260 lines
8.4 KiB
Rust
260 lines
8.4 KiB
Rust
use clippy_utils::diagnostics::span_lint;
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use clippy_utils::ty::{implements_trait, is_type_diagnostic_item};
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use clippy_utils::{higher, match_def_path, path_def_id, paths};
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use rustc_hir::{BorrowKind, Expr, ExprKind};
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use rustc_lint::{LateContext, LateLintPass};
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use rustc_session::{declare_lint_pass, declare_tool_lint};
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use rustc_span::symbol::{sym, Symbol};
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for iteration that is guaranteed to be infinite.
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///
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/// ### Why is this bad?
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/// While there may be places where this is acceptable
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/// (e.g., in event streams), in most cases this is simply an error.
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///
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/// ### Example
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/// ```no_run
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/// use std::iter;
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///
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/// iter::repeat(1_u8).collect::<Vec<_>>();
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub INFINITE_ITER,
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correctness,
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"infinite iteration"
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}
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declare_clippy_lint! {
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/// ### What it does
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/// Checks for iteration that may be infinite.
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///
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/// ### Why is this bad?
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/// While there may be places where this is acceptable
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/// (e.g., in event streams), in most cases this is simply an error.
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///
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/// ### Known problems
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/// The code may have a condition to stop iteration, but
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/// this lint is not clever enough to analyze it.
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///
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/// ### Example
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/// ```rust
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/// let infinite_iter = 0..;
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/// [0..].iter().zip(infinite_iter.take_while(|x| *x > 5));
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/// ```
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#[clippy::version = "pre 1.29.0"]
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pub MAYBE_INFINITE_ITER,
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pedantic,
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"possible infinite iteration"
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}
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declare_lint_pass!(InfiniteIter => [INFINITE_ITER, MAYBE_INFINITE_ITER]);
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impl<'tcx> LateLintPass<'tcx> for InfiniteIter {
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fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
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let (lint, msg) = match complete_infinite_iter(cx, expr) {
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Infinite => (INFINITE_ITER, "infinite iteration detected"),
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MaybeInfinite => (MAYBE_INFINITE_ITER, "possible infinite iteration detected"),
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Finite => {
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return;
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},
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};
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span_lint(cx, lint, expr.span, msg);
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}
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}
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#[derive(Copy, Clone, Debug, PartialEq, Eq)]
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enum Finiteness {
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Infinite,
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MaybeInfinite,
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Finite,
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}
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use self::Finiteness::{Finite, Infinite, MaybeInfinite};
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impl Finiteness {
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#[must_use]
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fn and(self, b: Self) -> Self {
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match (self, b) {
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(Finite, _) | (_, Finite) => Finite,
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(MaybeInfinite, _) | (_, MaybeInfinite) => MaybeInfinite,
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_ => Infinite,
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}
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}
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#[must_use]
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fn or(self, b: Self) -> Self {
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match (self, b) {
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(Infinite, _) | (_, Infinite) => Infinite,
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(MaybeInfinite, _) | (_, MaybeInfinite) => MaybeInfinite,
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_ => Finite,
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}
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}
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}
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impl From<bool> for Finiteness {
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#[must_use]
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fn from(b: bool) -> Self {
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if b { Infinite } else { Finite }
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}
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}
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/// This tells us what to look for to know if the iterator returned by
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/// this method is infinite
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#[derive(Copy, Clone)]
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enum Heuristic {
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/// infinite no matter what
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Always,
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/// infinite if the first argument is
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First,
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/// infinite if any of the supplied arguments is
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Any,
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/// infinite if all of the supplied arguments are
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All,
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}
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use self::Heuristic::{All, Always, Any, First};
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/// a slice of (method name, number of args, heuristic, bounds) tuples
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/// that will be used to determine whether the method in question
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/// returns an infinite or possibly infinite iterator. The finiteness
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/// is an upper bound, e.g., some methods can return a possibly
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/// infinite iterator at worst, e.g., `take_while`.
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const HEURISTICS: [(&str, usize, Heuristic, Finiteness); 19] = [
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("zip", 2, All, Infinite),
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("chain", 2, Any, Infinite),
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("cycle", 1, Always, Infinite),
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("map", 2, First, Infinite),
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("by_ref", 1, First, Infinite),
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("cloned", 1, First, Infinite),
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("rev", 1, First, Infinite),
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("inspect", 1, First, Infinite),
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("enumerate", 1, First, Infinite),
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("peekable", 2, First, Infinite),
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("fuse", 1, First, Infinite),
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("skip", 2, First, Infinite),
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("skip_while", 1, First, Infinite),
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("filter", 2, First, Infinite),
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("filter_map", 2, First, Infinite),
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("flat_map", 2, First, Infinite),
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("unzip", 1, First, Infinite),
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("take_while", 2, First, MaybeInfinite),
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("scan", 3, First, MaybeInfinite),
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];
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fn is_infinite(cx: &LateContext<'_>, expr: &Expr<'_>) -> Finiteness {
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match expr.kind {
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ExprKind::MethodCall(method, args, _) => {
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for &(name, len, heuristic, cap) in &HEURISTICS {
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if method.ident.name.as_str() == name && args.len() == len {
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return (match heuristic {
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Always => Infinite,
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First => is_infinite(cx, &args[0]),
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Any => is_infinite(cx, &args[0]).or(is_infinite(cx, &args[1])),
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All => is_infinite(cx, &args[0]).and(is_infinite(cx, &args[1])),
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})
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.and(cap);
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}
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}
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if method.ident.name == sym!(flat_map) && args.len() == 2 {
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if let ExprKind::Closure(_, _, body_id, _, _) = args[1].kind {
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let body = cx.tcx.hir().body(body_id);
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return is_infinite(cx, &body.value);
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}
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}
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Finite
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},
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ExprKind::Block(block, _) => block.expr.as_ref().map_or(Finite, |e| is_infinite(cx, e)),
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ExprKind::Box(e) | ExprKind::AddrOf(BorrowKind::Ref, _, e) => is_infinite(cx, e),
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ExprKind::Call(path, _) => path_def_id(cx, path)
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.map_or(false, |id| match_def_path(cx, id, &paths::ITER_REPEAT))
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.into(),
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ExprKind::Struct(..) => higher::Range::hir(expr).map_or(false, |r| r.end.is_none()).into(),
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_ => Finite,
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}
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}
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/// the names and argument lengths of methods that *may* exhaust their
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/// iterators
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const POSSIBLY_COMPLETING_METHODS: [(&str, usize); 6] = [
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("find", 2),
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("rfind", 2),
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("position", 2),
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("rposition", 2),
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("any", 2),
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("all", 2),
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];
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/// the names and argument lengths of methods that *always* exhaust
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/// their iterators
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const COMPLETING_METHODS: [(&str, usize); 12] = [
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("count", 1),
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("fold", 3),
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("for_each", 2),
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("partition", 2),
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("max", 1),
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("max_by", 2),
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("max_by_key", 2),
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("min", 1),
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("min_by", 2),
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("min_by_key", 2),
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("sum", 1),
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("product", 1),
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];
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/// the paths of types that are known to be infinitely allocating
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const INFINITE_COLLECTORS: &[Symbol] = &[
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sym::BinaryHeap,
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sym::BTreeMap,
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sym::BTreeSet,
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sym::HashMap,
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sym::HashSet,
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sym::LinkedList,
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sym::Vec,
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sym::VecDeque,
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];
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fn complete_infinite_iter(cx: &LateContext<'_>, expr: &Expr<'_>) -> Finiteness {
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match expr.kind {
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ExprKind::MethodCall(method, args, _) => {
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for &(name, len) in &COMPLETING_METHODS {
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if method.ident.name.as_str() == name && args.len() == len {
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return is_infinite(cx, &args[0]);
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}
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}
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for &(name, len) in &POSSIBLY_COMPLETING_METHODS {
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if method.ident.name.as_str() == name && args.len() == len {
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return MaybeInfinite.and(is_infinite(cx, &args[0]));
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}
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}
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if method.ident.name == sym!(last) && args.len() == 1 {
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let not_double_ended = cx
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.tcx
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.get_diagnostic_item(sym::DoubleEndedIterator)
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.map_or(false, |id| {
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!implements_trait(cx, cx.typeck_results().expr_ty(&args[0]), id, &[])
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});
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if not_double_ended {
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return is_infinite(cx, &args[0]);
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}
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} else if method.ident.name == sym!(collect) {
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let ty = cx.typeck_results().expr_ty(expr);
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if INFINITE_COLLECTORS
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.iter()
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.any(|diag_item| is_type_diagnostic_item(cx, ty, *diag_item))
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{
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return is_infinite(cx, &args[0]);
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}
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}
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},
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ExprKind::Binary(op, l, r) => {
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if op.node.is_comparison() {
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return is_infinite(cx, l).and(is_infinite(cx, r)).and(MaybeInfinite);
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}
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}, // TODO: ExprKind::Loop + Match
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_ => (),
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}
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Finite
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}
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