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use clippy_utils::diagnostics::span_lint_and_sugg;
use rustc_errors::Applicability;
use rustc_hir::{BinOpKind, Expr, ExprKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
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 = "1.64.0"]
pub MANUAL_INSTANT_ELAPSED,
pedantic,
"subtraction between `Instant::now()` and previous `Instant`"
}
declare_lint_pass!(ManualInstantElapsed => [MANUAL_INSTANT_ELAPSED]);
impl LateLintPass<'_> for ManualInstantElapsed {
fn check_expr(&mut self, cx: &LateContext<'_>, expr: &'_ Expr<'_>) {
if let ExprKind::Binary(Spanned {node: BinOpKind::Sub, ..}, lhs, rhs) = expr.kind
&& check_instant_now_call(cx, lhs)
&& let ty_resolved = cx.typeck_results().expr_ty(rhs)
&& let rustc_middle::ty::Adt(def, _) = ty_resolved.kind()
&& clippy_utils::match_def_path(cx, def.did(), &clippy_utils::paths::INSTANT)
&& let Some(sugg) = clippy_utils::sugg::Sugg::hir_opt(cx, rhs)
{
span_lint_and_sugg(
cx,
MANUAL_INSTANT_ELAPSED,
expr.span,
"manual implementation of `Instant::elapsed`",
"try",
format!("{}.elapsed()", sugg.maybe_par()),
Applicability::MachineApplicable,
);
}
}
}
fn check_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
}
}
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