1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::sugg::Sugg;
3 use clippy_utils::ty::is_type_diagnostic_item;
5 can_move_expr_to_closure, eager_or_lazy, in_constant, in_macro, is_else_clause, is_lang_ctor, peel_hir_expr_while,
8 use if_chain::if_chain;
9 use rustc_errors::Applicability;
10 use rustc_hir::LangItem::OptionSome;
12 def::Res, Arm, BindingAnnotation, Block, Expr, ExprKind, MatchSource, Mutability, PatKind, Path, QPath, UnOp,
14 use rustc_lint::{LateContext, LateLintPass};
15 use rustc_session::{declare_lint_pass, declare_tool_lint};
18 declare_clippy_lint! {
20 /// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
21 /// idiomatically done with `Option::map_or` (if the else bit is a pure
22 /// expression) or `Option::map_or_else` (if the else bit is an impure
25 /// ### Why is this bad?
26 /// Using the dedicated functions of the Option type is clearer and
27 /// more concise than an `if let` expression.
29 /// ### Known problems
30 /// This lint uses a deliberately conservative metric for checking
31 /// if the inside of either body contains breaks or continues which will
32 /// cause it to not suggest a fix if either block contains a loop with
33 /// continues or breaks contained within the loop.
37 /// # let optional: Option<u32> = Some(0);
38 /// # fn do_complicated_function() -> u32 { 5 };
39 /// let _ = if let Some(foo) = optional {
44 /// let _ = if let Some(foo) = optional {
47 /// let y = do_complicated_function();
55 /// # let optional: Option<u32> = Some(0);
56 /// # fn do_complicated_function() -> u32 { 5 };
57 /// let _ = optional.map_or(5, |foo| foo);
58 /// let _ = optional.map_or_else(||{
59 /// let y = do_complicated_function();
63 pub OPTION_IF_LET_ELSE,
65 "reimplementation of Option::map_or"
68 declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
70 /// Returns true iff the given expression is the result of calling `Result::ok`
71 fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
72 if let ExprKind::MethodCall(path, _, &[ref receiver], _) = &expr.kind {
73 path.ident.name.as_str() == "ok"
74 && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver), sym::result_type)
80 /// A struct containing information about occurrences of the
81 /// `if let Some(..) = .. else` construct that this lint detects.
82 struct OptionIfLetElseOccurence {
89 /// Extracts the body of a given arm. If the arm contains only an expression,
90 /// then it returns the expression. Otherwise, it returns the entire block
91 fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
92 if let ExprKind::Block(
101 if let [] = statements {
111 fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
114 Sugg::hir(cx, cond_expr, "..").maybe_par(),
125 /// If this expression is the option if let/else construct we're detecting, then
126 /// this function returns an `OptionIfLetElseOccurence` struct with details if
127 /// this construct is found, or None if this construct is not found.
128 fn detect_option_if_let_else<'tcx>(
129 cx: &'_ LateContext<'tcx>,
130 expr: &'_ Expr<'tcx>,
131 ) -> Option<OptionIfLetElseOccurence> {
133 if !in_macro(expr.span); // Don't lint macros, because it behaves weirdly
134 if !in_constant(cx, expr.hir_id);
135 if let ExprKind::Match(cond_expr, [some_arm, none_arm], MatchSource::IfLetDesugar{contains_else_clause: true})
137 if !is_else_clause(cx.tcx, expr);
138 if !is_result_ok(cx, cond_expr); // Don't lint on Result::ok because a different lint does it already
139 if let PatKind::TupleStruct(struct_qpath, [inner_pat], _) = &some_arm.pat.kind;
140 if is_lang_ctor(cx, struct_qpath, OptionSome);
141 if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
142 if let Some(some_captures) = can_move_expr_to_closure(cx, some_arm.body);
143 if let Some(none_captures) = can_move_expr_to_closure(cx, none_arm.body);
146 .filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2)))
147 .all(|(x, y)| x.is_imm_ref() && y.is_imm_ref());
150 let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
151 let some_body = extract_body_from_arm(some_arm)?;
152 let none_body = extract_body_from_arm(none_arm)?;
153 let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) {
158 let capture_name = id.name.to_ident_string();
159 let (as_ref, as_mut) = match &cond_expr.kind {
160 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
161 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
162 _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
164 let cond_expr = match &cond_expr.kind {
165 // Pointer dereferencing happens automatically, so we can omit it in the suggestion
166 ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
169 // Check if captures the closure will need conflict with borrows made in the scrutinee.
170 // TODO: check all the references made in the scrutinee expression. This will require interacting
171 // with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
172 if as_ref || as_mut {
173 let e = peel_hir_expr_while(cond_expr, |e| match e.kind {
174 ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
177 if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(l), .. })) = e.kind {
178 match some_captures.get(l)
179 .or_else(|| (method_sugg == "map_or_else").then(|| ()).and_then(|_| none_captures.get(l)))
181 Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return None,
182 Some(CaptureKind::Ref(Mutability::Not)) if as_mut => return None,
183 Some(CaptureKind::Ref(Mutability::Not)) | None => (),
187 Some(OptionIfLetElseOccurence {
188 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
189 method_sugg: method_sugg.to_string(),
190 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
191 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
199 impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
200 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
201 if let Some(detection) = detect_option_if_let_else(cx, expr) {
206 format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
210 detection.option, detection.method_sugg, detection.none_expr, detection.some_expr,
212 Applicability::MaybeIncorrect,