236 lines
7.3 KiB
Rust
236 lines
7.3 KiB
Rust
use rustc::hir::*;
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use rustc::lint::*;
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use crate::utils::{get_trait_def_id, higher, implements_trait, match_qpath, paths, span_lint};
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/// **What it does:** Checks for iteration that is guaranteed to be infinite.
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///
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/// **Why is this bad?** 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:** None.
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///
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/// **Example:**
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/// ```rust
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/// repeat(1_u8).iter().collect::<Vec<_>>()
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/// ```
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declare_clippy_lint! {
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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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/// **What it does:** Checks for iteration that may be infinite.
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///
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/// **Why is this bad?** 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:** 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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/// [0..].iter().zip(infinite_iter.take_while(|x| x > 5))
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/// ```
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declare_clippy_lint! {
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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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#[derive(Copy, Clone)]
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pub struct Pass;
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impl LintPass for Pass {
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fn get_lints(&self) -> LintArray {
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lint_array!(INFINITE_ITER, MAYBE_INFINITE_ITER)
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}
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}
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impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
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fn check_expr(&mut self, cx: &LateContext<'a, '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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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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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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fn from(b: bool) -> Self {
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if b {
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Infinite
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} else {
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Finite
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}
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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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static HEURISTICS: &[(&str, usize, Heuristic, Finiteness)] = &[
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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.node {
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ExprKind::MethodCall(ref method, _, ref args) => {
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for &(name, len, heuristic, cap) in HEURISTICS.iter() {
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if method.ident.name == 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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}).and(cap);
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}
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}
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if method.ident.name == "flat_map" && args.len() == 2 {
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if let ExprKind::Closure(_, _, body_id, _, _) = args[1].node {
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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(ref block, _) => block.expr.as_ref().map_or(Finite, |e| is_infinite(cx, e)),
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ExprKind::Box(ref e) | ExprKind::AddrOf(_, ref e) => is_infinite(cx, e),
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ExprKind::Call(ref path, _) => if let ExprKind::Path(ref qpath) = path.node {
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match_qpath(qpath, &paths::REPEAT).into()
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} else {
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Finite
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},
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ExprKind::Struct(..) => higher::range(cx, expr)
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.map_or(false, |r| r.end.is_none())
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.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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static POSSIBLY_COMPLETING_METHODS: &[(&str, usize)] = &[
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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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static COMPLETING_METHODS: &[(&str, usize)] = &[
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("count", 1),
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("collect", 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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fn complete_infinite_iter(cx: &LateContext, expr: &Expr) -> Finiteness {
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match expr.node {
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ExprKind::MethodCall(ref method, _, ref args) => {
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for &(name, len) in COMPLETING_METHODS.iter() {
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if method.ident.name == 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.iter() {
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if method.ident.name == 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 == "last" && args.len() == 1 {
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let not_double_ended = get_trait_def_id(cx, &paths::DOUBLE_ENDED_ITERATOR)
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.map_or(false, |id| !implements_trait(cx, cx.tables.expr_ty(&args[0]), id, &[]));
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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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}
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},
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ExprKind::Binary(op, ref l, ref r) => if op.node.is_comparison() {
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return is_infinite(cx, l)
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.and(is_infinite(cx, r))
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.and(MaybeInfinite);
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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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