clippy_lints/src/duration_subsec.rs

   1 // Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution.
   3 //
   4 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   5 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   6 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   7 // option. This file may not be copied, modified, or distributed
   8 // except according to those terms.
   9
  10 use if_chain::if_chain;
  11 use rustc::hir::*;
  12 use rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
  13 use rustc::{declare_tool_lint, lint_array};
  14 use rustc_errors::Applicability;
  15 use syntax::source_map::Spanned;
  16
  17 use crate::consts::{constant, Constant};
  18 use crate::utils::paths;
  19 use crate::utils::{match_type, snippet_with_applicability, span_lint_and_sugg, walk_ptrs_ty};
  20
  21 /// **What it does:** Checks for calculation of subsecond microseconds or milliseconds
  22 /// from other `Duration` methods.
  23 ///
  24 /// **Why is this bad?** It's more concise to call `Duration::subsec_micros()` or
  25 /// `Duration::subsec_millis()` than to calculate them.
  26 ///
  27 /// **Known problems:** None.
  28 ///
  29 /// **Example:**
  30 /// ```rust
  31 /// let dur = Duration::new(5, 0);
  32 /// let _micros = dur.subsec_nanos() / 1_000;
  33 /// let _millis = dur.subsec_nanos() / 1_000_000;
  34 /// ```
  35 declare_clippy_lint! {
  36     pub DURATION_SUBSEC,
  37     complexity,
  38     "checks for calculation of subsecond microseconds or milliseconds"
  39 }
  40
  41 #[derive(Copy, Clone)]
  42 pub struct DurationSubsec;
  43
  44 impl LintPass for DurationSubsec {
  45     fn get_lints(&self) -> LintArray {
  46         lint_array!(DURATION_SUBSEC)
  47     }
  48 }
  49
  50 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for DurationSubsec {
  51     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  52         if_chain! {
  53             if let ExprKind::Binary(Spanned { node: BinOpKind::Div, .. }, ref left, ref right) = expr.node;
  54             if let ExprKind::MethodCall(ref method_path, _ , ref args) = left.node;
  55             if match_type(cx, walk_ptrs_ty(cx.tables.expr_ty(&args[0])), &paths::DURATION);
  56             if let Some((Constant::Int(divisor), _)) = constant(cx, cx.tables, right);
  57             then {
  58                 let suggested_fn = match (method_path.ident.as_str().as_ref(), divisor) {
  59                     ("subsec_micros", 1_000) | ("subsec_nanos", 1_000_000) => "subsec_millis",
  60                     ("subsec_nanos", 1_000) => "subsec_micros",
  61                     _ => return,
  62                 };
  63                 let mut applicability = Applicability::MachineApplicable;
  64                 span_lint_and_sugg(
  65                     cx,
  66                     DURATION_SUBSEC,
  67                     expr.span,
  68                     &format!("Calling `{}()` is more concise than this calculation", suggested_fn),
  69                     "try",
  70                     format!(
  71                         "{}.{}()",
  72                         snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
  73                         suggested_fn
  74                     ),
  75                     applicability,
  76                 );
  77             }
  78         }
  79     }
  80 }