--- /dev/null
+use crate::utils::{
+ in_macro, match_def_path, match_qpath, meets_msrv, paths, snippet, snippet_with_applicability, span_lint_and_help,
+ span_lint_and_sugg, span_lint_and_then,
+};
+use if_chain::if_chain;
+use rustc_errors::Applicability;
+use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, QPath};
+use rustc_lint::{LateContext, LateLintPass, LintContext};
+use rustc_middle::lint::in_external_macro;
+use rustc_semver::RustcVersion;
+use rustc_session::{declare_tool_lint, impl_lint_pass};
+use rustc_span::source_map::Span;
+use rustc_span::symbol::sym;
+
+declare_clippy_lint! {
+ /// **What it does:** Checks for `mem::replace()` on an `Option` with
+ /// `None`.
+ ///
+ /// **Why is this bad?** `Option` already has the method `take()` for
+ /// taking its current value (Some(..) or None) and replacing it with
+ /// `None`.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ /// ```rust
+ /// use std::mem;
+ ///
+ /// let mut an_option = Some(0);
+ /// let replaced = mem::replace(&mut an_option, None);
+ /// ```
+ /// Is better expressed with:
+ /// ```rust
+ /// let mut an_option = Some(0);
+ /// let taken = an_option.take();
+ /// ```
+ pub MEM_REPLACE_OPTION_WITH_NONE,
+ style,
+ "replacing an `Option` with `None` instead of `take()`"
+}
+
+declare_clippy_lint! {
+ /// **What it does:** Checks for `mem::replace(&mut _, mem::uninitialized())`
+ /// and `mem::replace(&mut _, mem::zeroed())`.
+ ///
+ /// **Why is this bad?** This will lead to undefined behavior even if the
+ /// value is overwritten later, because the uninitialized value may be
+ /// observed in the case of a panic.
+ ///
+ /// **Known problems:** None.
+ ///
+ /// **Example:**
+ ///
+ /// ```
+ /// use std::mem;
+ ///# fn may_panic(v: Vec<i32>) -> Vec<i32> { v }
+ ///
+ /// #[allow(deprecated, invalid_value)]
+ /// fn myfunc (v: &mut Vec<i32>) {
+ /// let taken_v = unsafe { mem::replace(v, mem::uninitialized()) };
+ /// let new_v = may_panic(taken_v); // undefined behavior on panic
+ /// mem::forget(mem::replace(v, new_v));
+ /// }
+ /// ```
+ ///
+ /// The [take_mut](https://docs.rs/take_mut) crate offers a sound solution,
+ /// at the cost of either lazily creating a replacement value or aborting
+ /// on panic, to ensure that the uninitialized value cannot be observed.
+ pub MEM_REPLACE_WITH_UNINIT,
+ correctness,
+ "`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`"
+}
+
+impl_lint_pass!(MemReplace =>
+ [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<'_>, dest: &Expr<'_>, expr_span: Span) {
+ if_chain! {
+ // check if replacement is mem::MaybeUninit::uninit().assume_init()
+ if let Some(method_def_id) = cx.typeck_results().type_dependent_def_id(src.hir_id);
+ if cx.tcx.is_diagnostic_item(sym::assume_init, method_def_id);
+ then {
+ let mut applicability = Applicability::MachineApplicable;
+ span_lint_and_sugg(
+ cx,
+ MEM_REPLACE_WITH_UNINIT,
+ expr_span,
+ "replacing with `mem::MaybeUninit::uninit().assume_init()`",
+ "consider using",
+ format!(
+ "std::ptr::read({})",
+ snippet_with_applicability(cx, dest.span, "", &mut applicability)
+ ),
+ applicability,
+ );
+ return;
+ }
+ }
+
+ if_chain! {
+ if let ExprKind::Call(ref repl_func, ref repl_args) = src.kind;
+ if repl_args.is_empty();
+ if let ExprKind::Path(ref repl_func_qpath) = repl_func.kind;
+ if let Some(repl_def_id) = cx.qpath_res(repl_func_qpath, repl_func.hir_id).opt_def_id();
+ then {
+ if cx.tcx.is_diagnostic_item(sym::mem_uninitialized, repl_def_id) {
+ let mut applicability = Applicability::MachineApplicable;
+ span_lint_and_sugg(
+ cx,
+ MEM_REPLACE_WITH_UNINIT,
+ expr_span,
+ "replacing with `mem::uninitialized()`",
+ "consider using",
+ format!(
+ "std::ptr::read({})",
+ snippet_with_applicability(cx, dest.span, "", &mut applicability)
+ ),
+ applicability,
+ );
+ } else if cx.tcx.is_diagnostic_item(sym::mem_zeroed, repl_def_id) &&
+ !cx.typeck_results().expr_ty(src).is_primitive() {
+ span_lint_and_help(
+ cx,
+ MEM_REPLACE_WITH_UNINIT,
+ expr_span,
+ "replacing with `mem::zeroed()`",
+ None,
+ "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.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`",
+ |diag| {
+ if !in_macro(expr_span) {
+ let suggestion = format!("std::mem::take({})", snippet(cx, dest.span, ""));
+
+ diag.span_suggestion(
+ expr_span,
+ "consider using",
+ suggestion,
+ Applicability::MachineApplicable
+ );
+ }
+ }
+ );
+ }
+ }
+ }
+}
+
+const MEM_REPLACE_WITH_DEFAULT_MSRV: RustcVersion = RustcVersion::new(1, 40, 0);
+
+pub struct MemReplace {
+ msrv: Option<RustcVersion>,
+}
+
+impl MemReplace {
+ #[must_use]
+ pub fn new(msrv: Option<RustcVersion>) -> Self {
+ Self { msrv }
+ }
+}
+
+impl<'tcx> LateLintPass<'tcx> for MemReplace {
+ fn check_expr(&mut self, cx: &LateContext<'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 let ExprKind::Path(ref func_qpath) = func.kind;
+ if let Some(def_id) = cx.qpath_res(func_qpath, func.hir_id).opt_def_id();
+ if match_def_path(cx, def_id, &paths::MEM_REPLACE);
+ if let [dest, src] = &**func_args;
+ then {
+ check_replace_option_with_none(cx, src, dest, expr.span);
+ check_replace_with_uninit(cx, src, dest, expr.span);
+ if meets_msrv(self.msrv.as_ref(), &MEM_REPLACE_WITH_DEFAULT_MSRV) {
+ check_replace_with_default(cx, src, dest, expr.span);
+ }
+ }
+ }
+ }
+ extract_msrv_attr!(LateContext);
+}
projects / rustc.git / blobdiff