clippy_lints/src/ranges.rs

   1 use rustc::lint::*;
   2 use rustc::hir::*;
   3 use syntax::codemap::Spanned;
   4 use utils::{is_integer_literal, paths, snippet, span_lint};
   5 use utils::{higher, implements_trait, get_trait_def_id};
   6
   7 /// **What it does:** Checks for calling `.step_by(0)` on iterators,
   8 /// which never terminates.
   9 ///
  10 /// **Why is this bad?** This very much looks like an oversight, since with
  11 /// `loop { .. }` there is an obvious better way to endlessly loop.
  12 ///
  13 /// **Known problems:** None.
  14 ///
  15 /// **Example:**
  16 /// ```rust
  17 /// for x in (5..5).step_by(0) { .. }
  18 /// ```
  19 declare_lint! {
  20     pub ITERATOR_STEP_BY_ZERO,
  21     Warn,
  22     "using `Iterator::step_by(0)`, which produces an infinite iterator"
  23 }
  24
  25 /// **What it does:** Checks for zipping a collection with the range of `0.._.len()`.
  26 ///
  27 /// **Why is this bad?** The code is better expressed with `.enumerate()`.
  28 ///
  29 /// **Known problems:** None.
  30 ///
  31 /// **Example:**
  32 /// ```rust
  33 /// x.iter().zip(0..x.len())
  34 /// ```
  35 declare_lint! {
  36     pub RANGE_ZIP_WITH_LEN,
  37     Warn,
  38     "zipping iterator with a range when `enumerate()` would do"
  39 }
  40
  41 #[derive(Copy,Clone)]
  42 pub struct StepByZero;
  43
  44 impl LintPass for StepByZero {
  45     fn get_lints(&self) -> LintArray {
  46         lint_array!(ITERATOR_STEP_BY_ZERO, RANGE_ZIP_WITH_LEN)
  47     }
  48 }
  49
  50 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StepByZero {
  51     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) {
  52         if let ExprMethodCall(Spanned { node: ref name, .. }, _, ref args) = expr.node {
  53             let name = name.as_str();
  54
  55             // Range with step_by(0).
  56             if name == "step_by" && args.len() == 2 && has_step_by(cx, &args[0]) {
  57                 use consts::{Constant, constant};
  58                 use rustc_const_math::ConstInt::Usize;
  59                 if let Some((Constant::Int(Usize(us)), _)) = constant(cx, &args[1]) {
  60                     if us.as_u64(cx.sess().target.uint_type) == 0 {
  61                         span_lint(
  62                             cx,
  63                             ITERATOR_STEP_BY_ZERO,
  64                             expr.span,
  65                             "Iterator::step_by(0) will panic at runtime",
  66                         );
  67                     }
  68                 }
  69             } else if name == "zip" && args.len() == 2 {
  70                 let iter = &args[0].node;
  71                 let zip_arg = &args[1];
  72                 if_let_chain! {[
  73                     // .iter() call
  74                     let ExprMethodCall( Spanned { node: iter_name, .. }, _, ref iter_args ) = *iter,
  75                     iter_name == "iter",
  76                     // range expression in .zip() call: 0..x.len()
  77                     let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(zip_arg),
  78                     is_integer_literal(start, 0),
  79                     // .len() call
  80                     let ExprMethodCall(Spanned { node: len_name, .. }, _, ref len_args) = end.node,
  81                     len_name == "len" && len_args.len() == 1,
  82                     // .iter() and .len() called on same Path
  83                     let ExprPath(QPath::Resolved(_, ref iter_path)) = iter_args[0].node,
  84                     let ExprPath(QPath::Resolved(_, ref len_path)) = len_args[0].node,
  85                     iter_path.segments == len_path.segments
  86                  ], {
  87                      span_lint(cx,
  88                                RANGE_ZIP_WITH_LEN,
  89                                expr.span,
  90                                &format!("It is more idiomatic to use {}.iter().enumerate()",
  91                                         snippet(cx, iter_args[0].span, "_")));
  92                 }}
  93             }
  94         }
  95     }
  96 }
  97
  98 fn has_step_by(cx: &LateContext, expr: &Expr) -> bool {
  99     // No need for walk_ptrs_ty here because step_by moves self, so it
 100     // can't be called on a borrowed range.
 101     let ty = cx.tables.expr_ty_adjusted(expr);
 102
 103     get_trait_def_id(cx, &paths::ITERATOR)
 104         .map_or(
 105             false,
 106             |iterator_trait| implements_trait(cx, ty, iterator_trait, &[])
 107         )
 108 }