clippy_lints/src/duration_subsec.rs

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