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use rustc_errors::Applicability;
use rustc_hir::{
intravisit::{walk_expr, Visitor},
Closure, Expr, ExprKind, Stmt, StmtKind,
};
use rustc_lint::{LateContext, LateLintPass};
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::{source_map::Span, sym, Symbol};
use if_chain::if_chain;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::is_trait_method;
use clippy_utils::source::snippet_with_applicability;
use clippy_utils::ty::has_iter_method;
declare_clippy_lint! {
/// ### What it does
/// Checks for usage of `for_each` that would be more simply written as a
/// `for` loop.
///
/// ### Why is this bad?
/// `for_each` may be used after applying iterator transformers like
/// `filter` for better readability and performance. It may also be used to fit a simple
/// operation on one line.
/// But when none of these apply, a simple `for` loop is more idiomatic.
///
/// ### Example
/// ```rust
/// let v = vec![0, 1, 2];
/// v.iter().for_each(|elem| {
/// println!("{}", elem);
/// })
/// ```
/// Use instead:
/// ```rust
/// let v = vec![0, 1, 2];
/// for elem in v.iter() {
/// println!("{}", elem);
/// }
/// ```
#[clippy::version = "1.53.0"]
pub NEEDLESS_FOR_EACH,
pedantic,
"using `for_each` where a `for` loop would be simpler"
}
declare_lint_pass!(NeedlessForEach => [NEEDLESS_FOR_EACH]);
impl<'tcx> LateLintPass<'tcx> for NeedlessForEach {
fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
let expr = match stmt.kind {
StmtKind::Expr(expr) | StmtKind::Semi(expr) => expr,
_ => return,
};
if_chain! {
// Check the method name is `for_each`.
if let ExprKind::MethodCall(method_name, for_each_recv, [for_each_arg], _) = expr.kind;
if method_name.ident.name == Symbol::intern("for_each");
// Check `for_each` is an associated function of `Iterator`.
if is_trait_method(cx, expr, sym::Iterator);
// Checks the receiver of `for_each` is also a method call.
if let ExprKind::MethodCall(_, iter_recv, [], _) = for_each_recv.kind;
// Skip the lint if the call chain is too long. e.g. `v.field.iter().for_each()` or
// `v.foo().iter().for_each()` must be skipped.
if matches!(
iter_recv.kind,
ExprKind::Array(..) | ExprKind::Call(..) | ExprKind::Path(..)
);
// Checks the type of the `iter` method receiver is NOT a user defined type.
if has_iter_method(cx, cx.typeck_results().expr_ty(iter_recv)).is_some();
// Skip the lint if the body is not block because this is simpler than `for` loop.
// e.g. `v.iter().for_each(f)` is simpler and clearer than using `for` loop.
if let ExprKind::Closure(&Closure { body, .. }) = for_each_arg.kind;
let body = cx.tcx.hir().body(body);
if let ExprKind::Block(..) = body.value.kind;
then {
let mut ret_collector = RetCollector::default();
ret_collector.visit_expr(body.value);
// Skip the lint if `return` is used in `Loop` in order not to suggest using `'label`.
if ret_collector.ret_in_loop {
return;
}
let (mut applicability, ret_suggs) = if ret_collector.spans.is_empty() {
(Applicability::MachineApplicable, None)
} else {
(
Applicability::MaybeIncorrect,
Some(
ret_collector
.spans
.into_iter()
.map(|span| (span, "continue".to_string()))
.collect(),
),
)
};
let sugg = format!(
"for {} in {} {}",
snippet_with_applicability(cx, body.params[0].pat.span, "..", &mut applicability),
snippet_with_applicability(cx, for_each_recv.span, "..", &mut applicability),
snippet_with_applicability(cx, body.value.span, "..", &mut applicability),
);
span_lint_and_then(cx, NEEDLESS_FOR_EACH, stmt.span, "needless use of `for_each`", |diag| {
diag.span_suggestion(stmt.span, "try", sugg, applicability);
if let Some(ret_suggs) = ret_suggs {
diag.multipart_suggestion("...and replace `return` with `continue`", ret_suggs, applicability);
}
})
}
}
}
}
/// This type plays two roles.
/// 1. Collect spans of `return` in the closure body.
/// 2. Detect use of `return` in `Loop` in the closure body.
///
/// NOTE: The functionality of this type is similar to
/// [`clippy_utils::visitors::find_all_ret_expressions`], but we can't use
/// `find_all_ret_expressions` instead of this type. The reasons are:
/// 1. `find_all_ret_expressions` passes the argument of `ExprKind::Ret` to a callback, but what we
/// need here is `ExprKind::Ret` itself.
/// 2. We can't trace current loop depth with `find_all_ret_expressions`.
#[derive(Default)]
struct RetCollector {
spans: Vec<Span>,
ret_in_loop: bool,
loop_depth: u16,
}
impl<'tcx> Visitor<'tcx> for RetCollector {
fn visit_expr(&mut self, expr: &Expr<'_>) {
match expr.kind {
ExprKind::Ret(..) => {
if self.loop_depth > 0 && !self.ret_in_loop {
self.ret_in_loop = true;
}
self.spans.push(expr.span);
},
ExprKind::Loop(..) => {
self.loop_depth += 1;
walk_expr(self, expr);
self.loop_depth -= 1;
return;
},
_ => {},
}
walk_expr(self, expr);
}
}
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