mikros/rust
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Use mem::take instead of mem::replace when applicable

Browse Source 
`std::mem::take` can be used to replace a value of type `T`
with `T::default()` instead of `std::mem::replace`.
This commit is contained in:
Krishna Veera Reddy 2019-12-07 19:10:06 -08:00
parent 99dd0bb653
commit 8db319f957
7 changed files with 189 additions and 69 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
CHANGELOG.md
View File

@ -1173,6 +1173,7 @@ Released 2018-09-13
[`mem_discriminant_non_enum`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_discriminant_non_enum
[`mem_forget`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_forget
[`mem_replace_option_with_none`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_replace_option_with_none
[`mem_replace_with_default`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_replace_with_default
[`mem_replace_with_uninit`]: https://rust-lang.github.io/rust-clippy/master/index.html#mem_replace_with_uninit
[`min_max`]: https://rust-lang.github.io/rust-clippy/master/index.html#min_max
[`misaligned_transmute`]: https://rust-lang.github.io/rust-clippy/master/index.html#misaligned_transmute

2
clippy_lints/src/lib.rs
View File

@ -599,6 +599,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
&mem_discriminant::MEM_DISCRIMINANT_NON_ENUM,
&mem_forget::MEM_FORGET,
&mem_replace::MEM_REPLACE_OPTION_WITH_NONE,
&mem_replace::MEM_REPLACE_WITH_DEFAULT,
&mem_replace::MEM_REPLACE_WITH_UNINIT,
&methods::CHARS_LAST_CMP,
&methods::CHARS_NEXT_CMP,
@ -1594,6 +1595,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
store.register_group(true, "clippy::nursery", Some("clippy_nursery"), vec![
LintId::of(&attrs::EMPTY_LINE_AFTER_OUTER_ATTR),
LintId::of(&fallible_impl_from::FALLIBLE_IMPL_FROM),
LintId::of(&mem_replace::MEM_REPLACE_WITH_DEFAULT),
LintId::of(&missing_const_for_fn::MISSING_CONST_FOR_FN),
LintId::of(&mul_add::MANUAL_MUL_ADD),
LintId::of(&mutex_atomic::MUTEX_INTEGER),

186
clippy_lints/src/mem_replace.rs
View File

@ -3,7 +3,7 @@
};
use if_chain::if_chain;
use rustc::declare_lint_pass;
use rustc::hir::{BorrowKind, Expr, ExprKind, Mutability, QPath};
use rustc::hir::{BorrowKind, Expr, ExprKind, HirVec, Mutability, QPath};
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc_errors::Applicability;
use rustc_session::declare_tool_lint;
@ -67,8 +67,127 @@
"`mem::replace(&mut _, mem::uninitialized())` or `mem::replace(&mut _, mem::zeroed())`"
}
declare_clippy_lint! {
/// **What it does:** Checks for `std::mem::replace` on a value of type
/// `T` with `T::default()`.
///
/// **Why is this bad?** `std::mem` module already has the method `take` to
/// take the current value and replace it with the default value of that type.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust
/// let mut text = String::from("foo");
/// let replaced = std::mem::replace(&mut text, String::default());
/// ```
/// Is better expressed with:
/// ```rust
/// let mut text = String::from("foo");
/// let taken = std::mem::take(&mut text);
/// ```
pub MEM_REPLACE_WITH_DEFAULT,
nursery,
"replacing a value of type `T` with `T::default()` instead of using `std::mem::take`"
}
declare_lint_pass!(MemReplace =>
[MEM_REPLACE_OPTION_WITH_NONE, MEM_REPLACE_WITH_UNINIT]);
[MEM_REPLACE_OPTION_WITH_NONE, MEM_REPLACE_WITH_UNINIT, MEM_REPLACE_WITH_DEFAULT]);
fn check_replace_option_with_none(cx: &LateContext<'_, '_>, expr: &'_ Expr, args: &HirVec<Expr>) {
if let ExprKind::Path(ref replacement_qpath) = args[1].kind {
// Check that second argument is `Option::None`
if match_qpath(replacement_qpath, &paths::OPTION_NONE) {
// Since this is a late pass (already type-checked),
// and we already know that the second argument is an
// `Option`, we do not need to check the first
// argument's type. All that's left is to get
// replacee's path.
let replaced_path = match args[0].kind {
ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, ref replaced) => {
if let ExprKind::Path(QPath::Resolved(None, ref replaced_path)) = replaced.kind {
replaced_path
} else {
return;
}
},
ExprKind::Path(QPath::Resolved(None, ref replaced_path)) => replaced_path,
_ => return,
};
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
MEM_REPLACE_OPTION_WITH_NONE,
expr.span,
"replacing an `Option` with `None`",
"consider `Option::take()` instead",
format!(
"{}.take()",
snippet_with_applicability(cx, replaced_path.span, "", &mut applicability)
),
applicability,
);
}
}
}
fn check_replace_with_uninit(cx: &LateContext<'_, '_>, expr: &'_ Expr, args: &HirVec<Expr>) {
if let ExprKind::Call(ref repl_func, ref repl_args) = args[1].kind {
if_chain! {
if repl_args.is_empty();
if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
then {
if match_def_path(cx, repl_def_id, &paths::MEM_UNINITIALIZED) {
span_help_and_lint(
cx,
MEM_REPLACE_WITH_UNINIT,
expr.span,
"replacing with `mem::uninitialized()`",
"consider using the `take_mut` crate instead",
);
} else if match_def_path(cx, repl_def_id, &paths::MEM_ZEROED) &&
!cx.tables.expr_ty(&args[1]).is_primitive() {
span_help_and_lint(
cx,
MEM_REPLACE_WITH_UNINIT,
expr.span,
"replacing with `mem::zeroed()`",
"consider using a default value or the `take_mut` crate instead",
);
}
}
}
}
}
fn check_replace_with_default(cx: &LateContext<'_, '_>, expr: &'_ Expr, args: &HirVec<Expr>) {
if let ExprKind::Call(ref repl_func, ref repl_args) = args[1].kind {
if_chain! {
if repl_args.is_empty();
if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
if match_def_path(cx, repl_def_id, &paths::DEFAULT_TRAIT_METHOD);
then {
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
MEM_REPLACE_WITH_DEFAULT,
expr.span,
"replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`",
"consider using",
format!(
"std::mem::take({})",
snippet_with_applicability(cx, args[0].span, "", &mut applicability)
),
applicability,
);
}
}
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemReplace {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
@ -80,67 +199,10 @@ fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
if let Some(def_id) = cx.tables.qpath_res(func_qpath, func.hir_id).opt_def_id();
if match_def_path(cx, def_id, &paths::MEM_REPLACE);
// Check that second argument is `Option::None`
then {
if let ExprKind::Path(ref replacement_qpath) = func_args[1].kind {
if match_qpath(replacement_qpath, &paths::OPTION_NONE) {
// Since this is a late pass (already type-checked),
// and we already know that the second argument is an
// `Option`, we do not need to check the first
// argument's type. All that's left is to get
// replacee's path.
let replaced_path = match func_args[0].kind {
ExprKind::AddrOf(BorrowKind::Ref, Mutability::Mut, ref replaced) => {
if let ExprKind::Path(QPath::Resolved(None, ref replaced_path)) = replaced.kind {
replaced_path
} else {
return
}
},
ExprKind::Path(QPath::Resolved(None, ref replaced_path)) => replaced_path,
_ => return,
};
let mut applicability = Applicability::MachineApplicable;
span_lint_and_sugg(
cx,
MEM_REPLACE_OPTION_WITH_NONE,
expr.span,
"replacing an `Option` with `None`",
"consider `Option::take()` instead",
format!("{}.take()", snippet_with_applicability(cx, replaced_path.span, "", &mut applicability)),
applicability,
);
}
}
if let ExprKind::Call(ref repl_func, ref repl_args) = func_args[1].kind {
if_chain! {
if repl_args.is_empty();
if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
if let Some(repl_def_id) = cx.tables.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
then {
if match_def_path(cx, repl_def_id, &paths::MEM_UNINITIALIZED) {
span_help_and_lint(
cx,
MEM_REPLACE_WITH_UNINIT,
expr.span,
"replacing with `mem::uninitialized()`",
"consider using the `take_mut` crate instead",
);
} else if match_def_path(cx, repl_def_id, &paths::MEM_ZEROED) &&
!cx.tables.expr_ty(&func_args[1]).is_primitive() {
span_help_and_lint(
cx,
MEM_REPLACE_WITH_UNINIT,
expr.span,
"replacing with `mem::zeroed()`",
"consider using a default value or the `take_mut` crate instead",
);
}
}
}
}
check_replace_option_with_none(cx, expr, &func_args);
check_replace_with_uninit(cx, expr, &func_args);
check_replace_with_default(cx, expr, &func_args);
}
}
}

7
src/lintlist/mod.rs
View File

@ -1099,6 +1099,13 @@
deprecation: None,
module: "mem_replace",
},
Lint {
name: "mem_replace_with_default",
group: "nursery",
desc: "replacing a value of type `T` with `T::default()` instead of using `std::mem::take`",
deprecation: None,
module: "mem_replace",
},
Lint {
name: "mem_replace_with_uninit",
group: "correctness",

21
tests/ui/mem_replace.fixed
View File

@ -9,13 +9,30 @@
// run-rustfix
#![allow(unused_imports)]
#![warn(clippy::all, clippy::style, clippy::mem_replace_option_with_none)]
#![warn(
clippy::all,
clippy::style,
clippy::mem_replace_option_with_none,
clippy::mem_replace_with_default
)]
use std::mem;
fn main() {
fn replace_option_with_none() {
let mut an_option = Some(1);
let _ = an_option.take();
let an_option = &mut Some(1);
let _ = an_option.take();
}
fn replace_with_default() {
let mut s = String::from("foo");
let _ = std::mem::take(&mut s);
let s = &mut String::from("foo");
let _ = std::mem::take(s);
}
fn main() {
replace_option_with_none();
replace_with_default();
}

21
tests/ui/mem_replace.rs
View File

@ -9,13 +9,30 @@
// run-rustfix
#![allow(unused_imports)]
#![warn(clippy::all, clippy::style, clippy::mem_replace_option_with_none)]
#![warn(
clippy::all,
clippy::style,
clippy::mem_replace_option_with_none,
clippy::mem_replace_with_default
)]
use std::mem;
fn main() {
fn replace_option_with_none() {
let mut an_option = Some(1);
let _ = mem::replace(&mut an_option, None);
let an_option = &mut Some(1);
let _ = mem::replace(an_option, None);
}
fn replace_with_default() {
let mut s = String::from("foo");
let _ = std::mem::replace(&mut s, String::default());
let s = &mut String::from("foo");
let _ = std::mem::replace(s, String::default());
}
fn main() {
replace_option_with_none();
replace_with_default();
}

20
tests/ui/mem_replace.stderr
View File

@ -1,5 +1,5 @@
error: replacing an `Option` with `None`
--> $DIR/mem_replace.rs:18:13
--> $DIR/mem_replace.rs:23:13
|
LL | let _ = mem::replace(&mut an_option, None);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider `Option::take()` instead: `an_option.take()`
@ -7,10 +7,24 @@ LL | let _ = mem::replace(&mut an_option, None);
= note: `-D clippy::mem-replace-option-with-none` implied by `-D warnings`
error: replacing an `Option` with `None`
--> $DIR/mem_replace.rs:20:13
--> $DIR/mem_replace.rs:25:13
|
LL | let _ = mem::replace(an_option, None);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider `Option::take()` instead: `an_option.take()`
error: aborting due to 2 previous errors
error: replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`
--> $DIR/mem_replace.rs:30:13
|
LL | let _ = std::mem::replace(&mut s, String::default());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::mem::take(&mut s)`
|
= note: `-D clippy::mem-replace-with-default` implied by `-D warnings`
error: replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`
--> $DIR/mem_replace.rs:32:13
|
LL | let _ = std::mem::replace(s, String::default());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::mem::take(s)`
error: aborting due to 4 previous errors