rust/clippy_lints/src/swap.rs
2018-03-28 15:24:26 +02:00

185 lines
7.0 KiB
Rust

use rustc::hir::*;
use rustc::lint::*;
use rustc::ty;
use utils::{differing_macro_contexts, match_type, paths, snippet, span_lint_and_then, walk_ptrs_ty, SpanlessEq};
use utils::sugg::Sugg;
/// **What it does:** Checks for manual swapping.
///
/// **Why is this bad?** The `std::mem::swap` function exposes the intent better
/// without deinitializing or copying either variable.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// let t = b;
/// b = a;
/// a = t;
/// ```
declare_clippy_lint! {
pub MANUAL_SWAP,
complexity,
"manual swap of two variables"
}
/// **What it does:** Checks for `foo = bar; bar = foo` sequences.
///
/// **Why is this bad?** This looks like a failed attempt to swap.
///
/// **Known problems:** None.
///
/// **Example:**
/// ```rust,ignore
/// a = b;
/// b = a;
/// ```
declare_clippy_lint! {
pub ALMOST_SWAPPED,
correctness,
"`foo = bar; bar = foo` sequence"
}
#[derive(Copy, Clone)]
pub struct Swap;
impl LintPass for Swap {
fn get_lints(&self) -> LintArray {
lint_array![MANUAL_SWAP, ALMOST_SWAPPED]
}
}
impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Swap {
fn check_block(&mut self, cx: &LateContext<'a, 'tcx>, block: &'tcx Block) {
check_manual_swap(cx, block);
check_suspicious_swap(cx, block);
}
}
/// Implementation of the `MANUAL_SWAP` lint.
fn check_manual_swap(cx: &LateContext, block: &Block) {
for w in block.stmts.windows(3) {
if_chain! {
// let t = foo();
if let StmtDecl(ref tmp, _) = w[0].node;
if let DeclLocal(ref tmp) = tmp.node;
if let Some(ref tmp_init) = tmp.init;
if let PatKind::Binding(_, _, ref tmp_name, None) = tmp.pat.node;
// foo() = bar();
if let StmtSemi(ref first, _) = w[1].node;
if let ExprAssign(ref lhs1, ref rhs1) = first.node;
// bar() = t;
if let StmtSemi(ref second, _) = w[2].node;
if let ExprAssign(ref lhs2, ref rhs2) = second.node;
if let ExprPath(QPath::Resolved(None, ref rhs2)) = rhs2.node;
if rhs2.segments.len() == 1;
if tmp_name.node.as_str() == rhs2.segments[0].name.as_str();
if SpanlessEq::new(cx).ignore_fn().eq_expr(tmp_init, lhs1);
if SpanlessEq::new(cx).ignore_fn().eq_expr(rhs1, lhs2);
then {
fn check_for_slice<'a>(
cx: &LateContext,
lhs1: &'a Expr,
lhs2: &'a Expr,
) -> Option<(&'a Expr, &'a Expr, &'a Expr)> {
if let ExprIndex(ref lhs1, ref idx1) = lhs1.node {
if let ExprIndex(ref lhs2, ref idx2) = lhs2.node {
if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, lhs2) {
let ty = walk_ptrs_ty(cx.tables.expr_ty(lhs1));
if matches!(ty.sty, ty::TySlice(_)) ||
matches!(ty.sty, ty::TyArray(_, _)) ||
match_type(cx, ty, &paths::VEC) ||
match_type(cx, ty, &paths::VEC_DEQUE) {
return Some((lhs1, idx1, idx2));
}
}
}
}
None
}
let (replace, what, sugg) = if let Some((slice, idx1, idx2)) = check_for_slice(cx, lhs1, lhs2) {
if let Some(slice) = Sugg::hir_opt(cx, slice) {
(false,
format!(" elements of `{}`", slice),
format!("{}.swap({}, {})",
slice.maybe_par(),
snippet(cx, idx1.span, ".."),
snippet(cx, idx2.span, "..")))
} else {
(false, "".to_owned(), "".to_owned())
}
} else if let (Some(first), Some(second)) = (Sugg::hir_opt(cx, lhs1), Sugg::hir_opt(cx, rhs1)) {
(true, format!(" `{}` and `{}`", first, second),
format!("std::mem::swap({}, {})", first.mut_addr(), second.mut_addr()))
} else {
(true, "".to_owned(), "".to_owned())
};
let span = w[0].span.to(second.span);
span_lint_and_then(cx,
MANUAL_SWAP,
span,
&format!("this looks like you are swapping{} manually", what),
|db| {
if !sugg.is_empty() {
db.span_suggestion(span, "try", sugg);
if replace {
db.note("or maybe you should use `std::mem::replace`?");
}
}
});
}
}
}
}
/// Implementation of the `ALMOST_SWAPPED` lint.
fn check_suspicious_swap(cx: &LateContext, block: &Block) {
for w in block.stmts.windows(2) {
if_chain! {
if let StmtSemi(ref first, _) = w[0].node;
if let StmtSemi(ref second, _) = w[1].node;
if !differing_macro_contexts(first.span, second.span);
if let ExprAssign(ref lhs0, ref rhs0) = first.node;
if let ExprAssign(ref lhs1, ref rhs1) = second.node;
if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs0, rhs1);
if SpanlessEq::new(cx).ignore_fn().eq_expr(lhs1, rhs0);
then {
let lhs0 = Sugg::hir_opt(cx, lhs0);
let rhs0 = Sugg::hir_opt(cx, rhs0);
let (what, lhs, rhs) = if let (Some(first), Some(second)) = (lhs0, rhs0) {
(
format!(" `{}` and `{}`", first, second),
first.mut_addr().to_string(),
second.mut_addr().to_string(),
)
} else {
("".to_owned(), "".to_owned(), "".to_owned())
};
let span = first.span.to(second.span);
span_lint_and_then(cx,
ALMOST_SWAPPED,
span,
&format!("this looks like you are trying to swap{}", what),
|db| {
if !what.is_empty() {
db.span_suggestion(span, "try",
format!("std::mem::swap({}, {})", lhs, rhs));
db.note("or maybe you should use `std::mem::replace`?");
}
});
}
}
}
}