// Copyright 2014-2018 The Rust Project Developers. See the COPYRIGHT // file at the top-level directory of this distribution. // // Licensed under the Apache License, Version 2.0 or the MIT license // , at your // option. This file may not be copied, modified, or distributed // except according to those terms. use crate::rustc::hir::*; use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass}; use crate::rustc::{declare_tool_lint, lint_array}; use crate::rustc_errors::Applicability; use crate::syntax::ast::RangeLimits; use crate::syntax::source_map::Spanned; use crate::utils::sugg::Sugg; use crate::utils::{get_trait_def_id, higher, implements_trait, SpanlessEq}; use crate::utils::{is_integer_literal, paths, snippet, snippet_opt, span_lint, span_lint_and_then}; use if_chain::if_chain; /// **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_clippy_lint! { pub ITERATOR_STEP_BY_ZERO, correctness, "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_clippy_lint! { pub RANGE_ZIP_WITH_LEN, complexity, "zipping iterator with a range when `enumerate()` would do" } /// **What it does:** Checks for exclusive ranges where 1 is added to the /// upper bound, e.g. `x..(y+1)`. /// /// **Why is this bad?** The code is more readable with an inclusive range /// like `x..=y`. /// /// **Known problems:** Will add unnecessary pair of parentheses when the /// expression is not wrapped in a pair but starts with a opening parenthesis /// and ends with a closing one. /// I.e: `let _ = (f()+1)..(f()+1)` results in `let _ = ((f()+1)..=f())`. /// /// **Example:** /// ```rust /// for x..(y+1) { .. } /// ``` declare_clippy_lint! { pub RANGE_PLUS_ONE, complexity, "`x..(y+1)` reads better as `x..=y`" } /// **What it does:** Checks for inclusive ranges where 1 is subtracted from /// the upper bound, e.g. `x..=(y-1)`. /// /// **Why is this bad?** The code is more readable with an exclusive range /// like `x..y`. /// /// **Known problems:** None. /// /// **Example:** /// ```rust /// for x..=(y-1) { .. } /// ``` declare_clippy_lint! { pub RANGE_MINUS_ONE, complexity, "`x..=(y-1)` reads better as `x..y`" } #[derive(Copy, Clone)] pub struct Pass; impl LintPass for Pass { fn get_lints(&self) -> LintArray { lint_array!( ITERATOR_STEP_BY_ZERO, RANGE_ZIP_WITH_LEN, RANGE_PLUS_ONE, RANGE_MINUS_ONE ) } } impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass { fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx Expr) { if let ExprKind::MethodCall(ref path, _, ref args) = expr.node { let name = path.ident.as_str(); // Range with step_by(0). if name == "step_by" && args.len() == 2 && has_step_by(cx, &args[0]) { use crate::consts::{constant, Constant}; if let Some((Constant::Int(0), _)) = constant(cx, cx.tables, &args[1]) { 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_chain! { // .iter() call if let ExprKind::MethodCall(ref iter_path, _, ref iter_args ) = *iter; if iter_path.ident.name == "iter"; // range expression in .zip() call: 0..x.len() if let Some(higher::Range { start: Some(start), end: Some(end), .. }) = higher::range(cx, zip_arg); if is_integer_literal(start, 0); // .len() call if let ExprKind::MethodCall(ref len_path, _, ref len_args) = end.node; if len_path.ident.name == "len" && len_args.len() == 1; // .iter() and .len() called on same Path if let ExprKind::Path(QPath::Resolved(_, ref iter_path)) = iter_args[0].node; if let ExprKind::Path(QPath::Resolved(_, ref len_path)) = len_args[0].node; if SpanlessEq::new(cx).eq_path_segments(&iter_path.segments, &len_path.segments); then { span_lint(cx, RANGE_ZIP_WITH_LEN, expr.span, &format!("It is more idiomatic to use {}.iter().enumerate()", snippet(cx, iter_args[0].span, "_"))); } } } } // exclusive range plus one: x..(y+1) if_chain! { if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::HalfOpen }) = higher::range(cx, expr); if let Some(y) = y_plus_one(end); then { span_lint_and_then( cx, RANGE_PLUS_ONE, expr.span, "an inclusive range would be more readable", |db| { let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string()); let end = Sugg::hir(cx, y, "y"); if let Some(is_wrapped) = &snippet_opt(cx, expr.span) { if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') { db.span_suggestion_with_applicability( expr.span, "use", format!("({}..={})", start, end), Applicability::MaybeIncorrect, ); } else { db.span_suggestion_with_applicability( expr.span, "use", format!("{}..={}", start, end), Applicability::MachineApplicable, // snippet ); } } }, ); } } // inclusive range minus one: x..=(y-1) if_chain! { if let Some(higher::Range { start, end: Some(end), limits: RangeLimits::Closed }) = higher::range(cx, expr); if let Some(y) = y_minus_one(end); then { span_lint_and_then( cx, RANGE_MINUS_ONE, expr.span, "an exclusive range would be more readable", |db| { let start = start.map_or(String::new(), |x| Sugg::hir(cx, x, "x").to_string()); let end = Sugg::hir(cx, y, "y"); db.span_suggestion_with_applicability( expr.span, "use", format!("{}..{}", start, end), Applicability::MachineApplicable, // snippet ); }, ); } } } } 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, &[])) } fn y_plus_one(expr: &Expr) -> Option<&Expr> { match expr.node { ExprKind::Binary( Spanned { node: BinOpKind::Add, .. }, ref lhs, ref rhs, ) => { if is_integer_literal(lhs, 1) { Some(rhs) } else if is_integer_literal(rhs, 1) { Some(lhs) } else { None } }, _ => None, } } fn y_minus_one(expr: &Expr) -> Option<&Expr> { match expr.node { ExprKind::Binary( Spanned { node: BinOpKind::Sub, .. }, ref lhs, ref rhs, ) if is_integer_literal(rhs, 1) => Some(lhs), _ => None, } }