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Auto merge of #10570 - AlessioC31:redundant_type_annotations, r=xFrednet

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Add redundant type annotations lint

Hello, I'm trying to add the `redundat_type_annotations` lint.

It's still WIP but I'd like to start gathering some feedbacks to be sure that I'm not doing things 100% wrong :)

Right now it still misses lints like:

- [x] `let foo: u32 = 5_u32`,
- [x] `let foo: String = STest2::func()`
- [x] `let foo: String = self.func()` (`MethodCall`)
- [x] refs
- [ ] Generics

I've some problems regarding the second example above, in the `init` part of the `Local` I have:

```rust
init: Some(
                Expr {
                    hir_id: HirId(DefId(0:24 ~ playground[e1bd]::main).58),
                    kind: Call(
                        Expr {
                            hir_id: HirId(DefId(0:24 ~ playground[e1bd]::main).59),
                            kind: Path(
                                TypeRelative(
                                    Ty {
                                        hir_id: HirId(DefId(0:24 ~ playground[e1bd]::main).61),
                                        kind: Path(
                                            Resolved(
                                                None,
                                                Path {
                                                    span: src/main.rs:77:21: 77:27 (#0),
                                                    res: Def(
                                                        Struct,
                                                        DefId(0:17 ~ playground[e1bd]::STest2),
                                                    ),
                                                    segments: [
                                                        PathSegment {
                                                            ident: STest2#0,
                                                            hir_id: HirId(DefId(0:24 ~ playground[e1bd]::main).60),
                                                            res: Def(
                                                                Struct,
                                                                DefId(0:17 ~ playground[e1bd]::STest2),
                                                            ),
                                                            args: None,
                                                            infer_args: true,
                                                        },
                                                    ],
                                                },
                                            ),
                                        ),
                                        span: src/main.rs:77:21: 77:27 (#0),
                                    },
                                    PathSegment {
                                        ident: get_numb#0,
                                        hir_id: HirId(DefId(0:24 ~ playground[e1bd]::main).62),
                                        res: Err,
                                        args: None,
                                        infer_args: true,
                                    },
                                ),
                            ),
                            span: src/main.rs:77:21: 77:37 (#0),
                        },
                        [],
                    ),
                    span: src/main.rs:77:21: 77:39 (#0),
                },
            ),
```

And I'm not sure how to get the return type of the function `STest2::func()` since the resolved path `DefId` points to the struct itself and not the function. Do you have any idea on how I could get this information in this case?

Thanks!

changelog: changelog: [`redundant_type_annotations`]: New lint to warn on redundant type annotations

fixes #9155
This commit is contained in:
bors 2023-06-06 21:10:29 +00:00
commit cc8ead2cce
6 changed files with 496 additions and 0 deletions
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1
CHANGELOG.md
View file

@ -5110,6 +5110,7 @@ Released 2018-09-13
[`redundant_pub_crate`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_pub_crate
[`redundant_slicing`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_slicing
[`redundant_static_lifetimes`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_static_lifetimes
[`redundant_type_annotations`]: https://rust-lang.github.io/rust-clippy/master/index.html#redundant_type_annotations
[`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_ref`]: https://rust-lang.github.io/rust-clippy/master/index.html#ref_option_ref

1
clippy_lints/src/declared_lints.rs
View file

@ -543,6 +543,7 @@ pub(crate) static LINTS: &[&crate::LintInfo] = &[
crate::redundant_slicing::DEREF_BY_SLICING_INFO,
crate::redundant_slicing::REDUNDANT_SLICING_INFO,
crate::redundant_static_lifetimes::REDUNDANT_STATIC_LIFETIMES_INFO,
crate::redundant_type_annotations::REDUNDANT_TYPE_ANNOTATIONS_INFO,
crate::ref_option_ref::REF_OPTION_REF_INFO,
crate::ref_patterns::REF_PATTERNS_INFO,
crate::reference::DEREF_ADDROF_INFO,

2
clippy_lints/src/lib.rs
View file

@ -267,6 +267,7 @@ mod redundant_field_names;
mod redundant_pub_crate;
mod redundant_slicing;
mod redundant_static_lifetimes;
mod redundant_type_annotations;
mod ref_option_ref;
mod ref_patterns;
mod reference;
@ -1012,6 +1013,7 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
store.register_early_pass(|| Box::new(needless_else::NeedlessElse));
store.register_late_pass(|_| Box::new(missing_fields_in_debug::MissingFieldsInDebug));
store.register_late_pass(|_| Box::new(endian_bytes::EndianBytes));
store.register_late_pass(|_| Box::new(redundant_type_annotations::RedundantTypeAnnotations));
// add lints here, do not remove this comment, it's used in `new_lint`
}

210
clippy_lints/src/redundant_type_annotations.rs Normal file
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@ -0,0 +1,210 @@
use clippy_utils::diagnostics::span_lint;
use rustc_ast::LitKind;
use rustc_hir as hir;
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::ty::Ty;
use rustc_session::{declare_lint_pass, declare_tool_lint};
declare_clippy_lint! {
/// ### What it does
/// Warns about needless / redundant type annotations.
///
/// ### Why is this bad?
/// Code without type annotations is shorter and in most cases
/// more idiomatic and easier to modify.
///
/// ### Limitations
/// This lint doesn't support:
///
/// - Generics
/// - Refs returned from anything else than a `MethodCall`
/// - Complex types (tuples, arrays, etc...)
/// - `Path` to anything else than a primitive type.
///
/// ### Example
/// ```rust
/// let foo: String = String::new();
/// ```
/// Use instead:
/// ```rust
/// let foo = String::new();
/// ```
#[clippy::version = "1.70.0"]
pub REDUNDANT_TYPE_ANNOTATIONS,
restriction,
"warns about needless / redundant type annotations."
}
declare_lint_pass!(RedundantTypeAnnotations => [REDUNDANT_TYPE_ANNOTATIONS]);
fn is_same_type<'tcx>(cx: &LateContext<'tcx>, ty_resolved_path: hir::def::Res, func_return_type: Ty<'tcx>) -> bool {
// type annotation is primitive
if let hir::def::Res::PrimTy(primty) = ty_resolved_path
&& func_return_type.is_primitive()
&& let Some(func_return_type_sym) = func_return_type.primitive_symbol()
{
return primty.name() == func_return_type_sym;
}
// type annotation is any other non generic type
if let hir::def::Res::Def(_, defid) = ty_resolved_path
&& let Some(annotation_ty) = cx.tcx.type_of(defid).no_bound_vars()
{
return annotation_ty == func_return_type;
}
false
}
fn func_hir_id_to_func_ty<'tcx>(cx: &LateContext<'tcx>, hir_id: hir::hir_id::HirId) -> Option<Ty<'tcx>> {
if let Some((defkind, func_defid)) = cx.typeck_results().type_dependent_def(hir_id)
&& defkind == hir::def::DefKind::AssocFn
&& let Some(init_ty) = cx.tcx.type_of(func_defid).no_bound_vars()
{
Some(init_ty)
} else {
None
}
}
fn func_ty_to_return_type<'tcx>(cx: &LateContext<'tcx>, func_ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
if func_ty.is_fn() {
Some(func_ty.fn_sig(cx.tcx).output().skip_binder())
} else {
None
}
}
/// Extracts the fn Ty, e.g. `fn() -> std::string::String {f}`
fn extract_fn_ty<'tcx>(
cx: &LateContext<'tcx>,
call: &hir::Expr<'tcx>,
func_return_path: &hir::QPath<'tcx>,
) -> Option<Ty<'tcx>> {
match func_return_path {
// let a: String = f(); where f: fn f() -> String
hir::QPath::Resolved(_, resolved_path) => {
if let hir::def::Res::Def(_, defid) = resolved_path.res
&& let Some(middle_ty_init) = cx.tcx.type_of(defid).no_bound_vars()
{
Some(middle_ty_init)
} else {
None
}
},
// Associated functions like
// let a: String = String::new();
// let a: String = String::get_string();
hir::QPath::TypeRelative(..) => func_hir_id_to_func_ty(cx, call.hir_id),
hir::QPath::LangItem(..) => None,
}
}
fn is_redundant_in_func_call<'tcx>(
cx: &LateContext<'tcx>,
ty_resolved_path: hir::def::Res,
call: &hir::Expr<'tcx>,
) -> bool {
if let hir::ExprKind::Path(init_path) = &call.kind {
let func_type = extract_fn_ty(cx, call, init_path);
if let Some(func_type) = func_type
&& let Some(init_return_type) = func_ty_to_return_type(cx, func_type)
{
return is_same_type(cx, ty_resolved_path, init_return_type);
}
}
false
}
fn extract_primty(ty_kind: &hir::TyKind<'_>) -> Option<hir::PrimTy> {
if let hir::TyKind::Path(ty_path) = ty_kind
&& let hir::QPath::Resolved(_, resolved_path_ty) = ty_path
&& let hir::def::Res::PrimTy(primty) = resolved_path_ty.res
{
Some(primty)
} else {
None
}
}
impl LateLintPass<'_> for RedundantTypeAnnotations {
fn check_local<'tcx>(&mut self, cx: &LateContext<'tcx>, local: &'tcx rustc_hir::Local<'tcx>) {
// type annotation part
if !local.span.from_expansion()
&& let Some(ty) = &local.ty
// initialization part
&& let Some(init) = local.init
{
match &init.kind {
// When the initialization is a call to a function
hir::ExprKind::Call(init_call, _) => {
if let hir::TyKind::Path(ty_path) = &ty.kind
&& let hir::QPath::Resolved(_, resolved_path_ty) = ty_path
&& is_redundant_in_func_call(cx, resolved_path_ty.res, init_call) {
span_lint(cx, REDUNDANT_TYPE_ANNOTATIONS, local.span, "redundant type annotation");
}
},
hir::ExprKind::MethodCall(_, _, _, _) => {
let mut is_ref = false;
let mut ty_kind = &ty.kind;
// If the annotation is a ref we "peel" it
if let hir::TyKind::Ref(_, mut_ty) = &ty.kind {
is_ref = true;
ty_kind = &mut_ty.ty.kind;
}
if let hir::TyKind::Path(ty_path) = ty_kind
&& let hir::QPath::Resolved(_, resolved_path_ty) = ty_path
&& let Some(func_ty) = func_hir_id_to_func_ty(cx, init.hir_id)
&& let Some(return_type) = func_ty_to_return_type(cx, func_ty)
&& is_same_type(cx, resolved_path_ty.res, if is_ref {
return_type.peel_refs()
} else {
return_type
})
{
span_lint(cx, REDUNDANT_TYPE_ANNOTATIONS, local.span, "redundant type annotation");
}
},
// When the initialization is a path for example u32::MAX
hir::ExprKind::Path(init_path) => {
// TODO: check for non primty
if let Some(primty) = extract_primty(&ty.kind)
&& let hir::QPath::TypeRelative(init_ty, _) = init_path
&& let Some(primty_init) = extract_primty(&init_ty.kind)
&& primty == primty_init
{
span_lint(cx, REDUNDANT_TYPE_ANNOTATIONS, local.span, "redundant type annotation");
}
},
hir::ExprKind::Lit(init_lit) => {
match init_lit.node {
// In these cases the annotation is redundant
LitKind::Str(..)
| LitKind::ByteStr(..)
| LitKind::Byte(..)
| LitKind::Char(..)
| LitKind::Bool(..)
| LitKind::CStr(..) => {
span_lint(cx, REDUNDANT_TYPE_ANNOTATIONS, local.span, "redundant type annotation");
},
LitKind::Int(..) | LitKind::Float(..) => {
// If the initialization value is a suffixed literal we lint
if init_lit.node.is_suffixed() {
span_lint(cx, REDUNDANT_TYPE_ANNOTATIONS, local.span, "redundant type annotation");
}
},
LitKind::Err => (),
}
}
_ => ()
}
};
}
}

176
tests/ui/redundant_type_annotations.rs Normal file
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@ -0,0 +1,176 @@
#![allow(unused)]
#![warn(clippy::redundant_type_annotations)]
#[derive(Debug, Default)]
struct Cake<T> {
_data: T,
}
fn make_something<T: Default>() -> T {
T::default()
}
fn make_cake<T: Default>() -> Cake<T> {
Cake::<T>::default()
}
fn plus_one<T: std::ops::Add<u8, Output = T>>(val: T) -> T {
val + 1
}
#[derive(Default)]
struct Slice {
inner: u32,
}
#[derive(Default)]
struct Pie {
inner: u32,
inner_struct: Slice,
}
enum Pizza {
One,
Two,
}
fn return_a_string() -> String {
String::new()
}
fn return_a_struct() -> Pie {
Pie::default()
}
fn return_an_enum() -> Pizza {
Pizza::One
}
fn return_an_int() -> u32 {
5
}
impl Pie {
fn return_an_int(&self) -> u32 {
self.inner
}
fn return_a_ref(&self) -> &u32 {
&self.inner
}
fn return_a_ref_to_struct(&self) -> &Slice {
&self.inner_struct
}
fn associated_return_an_int() -> u32 {
5
}
fn new() -> Self {
Self::default()
}
fn associated_return_a_string() -> String {
String::from("")
}
fn test_method_call(&self) {
// Everything here should be lint
let v: u32 = self.return_an_int();
let v: &u32 = self.return_a_ref();
let v: &Slice = self.return_a_ref_to_struct();
}
}
fn test_generics() {
// The type annotation is needed to determine T
let _c: Cake<i32> = make_something();
// The type annotation is needed to determine the topic
let _c: Cake<u8> = make_cake();
// This could be lint, but currently doesn't
let _c: Cake<u8> = make_cake::<u8>();
// This could be lint, but currently doesn't
let _c: u8 = make_something::<u8>();
// This could be lint, but currently doesn't
let _c: u8 = plus_one(5_u8);
// Annotation needed otherwise T is i32
let _c: u8 = plus_one(5);
// This could be lint, but currently doesn't
let _return: String = String::from("test");
}
fn test_non_locals() {
// This shouldn't be lint
fn _arg(x: u32) -> u32 {
x
}
// This could lint, but probably shouldn't
let _closure_arg = |x: u32| x;
}
fn test_complex_types() {
// Shouldn't be lint, since the literal will be i32 otherwise
let _u8: u8 = 128;
// This could be lint, but currently doesn't
let _tuple_i32: (i32, i32) = (12, 13);
// Shouldn't be lint, since the tuple will be i32 otherwise
let _tuple_u32: (u32, u32) = (1, 2);
// Should be lint, since the type is determined by the init value, but currently doesn't
let _tuple_u32: (u32, u32) = (3_u32, 4_u32);
// This could be lint, but currently doesn't
let _array: [i32; 3] = [5, 6, 7];
// Shouldn't be lint
let _array: [u32; 2] = [8, 9];
}
fn test_functions() {
// Everything here should be lint
let _return: String = return_a_string();
let _return: Pie = return_a_struct();
let _return: Pizza = return_an_enum();
let _return: u32 = return_an_int();
let _return: String = String::new();
let new_pie: Pie = Pie::new();
let _return: u32 = new_pie.return_an_int();
let _return: u32 = Pie::associated_return_an_int();
let _return: String = Pie::associated_return_a_string();
}
fn test_simple_types() {
// Everything here should be lint
let _var: u32 = u32::MAX;
let _var: u32 = 5_u32;
let _var: &str = "test";
let _var: &[u8] = b"test";
let _var: bool = false;
}
fn main() {}

106
tests/ui/redundant_type_annotations.stderr Normal file
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@ -0,0 +1,106 @@
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:81:9
|
LL | let v: u32 = self.return_an_int();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: `-D clippy::redundant-type-annotations` implied by `-D warnings`
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:82:9
|
LL | let v: &u32 = self.return_a_ref();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:83:9
|
LL | let v: &Slice = self.return_a_ref_to_struct();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:143:5
|
LL | let _return: String = return_a_string();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:145:5
|
LL | let _return: Pie = return_a_struct();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:147:5
|
LL | let _return: Pizza = return_an_enum();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:149:5
|
LL | let _return: u32 = return_an_int();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:151:5
|
LL | let _return: String = String::new();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:153:5
|
LL | let new_pie: Pie = Pie::new();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:155:5
|
LL | let _return: u32 = new_pie.return_an_int();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:157:5
|
LL | let _return: u32 = Pie::associated_return_an_int();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:159:5
|
LL | let _return: String = Pie::associated_return_a_string();
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:165:5
|
LL | let _var: u32 = u32::MAX;
| ^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:167:5
|
LL | let _var: u32 = 5_u32;
| ^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:169:5
|
LL | let _var: &str = "test";
| ^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:171:5
|
LL | let _var: &[u8] = b"test";
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
error: redundant type annotation
--> $DIR/redundant_type_annotations.rs:173:5
|
LL | let _var: bool = false;
| ^^^^^^^^^^^^^^^^^^^^^^^
error: aborting due to 17 previous errors