clippy_lints/src/duration_subsec.rs

   1 use clippy_utils::source::snippet_with_applicability;
   2 use clippy_utils::ty::match_type;
   3 use if_chain::if_chain;
   4 use rustc_errors::Applicability;
   5 use rustc_hir::{BinOpKind, Expr, ExprKind};
   6 use rustc_lint::{LateContext, LateLintPass};
   7 use rustc_session::{declare_lint_pass, declare_tool_lint};
   8 use rustc_span::source_map::Spanned;
   9
  10 use crate::consts::{constant, Constant};
  11 use clippy_utils::diagnostics::span_lint_and_sugg;
  12 use clippy_utils::paths;
  13
  14 declare_clippy_lint! {
  15     /// **What it does:** Checks for calculation of subsecond microseconds or milliseconds
  16     /// from other `Duration` methods.
  17     ///
  18     /// **Why is this bad?** It's more concise to call `Duration::subsec_micros()` or
  19     /// `Duration::subsec_millis()` than to calculate them.
  20     ///
  21     /// **Known problems:** None.
  22     ///
  23     /// **Example:**
  24     /// ```rust
  25     /// # use std::time::Duration;
  26     /// let dur = Duration::new(5, 0);
  27     ///
  28     /// // Bad
  29     /// let _micros = dur.subsec_nanos() / 1_000;
  30     /// let _millis = dur.subsec_nanos() / 1_000_000;
  31     ///
  32     /// // Good
  33     /// let _micros = dur.subsec_micros();
  34     /// let _millis = dur.subsec_millis();
  35     /// ```
  36     pub DURATION_SUBSEC,
  37     complexity,
  38     "checks for calculation of subsecond microseconds or milliseconds"
  39 }
  40
  41 declare_lint_pass!(DurationSubsec => [DURATION_SUBSEC]);
  42
  43 impl<'tcx> LateLintPass<'tcx> for DurationSubsec {
  44     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  45         if_chain! {
  46             if let ExprKind::Binary(Spanned { node: BinOpKind::Div, .. }, left, right) = expr.kind;
  47             if let ExprKind::MethodCall(method_path, _ , args, _) = left.kind;
  48             if match_type(cx, cx.typeck_results().expr_ty(&args[0]).peel_refs(), &paths::DURATION);
  49             if let Some((Constant::Int(divisor), _)) = constant(cx, cx.typeck_results(), right);
  50             then {
  51                 let suggested_fn = match (method_path.ident.as_str().as_ref(), divisor) {
  52                     ("subsec_micros", 1_000) | ("subsec_nanos", 1_000_000) => "subsec_millis",
  53                     ("subsec_nanos", 1_000) => "subsec_micros",
  54                     _ => return,
  55                 };
  56                 let mut applicability = Applicability::MachineApplicable;
  57                 span_lint_and_sugg(
  58                     cx,
  59                     DURATION_SUBSEC,
  60                     expr.span,
  61                     &format!("calling `{}()` is more concise than this calculation", suggested_fn),
  62                     "try",
  63                     format!(
  64                         "{}.{}()",
  65                         snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
  66                         suggested_fn
  67                     ),
  68                     applicability,
  69                 );
  70             }
  71         }
  72     }
  73 }