1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::higher;
3 use clippy_utils::sugg::Sugg;
4 use clippy_utils::ty::is_type_diagnostic_item;
6 can_move_expr_to_closure, eager_or_lazy, in_macro, is_else_clause, is_lang_ctor, peel_hir_expr_while, CaptureKind,
8 use if_chain::if_chain;
9 use rustc_errors::Applicability;
10 use rustc_hir::LangItem::OptionSome;
11 use rustc_hir::{def::Res, BindingAnnotation, Block, Expr, ExprKind, Mutability, PatKind, Path, QPath, UnOp};
12 use rustc_lint::{LateContext, LateLintPass};
13 use rustc_session::{declare_lint_pass, declare_tool_lint};
16 declare_clippy_lint! {
18 /// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
19 /// idiomatically done with `Option::map_or` (if the else bit is a pure
20 /// expression) or `Option::map_or_else` (if the else bit is an impure
23 /// ### Why is this bad?
24 /// Using the dedicated functions of the Option type is clearer and
25 /// more concise than an `if let` expression.
27 /// ### Known problems
28 /// This lint uses a deliberately conservative metric for checking
29 /// if the inside of either body contains breaks or continues which will
30 /// cause it to not suggest a fix if either block contains a loop with
31 /// continues or breaks contained within the loop.
35 /// # let optional: Option<u32> = Some(0);
36 /// # fn do_complicated_function() -> u32 { 5 };
37 /// let _ = if let Some(foo) = optional {
42 /// let _ = if let Some(foo) = optional {
45 /// let y = do_complicated_function();
53 /// # let optional: Option<u32> = Some(0);
54 /// # fn do_complicated_function() -> u32 { 5 };
55 /// let _ = optional.map_or(5, |foo| foo);
56 /// let _ = optional.map_or_else(||{
57 /// let y = do_complicated_function();
61 pub OPTION_IF_LET_ELSE,
63 "reimplementation of Option::map_or"
66 declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
68 /// Returns true iff the given expression is the result of calling `Result::ok`
69 fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
70 if let ExprKind::MethodCall(path, _, &[ref receiver], _) = &expr.kind {
71 path.ident.name.as_str() == "ok"
72 && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver), sym::result_type)
78 /// A struct containing information about occurrences of the
79 /// `if let Some(..) = .. else` construct that this lint detects.
80 struct OptionIfLetElseOccurence {
87 /// Extracts the body of a given arm. If the arm contains only an expression,
88 /// then it returns the expression. Otherwise, it returns the entire block
89 fn extract_body_from_expr<'a>(expr: &'a Expr<'a>) -> Option<&'a Expr<'a>> {
90 if let ExprKind::Block(
93 expr: Some(block_expr),
99 if let [] = block_stmts {
109 fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
112 Sugg::hir(cx, cond_expr, "..").maybe_par(),
123 /// If this expression is the option if let/else construct we're detecting, then
124 /// this function returns an `OptionIfLetElseOccurence` struct with details if
125 /// this construct is found, or None if this construct is not found.
126 fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionIfLetElseOccurence> {
128 if !in_macro(expr.span); // Don't lint macros, because it behaves weirdly
129 if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
130 = higher::IfLet::hir(cx, expr);
131 if !is_else_clause(cx.tcx, expr);
132 if !is_result_ok(cx, let_expr); // Don't lint on Result::ok because a different lint does it already
133 if let PatKind::TupleStruct(struct_qpath, [inner_pat], _) = &let_pat.kind;
134 if is_lang_ctor(cx, struct_qpath, OptionSome);
135 if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
136 if let Some(some_captures) = can_move_expr_to_closure(cx, if_then);
137 if let Some(none_captures) = can_move_expr_to_closure(cx, if_else);
140 .filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2)))
141 .all(|(x, y)| x.is_imm_ref() && y.is_imm_ref());
144 let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
145 let some_body = extract_body_from_expr(if_then)?;
146 let none_body = extract_body_from_expr(if_else)?;
147 let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) {
152 let capture_name = id.name.to_ident_string();
153 let (as_ref, as_mut) = match &let_expr.kind {
154 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
155 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
156 _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
158 let cond_expr = match let_expr.kind {
159 // Pointer dereferencing happens automatically, so we can omit it in the suggestion
160 ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
163 // Check if captures the closure will need conflict with borrows made in the scrutinee.
164 // TODO: check all the references made in the scrutinee expression. This will require interacting
165 // with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
166 if as_ref || as_mut {
167 let e = peel_hir_expr_while(cond_expr, |e| match e.kind {
168 ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
171 if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(local_id), .. })) = e.kind {
172 match some_captures.get(local_id)
173 .or_else(|| (method_sugg == "map_or_else").then(|| ()).and_then(|_| none_captures.get(local_id)))
175 Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return None,
176 Some(CaptureKind::Ref(Mutability::Not)) if as_mut => return None,
177 Some(CaptureKind::Ref(Mutability::Not)) | None => (),
181 Some(OptionIfLetElseOccurence {
182 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
183 method_sugg: method_sugg.to_string(),
184 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
185 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
193 impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
194 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
195 if let Some(detection) = detect_option_if_let_else(cx, expr) {
200 format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
204 detection.option, detection.method_sugg, detection.none_expr, detection.some_expr,
206 Applicability::MaybeIncorrect,