1 use crate::utils::match_panic_def_id;
2 use clippy_utils::diagnostics::span_lint_and_then;
3 use clippy_utils::source::snippet_opt;
4 use if_chain::if_chain;
5 use rustc_errors::Applicability;
6 use rustc_hir::intravisit::FnKind;
7 use rustc_hir::{Body, Expr, ExprKind, FnDecl, HirId, MatchSource, StmtKind};
8 use rustc_lint::{LateContext, LateLintPass};
9 use rustc_session::{declare_lint_pass, declare_tool_lint};
10 use rustc_span::source_map::Span;
12 declare_clippy_lint! {
13 /// **What it does:** Checks for missing return statements at the end of a block.
15 /// **Why is this bad?** Actually omitting the return keyword is idiomatic Rust code. Programmers
16 /// coming from other languages might prefer the expressiveness of `return`. It's possible to miss
17 /// the last returning statement because the only difference is a missing `;`. Especially in bigger
18 /// code with multiple return paths having a `return` keyword makes it easier to find the
19 /// corresponding statements.
21 /// **Known problems:** None.
25 /// fn foo(x: usize) -> usize {
31 /// fn foo(x: usize) -> usize {
37 "use a return statement like `return expr` instead of an expression"
40 declare_lint_pass!(ImplicitReturn => [IMPLICIT_RETURN]);
42 static LINT_BREAK: &str = "change `break` to `return` as shown";
43 static LINT_RETURN: &str = "add `return` as shown";
45 fn lint(cx: &LateContext<'_>, outer_span: Span, inner_span: Span, msg: &str) {
46 let outer_span = outer_span.source_callsite();
47 let inner_span = inner_span.source_callsite();
49 span_lint_and_then(cx, IMPLICIT_RETURN, outer_span, "missing `return` statement", |diag| {
50 if let Some(snippet) = snippet_opt(cx, inner_span) {
54 format!("return {}", snippet),
55 Applicability::MachineApplicable,
61 fn expr_match(cx: &LateContext<'_>, expr: &Expr<'_>) {
63 // loops could be using `break` instead of `return`
64 ExprKind::Block(block, ..) | ExprKind::Loop(block, ..) => {
65 if let Some(expr) = &block.expr {
68 // only needed in the case of `break` with `;` at the end
69 else if let Some(stmt) = block.stmts.last() {
71 if let StmtKind::Semi(expr, ..) = &stmt.kind;
72 // make sure it's a break, otherwise we want to skip
73 if let ExprKind::Break(.., Some(break_expr)) = &expr.kind;
75 lint(cx, expr.span, break_expr.span, LINT_BREAK);
80 // use `return` instead of `break`
81 ExprKind::Break(.., break_expr) => {
82 if let Some(break_expr) = break_expr {
83 lint(cx, expr.span, break_expr.span, LINT_BREAK);
86 ExprKind::If(.., if_expr, else_expr) => {
87 expr_match(cx, if_expr);
89 if let Some(else_expr) = else_expr {
90 expr_match(cx, else_expr);
93 ExprKind::Match(.., arms, source) => {
94 let check_all_arms = match source {
95 MatchSource::IfLetDesugar {
96 contains_else_clause: has_else,
103 expr_match(cx, &arm.body);
106 expr_match(cx, &arms.first().expect("`if let` doesn't have a single arm").body);
109 // skip if it already has a return statement
110 ExprKind::Ret(..) => (),
111 // make sure it's not a call that panics
112 ExprKind::Call(expr, ..) => {
114 if let ExprKind::Path(qpath) = &expr.kind;
115 if let Some(path_def_id) = cx.qpath_res(qpath, expr.hir_id).opt_def_id();
116 if match_panic_def_id(cx, path_def_id);
119 lint(cx, expr.span, expr.span, LINT_RETURN)
123 // everything else is missing `return`
124 _ => lint(cx, expr.span, expr.span, LINT_RETURN),
128 impl<'tcx> LateLintPass<'tcx> for ImplicitReturn {
131 cx: &LateContext<'tcx>,
134 body: &'tcx Body<'_>,
138 if span.from_expansion() {
141 let body = cx.tcx.hir().body(body.id());
142 if cx.typeck_results().expr_ty(&body.value).is_unit() {
145 expr_match(cx, &body.value);