2 use crate::utils::sugg::Sugg;
3 use crate::utils::{match_type, paths, span_lint_and_sugg};
4 use if_chain::if_chain;
6 use rustc_errors::Applicability;
7 use rustc_hir::intravisit::{NestedVisitorMap, Visitor};
8 use rustc_hir::{Arm, BindingAnnotation, Block, Expr, ExprKind, MatchSource, Mutability, PatKind, UnOp};
9 use rustc_lint::{LateContext, LateLintPass};
10 use rustc_middle::hir::map::Map;
11 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 declare_clippy_lint! {
15 /// Lints usage of `if let Some(v) = ... { y } else { x }` which is more
16 /// idiomatically done with `Option::map_or` (if the else bit is a simple
17 /// expression) or `Option::map_or_else` (if the else bit is a longer
20 /// **Why is this bad?**
21 /// Using the dedicated functions of the Option type is clearer and
22 /// more concise than an if let expression.
24 /// **Known problems:**
25 /// This lint uses whether the block is just an expression or if it has
26 /// more statements to decide whether to use `Option::map_or` or
27 /// `Option::map_or_else`. If you have a single expression which calls
28 /// an expensive function, then it would be more efficient to use
29 /// `Option::map_or_else`, but this lint would suggest `Option::map_or`.
31 /// Also, this lint uses a deliberately conservative metric for checking
32 /// if the inside of either body contains breaks or continues which will
33 /// cause it to not suggest a fix if either block contains a loop with
34 /// continues or breaks contained within the loop.
39 /// # let optional: Option<u32> = Some(0);
40 /// # fn do_complicated_function() -> u32 { 5 };
41 /// let _ = if let Some(foo) = optional {
46 /// let _ = if let Some(foo) = optional {
49 /// let y = do_complicated_function();
57 /// # let optional: Option<u32> = Some(0);
58 /// # fn do_complicated_function() -> u32 { 5 };
59 /// let _ = optional.map_or(5, |foo| foo);
60 /// let _ = optional.map_or_else(||{
61 /// let y = do_complicated_function();
65 pub OPTION_IF_LET_ELSE,
67 "reimplementation of Option::map_or"
70 declare_lint_pass!(OptionIfLetElse => [OPTION_IF_LET_ELSE]);
72 /// Returns true iff the given expression is the result of calling `Result::ok`
73 fn is_result_ok(cx: &LateContext<'_>, expr: &'_ Expr<'_>) -> bool {
74 if let ExprKind::MethodCall(ref path, _, &[ref receiver], _) = &expr.kind {
75 path.ident.name.to_ident_string() == "ok" && match_type(cx, &cx.tables().expr_ty(&receiver), &paths::RESULT)
81 /// A struct containing information about occurences of the
82 /// `if let Some(..) = .. else` construct that this lint detects.
83 struct OptionIfLetElseOccurence {
91 struct ReturnBreakContinueMacroVisitor {
92 seen_return_break_continue: bool,
94 impl ReturnBreakContinueMacroVisitor {
95 fn new() -> ReturnBreakContinueMacroVisitor {
96 ReturnBreakContinueMacroVisitor {
97 seen_return_break_continue: false,
101 impl<'tcx> Visitor<'tcx> for ReturnBreakContinueMacroVisitor {
102 type Map = Map<'tcx>;
103 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
104 NestedVisitorMap::None
107 fn visit_expr(&mut self, ex: &'tcx Expr<'tcx>) {
108 if self.seen_return_break_continue {
109 // No need to look farther if we've already seen one of them
113 ExprKind::Ret(..) | ExprKind::Break(..) | ExprKind::Continue(..) => {
114 self.seen_return_break_continue = true;
116 // Something special could be done here to handle while or for loop
117 // desugaring, as this will detect a break if there's a while loop
118 // or a for loop inside the expression.
120 if utils::in_macro(ex.span) {
121 self.seen_return_break_continue = true;
123 rustc_hir::intravisit::walk_expr(self, ex);
130 fn contains_return_break_continue_macro(expression: &Expr<'_>) -> bool {
131 let mut recursive_visitor = ReturnBreakContinueMacroVisitor::new();
132 recursive_visitor.visit_expr(expression);
133 recursive_visitor.seen_return_break_continue
136 /// Extracts the body of a given arm. If the arm contains only an expression,
137 /// then it returns the expression. Otherwise, it returns the entire block
138 fn extract_body_from_arm<'a>(arm: &'a Arm<'a>) -> Option<&'a Expr<'a>> {
139 if let ExprKind::Block(
148 if let [] = statements {
158 /// If this is the else body of an if/else expression, then we need to wrap
159 /// it in curcly braces. Otherwise, we don't.
160 fn should_wrap_in_braces(cx: &LateContext<'_>, expr: &Expr<'_>) -> bool {
161 utils::get_enclosing_block(cx, expr.hir_id).map_or(false, |parent| {
167 MatchSource::IfDesugar {
168 contains_else_clause: true,
170 | MatchSource::IfLetDesugar {
171 contains_else_clause: true,
177 expr.hir_id == arms[1].body.hir_id
184 fn format_option_in_sugg(cx: &LateContext<'_>, cond_expr: &Expr<'_>, as_ref: bool, as_mut: bool) -> String {
187 Sugg::hir(cx, cond_expr, "..").maybe_par(),
198 /// If this expression is the option if let/else construct we're detecting, then
199 /// this function returns an `OptionIfLetElseOccurence` struct with details if
200 /// this construct is found, or None if this construct is not found.
201 fn detect_option_if_let_else(cx: &LateContext<'_>, expr: &Expr<'_>) -> Option<OptionIfLetElseOccurence> {
203 if !utils::in_macro(expr.span); // Don't lint macros, because it behaves weirdly
204 if let ExprKind::Match(cond_expr, arms, MatchSource::IfLetDesugar{contains_else_clause: true}) = &expr.kind;
206 if !is_result_ok(cx, cond_expr); // Don't lint on Result::ok because a different lint does it already
207 if let PatKind::TupleStruct(struct_qpath, &[inner_pat], _) = &arms[0].pat.kind;
208 if utils::match_qpath(struct_qpath, &paths::OPTION_SOME);
209 if let PatKind::Binding(bind_annotation, _, id, _) = &inner_pat.kind;
210 if !contains_return_break_continue_macro(arms[0].body);
211 if !contains_return_break_continue_macro(arms[1].body);
213 let capture_mut = if bind_annotation == &BindingAnnotation::Mutable { "mut " } else { "" };
214 let some_body = extract_body_from_arm(&arms[0])?;
215 let none_body = extract_body_from_arm(&arms[1])?;
216 let method_sugg = match &none_body.kind {
217 ExprKind::Block(..) => "map_or_else",
220 let capture_name = id.name.to_ident_string();
221 let wrap_braces = should_wrap_in_braces(cx, expr);
222 let (as_ref, as_mut) = match &cond_expr.kind {
223 ExprKind::AddrOf(_, Mutability::Not, _) => (true, false),
224 ExprKind::AddrOf(_, Mutability::Mut, _) => (false, true),
225 _ => (bind_annotation == &BindingAnnotation::Ref, bind_annotation == &BindingAnnotation::RefMut),
227 let cond_expr = match &cond_expr.kind {
228 // Pointer dereferencing happens automatically, so we can omit it in the suggestion
229 ExprKind::Unary(UnOp::UnDeref, expr) | ExprKind::AddrOf(_, _, expr) => expr,
232 Some(OptionIfLetElseOccurence {
233 option: format_option_in_sugg(cx, cond_expr, as_ref, as_mut),
234 method_sugg: method_sugg.to_string(),
235 some_expr: format!("|{}{}| {}", capture_mut, capture_name, Sugg::hir(cx, some_body, "..")),
236 none_expr: format!("{}{}", if method_sugg == "map_or" { "" } else { "|| " }, Sugg::hir(cx, none_body, "..")),
245 impl<'a> LateLintPass<'a> for OptionIfLetElse {
246 fn check_expr(&mut self, cx: &LateContext<'a>, expr: &Expr<'_>) {
247 if let Some(detection) = detect_option_if_let_else(cx, expr) {
252 format!("use Option::{} instead of an if let/else", detection.method_sugg).as_str(),
256 if detection.wrap_braces { "{ " } else { "" },
258 detection.method_sugg,
261 if detection.wrap_braces { " }" } else { "" },
263 Applicability::MaybeIncorrect,