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, in_macro, is_else_clause, 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 {
86 /// Extracts the body of a given arm. If the arm contains only an expression,
87 /// then it returns the expression. Otherwise, it returns the entire block
88 fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
89 if let ExprKind::Block(
98 if let [] = statements {
108 fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
111 Sugg::hir(cx, cond_expr, "..").maybe_par(),
122 /// If this expression is the option if let/else construct we're detecting, then
123 /// this function returns an `OptionIfLetElseOccurence` struct with details if
124 /// this construct is found, or None if this construct is not found.
125 fn detect_option_if_let_else<'tcx>(
126 cx: &'_ LateContext<'tcx>,
127 expr: &'_ Expr<'tcx>,
128 ) -> Option<OptionIfLetElseOccurence> {
130 if !in_macro(expr.span); // Don't lint macros, because it behaves weirdly
131 if let ExprKind::Match(cond_expr, arms, MatchSource::IfLetDesugar{contains_else_clause: true}) = &expr.kind;
132 if !is_else_clause(cx.tcx, expr);
134 if !is_result_ok(cx, cond_expr); // Don't lint on Result::ok because a different lint does it already
135 if let PatKind::TupleStruct(struct_qpath, [inner_pat], _) = &arms[0].pat.kind;
136 if is_lang_ctor(cx, struct_qpath, OptionSome);
137 if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
138 if !contains_return_break_continue_macro(arms[0].body);
139 if !contains_return_break_continue_macro(arms[1].body);
142 let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
143 let some_body = extract_body_from_arm(&arms[0])?;
144 let none_body = extract_body_from_arm(&arms[1])?;
145 let method_sugg = if eager_or_lazy::is_eagerness_candidate(cx, none_body) { "map_or" } else { "map_or_else" };
146 let capture_name = id.name.to_ident_string();
147 let (as_ref, as_mut) = match &cond_expr.kind {
148 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
149 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
150 _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
152 let cond_expr = match &cond_expr.kind {
153 // Pointer dereferencing happens automatically, so we can omit it in the suggestion
154 ExprKind::Unary(UnOp::Deref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
157 Some(OptionIfLetElseOccurence {
158 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
159 method_sugg: method_sugg.to_string(),
160 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
161 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
169 impl<'tcx> LateLintPass<'tcx> for OptionIfLetElse {
170 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
171 if let Some(detection) = detect_option_if_let_else(cx, expr) {
176 format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
180 detection.option, detection.method_sugg, detection.none_expr, detection.some_expr,
182 Applicability::MaybeIncorrect,