use rustc::lint::*; use rustc::hir::*; use utils::{is_integer_literal, paths, snippet, span_lint}; use utils::{get_trait_def_id, higher, implements_trait}; /// **What it does:** Checks for calling `.step_by(0)` on iterators, /// which never terminates. /// /// **Why is this bad?** This very much looks like an oversight, since with /// `loop { .. }` there is an obvious better way to endlessly loop. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// for x in (5..5).step_by(0) { .. } /// ``` declare_lint! { pub ITERATOR_STEP_BY_ZERO, Warn, "using `Iterator::step_by(0)`, which produces an infinite iterator" } /// **What it does:** Checks for zipping a collection with the range of /// `0.._.len()`. /// /// **Why is this bad?** The code is better expressed with `.enumerate()`. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// x.iter().zip(0..x.len()) /// ``` declare_lint! { pub RANGE_ZIP_WITH_LEN, Warn, "zipping iterator with a range when `enumerate()` would do" } #[derive(Copy, Clone)] pub struct StepByZero; impl LintPass for StepByZero { fn get_lints(&self) -> LintArray { lint_array!(ITERATOR_STEP_BY_ZERO, RANGE_ZIP_WITH_LEN) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for StepByZero { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { if let ExprMethodCall(ref path, _, ref args) = expr.node { let name = path.name.as_str(); // Range with step_by(0). if name == "step_by" && args.len() == 2 && has_step_by(cx, &args[0]) { use consts::{constant, Constant}; use rustc_const_math::ConstInt::Usize; if let Some((Constant::Int(Usize(us)), _)) = constant(cx, &args[1]) { if us.as_u64(cx.sess().target.uint_type) == 0 { span_lint( cx, ITERATOR_STEP_BY_ZERO, expr.span, "Iterator::step_by(0) will panic at runtime", ); } } } else if name == "zip" && args.len() == 2 { let iter = &args[0].node; let zip_arg = &args[1]; if_let_chain! {[ // .iter() call let ExprMethodCall(ref iter_path, _, ref iter_args ) = *iter, iter_path.name == "iter", // range expression in .zip() call: 0..x.len() let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(zip_arg), is_integer_literal(start, 0), // .len() call let ExprMethodCall(ref len_path, _, ref len_args) = end.node, len_path.name == "len" && len_args.len() == 1, // .iter() and .len() called on same Path let ExprPath(QPath::Resolved(_, ref iter_path)) = iter_args[0].node, let ExprPath(QPath::Resolved(_, ref len_path)) = len_args[0].node, iter_path.segments == len_path.segments ], { span_lint(cx, RANGE_ZIP_WITH_LEN, expr.span, &format!("It is more idiomatic to use {}.iter().enumerate()", snippet(cx, iter_args[0].span, "_"))); }} } } } } fn has_step_by(cx: &LateContext, expr: &Expr) -> bool { // No need for walk_ptrs_ty here because step_by moves self, so it // can't be called on a borrowed range. let ty = cx.tables.expr_ty_adjusted(expr); get_trait_def_id(cx, &paths::ITERATOR).map_or(false, |iterator_trait| implements_trait(cx, ty, iterator_trait, &[])) }