X-Git-Url: https://git.lizzy.rs/?a=blobdiff_plain;f=clippy_lints%2Fsrc%2Fmem_replace.rs;h=426c108d89fb59c2d5240e3c931ab7ea9efe5051;hb=b094bb1bd7f1cc702823c91ca509f338fedee24a;hp=7e83e836b8569750177e60d4bf81be456eeb3ffb;hpb=f0a767352bdf0a7c49bce5623826ddd1ec968316;p=rust.git diff --git a/clippy_lints/src/mem_replace.rs b/clippy_lints/src/mem_replace.rs index 7e83e836b85..426c108d89f 100644 --- a/clippy_lints/src/mem_replace.rs +++ b/clippy_lints/src/mem_replace.rs @@ -1,9 +1,17 @@ -use crate::utils::{match_def_path, match_qpath, paths, snippet_with_applicability, span_lint_and_sugg}; +use clippy_utils::diagnostics::{span_lint_and_help, span_lint_and_sugg, span_lint_and_then}; +use clippy_utils::is_diagnostic_assoc_item; +use clippy_utils::source::{snippet, snippet_with_applicability}; +use clippy_utils::{in_macro, match_def_path, match_qpath, meets_msrv, paths}; use if_chain::if_chain; -use rustc::hir::{Expr, ExprKind, MutMutable, QPath}; -use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; -use rustc::{declare_lint_pass, declare_tool_lint}; use rustc_errors::Applicability; +use rustc_hir::def_id::DefId; +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 @@ -32,51 +40,253 @@ "replacing an `Option` with `None` instead of `take()`" } -declare_lint_pass!(MemReplace => [MEM_REPLACE_OPTION_WITH_NONE]); +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) -> Vec { v } + /// + /// #[allow(deprecated, invalid_value)] + /// fn myfunc (v: &mut Vec) { + /// 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())`" +} -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.node; - if func_args.len() == 2; - if let ExprKind::Path(ref func_qpath) = func.node; - 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); +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`" +} - // Check that second argument is `Option::None` - if let ExprKind::Path(ref replacement_qpath) = func_args[1].node; - if match_qpath(replacement_qpath, &paths::OPTION_NONE); +impl_lint_pass!(MemReplace => + [MEM_REPLACE_OPTION_WITH_NONE, MEM_REPLACE_WITH_UNINIT, MEM_REPLACE_WITH_DEFAULT]); - then { - // 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].node { - ExprKind::AddrOf(MutMutable, ref replaced) => { - if let ExprKind::Path(QPath::Resolved(None, ref replaced_path)) = replaced.node { - replaced_path - } else { - return - } - }, - ExprKind::Path(QPath::Resolved(None, ref replaced_path)) => replaced_path, - _ => return, - }; +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_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)), + 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", + ); + } + } + } +} + +/// Returns true if the `def_id` associated with the `path` is recognized as a "default-equivalent" +/// constructor from the std library +fn is_default_equivalent_ctor(cx: &LateContext<'_>, def_id: DefId, path: &QPath<'_>) -> bool { + let std_types_symbols = &[ + sym::string_type, + sym::vec_type, + sym::vecdeque_type, + sym::LinkedList, + sym::hashmap_type, + sym::BTreeMap, + sym::hashset_type, + sym::BTreeSet, + sym::BinaryHeap, + ]; + + if std_types_symbols + .iter() + .any(|symbol| is_diagnostic_assoc_item(cx, def_id, *symbol)) + { + if let QPath::TypeRelative(_, ref method) = path { + if method.ident.name == sym::new { + return true; + } + } + } + + false +} + +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 is_diagnostic_assoc_item(cx, repl_def_id, sym::Default) + || is_default_equivalent_ctor(cx, repl_def_id, repl_func_qpath); + + 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, +} + +impl MemReplace { + #[must_use] + pub fn new(msrv: Option) -> 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); }