clippy_lints/src/duration_subsec.rs

   1 use clippy_utils::consts::{constant, Constant};
   2 use clippy_utils::diagnostics::span_lint_and_sugg;
   3 use clippy_utils::source::snippet_with_applicability;
   4 use clippy_utils::ty::is_type_diagnostic_item;
   5 use if_chain::if_chain;
   6 use rustc_errors::Applicability;
   7 use rustc_hir::{BinOpKind, Expr, ExprKind};
   8 use rustc_lint::{LateContext, LateLintPass};
   9 use rustc_session::{declare_lint_pass, declare_tool_lint};
  10 use rustc_span::source_map::Spanned;
  11 use rustc_span::sym;
  12
  13 declare_clippy_lint! {
  14     /// ### What it does
  15     /// Checks for calculation of subsecond microseconds or milliseconds
  16     /// from other `Duration` methods.
  17     ///
  18     /// ### Why is this bad?
  19     /// It's more concise to call `Duration::subsec_micros()` or
  20     /// `Duration::subsec_millis()` than to calculate them.
  21     ///
  22     /// ### Example
  23     /// ```rust
  24     /// # use std::time::Duration;
  25     /// # let duration = Duration::new(5, 0);
  26     /// let micros = duration.subsec_nanos() / 1_000;
  27     /// let millis = duration.subsec_nanos() / 1_000_000;
  28     /// ```
  29     ///
  30     /// Use instead:
  31     /// ```rust
  32     /// # use std::time::Duration;
  33     /// # let duration = Duration::new(5, 0);
  34     /// let micros = duration.subsec_micros();
  35     /// let millis = duration.subsec_millis();
  36     /// ```
  37     #[clippy::version = "pre 1.29.0"]
  38     pub DURATION_SUBSEC,
  39     complexity,
  40     "checks for calculation of subsecond microseconds or milliseconds"
  41 }
  42
  43 declare_lint_pass!(DurationSubsec => [DURATION_SUBSEC]);
  44
  45 impl<'tcx> LateLintPass<'tcx> for DurationSubsec {
  46     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
  47         if_chain! {
  48             if let ExprKind::Binary(Spanned { node: BinOpKind::Div, .. }, left, right) = expr.kind;
  49             if let ExprKind::MethodCall(method_path, args, _) = left.kind;
  50             if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&args[0]).peel_refs(), sym::Duration);
  51             if let Some((Constant::Int(divisor), _)) = constant(cx, cx.typeck_results(), right);
  52             then {
  53                 let suggested_fn = match (method_path.ident.as_str(), divisor) {
  54                     ("subsec_micros", 1_000) | ("subsec_nanos", 1_000_000) => "subsec_millis",
  55                     ("subsec_nanos", 1_000) => "subsec_micros",
  56                     _ => return,
  57                 };
  58                 let mut applicability = Applicability::MachineApplicable;
  59                 span_lint_and_sugg(
  60                     cx,
  61                     DURATION_SUBSEC,
  62                     expr.span,
  63                     &format!("calling `{}()` is more concise than this calculation", suggested_fn),
  64                     "try",
  65                     format!(
  66                         "{}.{}()",
  67                         snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
  68                         suggested_fn
  69                     ),
  70                     applicability,
  71                 );
  72             }
  73         }
  74     }
  75 }