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use clippy_utils::diagnostics::{self, span_lint_and_sugg};
use clippy_utils::msrvs::{self, Msrv};
use clippy_utils::source;
use clippy_utils::sugg::Sugg;
use clippy_utils::ty;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_tool_lint, impl_lint_pass};
use rustc_span::{source_map::Spanned, sym};
declare_clippy_lint! {
/// ### What it does
/// Lints subtraction between `Instant::now()` and another `Instant`.
///
/// ### Why is this bad?
/// It is easy to accidentally write `prev_instant - Instant::now()`, which will always be 0ns
/// as `Instant` subtraction saturates.
///
/// `prev_instant.elapsed()` also more clearly signals intention.
///
/// ### Example
/// ```rust
/// use std::time::Instant;
/// let prev_instant = Instant::now();
/// let duration = Instant::now() - prev_instant;
/// ```
/// Use instead:
/// ```rust
/// use std::time::Instant;
/// let prev_instant = Instant::now();
/// let duration = prev_instant.elapsed();
/// ```
#[clippy::version = "1.65.0"]
pub MANUAL_INSTANT_ELAPSED,
pedantic,
"subtraction between `Instant::now()` and previous `Instant`"
}
declare_clippy_lint! {
/// ### What it does
/// Lints subtraction between an [`Instant`] and a [`Duration`].
///
/// ### Why is this bad?
/// Unchecked subtraction could cause underflow on certain platforms, leading to
/// unintentional panics.
///
/// ### Example
/// ```rust
/// # use std::time::{Instant, Duration};
/// let time_passed = Instant::now() - Duration::from_secs(5);
/// ```
///
/// Use instead:
/// ```rust
/// # use std::time::{Instant, Duration};
/// let time_passed = Instant::now().checked_sub(Duration::from_secs(5));
/// ```
///
/// [`Duration`]: std::time::Duration
/// [`Instant::now()`]: std::time::Instant::now;
#[clippy::version = "1.67.0"]
pub UNCHECKED_DURATION_SUBTRACTION,
pedantic,
"finds unchecked subtraction of a 'Duration' from an 'Instant'"
}
pub struct InstantSubtraction {
msrv: Msrv,
}
impl InstantSubtraction {
#[must_use]
pub fn new(msrv: Msrv) -> Self {
Self { msrv }
}
}
impl_lint_pass!(InstantSubtraction => [MANUAL_INSTANT_ELAPSED, UNCHECKED_DURATION_SUBTRACTION]);
impl LateLintPass<'_> for InstantSubtraction {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ Expr<'_>) {
if let ExprKind::Binary(
Spanned {
node: BinOpKind::Sub, ..
},
lhs,
rhs,
) = expr.kind
{
if_chain! {
if is_instant_now_call(cx, lhs);
if is_an_instant(cx, rhs);
if let Some(sugg) = Sugg::hir_opt(cx, rhs);
then {
print_manual_instant_elapsed_sugg(cx, expr, sugg)
} else {
if_chain! {
if !expr.span.from_expansion();
if self.msrv.meets(msrvs::TRY_FROM);
if is_an_instant(cx, lhs);
if is_a_duration(cx, rhs);
then {
print_unchecked_duration_subtraction_sugg(cx, lhs, rhs, expr)
}
}
}
}
}
}
extract_msrv_attr!(LateContext);
}
fn is_instant_now_call(cx: &LateContext<'_>, expr_block: &'_ Expr<'_>) -> bool {
if let ExprKind::Call(fn_expr, []) = expr_block.kind
&& let Some(fn_id) = clippy_utils::path_def_id(cx, fn_expr)
&& clippy_utils::match_def_path(cx, fn_id, &clippy_utils::paths::INSTANT_NOW)
{
true
} else {
false
}
}
fn is_an_instant(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
let expr_ty = cx.typeck_results().expr_ty(expr);
match expr_ty.kind() {
rustc_middle::ty::Adt(def, _) => clippy_utils::match_def_path(cx, def.did(), &clippy_utils::paths::INSTANT),
_ => false,
}
}
fn is_a_duration(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
let expr_ty = cx.typeck_results().expr_ty(expr);
ty::is_type_diagnostic_item(cx, expr_ty, sym::Duration)
}
fn print_manual_instant_elapsed_sugg(cx: &LateContext<'_>, expr: &Expr<'_>, sugg: Sugg<'_>) {
span_lint_and_sugg(
cx,
MANUAL_INSTANT_ELAPSED,
expr.span,
"manual implementation of `Instant::elapsed`",
"try",
format!("{}.elapsed()", sugg.maybe_par()),
Applicability::MachineApplicable,
);
}
fn print_unchecked_duration_subtraction_sugg(
cx: &LateContext<'_>,
left_expr: &Expr<'_>,
right_expr: &Expr<'_>,
expr: &Expr<'_>,
) {
let mut applicability = Applicability::MachineApplicable;
let left_expr =
source::snippet_with_applicability(cx, left_expr.span, "std::time::Instant::now()", &mut applicability);
let right_expr = source::snippet_with_applicability(
cx,
right_expr.span,
"std::time::Duration::from_secs(1)",
&mut applicability,
);
diagnostics::span_lint_and_sugg(
cx,
UNCHECKED_DURATION_SUBTRACTION,
expr.span,
"unchecked subtraction of a 'Duration' from an 'Instant'",
"try",
format!("{left_expr}.checked_sub({right_expr}).unwrap()"),
applicability,
);
}
|
