rust-clippy/clippy_lints/src/duration_subsec.rs

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use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::match_type;
use if_chain::if_chain;
use rustc_errors::Applicability;
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use rustc_hir::{BinOpKind, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Spanned;
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use clippy_utils::consts::{constant, Constant};
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::paths;
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declare_clippy_lint! {
/// ### What it does
/// Checks for calculation of subsecond microseconds or milliseconds
/// from other `Duration` methods.
///
/// ### Why is this bad?
/// It's more concise to call `Duration::subsec_micros()` or
/// `Duration::subsec_millis()` than to calculate them.
///
/// ### Example
/// ```rust
/// # use std::time::Duration;
/// let dur = Duration::new(5, 0);
///
/// // Bad
/// let _micros = dur.subsec_nanos() / 1_000;
/// let _millis = dur.subsec_nanos() / 1_000_000;
///
/// // Good
/// let _micros = dur.subsec_micros();
/// let _millis = dur.subsec_millis();
/// ```
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pub DURATION_SUBSEC,
complexity,
"checks for calculation of subsecond microseconds or milliseconds"
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}
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declare_lint_pass!(DurationSubsec => [DURATION_SUBSEC]);
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impl<'tcx> LateLintPass<'tcx> for DurationSubsec {
fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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if_chain! {
if let ExprKind::Binary(Spanned { node: BinOpKind::Div, .. }, left, right) = expr.kind;
if let ExprKind::MethodCall(method_path, _ , args, _) = left.kind;
if match_type(cx, cx.typeck_results().expr_ty(&args[0]).peel_refs(), &paths::DURATION);
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if let Some((Constant::Int(divisor), _)) = constant(cx, cx.typeck_results(), right);
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then {
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let suggested_fn = match (method_path.ident.as_str().as_ref(), divisor) {
("subsec_micros", 1_000) | ("subsec_nanos", 1_000_000) => "subsec_millis",
("subsec_nanos", 1_000) => "subsec_micros",
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_ => return,
};
let mut applicability = Applicability::MachineApplicable;
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span_lint_and_sugg(
cx,
DURATION_SUBSEC,
expr.span,
&format!("calling `{}()` is more concise than this calculation", suggested_fn),
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"try",
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format!(
"{}.{}()",
snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
suggested_fn
),
applicability,
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);
}
}
}
}