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Suggest Option<&T> instead of &Option<T>
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nyurik committed Sep 28, 2024
1 parent b367d34 commit 87e6df6
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -5871,6 +5871,7 @@ Released 2018-09-13
[`ref_as_ptr`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_as_ptr
[`ref_binding_to_reference`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_binding_to_reference
[`ref_in_deref`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_in_deref
[`ref_option`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_option
[`ref_option_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_option_ref
[`ref_patterns`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_patterns
[`regex_macro`]: https://rust-lang.github.io/rust-clippy/master/index.html#regex_macro
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1 change: 1 addition & 0 deletions book/src/lint_configuration.md
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Expand Up @@ -353,6 +353,7 @@ Suppress lints whenever the suggested change would cause breakage for other crat
* [`rc_buffer`](https://rust-lang.github.io/rust-clippy/master/index.html#rc_buffer)
* [`rc_mutex`](https://rust-lang.github.io/rust-clippy/master/index.html#rc_mutex)
* [`redundant_allocation`](https://rust-lang.github.io/rust-clippy/master/index.html#redundant_allocation)
* [`ref_option`](https://rust-lang.github.io/rust-clippy/master/index.html#ref_option)
* [`single_call_fn`](https://rust-lang.github.io/rust-clippy/master/index.html#single_call_fn)
* [`trivially_copy_pass_by_ref`](https://rust-lang.github.io/rust-clippy/master/index.html#trivially_copy_pass_by_ref)
* [`unnecessary_box_returns`](https://rust-lang.github.io/rust-clippy/master/index.html#unnecessary_box_returns)
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1 change: 1 addition & 0 deletions clippy_config/src/conf.rs
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Expand Up @@ -378,6 +378,7 @@ define_Conf! {
rc_buffer,
rc_mutex,
redundant_allocation,
ref_option,
single_call_fn,
trivially_copy_pass_by_ref,
unnecessary_box_returns,
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1 change: 1 addition & 0 deletions clippy_lints/src/declared_lints.rs
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Expand Up @@ -202,6 +202,7 @@ pub static LINTS: &[&crate::LintInfo] = &[
crate::functions::MUST_USE_CANDIDATE_INFO,
crate::functions::MUST_USE_UNIT_INFO,
crate::functions::NOT_UNSAFE_PTR_ARG_DEREF_INFO,
crate::functions::REF_OPTION_INFO,
crate::functions::RENAMED_FUNCTION_PARAMS_INFO,
crate::functions::RESULT_LARGE_ERR_INFO,
crate::functions::RESULT_UNIT_ERR_INFO,
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48 changes: 48 additions & 0 deletions clippy_lints/src/functions/mod.rs
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Expand Up @@ -2,6 +2,7 @@ mod impl_trait_in_params;
mod misnamed_getters;
mod must_use;
mod not_unsafe_ptr_arg_deref;
mod ref_option;
mod renamed_function_params;
mod result;
mod too_many_arguments;
Expand Down Expand Up @@ -399,6 +400,41 @@ declare_clippy_lint! {
"renamed function parameters in trait implementation"
}

declare_clippy_lint! {
/// ### What it does
/// Warns when a function signature uses `&Option<T>` instead of `Option<&T>`.
///
/// ### Why is this bad?
/// More flexibility, better memory optimization, and more idiomatic Rust code.
/// See this [YouTube video](https://www.youtube.com/watch?v=6c7pZYP_iIE) by
/// Logan Smith for an in-depth explanation of why this is important.
///
/// ### Known problems
/// This lint recommends changing the function signatures, but it cannot
/// automatically change the function calls or the function implementations.
///
/// ### Example
/// ```no_run
/// fn foo(a: &Option<String>) {}
/// # struct Unit {}
/// # impl Unit {
/// fn bar(&self) -> &Option<String> { &None }
/// # }
/// ```
/// Use instead:
/// ```no_run
/// fn foo(a: Option<&String>) {}
/// # struct Unit {}
/// # impl Unit {
/// fn bar(&self) -> Option<&String> { None }
/// # }
/// ```
#[clippy::version = "1.82.0"]
pub REF_OPTION,
nursery,
"function signature uses `&Option<T>` instead of `Option<&T>`"
}

pub struct Functions {
too_many_arguments_threshold: u64,
too_many_lines_threshold: u64,
Expand Down Expand Up @@ -437,6 +473,7 @@ impl_lint_pass!(Functions => [
MISNAMED_GETTERS,
IMPL_TRAIT_IN_PARAMS,
RENAMED_FUNCTION_PARAMS,
REF_OPTION,
]);

impl<'tcx> LateLintPass<'tcx> for Functions {
Expand All @@ -455,6 +492,16 @@ impl<'tcx> LateLintPass<'tcx> for Functions {
not_unsafe_ptr_arg_deref::check_fn(cx, kind, decl, body, def_id);
misnamed_getters::check_fn(cx, kind, decl, body, span);
impl_trait_in_params::check_fn(cx, &kind, body, hir_id);
ref_option::check_fn(
cx,
kind,
decl,
span,
hir_id,
def_id,
body,
self.avoid_breaking_exported_api,
);
}

fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'_>) {
Expand All @@ -475,5 +522,6 @@ impl<'tcx> LateLintPass<'tcx> for Functions {
must_use::check_trait_item(cx, item);
result::check_trait_item(cx, item, self.large_error_threshold);
impl_trait_in_params::check_trait_item(cx, item, self.avoid_breaking_exported_api);
ref_option::check_trait_item(cx, item, self.avoid_breaking_exported_api);
}
}
122 changes: 122 additions & 0 deletions clippy_lints/src/functions/ref_option.rs
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@@ -0,0 +1,122 @@
use crate::functions::REF_OPTION;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::is_trait_impl_item;
use clippy_utils::source::snippet;
use clippy_utils::ty::is_type_diagnostic_item;
use rustc_errors::Applicability;
use rustc_hir as hir;
use rustc_hir::intravisit::FnKind;
use rustc_hir::{FnDecl, HirId};
use rustc_lint::LateContext;
use rustc_middle::ty::{self, GenericArgKind, Mutability, Ty};
use rustc_span::def_id::LocalDefId;
use rustc_span::{Span, sym};

fn check_ty<'a>(cx: &LateContext<'a>, param: &rustc_hir::Ty<'a>, param_ty: Ty<'a>, fixes: &mut Vec<(Span, String)>) {
if let ty::Ref(_, opt_ty, Mutability::Not) = param_ty.kind()
&& is_type_diagnostic_item(cx, *opt_ty, sym::Option)
&& let ty::Adt(_, opt_gen) = opt_ty.kind()
&& let [gen] = opt_gen.as_slice()
&& let GenericArgKind::Type(gen_ty) = gen.unpack()
&& !gen_ty.is_ref()
// Need to gen the original spans, so first parsing mid, and hir parsing afterward
&& let hir::TyKind::Ref(lifetime, hir::MutTy { ty, .. }) = param.kind
&& let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = ty.kind
&& let (Some(first), Some(last)) = (path.segments.first(), path.segments.last())
&& let Some(hir::GenericArgs {
args: [hir::GenericArg::Type(opt_ty)],
..
}) = last.args
{
let lifetime = snippet(cx, lifetime.ident.span, "..");
fixes.push((
param.span,
format!(
"{}<&{lifetime}{}{}>",
snippet(cx, first.ident.span.to(last.ident.span), ".."),
if lifetime.is_empty() { "" } else { " " },
snippet(cx, opt_ty.span, "..")
),
));
}
}

fn check_fn_sig<'a>(cx: &LateContext<'a>, decl: &FnDecl<'a>, span: Span, sig: ty::FnSig<'a>) {
let mut fixes = Vec::new();
// Check function arguments' types
for (param, param_ty) in decl.inputs.iter().zip(sig.inputs()) {
check_ty(cx, param, *param_ty, &mut fixes);
}
// Check return type
if let hir::FnRetTy::Return(ty) = &decl.output {
check_ty(cx, ty, sig.output(), &mut fixes);
}
if !fixes.is_empty() {
span_lint_and_then(
cx,
REF_OPTION,
span,
"it is more idiomatic to use `Option<&T>` instead of `&Option<T>`",
|diag| {
diag.multipart_suggestion("change this to", fixes, Applicability::Unspecified);
},
);
}
}

#[allow(clippy::too_many_arguments)]
pub(crate) fn check_fn<'a>(
cx: &LateContext<'a>,
kind: FnKind<'_>,
decl: &FnDecl<'a>,
span: Span,
hir_id: HirId,
def_id: LocalDefId,
body: &hir::Body<'_>,
avoid_breaking_exported_api: bool,
) {
if avoid_breaking_exported_api && cx.effective_visibilities.is_exported(def_id) {
return;
}

if let FnKind::Closure = kind {
// Compute the span of the closure parameters + return type if set
let span = if let hir::FnRetTy::Return(out_ty) = &decl.output {
if decl.inputs.is_empty() {
out_ty.span
} else {
span.with_hi(out_ty.span.hi())
}
} else if let (Some(first), Some(last)) = (decl.inputs.first(), decl.inputs.last()) {
first.span.to(last.span)
} else {
// No parameters - no point in checking
return;
};

// Figure out the signature of the closure
let ty::Closure(_, args) = cx.typeck_results().expr_ty(body.value).kind() else {
return;
};
let sig = args.as_closure().sig().skip_binder();

check_fn_sig(cx, decl, span, sig);
} else if !is_trait_impl_item(cx, hir_id) {
let sig = cx.tcx.fn_sig(def_id).instantiate_identity().skip_binder();
check_fn_sig(cx, decl, span, sig);
}
}

pub(super) fn check_trait_item<'a>(
cx: &LateContext<'a>,
trait_item: &hir::TraitItem<'a>,
avoid_breaking_exported_api: bool,
) {
if let hir::TraitItemKind::Fn(ref sig, _) = trait_item.kind
&& !(avoid_breaking_exported_api && cx.effective_visibilities.is_exported(trait_item.owner_id.def_id))
{
let def_id = trait_item.owner_id.def_id;
let ty_sig = cx.tcx.fn_sig(def_id).instantiate_identity().skip_binder();
check_fn_sig(cx, sig.decl, sig.span, ty_sig);
}
}
1 change: 1 addition & 0 deletions tests/ui/ref_option/all/clippy.toml
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@@ -0,0 +1 @@
avoid-breaking-exported-api = false
1 change: 1 addition & 0 deletions tests/ui/ref_option/private/clippy.toml
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
avoid-breaking-exported-api = true
56 changes: 56 additions & 0 deletions tests/ui/ref_option/ref_option.all.fixed
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@@ -0,0 +1,56 @@
//@revisions: private all
//@[private] rustc-env:CLIPPY_CONF_DIR=tests/ui/ref_option/private
//@[all] rustc-env:CLIPPY_CONF_DIR=tests/ui/ref_option/all

#![allow(unused, clippy::all)]
#![warn(clippy::ref_option)]

fn opt_u8(a: Option<&u8>) {}
fn opt_gen<T>(a: Option<&T>) {}
fn opt_string(a: std::option::Option<&String>) {}
fn ret_string<'a>(p: &'a String) -> Option<&'a u8> {
panic!()
}
fn ret_string_static() -> Option<&'static u8> {
panic!()
}
fn mult_string(a: Option<&String>, b: Option<&Vec<u8>>) {}
fn mut_u8(a: &mut Option<u8>) {} // valid, don't change
fn mut_u8_ref(a: &mut &Option<u8>) {} // probably valid, don't change

pub fn pub_opt_string(a: Option<&String>) {}
pub fn pub_mult_string(a: Option<&String>, b: Option<&Vec<u8>>) {}
pub fn pub_mut_u8(a: &mut Option<String>) {} // valid, don't change
pub fn pub_mut_u8_ref(a: &mut &Option<String>) {} // probably valid, don't change

pub trait PubTrait {
fn pub_trait_opt(&self, a: Option<&Vec<u8>>);
fn pub_trait_ret(&self) -> Option<&Vec<u8>>;
}

trait PrivateTrait {
fn trait_opt(&self, a: Option<&String>);
fn trait_ret(&self) -> Option<&String>;
}

pub struct PubStruct;

impl PubStruct {
pub fn pub_opt_params(&self, a: Option<&()>) {}
pub fn pub_opt_ret(&self) -> Option<&String> {
panic!()
}

fn private_opt_params(&self, a: Option<&()>) {}
fn private_opt_ret(&self) -> Option<&String> {
panic!()
}
}

fn lambdas() {
// Not handled for now, not sure if we should
let x = |a: &Option<String>| {};
let x = |a: &Option<String>| -> &Option<String> { panic!() };
}

fn main() {}
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