use rustc_lint::{EarlyContext, EarlyLintPass};
use rustc_session::declare_lint_pass;
use rustc_span::Span;
use rustc_span::symbol::kw;

declare_clippy_lint! {
Expand Down Expand Up @@ -65,73 +64,62 @@ enum Mode {
Value,
}

fn check_param_inner(cx: &EarlyContext<'_>, path: &Path, span: Span, binding_mode: &Mode, mutbl: Mutability) {
if let [segment] = &path.segments[..]
&& segment.ident.name == kw::SelfUpper
{
// In case we have a named lifetime, we check if the name comes from expansion.
// If it does, at this point we know the rest of the parameter was written by the user,
// so let them decide what the name of the lifetime should be.
// See #6089 for more details.
let mut applicability = Applicability::MachineApplicable;
let self_param = match (binding_mode, mutbl) {
(Mode::Ref(None), Mutability::Mut) => "&mut self".to_string(),
(Mode::Ref(Some(lifetime)), Mutability::Mut) => {
if lifetime.ident.span.from_expansion() {
applicability = Applicability::HasPlaceholders;
"&'_ mut self".to_string()
} else {
let lt_name = snippet_with_applicability(cx, lifetime.ident.span, "..", &mut applicability);
format!("&{lt_name} mut self")
}
},
(Mode::Ref(None), Mutability::Not) => "&self".to_string(),
(Mode::Ref(Some(lifetime)), Mutability::Not) => {
if lifetime.ident.span.from_expansion() {
applicability = Applicability::HasPlaceholders;
"&'_ self".to_string()
} else {
let lt_name = snippet_with_applicability(cx, lifetime.ident.span, "..", &mut applicability);
format!("&{lt_name} self")
}
},
(Mode::Value, Mutability::Mut) => "mut self".to_string(),
(Mode::Value, Mutability::Not) => "self".to_string(),
};

span_lint_and_sugg(
cx,
NEEDLESS_ARBITRARY_SELF_TYPE,
span,
"the type of the `self` parameter does not need to be arbitrary",
"consider to change this parameter to",
self_param,
applicability,
);
}
}

impl EarlyLintPass for NeedlessArbitrarySelfType {
fn check_param(&mut self, cx: &EarlyContext<'_>, p: &Param) {
// Bail out if the parameter it's not a receiver or was not written by the user
if !p.is_self() || p.span.from_expansion() {
return;
}

match &p.ty.kind {
TyKind::Path(None, path) => {
if let PatKind::Ident(BindingMode(ByRef::No, mutbl), _, _) = p.pat.kind {
check_param_inner(cx, path, p.span.to(p.ty.span), &Mode::Value, mutbl);
}
let (path, binding_mode, mutbl) = match &p.ty.kind {
TyKind::Path(None, path) if let PatKind::Ident(BindingMode(ByRef::No, mutbl), _, _) = p.pat.kind => {
(path, Mode::Value, mutbl)
},
TyKind::Ref(lifetime, mut_ty) => {
TyKind::Ref(lifetime, mut_ty)
if let TyKind::Path(None, path) = &mut_ty.ty.kind
&& let PatKind::Ident(BindingMode::NONE, _, _) = p.pat.kind
{
check_param_inner(cx, path, p.span.to(p.ty.span), &Mode::Ref(*lifetime), mut_ty.mutbl);
}
&& let PatKind::Ident(BindingMode::NONE, _, _) = p.pat.kind =>
{
(path, Mode::Ref(*lifetime), mut_ty.mutbl)
},
_ => {},
_ => return,
};

let span = p.span.to(p.ty.span);
if let [segment] = &path.segments[..]
&& segment.ident.name == kw::SelfUpper
{
span_lint_and_then(
cx,
NEEDLESS_ARBITRARY_SELF_TYPE,
span,
"the type of the `self` parameter does not need to be arbitrary",
|diag| {
let mut applicability = Applicability::MachineApplicable;
let add = match binding_mode {
Mode::Value => String::new(),
Mode::Ref(None) => mutbl.ref_prefix_str().to_string(),
Mode::Ref(Some(lifetime)) => {
// In case we have a named lifetime, we check if the name comes from expansion.
// If it does, at this point we know the rest of the parameter was written by the user,
// so let them decide what the name of the lifetime should be.
// See #6089 for more details.
let lt_name = if lifetime.ident.span.from_expansion() {
applicability = Applicability::HasPlaceholders;
"'_".into()
} else {
snippet_with_applicability(cx, lifetime.ident.span, "'_", &mut applicability)
};
format!("&{lt_name} {mut_}", mut_ = mutbl.prefix_str())
},
};

let mut sugg = vec![(p.ty.span.with_lo(p.span.hi()), String::new())];
if !add.is_empty() {
sugg.push((p.span.shrink_to_lo(), add));
}
diag.multipart_suggestion_verbose("remove the type", sugg, applicability);
},
);
}
}
}
63 changes: 55 additions & 8 deletions tests/ui/needless_arbitrary_self_type.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,52 +2,99 @@ error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type.rs:10:16
|
LL | pub fn bad(self: Self) {
| ^^^^^^^^^^ help: consider to change this parameter to: `self`
| ^^^^^^^^^^
|
= note: `-D clippy::needless-arbitrary-self-type` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::needless_arbitrary_self_type)]`
help: remove the type
|
LL - pub fn bad(self: Self) {
LL + pub fn bad(self) {
|

error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type.rs:19:20
|
LL | pub fn mut_bad(mut self: Self) {
| ^^^^^^^^^^^^^^ help: consider to change this parameter to: `mut self`
| ^^^^^^^^^^^^^^
|
help: remove the type
|
LL - pub fn mut_bad(mut self: Self) {
LL + pub fn mut_bad(mut self) {
|

error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type.rs:28:20
|
LL | pub fn ref_bad(self: &Self) {
| ^^^^^^^^^^^ help: consider to change this parameter to: `&self`
| ^^^^^^^^^^^
|
help: remove the type
|
LL - pub fn ref_bad(self: &Self) {
LL + pub fn ref_bad(&self) {
|

error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type.rs:37:38
|
LL | pub fn ref_bad_with_lifetime<'a>(self: &'a Self) {
| ^^^^^^^^^^^^^^ help: consider to change this parameter to: `&'a self`
| ^^^^^^^^^^^^^^
|
help: remove the type
|
LL - pub fn ref_bad_with_lifetime<'a>(self: &'a Self) {
LL + pub fn ref_bad_with_lifetime<'a>(&'a self) {
|

error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type.rs:46:24
|
LL | pub fn mut_ref_bad(self: &mut Self) {
| ^^^^^^^^^^^^^^^ help: consider to change this parameter to: `&mut self`
| ^^^^^^^^^^^^^^^
|
help: remove the type
|
LL - pub fn mut_ref_bad(self: &mut Self) {
LL + pub fn mut_ref_bad(&mut self) {
|

error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type.rs:55:42
|
LL | pub fn mut_ref_bad_with_lifetime<'a>(self: &'a mut Self) {
| ^^^^^^^^^^^^^^^^^^ help: consider to change this parameter to: `&'a mut self`
| ^^^^^^^^^^^^^^^^^^
|
help: remove the type
|
LL - pub fn mut_ref_bad_with_lifetime<'a>(self: &'a mut Self) {
LL + pub fn mut_ref_bad_with_lifetime<'a>(&'a mut self) {
|

error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type.rs:74:11
|
LL | fn f1(self: &'r#struct Self) {}
| ^^^^^^^^^^^^^^^^^^^^^ help: consider to change this parameter to: `&'r#struct self`
| ^^^^^^^^^^^^^^^^^^^^^
|
help: remove the type
|
LL - fn f1(self: &'r#struct Self) {}
LL + fn f1(&'r#struct self) {}
|

error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type.rs:76:11
|
LL | fn f2(self: &'r#struct mut Self) {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider to change this parameter to: `&'r#struct mut self`
| ^^^^^^^^^^^^^^^^^^^^^^^^^
|
help: remove the type
|
LL - fn f2(self: &'r#struct mut Self) {}
LL + fn f2(&'r#struct mut self) {}
|

error: aborting due to 8 previous errors

7 changes: 6 additions & 1 deletion tests/ui/needless_arbitrary_self_type_unfixable.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -2,10 +2,15 @@ error: the type of the `self` parameter does not need to be arbitrary
--> tests/ui/needless_arbitrary_self_type_unfixable.rs:42:31
|
LL | fn call_with_mut_self(self: &mut Self) {}
| ^^^^^^^^^^^^^^^ help: consider to change this parameter to: `&mut self`
| ^^^^^^^^^^^^^^^
|
= note: `-D clippy::needless-arbitrary-self-type` implied by `-D warnings`
= help: to override `-D warnings` add `#[allow(clippy::needless_arbitrary_self_type)]`
help: remove the type
|
LL - fn call_with_mut_self(self: &mut Self) {}
LL + fn call_with_mut_self(&mut self) {}
|

error: aborting due to 1 previous error