clippy_lints/src/duration_subsec.rs

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