rust-clippy/clippy_lints/src/unused_peekable.rs

231 lines
8.3 KiB
Rust

use clippy_utils::diagnostics::span_lint_and_help;
use clippy_utils::ty::{match_type, peel_mid_ty_refs_is_mutable};
use clippy_utils::{fn_def_id, is_trait_method, path_to_local_id, paths, peel_ref_operators};
use rustc_ast::Mutability;
use rustc_hir::intravisit::{walk_expr, Visitor};
use rustc_hir::{Block, Expr, ExprKind, HirId, Local, Node, PatKind, PathSegment, StmtKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_middle::hir::nested_filter::OnlyBodies;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::sym;
declare_clippy_lint! {
/// ### What it does
/// Checks for the creation of a `peekable` iterator that is never `.peek()`ed
///
/// ### Why is this bad?
/// Creating a peekable iterator without using any of its methods is likely a mistake,
/// or just a leftover after a refactor.
///
/// ### Example
/// ```rust
/// let collection = vec![1, 2, 3];
/// let iter = collection.iter().peekable();
///
/// for item in iter {
/// // ...
/// }
/// ```
///
/// Use instead:
/// ```rust
/// let collection = vec![1, 2, 3];
/// let iter = collection.iter();
///
/// for item in iter {
/// // ...
/// }
/// ```
#[clippy::version = "1.65.0"]
pub UNUSED_PEEKABLE,
nursery,
"creating a peekable iterator without using any of its methods"
}
declare_lint_pass!(UnusedPeekable => [UNUSED_PEEKABLE]);
impl<'tcx> LateLintPass<'tcx> for UnusedPeekable {
fn check_block(&mut self, cx: &LateContext<'tcx>, block: &Block<'tcx>) {
// Don't lint `Peekable`s returned from a block
if let Some(expr) = block.expr
&& let Some(ty) = cx.typeck_results().expr_ty_opt(peel_ref_operators(cx, expr))
&& match_type(cx, ty, &paths::PEEKABLE)
{
return;
}
for (idx, stmt) in block.stmts.iter().enumerate() {
if !stmt.span.from_expansion()
&& let StmtKind::Local(local) = stmt.kind
&& let PatKind::Binding(_, binding, ident, _) = local.pat.kind
&& let Some(init) = local.init
&& !init.span.from_expansion()
&& let Some(ty) = cx.typeck_results().expr_ty_opt(init)
&& let (ty, _, Mutability::Mut) = peel_mid_ty_refs_is_mutable(ty)
&& match_type(cx, ty, &paths::PEEKABLE)
{
let mut vis = PeekableVisitor::new(cx, binding);
if idx + 1 == block.stmts.len() && block.expr.is_none() {
return;
}
for stmt in &block.stmts[idx..] {
vis.visit_stmt(stmt);
}
if let Some(expr) = block.expr {
vis.visit_expr(expr);
}
if !vis.found_peek_call {
span_lint_and_help(
cx,
UNUSED_PEEKABLE,
ident.span,
"`peek` never called on `Peekable` iterator",
None,
"consider removing the call to `peekable`"
);
}
}
}
}
}
struct PeekableVisitor<'a, 'tcx> {
cx: &'a LateContext<'tcx>,
expected_hir_id: HirId,
found_peek_call: bool,
}
impl<'a, 'tcx> PeekableVisitor<'a, 'tcx> {
fn new(cx: &'a LateContext<'tcx>, expected_hir_id: HirId) -> Self {
Self {
cx,
expected_hir_id,
found_peek_call: false,
}
}
}
impl<'tcx> Visitor<'tcx> for PeekableVisitor<'_, 'tcx> {
type NestedFilter = OnlyBodies;
fn nested_visit_map(&mut self) -> Self::Map {
self.cx.tcx.hir()
}
fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
if self.found_peek_call {
return;
}
if path_to_local_id(ex, self.expected_hir_id) {
for (_, node) in self.cx.tcx.hir().parent_iter(ex.hir_id) {
match node {
Node::Expr(expr) => {
match expr.kind {
// some_function(peekable)
//
// If the Peekable is passed to a function, stop
ExprKind::Call(_, args) => {
if let Some(func_did) = fn_def_id(self.cx, expr)
&& let Some(into_iter_did) = self
.cx
.tcx
.lang_items()
.into_iter_fn()
&& func_did == into_iter_did
{
// Probably a for loop desugar, stop searching
return;
}
if args.iter().any(|arg| arg_is_mut_peekable(self.cx, arg)) {
self.found_peek_call = true;
}
return;
},
// Catch anything taking a Peekable mutably
ExprKind::MethodCall(
PathSegment {
ident: method_name_ident,
..
},
self_arg,
remaining_args,
_,
) => {
let method_name = method_name_ident.name.as_str();
// `Peekable` methods
if matches!(method_name, "peek" | "peek_mut" | "next_if" | "next_if_eq")
&& arg_is_mut_peekable(self.cx, self_arg)
{
self.found_peek_call = true;
return;
}
// foo.some_method() excluding Iterator methods
if remaining_args.iter().any(|arg| arg_is_mut_peekable(self.cx, arg))
&& !is_trait_method(self.cx, expr, sym::Iterator)
{
self.found_peek_call = true;
return;
}
// foo.by_ref(), keep checking for `peek`
if method_name == "by_ref" {
continue;
}
return;
},
ExprKind::AddrOf(_, Mutability::Mut, _) | ExprKind::Unary(..) | ExprKind::DropTemps(_) => {
},
ExprKind::AddrOf(_, Mutability::Not, _) => return,
_ => {
self.found_peek_call = true;
return;
},
}
},
Node::Local(Local { init: Some(init), .. }) => {
if arg_is_mut_peekable(self.cx, init) {
self.found_peek_call = true;
}
return;
},
Node::Stmt(stmt) => {
match stmt.kind {
StmtKind::Local(_) | StmtKind::Item(_) => self.found_peek_call = true,
StmtKind::Expr(_) | StmtKind::Semi(_) => {},
}
return;
},
Node::Block(_) | Node::ExprField(_) => {},
_ => {
return;
},
}
}
}
walk_expr(self, ex);
}
}
fn arg_is_mut_peekable(cx: &LateContext<'_>, arg: &Expr<'_>) -> bool {
if let Some(ty) = cx.typeck_results().expr_ty_opt(arg)
&& let (ty, _, Mutability::Mut) = peel_mid_ty_refs_is_mutable(ty)
&& match_type(cx, ty, &paths::PEEKABLE)
{
true
} else {
false
}
}