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Make trivial-copy-size-limit consistently the size of the target pointer (#13319)

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Fixes
https://rust-lang.zulipchat.com/#narrow/stream/257328-clippy/topic/Ambiguous.20default.20value.20for.20.60trivial-copy-size-limit.60

The current situation is

| Target width | `trivial-copy-size-limit`|
|--------|--------|
| 8-bit | 2 |
| 16-bit | 4 |
| 32-bit | 8 |
| 64-bit | 8 |

~~Since practically speaking it's almost always 8, let's go with that as
the unconditional default to make it easier to understand~~

Now defaults to `target_pointer_width`

changelog: [`trivial-copy-size-limit`] now also defaults to the size of
a target pointer (unchanged for 64-bit targets)
This commit is contained in:
Jason Newcomb 2025-05-21 20:05:31 +00:00 • committed by GitHub
commit 9fa448a119
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GPG key ID: B5690EEEBB952194
6 changed files with 251 additions and 94 deletions
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2
book/src/lint_configuration.md
View file

@ -1026,7 +1026,7 @@ The order of associated items in traits.
The maximum size (in bytes) to consider a `Copy` type for passing by value instead of by
reference.
**Default Value:** `target_pointer_width * 2`
**Default Value:** `target_pointer_width`
---
**Affected lints:**

2
clippy_config/src/conf.rs
View file

@ -828,7 +828,7 @@ define_Conf! {
trait_assoc_item_kinds_order: SourceItemOrderingTraitAssocItemKinds = DEFAULT_TRAIT_ASSOC_ITEM_KINDS_ORDER.into(),
/// The maximum size (in bytes) to consider a `Copy` type for passing by value instead of by
/// reference.
#[default_text = "target_pointer_width * 2"]
#[default_text = "target_pointer_width"]
#[lints(trivially_copy_pass_by_ref)]
trivial_copy_size_limit: Option<u64> = None,
/// The maximum complexity a type can have

22
clippy_lints/src/pass_by_ref_or_value.rs
View file

@ -1,5 +1,3 @@
use std::{cmp, iter};
use clippy_config::Conf;
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::snippet;
@ -20,6 +18,7 @@ use rustc_middle::ty::{self, RegionKind, TyCtxt};
use rustc_session::impl_lint_pass;
use rustc_span::def_id::LocalDefId;
use rustc_span::{Span, sym};
use std::iter;
declare_clippy_lint! {
/// ### What it does
@ -33,10 +32,8 @@ declare_clippy_lint! {
/// registers.
///
/// ### Known problems
/// This lint is target register size dependent, it is
/// limited to 32-bit to try and reduce portability problems between 32 and
/// 64-bit, but if you are compiling for 8 or 16-bit targets then the limit
/// will be different.
/// This lint is target dependent, some cases will lint on 64-bit targets but
/// not 32-bit or lower targets.
///
/// The configuration option `trivial_copy_size_limit` can be set to override
/// this limit for a project.
@ -112,16 +109,9 @@ pub struct PassByRefOrValue {
impl PassByRefOrValue {
pub fn new(tcx: TyCtxt<'_>, conf: &'static Conf) -> Self {
let ref_min_size = conf.trivial_copy_size_limit.unwrap_or_else(|| {
let bit_width = u64::from(tcx.sess.target.pointer_width);
// Cap the calculated bit width at 32-bits to reduce
// portability problems between 32 and 64-bit targets
let bit_width = cmp::min(bit_width, 32);
#[expect(clippy::integer_division)]
let byte_width = bit_width / 8;
// Use a limit of 2 times the register byte width
byte_width * 2
});
let ref_min_size = conf
.trivial_copy_size_limit
.unwrap_or_else(|| u64::from(tcx.sess.target.pointer_width / 8));
Self {
ref_min_size,

179
tests/ui/trivially_copy_pass_by_ref.fixed Normal file
View file

@ -0,0 +1,179 @@
//@normalize-stderr-test: "\(\d+ byte\)" -> "(N byte)"
//@normalize-stderr-test: "\(limit: \d+ byte\)" -> "(limit: N byte)"
#![deny(clippy::trivially_copy_pass_by_ref)]
#![allow(
clippy::disallowed_names,
clippy::extra_unused_lifetimes,
clippy::needless_lifetimes,
clippy::needless_pass_by_ref_mut,
clippy::redundant_field_names,
clippy::uninlined_format_args
)]
#[derive(Copy, Clone)]
struct Foo(u32);
#[derive(Copy, Clone)]
struct Bar([u8; 24]);
#[derive(Copy, Clone)]
pub struct Color {
pub r: u8,
pub g: u8,
pub b: u8,
pub a: u8,
}
struct FooRef<'a> {
foo: &'a Foo,
}
type Baz = u32;
fn good(a: &mut u32, b: u32, c: &Bar) {}
fn good_return_implicit_lt_ref(foo: &Foo) -> &u32 {
&foo.0
}
#[allow(clippy::needless_lifetimes)]
fn good_return_explicit_lt_ref<'a>(foo: &'a Foo) -> &'a u32 {
&foo.0
}
fn good_return_implicit_lt_struct(foo: &Foo) -> FooRef {
FooRef { foo }
}
#[allow(clippy::needless_lifetimes)]
fn good_return_explicit_lt_struct<'a>(foo: &'a Foo) -> FooRef<'a> {
FooRef { foo }
}
fn bad(x: u32, y: Foo, z: Baz) {}
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
impl Foo {
fn good(self, a: &mut u32, b: u32, c: &Bar) {}
fn good2(&mut self) {}
fn bad(self, x: u32, y: Foo, z: Baz) {}
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
fn bad2(x: u32, y: Foo, z: Baz) {}
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
fn bad_issue7518(self, other: Self) {}
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if
}
impl AsRef<u32> for Foo {
fn as_ref(&self) -> &u32 {
&self.0
}
}
impl Bar {
fn good(&self, a: &mut u32, b: u32, c: &Bar) {}
fn bad2(x: u32, y: Foo, z: Baz) {}
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if
//~| ERROR: this argument (4 byte) is passed by reference, but would be more efficient if
}
trait MyTrait {
fn trait_method(&self, foo: Foo);
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if
}
pub trait MyTrait2 {
fn trait_method2(&self, color: &Color);
}
trait MyTrait3 {
#[expect(clippy::trivially_copy_pass_by_ref)]
fn trait_method(&self, foo: &Foo);
}
// Trait impls should not warn
impl MyTrait3 for Foo {
fn trait_method(&self, foo: &Foo) {
unimplemented!()
}
}
mod issue3992 {
pub trait A {
#[allow(clippy::trivially_copy_pass_by_ref)]
fn a(b: &u16) {}
}
#[allow(clippy::trivially_copy_pass_by_ref)]
pub fn c(d: &u16) {}
}
mod issue5876 {
// Don't lint here as it is always inlined
#[inline(always)]
fn foo_always(x: &i32) {
println!("{}", x);
}
#[inline(never)]
fn foo_never(x: i32) {
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
println!("{}", x);
}
#[inline]
fn foo(x: i32) {
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
println!("{}", x);
}
}
fn ref_to_opt_ref_implicit(x: &u32) -> Option<&u32> {
Some(x)
}
fn ref_to_opt_ref_explicit<'a>(x: &'a u32) -> Option<&'a u32> {
Some(x)
}
fn with_constraint<'a, 'b: 'a>(x: &'b u32, y: &'a u32) -> &'a u32 {
if true { x } else { y }
}
async fn async_implicit(x: &u32) -> &u32 {
x
}
async fn async_explicit<'a>(x: &'a u32) -> &'a u32 {
x
}
fn unrelated_lifetimes<'a, 'b>(_x: u32, y: &'b u32) -> &'b u32 {
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
y
}
fn return_ptr(x: &u32) -> *const u32 {
x
}
fn return_field_ptr(x: &(u32, u32)) -> *const u32 {
&x.0
}
fn return_field_ptr_addr_of(x: &(u32, u32)) -> *const u32 {
core::ptr::addr_of!(x.0)
}

60
tests/ui/trivially_copy_pass_by_ref.rs
View file

@ -1,14 +1,15 @@
//@normalize-stderr-test: "\(\d+ byte\)" -> "(N byte)"
//@normalize-stderr-test: "\(limit: \d+ byte\)" -> "(limit: 8 byte)"
//@normalize-stderr-test: "\(limit: \d+ byte\)" -> "(limit: N byte)"
#![deny(clippy::trivially_copy_pass_by_ref)]
#![allow(
clippy::disallowed_names,
clippy::extra_unused_lifetimes,
clippy::needless_lifetimes,
clippy::needless_pass_by_ref_mut,
clippy::redundant_field_names,
clippy::uninlined_format_args,
clippy::needless_pass_by_ref_mut
clippy::uninlined_format_args
)]
//@no-rustfix
#[derive(Copy, Clone)]
struct Foo(u32);
@ -90,21 +91,26 @@ impl Bar {
}
trait MyTrait {
fn trait_method(&self, _foo: &Foo);
fn trait_method(&self, foo: &Foo);
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if
}
pub trait MyTrait2 {
fn trait_method2(&self, _color: &Color);
fn trait_method2(&self, color: &Color);
}
impl MyTrait for Foo {
fn trait_method(&self, _foo: &Foo) {
trait MyTrait3 {
#[expect(clippy::trivially_copy_pass_by_ref)]
fn trait_method(&self, foo: &Foo);
}
// Trait impls should not warn
impl MyTrait3 for Foo {
fn trait_method(&self, foo: &Foo) {
unimplemented!()
}
}
#[allow(unused_variables)]
mod issue3992 {
pub trait A {
#[allow(clippy::trivially_copy_pass_by_ref)]
@ -135,57 +141,39 @@ mod issue5876 {
}
}
fn _ref_to_opt_ref_implicit(x: &u32) -> Option<&u32> {
fn ref_to_opt_ref_implicit(x: &u32) -> Option<&u32> {
Some(x)
}
#[allow(clippy::needless_lifetimes)]
fn _ref_to_opt_ref_explicit<'a>(x: &'a u32) -> Option<&'a u32> {
fn ref_to_opt_ref_explicit<'a>(x: &'a u32) -> Option<&'a u32> {
Some(x)
}
fn _with_constraint<'a, 'b: 'a>(x: &'b u32, y: &'a u32) -> &'a u32 {
fn with_constraint<'a, 'b: 'a>(x: &'b u32, y: &'a u32) -> &'a u32 {
if true { x } else { y }
}
async fn _async_implicit(x: &u32) -> &u32 {
async fn async_implicit(x: &u32) -> &u32 {
x
}
#[allow(clippy::needless_lifetimes)]
async fn _async_explicit<'a>(x: &'a u32) -> &'a u32 {
async fn async_explicit<'a>(x: &'a u32) -> &'a u32 {
x
}
fn _unrelated_lifetimes<'a, 'b>(_x: &'a u32, y: &'b u32) -> &'b u32 {
fn unrelated_lifetimes<'a, 'b>(_x: &'a u32, y: &'b u32) -> &'b u32 {
//~^ ERROR: this argument (4 byte) is passed by reference, but would be more efficient if passed by
y
}
fn _return_ptr(x: &u32) -> *const u32 {
fn return_ptr(x: &u32) -> *const u32 {
x
}
fn _return_field_ptr(x: &(u32, u32)) -> *const u32 {
fn return_field_ptr(x: &(u32, u32)) -> *const u32 {
&x.0
}
fn _return_field_ptr_addr_of(x: &(u32, u32)) -> *const u32 {
fn return_field_ptr_addr_of(x: &(u32, u32)) -> *const u32 {
core::ptr::addr_of!(x.0)
}
fn main() {
let (mut foo, bar) = (Foo(0), Bar([0; 24]));
let (mut a, b, c, x, y, z) = (0, 0, Bar([0; 24]), 0, Foo(0), 0);
good(&mut a, b, &c);
good_return_implicit_lt_ref(&y);
good_return_explicit_lt_ref(&y);
bad(&x, &y, &z);
foo.good(&mut a, b, &c);
foo.good2();
foo.bad(&x, &y, &z);
Foo::bad2(&x, &y, &z);
bar.good(&mut a, b, &c);
Bar::bad2(&x, &y, &z);
foo.as_ref();
}

80
tests/ui/trivially_copy_pass_by_ref.stderr
View file

@ -1,5 +1,5 @@
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:52:11
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:53:11
|
LL | fn bad(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `u32`
@ -10,107 +10,107 @@ note: the lint level is defined here
LL | #![deny(clippy::trivially_copy_pass_by_ref)]
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:52:20
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:53:20
|
LL | fn bad(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `Foo`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:52:29
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:53:29
|
LL | fn bad(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `Baz`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:62:12
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:63:12
|
LL | fn bad(&self, x: &u32, y: &Foo, z: &Baz) {}
| ^^^^^ help: consider passing by value instead: `self`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:62:22
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:63:22
|
LL | fn bad(&self, x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `u32`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:62:31
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:63:31
|
LL | fn bad(&self, x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `Foo`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:62:40
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:63:40
|
LL | fn bad(&self, x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `Baz`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:68:16
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:69:16
|
LL | fn bad2(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `u32`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:68:25
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:69:25
|
LL | fn bad2(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `Foo`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:68:34
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:69:34
|
LL | fn bad2(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `Baz`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:73:35
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:74:35
|
LL | fn bad_issue7518(self, other: &Self) {}
| ^^^^^ help: consider passing by value instead: `Self`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:86:16
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:87:16
|
LL | fn bad2(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `u32`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:86:25
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:87:25
|
LL | fn bad2(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `Foo`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:86:34
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:87:34
|
LL | fn bad2(x: &u32, y: &Foo, z: &Baz) {}
| ^^^^ help: consider passing by value instead: `Baz`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:93:34
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:94:33
|
LL | fn trait_method(&self, _foo: &Foo);
| ^^^^ help: consider passing by value instead: `Foo`
LL | fn trait_method(&self, foo: &Foo);
| ^^^^ help: consider passing by value instead: `Foo`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:126:21
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:132:21
|
LL | fn foo_never(x: &i32) {
| ^^^^ help: consider passing by value instead: `i32`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:132:15
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:138:15
|
LL | fn foo(x: &i32) {
| ^^^^ help: consider passing by value instead: `i32`
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: 8 byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:160:37
error: this argument (N byte) is passed by reference, but would be more efficient if passed by value (limit: N byte)
--> tests/ui/trivially_copy_pass_by_ref.rs:164:36
|
LL | fn _unrelated_lifetimes<'a, 'b>(_x: &'a u32, y: &'b u32) -> &'b u32 {
| ^^^^^^^ help: consider passing by value instead: `u32`
LL | fn unrelated_lifetimes<'a, 'b>(_x: &'a u32, y: &'b u32) -> &'b u32 {
| ^^^^^^^ help: consider passing by value instead: `u32`
error: aborting due to 18 previous errors