2 diagnostics::span_lint_hir_and_then,
3 get_async_fn_body, is_async_fn,
4 source::{snippet_with_applicability, snippet_with_context, walk_span_to_context},
5 visitors::for_each_expr,
7 use core::ops::ControlFlow;
8 use rustc_errors::Applicability;
9 use rustc_hir::intravisit::FnKind;
10 use rustc_hir::{Block, Body, Expr, ExprKind, FnDecl, FnRetTy, HirId};
11 use rustc_lint::{LateContext, LateLintPass, LintContext};
12 use rustc_middle::lint::in_external_macro;
13 use rustc_session::{declare_lint_pass, declare_tool_lint};
14 use rustc_span::{Span, SyntaxContext};
16 declare_clippy_lint! {
18 /// Checks for missing return statements at the end of a block.
20 /// ### Why is this bad?
21 /// Actually omitting the return keyword is idiomatic Rust code. Programmers
22 /// coming from other languages might prefer the expressiveness of `return`. It's possible to miss
23 /// the last returning statement because the only difference is a missing `;`. Especially in bigger
24 /// code with multiple return paths having a `return` keyword makes it easier to find the
25 /// corresponding statements.
29 /// fn foo(x: usize) -> usize {
35 /// fn foo(x: usize) -> usize {
39 #[clippy::version = "1.33.0"]
42 "use a return statement like `return expr` instead of an expression"
45 declare_lint_pass!(ImplicitReturn => [IMPLICIT_RETURN]);
47 fn lint_return(cx: &LateContext<'_>, emission_place: HirId, span: Span) {
48 let mut app = Applicability::MachineApplicable;
49 let snip = snippet_with_applicability(cx, span, "..", &mut app);
50 span_lint_hir_and_then(
55 "missing `return` statement",
57 diag.span_suggestion(span, "add `return` as shown", format!("return {snip}"), app);
62 fn lint_break(cx: &LateContext<'_>, emission_place: HirId, break_span: Span, expr_span: Span) {
63 let mut app = Applicability::MachineApplicable;
64 let snip = snippet_with_context(cx, expr_span, break_span.ctxt(), "..", &mut app).0;
65 span_lint_hir_and_then(
70 "missing `return` statement",
74 "change `break` to `return` as shown",
75 format!("return {snip}"),
82 #[derive(Clone, Copy, PartialEq, Eq)]
84 /// The lint was applied to a parent expression.
86 /// The lint was applied to this expression, a child, or not applied.
90 fn still_parent(self, b: bool) -> Self {
91 if b { self } else { Self::Inner }
94 fn is_parent(self) -> bool {
99 // Gets the call site if the span is in a child context. Otherwise returns `None`.
100 fn get_call_site(span: Span, ctxt: SyntaxContext) -> Option<Span> {
101 (span.ctxt() != ctxt).then(|| walk_span_to_context(span, ctxt).unwrap_or(span))
104 fn lint_implicit_returns(
105 cx: &LateContext<'_>,
107 // The context of the function body.
109 // Whether the expression is from a macro expansion.
110 call_site_span: Option<Span>,
115 expr: Some(block_expr), ..
118 ) => lint_implicit_returns(
122 call_site_span.or_else(|| get_call_site(block_expr.span, ctxt)),
124 .still_parent(call_site_span.is_some()),
126 ExprKind::If(_, then_expr, Some(else_expr)) => {
127 // Both `then_expr` or `else_expr` are required to be blocks in the same context as the `if`. Don't
129 let res = lint_implicit_returns(cx, then_expr, ctxt, call_site_span).still_parent(call_site_span.is_some());
131 // The return was added as a parent of this if expression.
134 lint_implicit_returns(cx, else_expr, ctxt, call_site_span).still_parent(call_site_span.is_some())
137 ExprKind::Match(_, arms, _) => {
139 let res = lint_implicit_returns(
143 call_site_span.or_else(|| get_call_site(arm.body.span, ctxt)),
145 .still_parent(call_site_span.is_some());
147 // The return was added as a parent of this match expression.
154 ExprKind::Loop(block, ..) => {
155 let mut add_return = false;
156 let _: Option<!> = for_each_expr(block, |e| {
157 if let ExprKind::Break(dest, sub_expr) = e.kind {
158 if dest.target_id.ok() == Some(expr.hir_id) {
159 if call_site_span.is_none() && e.span.ctxt() == ctxt {
160 // At this point sub_expr can be `None` in async functions which either diverge, or return
162 if let Some(sub_expr) = sub_expr {
163 lint_break(cx, e.hir_id, e.span, sub_expr.span);
166 // the break expression is from a macro call, add a return to the loop
171 ControlFlow::Continue(())
174 #[expect(clippy::option_if_let_else)]
175 if let Some(span) = call_site_span {
176 lint_return(cx, expr.hir_id, span);
179 lint_return(cx, expr.hir_id, expr.span);
187 // If expressions without an else clause, and blocks without a final expression can only be the final expression
188 // if they are divergent, or return the unit type.
189 ExprKind::If(_, _, None) | ExprKind::Block(Block { expr: None, .. }, _) | ExprKind::Ret(_) => {
193 // Any divergent expression doesn't need a return statement.
194 ExprKind::MethodCall(..)
196 | ExprKind::Binary(..)
197 | ExprKind::Unary(..)
198 | ExprKind::Index(..)
199 if cx.typeck_results().expr_ty(expr).is_never() =>
206 #[expect(clippy::option_if_let_else)]
207 if let Some(span) = call_site_span {
208 lint_return(cx, expr.hir_id, span);
211 lint_return(cx, expr.hir_id, expr.span);
218 impl<'tcx> LateLintPass<'tcx> for ImplicitReturn {
221 cx: &LateContext<'tcx>,
223 decl: &'tcx FnDecl<'_>,
224 body: &'tcx Body<'_>,
228 if (!matches!(kind, FnKind::Closure) && matches!(decl.output, FnRetTy::DefaultReturn(_)))
229 || span.ctxt() != body.value.span.ctxt()
230 || in_external_macro(cx.sess(), span)
235 let res_ty = cx.typeck_results().expr_ty(body.value);
236 if res_ty.is_unit() || res_ty.is_never() {
240 let expr = if is_async_fn(kind) {
241 match get_async_fn_body(cx.tcx, body) {
248 lint_implicit_returns(cx, expr, expr.span.ctxt(), None);