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, path_to_local_id};
8 use if_chain::if_chain;
9 use rustc_errors::Applicability;
10 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultOk};
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() {
35 #[clippy::version = "pre 1.29.0"]
38 "checks for expressions that could be replaced by the question mark operator"
41 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
44 /// Checks if the given expression on the given context matches the following structure:
47 /// if option.is_none() {
53 /// if result.is_err() {
58 /// If it matches, it will suggest to use the question mark operator instead
59 fn check_is_none_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
61 if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
62 if let ExprKind::MethodCall(segment, _, args, _) = &cond.kind;
63 if let Some(subject) = args.get(0);
64 if (Self::option_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_none)) ||
65 (Self::result_check_and_early_return(cx, subject, then) && segment.ident.name == sym!(is_err));
67 let mut applicability = Applicability::MachineApplicable;
68 let receiver_str = &Sugg::hir_with_applicability(cx, subject, "..", &mut applicability);
69 let mut replacement: Option<String> = None;
70 if let Some(else_inner) = r#else {
72 if let ExprKind::Block(block, None) = &else_inner.kind;
73 if block.stmts.is_empty();
74 if let Some(block_expr) = &block.expr;
75 if eq_expr_value(cx, subject, block_expr);
77 replacement = Some(format!("Some({}?)", receiver_str));
80 } else if Self::moves_by_default(cx, subject)
81 && !matches!(subject.kind, ExprKind::Call(..) | ExprKind::MethodCall(..))
83 replacement = Some(format!("{}.as_ref()?;", receiver_str));
85 replacement = Some(format!("{}?;", receiver_str));
88 if let Some(replacement_str) = replacement {
93 "this block may be rewritten with the `?` operator",
103 fn check_if_let_some_or_err_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>) {
105 if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else: Some(if_else) })
106 = higher::IfLet::hir(cx, expr);
107 if let PatKind::TupleStruct(ref path1, fields, None) = let_pat.kind;
108 if (Self::option_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, OptionSome)) ||
109 (Self::result_check_and_early_return(cx, let_expr, if_else) && is_lang_ctor(cx, path1, ResultOk));
111 if let PatKind::Binding(annot, bind_id, _, _) = fields[0].kind;
112 let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
113 if let ExprKind::Block(block, None) = if_then.kind;
114 if block.stmts.is_empty();
115 if let Some(trailing_expr) = &block.expr;
116 if path_to_local_id(trailing_expr, bind_id);
118 let mut applicability = Applicability::MachineApplicable;
119 let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
120 let replacement = format!("{}{}?", receiver_str, if by_ref { ".as_ref()" } else { "" },);
126 "this if-let-else may be rewritten with the `?` operator",
135 fn result_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
136 Self::is_result(cx, expr) && Self::expression_returns_unmodified_err(cx, nested_expr, expr)
139 fn option_check_and_early_return(cx: &LateContext<'_>, expr: &Expr<'_>, nested_expr: &Expr<'_>) -> bool {
140 Self::is_option(cx, expr) && Self::expression_returns_none(cx, nested_expr)
143 fn moves_by_default(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
144 let expr_ty = cx.typeck_results().expr_ty(expression);
146 !expr_ty.is_copy_modulo_regions(cx.tcx.at(expression.span), cx.param_env)
149 fn is_option(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
150 let expr_ty = cx.typeck_results().expr_ty(expression);
152 is_type_diagnostic_item(cx, expr_ty, sym::Option)
155 fn is_result(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
156 let expr_ty = cx.typeck_results().expr_ty(expression);
158 is_type_diagnostic_item(cx, expr_ty, sym::Result)
161 fn expression_returns_none(cx: &LateContext<'_>, expression: &Expr<'_>) -> bool {
162 match expression.kind {
163 ExprKind::Block(block, _) => {
164 if let Some(return_expression) = Self::return_expression(block) {
165 return Self::expression_returns_none(cx, return_expression);
170 ExprKind::Ret(Some(expr)) => Self::expression_returns_none(cx, expr),
171 ExprKind::Path(ref qpath) => is_lang_ctor(cx, qpath, OptionNone),
176 fn expression_returns_unmodified_err(cx: &LateContext<'_>, expr: &Expr<'_>, cond_expr: &Expr<'_>) -> bool {
178 ExprKind::Block(block, _) => {
179 if let Some(return_expression) = Self::return_expression(block) {
180 return Self::expression_returns_unmodified_err(cx, return_expression, cond_expr);
185 ExprKind::Ret(Some(ret_expr)) => Self::expression_returns_unmodified_err(cx, ret_expr, cond_expr),
186 ExprKind::Path(_) => path_to_local(expr) == path_to_local(cond_expr),
191 fn return_expression<'tcx>(block: &Block<'tcx>) -> Option<&'tcx Expr<'tcx>> {
192 // Check if last expression is a return statement. Then, return the expression
194 if block.stmts.len() == 1;
195 if let Some(expr) = block.stmts.iter().last();
196 if let StmtKind::Semi(expr) = expr.kind;
197 if let ExprKind::Ret(Some(ret_expr)) = expr.kind;
200 return Some(ret_expr);
204 // Check for `return` without a semicolon.
206 if block.stmts.is_empty();
207 if let Some(ExprKind::Ret(Some(ret_expr))) = block.expr.as_ref().map(|e| &e.kind);
209 return Some(ret_expr);
217 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
218 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
219 Self::check_is_none_or_err_and_early_return(cx, expr);
220 Self::check_if_let_some_or_err_and_early_return(cx, expr);