1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::sugg::Sugg;
3 use clippy_utils::ty::is_type_diagnostic_item;
4 use clippy_utils::usage::contains_return_break_continue_macro;
5 use clippy_utils::{eager_or_lazy, get_enclosing_block, in_macro, is_lang_ctor};
6 use if_chain::if_chain;
7 use rustc_errors::Applicability;
8 use rustc_hir::LangItem::OptionSome;
9 use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, MatchSource, Mutability, PatKind, UnOp};
10 use rustc_lint::{LateContext, LateLintPass};
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
14 declare_clippy_lint! {
16 /// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
17 /// idiomatically done with `Option::map_or` (if the else bit is a pure
18 /// expression) or `Option::map_or_else` (if the else bit is an impure
21 /// **Why is this bad?**
22 /// Using the dedicated functions of the Option type is clearer and
23 /// more concise than an `if let` expression.
25 /// **Known problems:**
26 /// This lint uses a deliberately conservative metric for checking
27 /// if the inside of either body contains breaks or continues which will
28 /// cause it to not suggest a fix if either block contains a loop with
29 /// continues or breaks contained within the loop.
34 /// # let optional: Option<u32> = Some(0);
35 /// # fn do_complicated_function() -> u32 { 5 };
36 /// let _ = if let Some(foo) = optional {
41 /// let _ = if let Some(foo) = optional {
44 /// let y = do_complicated_function();
52 /// # let optional: Option<u32> = Some(0);
53 /// # fn do_complicated_function() -> u32 { 5 };
54 /// let _ = optional.map_or(5, |foo| foo);
55 /// let _ = optional.map_or_else(||{
56 /// let y = do_complicated_function();
60 pub OPTION_IF_LET_ELSE,
62 "reimplementation of Option::map_or"
65 declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
67 /// Returns true iff the given expression is the result of calling `Result::ok`
68 fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
69 if let ExprKind::MethodCall(path, _, &[ref receiver], _) = &expr.kind {
70 path.ident.name.as_str() == "ok"
71 && is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(receiver), sym::result_type)
77 /// A struct containing information about occurrences of the
78 /// `if let Some(..) = .. else` construct that this lint detects.
79 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_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
90 if let ExprKind::Block(
99 if let [] = statements {
109 /// If this is the else body of an if/else expression, then we need to wrap
110 /// it in curly braces. Otherwise, we don't.
111 fn should_wrap_in_braces(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
112 get_enclosing_block(cx, expr.hir_id).map_or(false, |parent| {
113 let mut should_wrap = false;
120 MatchSource::IfLetDesugar {
121 contains_else_clause: true,
127 should_wrap = expr.hir_id == arms[1].body.hir_id;
128 } else if let Some(Expr {
129 kind: ExprKind::If(_, _, Some(else_clause)),
133 should_wrap = expr.hir_id == else_clause.hir_id;
140 fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
143 Sugg::hir(cx, cond_expr, "..").maybe_par(),
154 /// If this expression is the option if let/else construct we're detecting, then
155 /// this function returns an `OptionIfLetElseOccurence` struct with details if
156 /// this construct is found, or None if this construct is not found.
157 fn detect_option_if_let_else<'tcx>(
158 cx: &'_ LateContext<'tcx>,
159 expr: &'_ Expr<'tcx>,
160 ) -> Option<OptionIfLetElseOccurence> {
162 if !in_macro(expr.span); // Don't lint macros, because it behaves weirdly
163 if let ExprKind::Match(cond_expr, arms, MatchSource::IfLetDesugar{contains_else_clause: true}) = &expr.kind;
165 if !is_result_ok(cx, cond_expr); // Don't lint on Result::ok because a different lint does it already
166 if let PatKind::TupleStruct(struct_qpath, &[inner_pat], _) = &arms[0].pat.kind;
167 if is_lang_ctor(cx, struct_qpath, OptionSome);
168 if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
169 if !contains_return_break_continue_macro(arms[0].body);
170 if !contains_return_break_continue_macro(arms[1].body);
172 let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
173 let some_body = extract_body_from_arm(&arms[0])?;
174 let none_body = extract_body_from_arm(&arms[1])?;
175 let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) { "map_or" } else { "map_or_else" };
176 let capture_name = id.name.to_ident_string();
177 let wrap_braces = should_wrap_in_braces(cx, expr);
178 let (as_ref, as_mut) = match &cond_expr.kind {
179 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
180 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
181 _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
183 let cond_expr = match &cond_expr.kind {
184 // Pointer dereferencing happens automatically, so we can omit it in the suggestion
185 ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
188 Some(OptionIfLetElseOccurence {
189 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
190 method_sugg: method_sugg.to_string(),
191 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
192 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
201 impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
202 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
203 if let Some(detection) = detect_option_if_let_else(cx, expr) {
208 format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
212 if detection.wrap_braces { "{ " } else { "" },
214 detection.method_sugg,
217 if detection.wrap_braces { " }" } else { "" },
219 Applicability::MaybeIncorrect,