fix: unreachable err on Fn with None block

Author: calebcartwright

src/visitor.rs

@@ -514,7 +514,7 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
                 ast::ItemKind::Static(..) | ast::ItemKind::Const(..) => {
                     self.visit_static(&StaticParts::from_item(item));
                 }
-                ast::ItemKind::Fn(defaultness, ref fn_signature, ref generics, ref body) => {
+                ast::ItemKind::Fn(defaultness, ref fn_signature, ref generics, Some(ref body)) => {
                     let inner_attrs = inner_attributes(&item.attrs);
                     let fn_ctxt = match fn_signature.header.ext {
                         ast::Extern::None => visit::FnCtxt::Free,
@@ -526,7 +526,7 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
                             item.ident,
                             &fn_signature,
                             &item.vis,
-                            body.as_deref(),
+                            Some(body),
                         ),
                         generics,
                         &fn_signature.decl,
@@ -535,6 +535,18 @@ impl<'b, 'a: 'b> FmtVisitor<'a> {
                         Some(&inner_attrs),
                     )
                 }
+                ast::ItemKind::Fn(_, ref fn_signature, ref generics, None) => {
+                    let indent = self.block_indent;
+                    let rewrite = self.rewrite_required_fn(
+                        indent,
+                        item.ident,
+                        &fn_signature,
+                        generics,
+                        item.span,
+                    );
+
+                    self.push_rewrite(item.span, rewrite);
+                }
                 ast::ItemKind::TyAlias(_, ref generics, ref generic_bounds, ref ty) => match ty {
                     Some(ty) => {
                         let rewrite = rewrite_type_alias(

tests/source/issue_4057.rs

@@ -0,0 +1,15 @@
+// rustfmt-format_code_in_doc_comments: true
+
+/// ```
+/// # #[rustversion::since(1.36)]
+/// # fn dox() {
+/// # use std::pin::Pin;
+/// # type Projection<'a> = &'a ();
+/// # type ProjectionRef<'a> = &'a ();
+/// # trait Dox {
+/// fn   project_ex (self: Pin<&mut Self>) -> Projection<'_>;
+/// fn   project_ref(self: Pin<&Self>) -> ProjectionRef<'_>;
+/// # }
+/// # }
+/// ```
+struct Foo;

tests/target/issue-4068.rs

@@ -0,0 +1,3 @@
+fn main() {
+    extern "C" fn packet_records_options_impl_layout_length_encoding_option_len_multiplier();
+}

tests/target/issue_4057.rs

@@ -0,0 +1,15 @@
+// rustfmt-format_code_in_doc_comments: true
+
+/// ```
+/// # #[rustversion::since(1.36)]
+/// # fn dox() {
+/// # use std::pin::Pin;
+/// # type Projection<'a> = &'a ();
+/// # type ProjectionRef<'a> = &'a ();
+/// # trait Dox {
+/// fn project_ex(self: Pin<&mut Self>) -> Projection<'_>;
+/// fn project_ref(self: Pin<&Self>) -> ProjectionRef<'_>;
+/// # }
+/// # }
+/// ```
+struct Foo;