src/tools/clippy/clippy_lints/src/duration_subsec.rs

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