clippy_lints/src/duration_subsec.rs

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