rust/clippy_lints/src/ranges.rs

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// 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 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
use crate::rustc::lint::{LateContext, LateLintPass, LintArray, LintPass};
use crate::rustc::{declare_tool_lint, lint_array};
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use if_chain::if_chain;
use crate::rustc::hir::*;
use crate::syntax::ast::RangeLimits;
use crate::syntax::source_map::Spanned;
use crate::utils::{is_integer_literal, paths, snippet, span_lint, span_lint_and_then, snippet_opt};
use crate::utils::{get_trait_def_id, higher, implements_trait, SpanlessEq};
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use crate::utils::sugg::Sugg;
use crate::rustc_errors::Applicability;
/// **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.
///
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/// **Example:**
/// ```rust
/// for x in (5..5).step_by(0) { .. }
/// ```
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declare_clippy_lint! {
pub ITERATOR_STEP_BY_ZERO,
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correctness,
"using `Iterator::step_by(0)`, which produces an infinite iterator"
}
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/// **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.
///
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/// **Example:**
/// ```rust
/// x.iter().zip(0..x.len())
/// ```
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declare_clippy_lint! {
pub RANGE_ZIP_WITH_LEN,
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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.
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/// I.e: `let _ = (f()+1)..(f()+1)` results in `let _ = ((f()+1)..=f())`.
///
/// **Example:**
/// ```rust
/// for x..(y+1) { .. }
/// ```
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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) { .. }
/// ```
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declare_clippy_lint! {
pub RANGE_MINUS_ONE,
complexity,
"`x..=(y-1)` reads better as `x..y`"
}
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#[derive(Copy, Clone)]
pub struct Pass;
impl LintPass for Pass {
fn get_lints(&self) -> LintArray {
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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) {
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if let ExprKind::MethodCall(ref path, _, ref args) = expr.node {
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let name = path.ident.as_str();
// Range with step_by(0).
if name == "step_by" && args.len() == 2 && has_step_by(cx, &args[0]) {
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use crate::consts::{constant, Constant};
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if let Some((Constant::Int(0), _)) = constant(cx, cx.tables, &args[1]) {
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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! {
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// .iter() call
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if let ExprKind::MethodCall(ref iter_path, _, ref iter_args ) = *iter;
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if iter_path.ident.name == "iter";
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// 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);
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// .len() call
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if let ExprKind::MethodCall(ref len_path, _, ref len_args) = end.node;
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if len_path.ident.name == "len" && len_args.len() == 1;
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// .iter() and .len() called on same Path
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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) {
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if is_wrapped.starts_with('(') && is_wrapped.ends_with(')') {
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db.span_suggestion_with_applicability(
expr.span,
"use",
format!("({}..={})", start, end),
Applicability::MaybeIncorrect,
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);
} else {
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db.span_suggestion_with_applicability(
expr.span,
"use",
format!("{}..={}", start, end),
Applicability::MachineApplicable, // snippet
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);
}
}
},
);
}
}
// 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");
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db.span_suggestion_with_applicability(
expr.span,
"use",
format!("{}..{}", start, end),
Applicability::MachineApplicable, // snippet
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);
},
);
}
}
}
}
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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);
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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 {
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ExprKind::Binary(Spanned { node: BinOpKind::Add, .. }, ref lhs, ref rhs) => if is_integer_literal(lhs, 1) {
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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 {
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ExprKind::Binary(Spanned { node: BinOpKind::Sub, .. }, ref lhs, ref rhs) if is_integer_literal(rhs, 1) => Some(lhs),
_ => None,
}
}