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Auto merge of #4881 - krishna-veerareddy:issue-4871-use-mem-take, r=flip1995

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

`std::mem::take` can be used to replace a value of type `T` with `T::default()` instead of `std::mem::replace`.

Fixes issue #4871

changelog: Added lint for [`mem_replace_with_default`]
This commit is contained in:
bors 2020-01-04 08:09:43 +00:00
commit fa9b85d4df
11 changed files with 249 additions and 74 deletions
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1
CHANGELOG.md
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@ -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
README.md
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@ -6,7 +6,7 @@
A collection of lints to catch common mistakes and improve your [Rust](https://github.com/rust-lang/rust) code.
[There are 342 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
[There are 343 lints included in this crate!](https://rust-lang.github.io/rust-clippy/master/index.html)
We have a bunch of lint categories to allow you to choose how much Clippy is supposed to ~~annoy~~ help you:

3
clippy_lints/src/lib.rs
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@ -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,
@ -1182,6 +1183,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
LintId::of(&matches::SINGLE_MATCH),
LintId::of(&mem_discriminant::MEM_DISCRIMINANT_NON_ENUM),
LintId::of(&mem_replace::MEM_REPLACE_OPTION_WITH_NONE),
LintId::of(&mem_replace::MEM_REPLACE_WITH_DEFAULT),
LintId::of(&mem_replace::MEM_REPLACE_WITH_UNINIT),
LintId::of(&methods::CHARS_LAST_CMP),
LintId::of(&methods::CHARS_NEXT_CMP),
@ -1369,6 +1371,7 @@ pub fn register_plugins(store: &mut lint::LintStore, sess: &Session, conf: &Conf
LintId::of(&matches::MATCH_WILD_ERR_ARM),
LintId::of(&matches::SINGLE_MATCH),
LintId::of(&mem_replace::MEM_REPLACE_OPTION_WITH_NONE),
LintId::of(&mem_replace::MEM_REPLACE_WITH_DEFAULT),
LintId::of(&methods::CHARS_LAST_CMP),
LintId::of(&methods::INTO_ITER_ON_REF),
LintId::of(&methods::ITER_CLONED_COLLECT),

197
clippy_lints/src/mem_replace.rs
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@ -1,12 +1,14 @@
use crate::utils::{
match_def_path, match_qpath, paths, snippet_with_applicability, span_help_and_lint, span_lint_and_sugg,
in_macro, match_def_path, match_qpath, paths, snippet, snippet_with_applicability, span_help_and_lint,
span_lint_and_sugg, span_lint_and_then,
};
use if_chain::if_chain;
use rustc::declare_lint_pass;
use rustc::hir::{BorrowKind, Expr, ExprKind, Mutability, QPath};
use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use rustc::lint::{in_external_macro, LateContext, LateLintPass, LintArray, LintPass};
use rustc_errors::Applicability;
use rustc_session::declare_tool_lint;
use syntax::source_map::Span;
declare_clippy_lint! {
/// **What it does:** Checks for `mem::replace()` on an `Option` with
@ -67,80 +69,145 @@ declare_clippy_lint! {
"`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,
style,
"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<'_, '_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
if let ExprKind::Path(ref replacement_qpath) = src.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 dest.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<'_, '_>, src: &Expr<'_>, expr_span: Span) {
if let ExprKind::Call(ref repl_func, ref repl_args) = src.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(src).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<'_, '_>, src: &Expr<'_>, dest: &Expr<'_>, expr_span: Span) {
if let ExprKind::Call(ref repl_func, _) = src.kind {
if_chain! {
if !in_external_macro(cx.tcx.sess, expr_span);
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 {
span_lint_and_then(
cx,
MEM_REPLACE_WITH_DEFAULT,
expr_span,
"replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`",
|db| {
if !in_macro(expr_span) {
let suggestion = format!("std::mem::take({})", snippet(cx, dest.span, ""));
db.span_suggestion(
expr_span,
"consider using",
suggestion,
Applicability::MachineApplicable
);
}
}
);
}
}
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemReplace {
fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr<'_>) {
if_chain! {
// Check that `expr` is a call to `mem::replace()`
if let ExprKind::Call(ref func, ref func_args) = expr.kind;
if func_args.len() == 2;
if let ExprKind::Path(ref func_qpath) = func.kind;
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`
if let [dest, src] = &**func_args;
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, src, dest, expr.span);
check_replace_with_uninit(cx, src, expr.span);
check_replace_with_default(cx, src, dest, expr.span);
}
}
}

9
src/lintlist/mod.rs
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@ -6,7 +6,7 @@ pub use lint::Lint;
pub use lint::LINT_LEVELS;
// begin lint list, do not remove this comment, it’s used in `update_lints`
pub const ALL_LINTS: [Lint; 342] = [
pub const ALL_LINTS: [Lint; 343] = [
Lint {
name: "absurd_extreme_comparisons",
group: "correctness",
@ -1099,6 +1099,13 @@ pub const ALL_LINTS: [Lint; 342] = [
deprecation: None,
module: "mem_replace",
},
Lint {
name: "mem_replace_with_default",
group: "style",
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",

7
tests/ui/auxiliary/macro_rules.rs
View File

@ -39,3 +39,10 @@ macro_rules! string_add {
let z = y + "...";
};
}
#[macro_export]
macro_rules! take_external {
($s:expr) => {
std::mem::replace($s, Default::default())
};
}

22
tests/ui/mem_replace.fixed
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@ -9,13 +9,31 @@
// 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);
let _ = std::mem::take(s);
}
fn main() {
replace_option_with_none();
replace_with_default();
}

22
tests/ui/mem_replace.rs
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@ -9,13 +9,31 @@
// 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());
let _ = std::mem::replace(s, Default::default());
}
fn main() {
replace_option_with_none();
replace_with_default();
}

26
tests/ui/mem_replace.stderr
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@ -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 +7,30 @@ 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: replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`
--> $DIR/mem_replace.rs:33:13
|
LL | let _ = std::mem::replace(s, Default::default());
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::mem::take(s)`
error: aborting due to 5 previous errors

21
tests/ui/mem_replace_macro.rs Normal file
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@ -0,0 +1,21 @@
// aux-build:macro_rules.rs
#![warn(clippy::mem_replace_with_default)]
#[macro_use]
extern crate macro_rules;
macro_rules! take {
($s:expr) => {
std::mem::replace($s, Default::default())
};
}
fn replace_with_default() {
let s = &mut String::from("foo");
take!(s);
take_external!(s);
}
fn main() {
replace_with_default();
}

13
tests/ui/mem_replace_macro.stderr Normal file
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@ -0,0 +1,13 @@
error: replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`
--> $DIR/mem_replace_macro.rs:9:9
|
LL | std::mem::replace($s, Default::default())
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
...
LL | take!(s);
| --------- in this macro invocation
|
= note: `-D clippy::mem-replace-with-default` implied by `-D warnings`
error: aborting due to previous error