1 use if_chain::if_chain;
2 use rustc_errors::Applicability;
3 use rustc_hir::def::{DefKind, Res};
4 use rustc_hir::{def, BindingAnnotation, Block, Expr, ExprKind, MatchSource, PatKind, StmtKind};
5 use rustc_lint::{LateContext, LateLintPass};
6 use rustc_session::{declare_lint_pass, declare_tool_lint};
9 use crate::utils::sugg::Sugg;
11 eq_expr_value, higher, is_type_diagnostic_item, match_def_path, match_qpath, paths, snippet_with_applicability,
15 declare_clippy_lint! {
16 /// **What it does:** Checks for expressions that could be replaced by the question mark operator.
18 /// **Why is this bad?** Question mark usage is more idiomatic.
20 /// **Known problems:** None
24 /// if option.is_none() {
36 "checks for expressions that could be replaced by the question mark operator"
39 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
42 /// Checks if the given expression on the given context matches the following structure:
45 /// if option.is_none() {
50 /// If it matches, it will suggest to use the question mark operator instead
51 fn check_is_none_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
53 if let Some((if_expr, body, else_)) = higher::if_block(&expr);
54 if let ExprKind::MethodCall(segment, _, args, _) = &if_expr.kind;
55 if segment.ident.name == sym!(is_none);
56 if Self::expression_returns_none(cx, body);
57 if let Some(subject) = args.get(0);
58 if Self::is_option(cx, subject);
61 let mut applicability = Applicability::MachineApplicable;
62 let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
63 let mut replacement: Option<String> = None;
64 if let Some(else_) = else_ {
66 if let ExprKind::Block(block, None) = &else_.kind;
67 if block.stmts.is_empty();
68 if let Some(block_expr) = &block.expr;
69 if eq_expr_value(cx, subject, block_expr);
71 replacement = Some(format!("Some({}?)", receiver_str));
74 } else if Self::moves_by_default(cx, subject)
75 && !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
77 replacement = Some(format!("{}.as_ref()?;", receiver_str));
79 replacement = Some(format!("{}?;", receiver_str));
82 if let Some(replacement_str) = replacement {
87 "this block may be rewritten with the `?` operator",
97 fn check_if_let_some_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
99 if let ExprKind::Match(subject, arms, source) = &expr.kind;
100 if *source == MatchSource::IfLetDesugar { contains_else_clause: true };
101 if Self::is_option(cx, subject);
103 if let PatKind::TupleStruct(path1, fields, None) = &arms[0].pat.kind;
104 if match_qpath(path1, &["Some"]);
105 if let PatKind::Binding(annot, _, bind, _) = &fields[0].kind;
106 let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
108 if let ExprKind::Block(block, None) = &arms[0].body.kind;
109 if block.stmts.is_empty();
110 if let Some(trailing_expr) = &block.expr;
111 if let ExprKind::Path(path) = &trailing_expr.kind;
112 if match_qpath(path, &[&bind.as_str()]);
114 if let PatKind::Wild = arms[1].pat.kind;
115 if Self::expression_returns_none(cx, arms[1].body);
117 let mut applicability = Applicability::MachineApplicable;
118 let receiver_str = snippet_with_applicability(cx, subject.span, "..", &mut applicability);
119 let replacement = format!(
122 if by_ref { ".as_ref()" } else { "" },
129 "this if-let-else may be rewritten with the `?` operator",
138 fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
139 let expr_ty = cx.typeck_results().expr_ty(expression);
141 !expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
144 fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
145 let expr_ty = cx.typeck_results().expr_ty(expression);
147 is_type_diagnostic_item(cx, expr_ty, sym::option_type)
150 fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
151 match expression.kind {
152 ExprKind::Block(ref block, _) => {
153 if let Some(return_expression) = Self::return_expression(block) {
154 return Self::expression_returns_none(cx, &return_expression);
159 ExprKind::Ret(Some(ref expr)) => Self::expression_returns_none(cx, expr),
160 ExprKind::Path(ref qp) => {
161 if let Res::Def(DefKind::Ctor(def::CtorOf::Variant, def::CtorKind::Const), def_id) =
162 cx.qpath_res(qp, expression.hir_id)
164 return match_def_path(cx, def_id, &paths::OPTION_NONE);
173 fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
174 // Check if last expression is a return statement. Then, return the expression
176 if block.stmts.len() == 1;
177 if let Some(expr) = block.stmts.iter().last();
178 if let StmtKind::Semi(ref expr) = expr.kind;
179 if let ExprKind::Ret(ret_expr) = expr.kind;
180 if let Some(ret_expr) = ret_expr;
183 return Some(ret_expr);
187 // Check for `return` without a semicolon.
189 if block.stmts.is_empty();
190 if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
192 return Some(ret_expr);
200 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
201 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
202 Self::check_is_none_and_early_return_none(cx, expr);
203 Self::check_if_let_some_and_early_return_none(cx, expr);