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;
5 use clippy_utils::{
6 can_move_expr_to_closure, eager_or_lazy, in_constant, in_macro, is_else_clause, is_lang_ctor, peel_hir_expr_while,
7 CaptureKind,
8 };
9 use if_chain::if_chain;
10 use rustc_errors::Applicability;
11 use rustc_hir::LangItem::OptionSome;
12 use rustc_hir::{def::Res, BindingAnnotation, Block, Expr, ExprKind, Mutability, PatKind, Path, QPath, UnOp};
13 use rustc_lint::{LateContext, LateLintPass};
14 use rustc_session::{declare_lint_pass, declare_tool_lint};
15 use rustc_span::sym;
16
17 declare_clippy_lint! {
18 /// ### What it does
19 /// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
20 /// idiomatically done with `Option::map_or` (if the else bit is a pure
21 /// expression) or `Option::map_or_else` (if the else bit is an impure
22 /// expression).
23 ///
24 /// ### Why is this bad?
25 /// Using the dedicated functions of the `Option` type is clearer and
26 /// more concise than an `if let` expression.
27 ///
28 /// ### Known problems
29 /// This lint uses a deliberately conservative metric for checking
30 /// if the inside of either body contains breaks or continues which will
31 /// cause it to not suggest a fix if either block contains a loop with
32 /// continues or breaks contained within the loop.
33 ///
34 /// ### Example
35 /// ```rust
36 /// # let optional: Option<u32> = Some(0);
37 /// # fn do_complicated_function() -> u32 { 5 };
38 /// let _ = if let Some(foo) = optional {
39 /// foo
40 /// } else {
41 /// 5
42 /// };
43 /// let _ = if let Some(foo) = optional {
44 /// foo
45 /// } else {
46 /// let y = do_complicated_function();
47 /// y*y
48 /// };
49 /// ```
50 ///
51 /// should be
52 ///
53 /// ```rust
54 /// # let optional: Option<u32> = Some(0);
55 /// # fn do_complicated_function() -> u32 { 5 };
56 /// let _ = optional.map_or(5, |foo| foo);
57 /// let _ = optional.map_or_else(||{
58 /// let y = do_complicated_function();
59 /// y*y
60 /// }, |foo| foo);
61 /// ```
62 pub OPTION_IF_LET_ELSE,
63 nursery,
64 "reimplementation of Option::map_or"
65 }
66
67 declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
68
69 /// Returns true iff the given expression is the result of calling `Result::ok`
is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool70 fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
71 if let ExprKind::MethodCall(path, _, &[ref receiver], _) = &expr.kind {
72 path.ident.name.as_str() == "ok"
73 && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver), sym::Result)
74 } else {
75 false
76 }
77 }
78
79 /// A struct containing information about occurrences of the
80 /// `if let Some(..) = .. else` construct that this lint detects.
81 struct OptionIfLetElseOccurence {
82 option: String,
83 method_sugg: String,
84 some_expr: String,
85 none_expr: String,
86 }
87
88 /// Extracts the body of a given arm. If the arm contains only an expression,
89 /// then it returns the expression. Otherwise, it returns the entire block
extract_body_from_expr<'a>(expr: &'a Expr<'a>) -> Option<&'a Expr<'a>>90 fn extract_body_from_expr<'a>(expr: &'a Expr<'a>) -> Option<&'a Expr<'a>> {
91 if let ExprKind::Block(
92 Block {
93 stmts: block_stmts,
94 expr: Some(block_expr),
95 ..
96 },
97 _,
98 ) = expr.kind
99 {
100 if let [] = block_stmts {
101 Some(block_expr)
102 } else {
103 Some(expr)
104 }
105 } else {
106 None
107 }
108 }
109
format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String110 fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
111 format!(
112 "{}{}",
113 Sugg::hir(cx, cond_expr, "..").maybe_par(),
114 if as_mut {
115 ".as_mut()"
116 } else if as_ref {
117 ".as_ref()"
118 } else {
119 ""
120 }
121 )
122 }
123
124 /// If this expression is the option if let/else construct we're detecting, then
125 /// this function returns an `OptionIfLetElseOccurence` struct with details if
126 /// this construct is found, or None if this construct is not found.
detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionIfLetElseOccurence>127 fn detect_option_if_let_else<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) -> Option<OptionIfLetElseOccurence> {
128 if_chain! {
129 if !in_macro(expr.span); // Don't lint macros, because it behaves weirdly
130 if !in_constant(cx, expr.hir_id);
131 if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
132 = higher::IfLet::hir(cx, expr);
133 if !is_else_clause(cx.tcx, expr);
134 if !is_result_ok(cx, let_expr); // Don't lint on Result::ok because a different lint does it already
135 if let PatKind::TupleStruct(struct_qpath, [inner_pat], _) = &let_pat.kind;
136 if is_lang_ctor(cx, struct_qpath, OptionSome);
137 if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
138 if let Some(some_captures) = can_move_expr_to_closure(cx, if_then);
139 if let Some(none_captures) = can_move_expr_to_closure(cx, if_else);
140 if some_captures
141 .iter()
142 .filter_map(|(id, &c)| none_captures.get(id).map(|&c2| (c, c2)))
143 .all(|(x, y)| x.is_imm_ref() && y.is_imm_ref());
144
145 then {
146 let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
147 let some_body = extract_body_from_expr(if_then)?;
148 let none_body = extract_body_from_expr(if_else)?;
149 let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) {
150 "map_or"
151 } else {
152 "map_or_else"
153 };
154 let capture_name = id.name.to_ident_string();
155 let (as_ref, as_mut) = match &let_expr.kind {
156 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
157 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
158 _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
159 };
160 let cond_expr = match let_expr.kind {
161 // Pointer dereferencing happens automatically, so we can omit it in the suggestion
162 ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
163 _ => let_expr,
164 };
165 // Check if captures the closure will need conflict with borrows made in the scrutinee.
166 // TODO: check all the references made in the scrutinee expression. This will require interacting
167 // with the borrow checker. Currently only `<local>[.<field>]*` is checked for.
168 if as_ref || as_mut {
169 let e = peel_hir_expr_while(cond_expr, |e| match e.kind {
170 ExprKind::Field(e, _) | ExprKind::AddrOf(_, _, e) => Some(e),
171 _ => None,
172 });
173 if let ExprKind::Path(QPath::Resolved(None, Path { res: Res::Local(local_id), .. })) = e.kind {
174 match some_captures.get(local_id)
175 .or_else(|| (method_sugg == "map_or_else").then(|| ()).and_then(|_| none_captures.get(local_id)))
176 {
177 Some(CaptureKind::Value | CaptureKind::Ref(Mutability::Mut)) => return None,
178 Some(CaptureKind::Ref(Mutability::Not)) if as_mut => return None,
179 Some(CaptureKind::Ref(Mutability::Not)) | None => (),
180 }
181 }
182 }
183 Some(OptionIfLetElseOccurence {
184 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
185 method_sugg: method_sugg.to_string(),
186 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
187 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
188 })
189 } else {
190 None
191 }
192 }
193 }
194
195 impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>)196 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
197 if let Some(detection) = detect_option_if_let_else(cx, expr) {
198 span_lint_and_sugg(
199 cx,
200 OPTION_IF_LET_ELSE,
201 expr.span,
202 format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
203 "try",
204 format!(
205 "{}.{}({}, {})",
206 detection.option, detection.method_sugg, detection.none_expr, detection.some_expr,
207 ),
208 Applicability::MaybeIncorrect,
209 );
210 }
211 }
212 }
213