2 use crate::utils::eager_or_lazy;
3 use crate::utils::paths;
4 use crate::utils::sugg::Sugg;
5 use clippy_utils::diagnostics::span_lint_and_sugg;
6 use clippy_utils::ty::is_type_diagnostic_item;
7 use if_chain::if_chain;
9 use rustc_errors::Applicability;
10 use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, MatchSource, Mutability, PatKind, UnOp};
11 use rustc_lint::{LateContext, LateLintPass};
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
15 declare_clippy_lint! {
17 /// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
18 /// idiomatically done with `Option::map_or` (if the else bit is a pure
19 /// expression) or `Option::map_or_else` (if the else bit is an impure
22 /// **Why is this bad?**
23 /// Using the dedicated functions of the Option type is clearer and
24 /// more concise than an `if let` expression.
26 /// **Known problems:**
27 /// This lint uses a deliberately conservative metric for checking
28 /// if the inside of either body contains breaks or continues which will
29 /// cause it to not suggest a fix if either block contains a loop with
30 /// 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(ref 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 {
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
90 fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
91 if let ExprKind::Block(
100 if let [] = statements {
110 /// If this is the else body of an if/else expression, then we need to wrap
111 /// it in curly braces. Otherwise, we don't.
112 fn should_wrap_in_braces(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
113 utils::get_enclosing_block(cx, expr.hir_id).map_or(false, |parent| {
114 let mut should_wrap = false;
121 MatchSource::IfLetDesugar {
122 contains_else_clause: true,
128 should_wrap = expr.hir_id == arms[1].body.hir_id;
129 } else if let Some(Expr {
130 kind: ExprKind::If(_, _, Some(else_clause)),
134 should_wrap = expr.hir_id == else_clause.hir_id;
141 fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
144 Sugg::hir(cx, cond_expr, "..").maybe_par(),
155 /// If this expression is the option if let/else construct we're detecting, then
156 /// this function returns an `OptionIfLetElseOccurence` struct with details if
157 /// this construct is found, or None if this construct is not found.
158 fn detect_option_if_let_else<'tcx>(
159 cx: &'_ LateContext<'tcx>,
160 expr: &'_ Expr<'tcx>,
161 ) -> Option<OptionIfLetElseOccurence> {
163 if !utils::in_macro(expr.span); // Don't lint macros, because it behaves weirdly
164 if let ExprKind::Match(cond_expr, arms, MatchSource::IfLetDesugar{contains_else_clause: true}) = &expr.kind;
166 if !is_result_ok(cx, cond_expr); // Don't lint on Result::ok because a different lint does it already
167 if let PatKind::TupleStruct(struct_qpath, &[inner_pat], _) = &arms[0].pat.kind;
168 if utils::match_qpath(struct_qpath, &paths::OPTION_SOME);
169 if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
170 if !utils::usage::contains_return_break_continue_macro(arms[0].body);
171 if !utils::usage::contains_return_break_continue_macro(arms[1].body);
173 let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
174 let some_body = extract_body_from_arm(&arms[0])?;
175 let none_body = extract_body_from_arm(&arms[1])?;
176 let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) { "map_or" } else { "map_or_else" };
177 let capture_name = id.name.to_ident_string();
178 let wrap_braces = should_wrap_in_braces(cx, expr);
179 let (as_ref, as_mut) = match &cond_expr.kind {
180 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
181 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
182 _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
184 let cond_expr = match &cond_expr.kind {
185 // Pointer dereferencing happens automatically, so we can omit it in the suggestion
186 ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
189 Some(OptionIfLetElseOccurence {
190 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
191 method_sugg: method_sugg.to_string(),
192 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
193 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
202 impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
203 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
204 if let Some(detection) = detect_option_if_let_else(cx, expr) {
209 format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
213 if detection.wrap_braces { "{ " } else { "" },
215 detection.method_sugg,
218 if detection.wrap_braces { " }" } else { "" },
220 Applicability::MaybeIncorrect,