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

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`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
Download patch file Download diff file Expand all files Collapse all files

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 crate::utils::{
};
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 @@ 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,
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 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MemReplace {
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);
}
}
}