266 lines
9.4 KiB
Rust
266 lines
9.4 KiB
Rust
use crate::utils::sugg::Sugg;
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use crate::utils::{
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differing_macro_contexts, is_type_diagnostic_item, match_type, paths, snippet_with_applicability,
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span_lint_and_then, walk_ptrs_ty, SpanlessEq,
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};
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use if_chain::if_chain;
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use matches::matches;
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use rustc::ty;
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use rustc_errors::Applicability;
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use rustc_hir::{Block, Expr, ExprKind, PatKind, QPath, StmtKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::Symbol;
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declare_clippy_lint! {
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/// **What it does:** Checks for manual swapping.
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///
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/// **Why is this bad?** The `std::mem::swap` function exposes the intent better
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/// without deinitializing or copying either variable.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// let mut a = 42;
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/// let mut b = 1337;
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///
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/// let t = b;
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/// b = a;
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/// a = t;
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/// ```
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/// Use std::mem::swap():
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/// ```rust
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/// let mut a = 1;
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/// let mut b = 2;
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/// std::mem::swap(&mut a, &mut b);
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/// ```
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pub MANUAL_SWAP,
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complexity,
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"manual swap of two variables"
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}
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declare_clippy_lint! {
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/// **What it does:** Checks for `foo = bar; bar = foo` sequences.
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///
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/// **Why is this bad?** This looks like a failed attempt to swap.
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///
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/// **Known problems:** None.
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///
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/// **Example:**
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/// ```rust
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/// # let mut a = 1;
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/// # let mut b = 2;
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/// a = b;
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/// b = a;
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/// ```
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/// If swapping is intended, use `swap()` instead:
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/// ```rust
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/// # let mut a = 1;
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/// # let mut b = 2;
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/// std::mem::swap(&mut a, &mut b);
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/// ```
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pub ALMOST_SWAPPED,
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correctness,
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"`foo = bar; bar = foo` sequence"
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}
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declare_lint_pass!(Swap => [MANUAL_SWAP, ALMOST_SWAPPED]);
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Swap {
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fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block<'_>) {
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check_manual_swap(cx, block);
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check_suspicious_swap(cx, block);
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}
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}
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/// Implementation of the `MANUAL_SWAP` lint.
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fn check_manual_swap(cx: &LateContext<'_, '_>, block: &Block<'_>) {
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for w in block.stmts.windows(3) {
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if_chain! {
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// let t = foo();
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if let StmtKind::Local(ref tmp) = w[0].kind;
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if let Some(ref tmp_init) = tmp.init;
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if let PatKind::Binding(.., ident, None) = tmp.pat.kind;
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// foo() = bar();
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if let StmtKind::Semi(ref first) = w[1].kind;
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if let ExprKind::Assign(ref lhs1, ref rhs1, _) = first.kind;
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// bar() = t;
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if let StmtKind::Semi(ref second) = w[2].kind;
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if let ExprKind::Assign(ref lhs2, ref rhs2, _) = second.kind;
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if let ExprKind::Path(QPath::Resolved(None, ref rhs2)) = rhs2.kind;
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if rhs2.segments.len() == 1;
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if ident.as_str() == rhs2.segments[0].ident.as_str();
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if SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1);
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if SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2);
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then {
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if let ExprKind::Field(ref lhs1, _) = lhs1.kind {
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if let ExprKind::Field(ref lhs2, _) = lhs2.kind {
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if lhs1.hir_id.owner_def_id() == lhs2.hir_id.owner_def_id() {
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return;
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}
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}
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}
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let mut applicability = Applicability::MachineApplicable;
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let slice = check_for_slice(cx, lhs1, lhs2);
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let (replace, what, sugg) = if let Slice::NotSwappable = slice {
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return;
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} else if let Slice::Swappable(slice, idx1, idx2) = slice {
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if let Some(slice) = Sugg::hir_opt(cx, slice) {
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(
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false,
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format!(" elements of `{}`", slice),
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format!(
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"{}.swap({}, {})",
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slice.maybe_par(),
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snippet_with_applicability(cx, idx1.span, "..", &mut applicability),
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snippet_with_applicability(cx, idx2.span, "..", &mut applicability),
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),
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)
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} else {
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(false, String::new(), String::new())
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}
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} else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
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(
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true,
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format!(" `{}` and `{}`", first, second),
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format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()),
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)
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} else {
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(true, String::new(), String::new())
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};
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let span = w[0].span.to(second.span);
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span_lint_and_then(
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cx,
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MANUAL_SWAP,
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span,
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&format!("this looks like you are swapping{} manually", what),
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|db| {
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if !sugg.is_empty() {
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db.span_suggestion(
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span,
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"try",
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sugg,
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applicability,
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);
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if replace {
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db.note("or maybe you should use `std::mem::replace`?");
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}
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}
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}
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);
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}
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}
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}
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}
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enum Slice<'a> {
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/// `slice.swap(idx1, idx2)` can be used
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///
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/// ## Example
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///
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/// ```rust
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/// # let mut a = vec![0, 1];
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/// let t = a[1];
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/// a[1] = a[0];
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/// a[0] = t;
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/// // can be written as
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/// a.swap(0, 1);
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/// ```
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Swappable(&'a Expr<'a>, &'a Expr<'a>, &'a Expr<'a>),
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/// The `swap` function cannot be used.
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///
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/// ## Example
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///
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/// ```rust
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/// # let mut a = [vec![1, 2], vec![3, 4]];
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/// let t = a[0][1];
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/// a[0][1] = a[1][0];
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/// a[1][0] = t;
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/// ```
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NotSwappable,
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/// Not a slice
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None,
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}
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/// Checks if both expressions are index operations into "slice-like" types.
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fn check_for_slice<'a>(cx: &LateContext<'_, '_>, lhs1: &'a Expr<'_>, lhs2: &'a Expr<'_>) -> Slice<'a> {
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if let ExprKind::Index(ref lhs1, ref idx1) = lhs1.kind {
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if let ExprKind::Index(ref lhs2, ref idx2) = lhs2.kind {
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if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
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let ty = walk_ptrs_ty(cx.tables.expr_ty(lhs1));
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if matches!(ty.kind, ty::Slice(_))
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|| matches!(ty.kind, ty::Array(_, _))
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|| is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type"))
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|| match_type(cx, ty, &paths::VEC_DEQUE)
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{
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return Slice::Swappable(lhs1, idx1, idx2);
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}
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} else {
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return Slice::NotSwappable;
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}
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}
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}
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Slice::None
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}
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/// Implementation of the `ALMOST_SWAPPED` lint.
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fn check_suspicious_swap(cx: &LateContext<'_, '_>, block: &Block<'_>) {
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for w in block.stmts.windows(2) {
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if_chain! {
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if let StmtKind::Semi(ref first) = w[0].kind;
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if let StmtKind::Semi(ref second) = w[1].kind;
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if !differing_macro_contexts(first.span, second.span);
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if let ExprKind::Assign(ref lhs0, ref rhs0, _) = first.kind;
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if let ExprKind::Assign(ref lhs1, ref rhs1, _) = second.kind;
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if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
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if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
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then {
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let lhs0 = Sugg::hir_opt(cx, lhs0);
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let rhs0 = Sugg::hir_opt(cx, rhs0);
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let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
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(
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format!(" `{}` and `{}`", first, second),
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first.mut_addr().to_string(),
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second.mut_addr().to_string(),
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)
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} else {
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(String::new(), String::new(), String::new())
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};
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let span = first.span.to(second.span);
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span_lint_and_then(cx,
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ALMOST_SWAPPED,
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span,
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&format!("this looks like you are trying to swap{}", what),
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|db| {
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if !what.is_empty() {
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db.span_suggestion(
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span,
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"try",
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format!(
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"std::mem::swap({}, {})",
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lhs,
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rhs,
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),
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Applicability::MaybeIncorrect,
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);
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db.note("or maybe you should use `std::mem::replace`?");
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}
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});
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}
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}
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}
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}
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