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use clippy_utils::{diagnostics::span_lint_and_sugg, ty::is_type_lang_item};
use rustc_ast::ast::LitKind;
use rustc_errors::Applicability;
use rustc_hir::{Expr, ExprKind, LangItem};
use rustc_lint::LateContext;
use rustc_middle::ty::{Ref, Slice};
use rustc_span::Span;
use super::UNNECESSARY_JOIN;
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'tcx>,
join_self_arg: &'tcx Expr<'tcx>,
join_arg: &'tcx Expr<'tcx>,
span: Span,
) {
let applicability = Applicability::MachineApplicable;
let collect_output_adjusted_type = cx.typeck_results().expr_ty_adjusted(join_self_arg);
if_chain! {
// the turbofish for collect is ::<Vec<String>>
if let Ref(_, ref_type, _) = collect_output_adjusted_type.kind();
if let Slice(slice) = ref_type.kind();
if is_type_lang_item(cx, *slice, LangItem::String);
// the argument for join is ""
if let ExprKind::Lit(spanned) = &join_arg.kind;
if let LitKind::Str(symbol, _) = spanned.node;
if symbol.is_empty();
then {
span_lint_and_sugg(
cx,
UNNECESSARY_JOIN,
span.with_hi(expr.span.hi()),
r#"called `.collect::<Vec<String>>().join("")` on an iterator"#,
"try using",
"collect::<String>()".to_owned(),
applicability,
);
}
}
}
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