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use super::SINGLE_ELEMENT_LOOP;
use clippy_utils::diagnostics::span_lint_and_sugg;
use clippy_utils::source::{indent_of, snippet_with_applicability};
use if_chain::if_chain;
use rustc_ast::util::parser::PREC_PREFIX;
use rustc_ast::Mutability;
use rustc_errors::Applicability;
use rustc_hir::{is_range_literal, BorrowKind, Expr, ExprKind, Pat};
use rustc_lint::LateContext;
use rustc_span::edition::Edition;
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
expr: &'tcx Expr<'_>,
) {
let (arg_expression, prefix) = match arg.kind {
ExprKind::AddrOf(
BorrowKind::Ref,
Mutability::Not,
Expr {
kind: ExprKind::Array([arg]),
..
},
) => (arg, "&"),
ExprKind::AddrOf(
BorrowKind::Ref,
Mutability::Mut,
Expr {
kind: ExprKind::Array([arg]),
..
},
) => (arg, "&mut "),
ExprKind::MethodCall(
method,
Expr {
kind: ExprKind::Array([arg]),
..
},
[],
_,
) if method.ident.name == rustc_span::sym::iter => (arg, "&"),
ExprKind::MethodCall(
method,
Expr {
kind: ExprKind::Array([arg]),
..
},
[],
_,
) if method.ident.name.as_str() == "iter_mut" => (arg, "&mut "),
ExprKind::MethodCall(
method,
Expr {
kind: ExprKind::Array([arg]),
..
},
[],
_,
) if method.ident.name == rustc_span::sym::into_iter => (arg, ""),
// Only check for arrays edition 2021 or later, as this case will trigger a compiler error otherwise.
ExprKind::Array([arg]) if cx.tcx.sess.edition() >= Edition::Edition2021 => (arg, ""),
_ => return,
};
if_chain! {
if let ExprKind::Block(block, _) = body.kind;
if !block.stmts.is_empty();
then {
let mut applicability = Applicability::MachineApplicable;
let pat_snip = snippet_with_applicability(cx, pat.span, "..", &mut applicability);
let mut arg_snip = snippet_with_applicability(cx, arg_expression.span, "..", &mut applicability);
let mut block_str = snippet_with_applicability(cx, block.span, "..", &mut applicability).into_owned();
block_str.remove(0);
block_str.pop();
let indent = " ".repeat(indent_of(cx, block.stmts[0].span).unwrap_or(0));
// Reference iterator from `&(mut) []` or `[].iter(_mut)()`.
if !prefix.is_empty() && (
// Precedence of internal expression is less than or equal to precedence of `&expr`.
arg_expression.precedence().order() <= PREC_PREFIX || is_range_literal(arg_expression)
) {
arg_snip = format!("({arg_snip})").into();
}
span_lint_and_sugg(
cx,
SINGLE_ELEMENT_LOOP,
expr.span,
"for loop over a single element",
"try",
format!("{{\n{indent}let {pat_snip} = {prefix}{arg_snip};{block_str}}}"),
applicability,
)
}
}
}
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