1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::higher;
3 use clippy_utils::is_lang_ctor;
4 use clippy_utils::source::snippet_with_applicability;
5 use clippy_utils::sugg::Sugg;
6 use clippy_utils::ty::is_type_diagnostic_item;
7 use clippy_utils::{eq_expr_value, path_to_local_id};
8 use if_chain::if_chain;
9 use rustc_errors::Applicability;
10 use rustc_hir::LangItem::{OptionNone, OptionSome};
11 use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, PatKind, StmtKind};
12 use rustc_lint::{LateContext, LateLintPass};
13 use rustc_session::{declare_lint_pass, declare_tool_lint};
16 declare_clippy_lint! {
18 /// Checks for expressions that could be replaced by the question mark operator.
20 /// ### Why is this bad?
21 /// Question mark usage is more idiomatic.
25 /// if option.is_none() {
37 "checks for expressions that could be replaced by the question mark operator"
40 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
43 /// Checks if the given expression on the given context matches the following structure:
46 /// if option.is_none() {
51 /// If it matches, it will suggest to use the question mark operator instead
52 fn check_is_none_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
54 if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
55 if let ExprKind::MethodCall(segment, _, args, _) = &cond.kind;
56 if segment.ident.name == sym!(is_none);
57 if Self::expression_returns_none(cx, then);
58 if let Some(subject) = args.get(0);
59 if Self::is_option(cx, subject);
62 let mut applicability = Applicability::MachineApplicable;
63 let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
64 let mut replacement: Option<String> = None;
65 if let Some(else_inner) = r#else {
67 if let ExprKind::Block(block, None) = &else_inner.kind;
68 if block.stmts.is_empty();
69 if let Some(block_expr) = &block.expr;
70 if eq_expr_value(cx, subject, block_expr);
72 replacement = Some(format!("Some({}?)", receiver_str));
75 } else if Self::moves_by_default(cx, subject)
76 && !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
78 replacement = Some(format!("{}.as_ref()?;", receiver_str));
80 replacement = Some(format!("{}?;", receiver_str));
83 if let Some(replacement_str) = replacement {
88 "this block may be rewritten with the `?` operator",
98 fn check_if_let_some_and_early_return_none(cx: &LateContext<'_>, expr: &Expr<'_>) {
100 if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
101 = higher::IfLet::hir(cx, expr);
102 if Self::is_option(cx, let_expr);
104 if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
105 if is_lang_ctor(cx, path1, OptionSome);
106 if let PatKind::Binding(annot, bind_id, _, _) = fields[0].kind;
107 let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
109 if let ExprKind::Block(block, None) = if_then.kind;
110 if block.stmts.is_empty();
111 if let Some(trailing_expr) = &block.expr;
112 if path_to_local_id(trailing_expr, bind_id);
114 if Self::expression_returns_none(cx, if_else);
116 let mut applicability = Applicability::MachineApplicable;
117 let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
118 let replacement = format!(
121 if by_ref { ".as_ref()" } else { "" },
128 "this if-let-else may be rewritten with the `?` operator",
137 fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
138 let expr_ty = cx.typeck_results().expr_ty(expression);
140 !expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
143 fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
144 let expr_ty = cx.typeck_results().expr_ty(expression);
146 is_type_diagnostic_item(cx, expr_ty, sym::option_type)
149 fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
150 match expression.kind {
151 ExprKind::Block(block, _) => {
152 if let Some(return_expression) = Self::return_expression(block) {
153 return Self::expression_returns_none(cx, return_expression);
158 ExprKind::Ret(Some(expr)) => Self::expression_returns_none(cx, expr),
159 ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
164 fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
165 // Check if last expression is a return statement. Then, return the expression
167 if block.stmts.len() == 1;
168 if let Some(expr) = block.stmts.iter().last();
169 if let StmtKind::Semi(expr) = expr.kind;
170 if let ExprKind::Ret(Some(ret_expr)) = expr.kind;
173 return Some(ret_expr);
177 // Check for `return` without a semicolon.
179 if block.stmts.is_empty();
180 if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
182 return Some(ret_expr);
190 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
191 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
192 Self::check_is_none_and_early_return_none(cx, expr);
193 Self::check_if_let_some_and_early_return_none(cx, expr);