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Auto merge of #6951 - Jarcho:implicit_return_fp, r=flip1995

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`implicit_return` improvements

fixes: #6940

changelog: Fix `implicit_return` suggestion for async functions
changelog: Improve `implicit_return` suggestions when returning the result of a macro
changelog: Check for `break` expressions inside a loop which are then implicitly returned
changelog: Allow all diverging functions in `implicit_return`, not just panic functions
This commit is contained in:
bors 2021-04-30 14:55:56 +00:00
parent 14f1551075 3d793f3111
commit 5e49c4bd67
7 changed files with 452 additions and 142 deletions
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245
clippy_lints/src/implicit_return.rs
View file

@ -1,13 +1,16 @@
use clippy_utils::diagnostics::span_lint_and_then;
use clippy_utils::match_panic_def_id;
use clippy_utils::source::snippet_opt;
use if_chain::if_chain;
use clippy_utils::{
diagnostics::span_lint_and_sugg,
get_async_fn_body, is_async_fn,
source::{snippet_with_applicability, snippet_with_context, walk_span_to_context},
visitors::visit_break_exprs,
};
use rustc_errors::Applicability;
use rustc_hir::intravisit::FnKind;
use rustc_hir::{Body, Expr, ExprKind, FnDecl, HirId, MatchSource, StmtKind};
use rustc_lint::{LateContext, LateLintPass};
use rustc_hir::{Block, Body, Expr, ExprKind, FnDecl, FnRetTy, HirId};
use rustc_lint::{LateContext, LateLintPass, LintContext};
use rustc_middle::lint::in_external_macro;
use rustc_session::{declare_lint_pass, declare_tool_lint};
use rustc_span::source_map::Span;
use rustc_span::{Span, SyntaxContext};
declare_clippy_lint! {
/// **What it does:** Checks for missing return statements at the end of a block.
@ -39,89 +42,160 @@ declare_clippy_lint! {
declare_lint_pass!(ImplicitReturn => [IMPLICIT_RETURN]);
static LINT_BREAK: &str = "change `break` to `return` as shown";
static LINT_RETURN: &str = "add `return` as shown";
fn lint(cx: &LateContext<'_>, outer_span: Span, inner_span: Span, msg: &str) {
let outer_span = outer_span.source_callsite();
let inner_span = inner_span.source_callsite();
span_lint_and_then(cx, IMPLICIT_RETURN, outer_span, "missing `return` statement", |diag| {
if let Some(snippet) = snippet_opt(cx, inner_span) {
diag.span_suggestion(
outer_span,
msg,
format!("return {}", snippet),
Applicability::MachineApplicable,
fn lint_return(cx: &LateContext<'_>, span: Span) {
let mut app = Applicability::MachineApplicable;
let snip = snippet_with_applicability(cx, span, "..", &mut app);
span_lint_and_sugg(
cx,
IMPLICIT_RETURN,
span,
"missing `return` statement",
"add `return` as shown",
format!("return {}", snip),
app,
);
}
});
fn lint_break(cx: &LateContext<'_>, break_span: Span, expr_span: Span) {
let mut app = Applicability::MachineApplicable;
let snip = snippet_with_context(cx, expr_span, break_span.ctxt(), "..", &mut app).0;
span_lint_and_sugg(
cx,
IMPLICIT_RETURN,
break_span,
"missing `return` statement",
"change `break` to `return` as shown",
format!("return {}", snip),
app,
)
}
fn expr_match(cx: &LateContext<'_>, expr: &Expr<'_>) {
#[derive(Clone, Copy, PartialEq, Eq)]
enum LintLocation {
/// The lint was applied to a parent expression.
Parent,
/// The lint was applied to this expression, a child, or not applied.
Inner,
}
impl LintLocation {
fn still_parent(self, b: bool) -> Self {
if b { self } else { Self::Inner }
}
fn is_parent(self) -> bool {
self == Self::Parent
}
}
// Gets the call site if the span is in a child context. Otherwise returns `None`.
fn get_call_site(span: Span, ctxt: SyntaxContext) -> Option<Span> {
(span.ctxt() != ctxt).then(|| walk_span_to_context(span, ctxt).unwrap_or(span))
}
fn lint_implicit_returns(
cx: &LateContext<'tcx>,
expr: &'tcx Expr<'_>,
// The context of the function body.
ctxt: SyntaxContext,
// Whether the expression is from a macro expansion.
call_site_span: Option<Span>,
) -> LintLocation {
match expr.kind {
// loops could be using `break` instead of `return`
ExprKind::Block(block, ..) | ExprKind::Loop(block, ..) => {
if let Some(expr) = &block.expr {
expr_match(cx, expr);
}
// only needed in the case of `break` with `;` at the end
else if let Some(stmt) = block.stmts.last() {
if_chain! {
if let StmtKind::Semi(expr, ..) = &stmt.kind;
// make sure it's a break, otherwise we want to skip
if let ExprKind::Break(.., Some(break_expr)) = &expr.kind;
then {
lint(cx, expr.span, break_expr.span, LINT_BREAK);
}
}
}
ExprKind::Block(
Block {
expr: Some(block_expr), ..
},
// use `return` instead of `break`
ExprKind::Break(.., break_expr) => {
if let Some(break_expr) = break_expr {
lint(cx, expr.span, break_expr.span, LINT_BREAK);
}
},
ExprKind::If(.., if_expr, else_expr) => {
expr_match(cx, if_expr);
_,
) => lint_implicit_returns(
cx,
block_expr,
ctxt,
call_site_span.or_else(|| get_call_site(block_expr.span, ctxt)),
)
.still_parent(call_site_span.is_some()),
if let Some(else_expr) = else_expr {
expr_match(cx, else_expr);
ExprKind::If(_, then_expr, Some(else_expr)) => {
// Both `then_expr` or `else_expr` are required to be blocks in the same context as the `if`. Don't
// bother checking.
let res = lint_implicit_returns(cx, then_expr, ctxt, call_site_span).still_parent(call_site_span.is_some());
if res.is_parent() {
// The return was added as a parent of this if expression.
return res;
}
lint_implicit_returns(cx, else_expr, ctxt, call_site_span).still_parent(call_site_span.is_some())
},
ExprKind::Match(.., arms, source) => {
let check_all_arms = match source {
MatchSource::IfLetDesugar {
contains_else_clause: has_else,
} => has_else,
_ => true,
};
if check_all_arms {
ExprKind::Match(_, arms, _) => {
for arm in arms {
expr_match(cx, arm.body);
let res = lint_implicit_returns(
cx,
arm.body,
ctxt,
call_site_span.or_else(|| get_call_site(arm.body.span, ctxt)),
)
.still_parent(call_site_span.is_some());
if res.is_parent() {
// The return was added as a parent of this match expression.
return res;
}
}
LintLocation::Inner
},
ExprKind::Loop(block, ..) => {
let mut add_return = false;
visit_break_exprs(block, |break_expr, dest, sub_expr| {
if dest.target_id.ok() == Some(expr.hir_id) {
if call_site_span.is_none() && break_expr.span.ctxt() == ctxt {
lint_break(cx, break_expr.span, sub_expr.unwrap().span);
} else {
// the break expression is from a macro call, add a return to the loop
add_return = true;
}
}
});
if add_return {
#[allow(clippy::option_if_let_else)]
if let Some(span) = call_site_span {
lint_return(cx, span);
LintLocation::Parent
} else {
lint_return(cx, expr.span);
LintLocation::Inner
}
} else {
expr_match(cx, arms.first().expect("`if let` doesn't have a single arm").body);
LintLocation::Inner
}
},
// skip if it already has a return statement
ExprKind::Ret(..) => (),
// make sure it's not a call that panics
ExprKind::Call(expr, ..) => {
if_chain! {
if let ExprKind::Path(qpath) = &expr.kind;
if let Some(path_def_id) = cx.qpath_res(qpath, expr.hir_id).opt_def_id();
if match_panic_def_id(cx, path_def_id);
then { }
else {
lint(cx, expr.span, expr.span, LINT_RETURN)
}
// If expressions without an else clause, and blocks without a final expression can only be the final expression
// if they are divergent, or return the unit type.
ExprKind::If(_, _, None) | ExprKind::Block(Block { expr: None, .. }, _) | ExprKind::Ret(_) => {
LintLocation::Inner
},
// Any divergent expression doesn't need a return statement.
ExprKind::MethodCall(..)
| ExprKind::Call(..)
| ExprKind::Binary(..)
| ExprKind::Unary(..)
| ExprKind::Index(..)
if cx.typeck_results().expr_ty(expr).is_never() =>
{
LintLocation::Inner
},
_ =>
{
#[allow(clippy::option_if_let_else)]
if let Some(span) = call_site_span {
lint_return(cx, span);
LintLocation::Parent
} else {
lint_return(cx, expr.span);
LintLocation::Inner
}
},
// everything else is missing `return`
_ => lint(cx, expr.span, expr.span, LINT_RETURN),
}
}
@ -129,19 +203,32 @@ impl<'tcx> LateLintPass<'tcx> for ImplicitReturn {
fn check_fn(
&mut self,
cx: &LateContext<'tcx>,
_: FnKind<'tcx>,
_: &'tcx FnDecl<'_>,
kind: FnKind<'tcx>,
decl: &'tcx FnDecl<'_>,
body: &'tcx Body<'_>,
span: Span,
_: HirId,
) {
if span.from_expansion() {
if (!matches!(kind, FnKind::Closure) && matches!(decl.output, FnRetTy::DefaultReturn(_)))
|| span.ctxt() != body.value.span.ctxt()
|| in_external_macro(cx.sess(), span)
{
return;
}
let body = cx.tcx.hir().body(body.id());
if cx.typeck_results().expr_ty(&body.value).is_unit() {
let res_ty = cx.typeck_results().expr_ty(&body.value);
if res_ty.is_unit() || res_ty.is_never() {
return;
}
expr_match(cx, &body.value);
let expr = if is_async_fn(kind) {
match get_async_fn_body(cx.tcx, body) {
Some(e) => e,
None => return,
}
} else {
&body.value
};
lint_implicit_returns(cx, expr, expr.span.ctxt(), None);
}
}

40
clippy_utils/src/lib.rs
View file

@ -61,12 +61,12 @@ use rustc_data_structures::fx::FxHashMap;
use rustc_hir as hir;
use rustc_hir::def::{DefKind, Res};
use rustc_hir::def_id::{DefId, LOCAL_CRATE};
use rustc_hir::intravisit::{self, walk_expr, ErasedMap, NestedVisitorMap, Visitor};
use rustc_hir::intravisit::{self, walk_expr, ErasedMap, FnKind, NestedVisitorMap, Visitor};
use rustc_hir::LangItem::{ResultErr, ResultOk};
use rustc_hir::{
def, Arm, BindingAnnotation, Block, Body, Constness, Destination, Expr, ExprKind, FnDecl, GenericArgs, HirId, Impl,
ImplItem, ImplItemKind, Item, ItemKind, LangItem, Local, MatchSource, Node, Param, Pat, PatKind, Path, PathSegment,
QPath, Stmt, StmtKind, TraitItem, TraitItemKind, TraitRef, TyKind,
ImplItem, ImplItemKind, IsAsync, Item, ItemKind, LangItem, Local, MatchSource, Node, Param, Pat, PatKind, Path,
PathSegment, QPath, Stmt, StmtKind, TraitItem, TraitItemKind, TraitRef, TyKind,
};
use rustc_lint::{LateContext, Level, Lint, LintContext};
use rustc_middle::hir::exports::Export;
@ -1301,6 +1301,40 @@ pub fn if_sequence<'tcx>(mut expr: &'tcx Expr<'tcx>) -> (Vec<&'tcx Expr<'tcx>>,
(conds, blocks)
}
/// Checks if the given function kind is an async function.
pub fn is_async_fn(kind: FnKind) -> bool {
matches!(kind, FnKind::ItemFn(_, _, header, _) if header.asyncness == IsAsync::Async)
}
/// Peels away all the compiler generated code surrounding the body of an async function,
pub fn get_async_fn_body(tcx: TyCtxt<'tcx>, body: &Body<'_>) -> Option<&'tcx Expr<'tcx>> {
if let ExprKind::Call(
_,
&[Expr {
kind: ExprKind::Closure(_, _, body, _, _),
..
}],
) = body.value.kind
{
if let ExprKind::Block(
Block {
stmts: [],
expr:
Some(Expr {
kind: ExprKind::DropTemps(expr),
..
}),
..
},
_,
) = tcx.hir().body(body).value.kind
{
return Some(expr);
}
};
None
}
// Finds the `#[must_use]` attribute, if any
pub fn must_use_attr(attrs: &[Attribute]) -> Option<&Attribute> {
attrs.iter().find(|a| a.has_name(sym::must_use))

41
clippy_utils/src/source.rs
View file

@ -280,17 +280,17 @@ pub fn snippet_with_context(
default: &'a str,
applicability: &mut Applicability,
) -> (Cow<'a, str>, bool) {
let outer_span = hygiene::walk_chain(span, outer);
let (span, is_macro_call) = if outer_span.ctxt() == outer {
(outer_span, span.ctxt() != outer)
} else {
let (span, is_macro_call) = walk_span_to_context(span, outer).map_or_else(
|| {
// The span is from a macro argument, and the outer context is the macro using the argument
if *applicability != Applicability::Unspecified {
*applicability = Applicability::MaybeIncorrect;
}
// TODO: get the argument span.
(span, false)
};
},
|outer_span| (outer_span, span.ctxt() != outer),
);
(
snippet_with_applicability(cx, span, default, applicability),
@ -298,6 +298,37 @@ pub fn snippet_with_context(
)
}
/// Walks the span up to the target context, thereby returning the macro call site if the span is
/// inside a macro expansion, or the original span if it is not. Note this will return `None` in the
/// case of the span being in a macro expansion, but the target context is from expanding a macro
/// argument.
///
/// Given the following
///
/// ```rust,ignore
/// macro_rules! m { ($e:expr) => { f($e) }; }
/// g(m!(0))
/// ```
///
/// If called with a span of the call to `f` and a context of the call to `g` this will return a
/// span containing `m!(0)`. However, if called with a span of the literal `0` this will give a span
/// containing `0` as the context is the same as the outer context.
///
/// This will traverse through multiple macro calls. Given the following:
///
/// ```rust,ignore
/// macro_rules! m { ($e:expr) => { n!($e, 0) }; }
/// macro_rules! n { ($e:expr, $f:expr) => { f($e, $f) }; }
/// g(m!(0))
/// ```
///
/// If called with a span of the call to `f` and a context of the call to `g` this will return a
/// span containing `m!(0)`.
pub fn walk_span_to_context(span: Span, outer: SyntaxContext) -> Option<Span> {
let outer_span = hygiene::walk_chain(span, outer);
(outer_span.ctxt() == outer).then(|| outer_span)
}
/// Removes block comments from the given `Vec` of lines.
///
/// # Examples

55
clippy_utils/src/visitors.rs
View file

@ -1,7 +1,7 @@
use crate::path_to_local_id;
use rustc_hir as hir;
use rustc_hir::intravisit::{self, walk_expr, NestedVisitorMap, Visitor};
use rustc_hir::{Arm, Body, Expr, HirId, Stmt};
use rustc_hir::intravisit::{self, walk_expr, ErasedMap, NestedVisitorMap, Visitor};
use rustc_hir::{Arm, Block, Body, Destination, Expr, ExprKind, HirId, Stmt};
use rustc_lint::LateContext;
use rustc_middle::hir::map::Map;
@ -188,3 +188,54 @@ impl<'v> Visitor<'v> for LocalUsedVisitor<'v> {
NestedVisitorMap::OnlyBodies(self.hir)
}
}
pub trait Visitable<'tcx> {
fn visit<V: Visitor<'tcx>>(self, v: &mut V);
}
impl Visitable<'tcx> for &'tcx Expr<'tcx> {
fn visit<V: Visitor<'tcx>>(self, v: &mut V) {
v.visit_expr(self)
}
}
impl Visitable<'tcx> for &'tcx Block<'tcx> {
fn visit<V: Visitor<'tcx>>(self, v: &mut V) {
v.visit_block(self)
}
}
impl<'tcx> Visitable<'tcx> for &'tcx Stmt<'tcx> {
fn visit<V: Visitor<'tcx>>(self, v: &mut V) {
v.visit_stmt(self)
}
}
impl<'tcx> Visitable<'tcx> for &'tcx Body<'tcx> {
fn visit<V: Visitor<'tcx>>(self, v: &mut V) {
v.visit_body(self)
}
}
impl<'tcx> Visitable<'tcx> for &'tcx Arm<'tcx> {
fn visit<V: Visitor<'tcx>>(self, v: &mut V) {
v.visit_arm(self)
}
}
pub fn visit_break_exprs<'tcx>(
node: impl Visitable<'tcx>,
f: impl FnMut(&'tcx Expr<'tcx>, Destination, Option<&'tcx Expr<'tcx>>),
) {
struct V<F>(F);
impl<'tcx, F: FnMut(&'tcx Expr<'tcx>, Destination, Option<&'tcx Expr<'tcx>>)> Visitor<'tcx> for V<F> {
type Map = ErasedMap<'tcx>;
fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
NestedVisitorMap::None
}
fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
if let ExprKind::Break(dest, sub_expr) = e.kind {
self.0(e, dest, sub_expr)
}
walk_expr(self, e);
}
}
node.visit(&mut V(f));
}

68
tests/ui/implicit_return.fixed
View file

@ -1,7 +1,8 @@
// edition:2018
// run-rustfix
#![warn(clippy::implicit_return)]
#![allow(clippy::needless_return, unused)]
#![allow(clippy::needless_return, clippy::needless_bool, unused, clippy::never_loop)]
fn test_end_of_fn() -> bool {
if true {
@ -12,7 +13,6 @@ fn test_end_of_fn() -> bool {
return true
}
#[allow(clippy::needless_bool)]
fn test_if_block() -> bool {
if true { return true } else { return false }
}
@ -25,7 +25,6 @@ fn test_match(x: bool) -> bool {
}
}
#[allow(clippy::needless_return)]
fn test_match_with_unreachable(x: bool) -> bool {
match x {
true => return false,
@ -33,14 +32,12 @@ fn test_match_with_unreachable(x: bool) -> bool {
}
}
#[allow(clippy::never_loop)]
fn test_loop() -> bool {
loop {
return true;
}
}
#[allow(clippy::never_loop)]
fn test_loop_with_block() -> bool {
loop {
{
@ -49,7 +46,6 @@ fn test_loop_with_block() -> bool {
}
}
#[allow(clippy::never_loop)]
fn test_loop_with_nests() -> bool {
loop {
if true {
@ -83,15 +79,53 @@ fn test_return_macro() -> String {
return format!("test {}", "test")
}
fn main() {
let _ = test_end_of_fn();
let _ = test_if_block();
let _ = test_match(true);
let _ = test_match_with_unreachable(true);
let _ = test_loop();
let _ = test_loop_with_block();
let _ = test_loop_with_nests();
let _ = test_loop_with_if_let();
test_closure();
let _ = test_return_macro();
fn macro_branch_test() -> bool {
macro_rules! m {
($t:expr, $f:expr) => {
if true { $t } else { $f }
};
}
return m!(true, false)
}
fn loop_test() -> bool {
'outer: loop {
if true {
return true;
}
let _ = loop {
if false {
return false;
}
if true {
break true;
}
};
}
}
fn loop_macro_test() -> bool {
macro_rules! m {
($e:expr) => {
break $e
};
}
return loop {
m!(true);
}
}
fn divergent_test() -> bool {
fn diverge() -> ! {
panic!()
}
diverge()
}
// issue #6940
async fn foo() -> bool {
return true
}
fn main() {}

68
tests/ui/implicit_return.rs
View file

@ -1,7 +1,8 @@
// edition:2018
// run-rustfix
#![warn(clippy::implicit_return)]
#![allow(clippy::needless_return, unused)]
#![allow(clippy::needless_return, clippy::needless_bool, unused, clippy::never_loop)]
fn test_end_of_fn() -> bool {
if true {
@ -12,7 +13,6 @@ fn test_end_of_fn() -> bool {
true
}
#[allow(clippy::needless_bool)]
fn test_if_block() -> bool {
if true { true } else { false }
}
@ -25,7 +25,6 @@ fn test_match(x: bool) -> bool {
}
}
#[allow(clippy::needless_return)]
fn test_match_with_unreachable(x: bool) -> bool {
match x {
true => return false,
@ -33,14 +32,12 @@ fn test_match_with_unreachable(x: bool) -> bool {
}
}
#[allow(clippy::never_loop)]
fn test_loop() -> bool {
loop {
break true;
}
}
#[allow(clippy::never_loop)]
fn test_loop_with_block() -> bool {
loop {
{
@ -49,7 +46,6 @@ fn test_loop_with_block() -> bool {
}
}
#[allow(clippy::never_loop)]
fn test_loop_with_nests() -> bool {
loop {
if true {
@ -83,15 +79,53 @@ fn test_return_macro() -> String {
format!("test {}", "test")
}
fn main() {
let _ = test_end_of_fn();
let _ = test_if_block();
let _ = test_match(true);
let _ = test_match_with_unreachable(true);
let _ = test_loop();
let _ = test_loop_with_block();
let _ = test_loop_with_nests();
let _ = test_loop_with_if_let();
test_closure();
let _ = test_return_macro();
fn macro_branch_test() -> bool {
macro_rules! m {
($t:expr, $f:expr) => {
if true { $t } else { $f }
};
}
m!(true, false)
}
fn loop_test() -> bool {
'outer: loop {
if true {
break true;
}
let _ = loop {
if false {
break 'outer false;
}
if true {
break true;
}
};
}
}
fn loop_macro_test() -> bool {
macro_rules! m {
($e:expr) => {
break $e
};
}
loop {
m!(true);
}
}
fn divergent_test() -> bool {
fn diverge() -> ! {
panic!()
}
diverge()
}
// issue #6940
async fn foo() -> bool {
true
}
fn main() {}

55
tests/ui/implicit_return.stderr
View file

@ -1,5 +1,5 @@
error: missing `return` statement
--> $DIR/implicit_return.rs:12:5
--> $DIR/implicit_return.rs:13:5
|
LL | true
| ^^^^ help: add `return` as shown: `return true`
@ -31,40 +31,79 @@ LL | false => { true },
| ^^^^ help: add `return` as shown: `return true`
error: missing `return` statement
--> $DIR/implicit_return.rs:39:9
--> $DIR/implicit_return.rs:37:9
|
LL | break true;
| ^^^^^^^^^^ help: change `break` to `return` as shown: `return true`
error: missing `return` statement
--> $DIR/implicit_return.rs:47:13
--> $DIR/implicit_return.rs:44:13
|
LL | break true;
| ^^^^^^^^^^ help: change `break` to `return` as shown: `return true`
error: missing `return` statement
--> $DIR/implicit_return.rs:56:13
--> $DIR/implicit_return.rs:52:13
|
LL | break true;
| ^^^^^^^^^^ help: change `break` to `return` as shown: `return true`
error: missing `return` statement
--> $DIR/implicit_return.rs:74:18
--> $DIR/implicit_return.rs:70:18
|
LL | let _ = || { true };
| ^^^^ help: add `return` as shown: `return true`
error: missing `return` statement
--> $DIR/implicit_return.rs:75:16
--> $DIR/implicit_return.rs:71:16
|
LL | let _ = || true;
| ^^^^ help: add `return` as shown: `return true`
error: missing `return` statement
--> $DIR/implicit_return.rs:83:5
--> $DIR/implicit_return.rs:79:5
|
LL | format!("test {}", "test")
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: add `return` as shown: `return format!("test {}", "test")`
error: aborting due to 11 previous errors
error: missing `return` statement
--> $DIR/implicit_return.rs:88:5
|
LL | m!(true, false)
| ^^^^^^^^^^^^^^^ help: add `return` as shown: `return m!(true, false)`
error: missing `return` statement
--> $DIR/implicit_return.rs:94:13
|
LL | break true;
| ^^^^^^^^^^ help: change `break` to `return` as shown: `return true`
error: missing `return` statement
--> $DIR/implicit_return.rs:99:17
|
LL | break 'outer false;
| ^^^^^^^^^^^^^^^^^^ help: change `break` to `return` as shown: `return false`
error: missing `return` statement
--> $DIR/implicit_return.rs:114:5
|
LL | / loop {
LL | | m!(true);
LL | | }
| |_____^
|
help: add `return` as shown
|
LL | return loop {
LL | m!(true);
LL | }
|
error: missing `return` statement
--> $DIR/implicit_return.rs:128:5
|
LL | true
| ^^^^ help: add `return` as shown: `return true`
error: aborting due to 16 previous errors