clippy_lints/src/duration_subsec.rs

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