2 diagnostics::span_lint_and_sugg,
3 get_async_fn_body, is_async_fn,
4 source::{snippet_with_applicability, snippet_with_context, walk_span_to_context},
5 visitors::expr_visitor_no_bodies,
7 use rustc_errors::Applicability;
8 use rustc_hir::intravisit::{FnKind, Visitor};
9 use rustc_hir::{Block, Body, Expr, ExprKind, FnDecl, FnRetTy, HirId};
10 use rustc_lint::{LateContext, LateLintPass, LintContext};
11 use rustc_middle::lint::in_external_macro;
12 use rustc_session::{declare_lint_pass, declare_tool_lint};
13 use rustc_span::{Span, SyntaxContext};
15 declare_clippy_lint! {
17 /// Checks for missing return statements at the end of a block.
19 /// ### Why is this bad?
20 /// Actually omitting the return keyword is idiomatic Rust code. Programmers
21 /// coming from other languages might prefer the expressiveness of `return`. It's possible to miss
22 /// the last returning statement because the only difference is a missing `;`. Especially in bigger
23 /// code with multiple return paths having a `return` keyword makes it easier to find the
24 /// corresponding statements.
28 /// fn foo(x: usize) -> usize {
34 /// fn foo(x: usize) -> usize {
38 #[clippy::version = "1.33.0"]
41 "use a return statement like `return expr` instead of an expression"
44 declare_lint_pass!(ImplicitReturn => [IMPLICIT_RETURN]);
46 fn lint_return(cx: &LateContext<'_>, span: Span) {
47 let mut app = Applicability::MachineApplicable;
48 let snip = snippet_with_applicability(cx, span, "..", &mut app);
53 "missing `return` statement",
54 "add `return` as shown",
55 format!("return {}", snip),
60 fn lint_break(cx: &LateContext<'_>, break_span: Span, expr_span: Span) {
61 let mut app = Applicability::MachineApplicable;
62 let snip = snippet_with_context(cx, expr_span, break_span.ctxt(), "..", &mut app).0;
67 "missing `return` statement",
68 "change `break` to `return` as shown",
69 format!("return {}", snip),
74 #[derive(Clone, Copy, PartialEq, Eq)]
76 /// The lint was applied to a parent expression.
78 /// The lint was applied to this expression, a child, or not applied.
82 fn still_parent(self, b: bool) -> Self {
83 if b { self } else { Self::Inner }
86 fn is_parent(self) -> bool {
91 // Gets the call site if the span is in a child context. Otherwise returns `None`.
92 fn get_call_site(span: Span, ctxt: SyntaxContext) -> Option<Span> {
93 (span.ctxt() != ctxt).then(|| walk_span_to_context(span, ctxt).unwrap_or(span))
96 fn lint_implicit_returns(
97 cx: &LateContext<'tcx>,
99 // The context of the function body.
101 // Whether the expression is from a macro expansion.
102 call_site_span: Option<Span>,
107 expr: Some(block_expr), ..
110 ) => lint_implicit_returns(
114 call_site_span.or_else(|| get_call_site(block_expr.span, ctxt)),
116 .still_parent(call_site_span.is_some()),
118 ExprKind::If(_, then_expr, Some(else_expr)) => {
119 // Both `then_expr` or `else_expr` are required to be blocks in the same context as the `if`. Don't
121 let res = lint_implicit_returns(cx, then_expr, ctxt, call_site_span).still_parent(call_site_span.is_some());
123 // The return was added as a parent of this if expression.
126 lint_implicit_returns(cx, else_expr, ctxt, call_site_span).still_parent(call_site_span.is_some())
129 ExprKind::Match(_, arms, _) => {
131 let res = lint_implicit_returns(
135 call_site_span.or_else(|| get_call_site(arm.body.span, ctxt)),
137 .still_parent(call_site_span.is_some());
139 // The return was added as a parent of this match expression.
146 ExprKind::Loop(block, ..) => {
147 let mut add_return = false;
148 expr_visitor_no_bodies(|e| {
149 if let ExprKind::Break(dest, sub_expr) = e.kind {
150 if dest.target_id.ok() == Some(expr.hir_id) {
151 if call_site_span.is_none() && e.span.ctxt() == ctxt {
152 // At this point sub_expr can be `None` in async functions which either diverge, or return
154 if let Some(sub_expr) = sub_expr {
155 lint_break(cx, e.span, sub_expr.span);
158 // the break expression is from a macro call, add a return to the loop
167 #[allow(clippy::option_if_let_else)]
168 if let Some(span) = call_site_span {
169 lint_return(cx, span);
172 lint_return(cx, expr.span);
180 // If expressions without an else clause, and blocks without a final expression can only be the final expression
181 // if they are divergent, or return the unit type.
182 ExprKind::If(_, _, None) | ExprKind::Block(Block { expr: None, .. }, _) | ExprKind::Ret(_) => {
186 // Any divergent expression doesn't need a return statement.
187 ExprKind::MethodCall(..)
189 | ExprKind::Binary(..)
190 | ExprKind::Unary(..)
191 | ExprKind::Index(..)
192 if cx.typeck_results().expr_ty(expr).is_never() =>
199 #[allow(clippy::option_if_let_else)]
200 if let Some(span) = call_site_span {
201 lint_return(cx, span);
204 lint_return(cx, expr.span);
211 impl<'tcx> LateLintPass<'tcx> for ImplicitReturn {
214 cx: &LateContext<'tcx>,
216 decl: &'tcx FnDecl<'_>,
217 body: &'tcx Body<'_>,
221 if (!matches!(kind, FnKind::Closure) && matches!(decl.output, FnRetTy::DefaultReturn(_)))
222 || span.ctxt() != body.value.span.ctxt()
223 || in_external_macro(cx.sess(), span)
228 let res_ty = cx.typeck_results().expr_ty(&body.value);
229 if res_ty.is_unit() || res_ty.is_never() {
233 let expr = if is_async_fn(kind) {
234 match get_async_fn_body(cx.tcx, body) {
241 lint_implicit_returns(cx, expr, expr.span.ctxt(), None);