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use super::utils::make_iterator_snippet;
use super::MANUAL_FLATTEN;
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::higher;
use clippy_utils::visitors::is_local_used;
use clippy_utils::{is_lang_ctor, path_to_local_id, peel_blocks_with_stmt};
use if_chain::if_chain;
use rustc_errors::Applicability;
use rustc_hir::LangItem::{OptionSome, ResultOk};
use rustc_hir::{Expr, Pat, PatKind};
use rustc_lint::LateContext;
use rustc_middle::ty;
use rustc_span::source_map::Span;
/// Check for unnecessary `if let` usage in a for loop where only the `Some` or `Ok` variant of the
/// iterator element is used.
pub(super) fn check<'tcx>(
cx: &LateContext<'tcx>,
pat: &'tcx Pat<'_>,
arg: &'tcx Expr<'_>,
body: &'tcx Expr<'_>,
span: Span,
) {
let inner_expr = peel_blocks_with_stmt(body);
if_chain! {
if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: None })
= higher::IfLet::hir(cx, inner_expr);
// Ensure match_expr in `if let` statement is the same as the pat from the for-loop
if let PatKind::Binding(_, pat_hir_id, _, _) = pat.kind;
if path_to_local_id(let_expr, pat_hir_id);
// Ensure the `if let` statement is for the `Some` variant of `Option` or the `Ok` variant of `Result`
if let PatKind::TupleStruct(ref qpath, _, _) = let_pat.kind;
let some_ctor = is_lang_ctor(cx, qpath, OptionSome);
let ok_ctor = is_lang_ctor(cx, qpath, ResultOk);
if some_ctor || ok_ctor;
// Ensure expr in `if let` is not used afterwards
if !is_local_used(cx, if_then, pat_hir_id);
then {
let if_let_type = if some_ctor { "Some" } else { "Ok" };
// Prepare the error message
let msg = format!("unnecessary `if let` since only the `{}` variant of the iterator element is used", if_let_type);
// Prepare the help message
let mut applicability = Applicability::MaybeIncorrect;
let arg_snippet = make_iterator_snippet(cx, arg, &mut applicability);
let copied = match cx.typeck_results().expr_ty(let_expr).kind() {
ty::Ref(_, inner, _) => match inner.kind() {
ty::Ref(..) => ".copied()",
_ => ""
}
_ => ""
};
let sugg = format!("{arg_snippet}{copied}.flatten()");
// If suggestion is not a one-liner, it won't be shown inline within the error message. In that case,
// it will be shown in the extra `help` message at the end, which is why the first `help_msg` needs
// to refer to the correct relative position of the suggestion.
let help_msg = if sugg.contains('\n') {
"remove the `if let` statement in the for loop and then..."
} else {
"...and remove the `if let` statement in the for loop"
};
span_lint_and_then(
cx,
MANUAL_FLATTEN,
span,
&msg,
|diag| {
diag.span_suggestion(
arg.span,
"try",
sugg,
applicability,
);
diag.span_help(
inner_expr.span,
help_msg,
);
}
);
}
}
}
|
