1 use clippy_utils::diagnostics::span_lint_and_sugg;
2 use clippy_utils::higher;
3 use clippy_utils::source::snippet_with_applicability;
4 use clippy_utils::ty::is_type_diagnostic_item;
6 eq_expr_value, get_parent_node, is_else_clause, is_lang_ctor, path_to_local, path_to_local_id, peel_blocks,
9 use if_chain::if_chain;
10 use rustc_errors::Applicability;
11 use rustc_hir::LangItem::{OptionNone, OptionSome, ResultErr, ResultOk};
12 use rustc_hir::{BindingAnnotation, Expr, ExprKind, Node, PatKind, PathSegment, QPath};
13 use rustc_lint::{LateContext, LateLintPass};
14 use rustc_middle::ty::Ty;
15 use rustc_session::{declare_lint_pass, declare_tool_lint};
16 use rustc_span::{sym, symbol::Symbol};
18 declare_clippy_lint! {
20 /// Checks for expressions that could be replaced by the question mark operator.
22 /// ### Why is this bad?
23 /// Question mark usage is more idiomatic.
27 /// if option.is_none() {
37 #[clippy::version = "pre 1.29.0"]
40 "checks for expressions that could be replaced by the question mark operator"
43 declare_lint_pass!(QuestionMark => [QUESTION_MARK]);
45 enum IfBlockType<'hir> {
46 /// An `if x.is_xxx() { a } else { b } ` expression.
48 /// Contains: caller (x), caller_type, call_sym (is_xxx), if_then (a), if_else (b)
54 Option<&'hir Expr<'hir>>,
56 /// An `if let Xxx(a) = b { c } else { d }` expression.
58 /// Contains: let_pat_qpath (Xxx), let_pat_type, let_pat_sym (a), let_expr (b), if_then (c),
66 Option<&'hir Expr<'hir>>,
70 /// Checks if the given expression on the given context matches the following structure:
73 /// if option.is_none() {
79 /// if result.is_err() {
84 /// If it matches, it will suggest to use the question mark operator instead
85 fn check_is_none_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
87 if let Some(higher::If { cond, then, r#else }) = higher::If::hir(expr);
88 if !is_else_clause(cx.tcx, expr);
89 if let ExprKind::MethodCall(segment, caller, ..) = &cond.kind;
90 let caller_ty = cx.typeck_results().expr_ty(caller);
91 let if_block = IfBlockType::IfIs(caller, caller_ty, segment.ident.name, then, r#else);
92 if is_early_return(sym::Option, cx, &if_block) || is_early_return(sym::Result, cx, &if_block);
94 let mut applicability = Applicability::MachineApplicable;
95 let receiver_str = snippet_with_applicability(cx, caller.span, "..", &mut applicability);
96 let by_ref = !caller_ty.is_copy_modulo_regions(cx.tcx.at(caller.span), cx.param_env) &&
97 !matches!(caller.kind, ExprKind::Call(..) | ExprKind::MethodCall(..));
98 let sugg = if let Some(else_inner) = r#else {
99 if eq_expr_value(cx, caller, peel_blocks(else_inner)) {
100 format!("Some({}?)", receiver_str)
105 format!("{}{}?;", receiver_str, if by_ref { ".as_ref()" } else { "" })
112 "this block may be rewritten with the `?` operator",
121 fn check_if_let_some_or_err_and_early_return<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'tcx>) {
123 if let Some(higher::IfLet { let_pat, let_expr, if_then, if_else }) = higher::IfLet::hir(cx, expr);
124 if !is_else_clause(cx.tcx, expr);
125 if let PatKind::TupleStruct(ref path1, [field], None) = let_pat.kind;
126 if let PatKind::Binding(annot, bind_id, ident, None) = field.kind;
127 let caller_ty = cx.typeck_results().expr_ty(let_expr);
128 let if_block = IfBlockType::IfLet(path1, caller_ty, ident.name, let_expr, if_then, if_else);
129 if (is_early_return(sym::Option, cx, &if_block) && path_to_local_id(peel_blocks(if_then), bind_id))
130 || is_early_return(sym::Result, cx, &if_block);
131 if if_else.map(|e| eq_expr_value(cx, let_expr, peel_blocks(e))).filter(|e| *e).is_none();
133 let mut applicability = Applicability::MachineApplicable;
134 let receiver_str = snippet_with_applicability(cx, let_expr.span, "..", &mut applicability);
135 let by_ref = matches!(annot, BindingAnnotation::Ref | BindingAnnotation::RefMut);
136 let requires_semi = matches!(get_parent_node(cx.tcx, expr.hir_id), Some(Node::Stmt(_)));
140 if by_ref { ".as_ref()" } else { "" },
141 if requires_semi { ";" } else { "" }
147 "this block may be rewritten with the `?` operator",
156 fn is_early_return(smbl: Symbol, cx: &LateContext<'_>, if_block: &IfBlockType<'_>) -> bool {
158 IfBlockType::IfIs(caller, caller_ty, call_sym, if_then, _) => {
159 // If the block could be identified as `if x.is_none()/is_err()`,
160 // we then only need to check the if_then return to see if it is none/err.
161 is_type_diagnostic_item(cx, caller_ty, smbl)
162 && expr_return_none_or_err(smbl, cx, if_then, caller, None)
164 sym::Option => call_sym == sym!(is_none),
165 sym::Result => call_sym == sym!(is_err),
169 IfBlockType::IfLet(qpath, let_expr_ty, let_pat_sym, let_expr, if_then, if_else) => {
170 is_type_diagnostic_item(cx, let_expr_ty, smbl)
173 // We only need to check `if let Some(x) = option` not `if let None = option`,
174 // because the later one will be suggested as `if option.is_none()` thus causing conflict.
175 is_lang_ctor(cx, qpath, OptionSome)
177 && expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, None)
180 (is_lang_ctor(cx, qpath, ResultOk)
182 && expr_return_none_or_err(smbl, cx, if_else.unwrap(), let_expr, Some(let_pat_sym)))
183 || is_lang_ctor(cx, qpath, ResultErr)
184 && expr_return_none_or_err(smbl, cx, if_then, let_expr, Some(let_pat_sym))
192 fn expr_return_none_or_err(
194 cx: &LateContext<'_>,
196 cond_expr: &Expr<'_>,
197 err_sym: Option<Symbol>,
199 match peel_blocks_with_stmt(expr).kind {
200 ExprKind::Ret(Some(ret_expr)) => expr_return_none_or_err(smbl, cx, ret_expr, cond_expr, err_sym),
201 ExprKind::Path(ref qpath) => match smbl {
202 sym::Option => is_lang_ctor(cx, qpath, OptionNone),
203 sym::Result => path_to_local(expr).is_some() && path_to_local(expr) == path_to_local(cond_expr),
206 ExprKind::Call(call_expr, args_expr) => {
208 if smbl == sym::Result;
209 if let ExprKind::Path(QPath::Resolved(_, path)) = &call_expr.kind;
210 if let Some(segment) = path.segments.first();
211 if let Some(err_sym) = err_sym;
212 if let Some(arg) = args_expr.first();
213 if let ExprKind::Path(QPath::Resolved(_, arg_path)) = &arg.kind;
214 if let Some(PathSegment { ident, .. }) = arg_path.segments.first();
216 return segment.ident.name == sym::Err && err_sym == ident.name;
225 impl<'tcx> LateLintPass<'tcx> for QuestionMark {
226 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
227 check_is_none_or_err_and_early_return(cx, expr);
228 check_if_let_some_or_err_and_early_return(cx, expr);