From c837b285525b869ffc3b05ba8f92d0679661bb93 Mon Sep 17 00:00:00 2001
From: Aaron Hill <aa1ronham@gmail.com>
Date: Mon, 29 Jun 2020 10:35:41 -0400
Subject: [PATCH] fix(clap_derive): Unwrap `syn::TypeGroup` when checking field
 types

Due to macro expansions, a `syn` type may be wrapped in multiple
'layers' of `syn::Type::Group`. However, `clap_derive` currently does
not check for `syn::Type::Group`, which will cause an `Option` (along
with other matched types) to fail to be detected when it results from a
macro expansion.

This commit 'unwraps' outer type groups before checking the
user-provided types against well-known types. Currently, these groups
may not be present due to a rustc bug (rust-lang/rust#43081)

However, once https://github.com/rust-lang/rust/pull/73084 is merged,
these groups will be present in more cases. This commit makes `clap`
compatible with both older and newer versions of rustc.
---
 clap_derive/src/utils/ty.rs |  5 ++++-
 clap_derive/tests/nested.rs | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 clap_derive/tests/nested.rs

diff --git a/clap_derive/src/utils/ty.rs b/clap_derive/src/utils/ty.rs
index c2cec83fb56..e180758ea86 100644
--- a/clap_derive/src/utils/ty.rs
+++ b/clap_derive/src/utils/ty.rs
@@ -44,7 +44,10 @@ pub fn sub_type(ty: &syn::Type) -> Option<&syn::Type> {
     subty_if(ty, |_| true)
 }
 
-fn only_last_segment(ty: &syn::Type) -> Option<&PathSegment> {
+fn only_last_segment(mut ty: &syn::Type) -> Option<&PathSegment> {
+    while let syn::Type::Group(syn::TypeGroup { elem, .. }) = ty {
+        ty = elem;
+    }
     match ty {
         Type::Path(TypePath {
             qself: None,
diff --git a/clap_derive/tests/nested.rs b/clap_derive/tests/nested.rs
new file mode 100644
index 00000000000..1642aba04fa
--- /dev/null
+++ b/clap_derive/tests/nested.rs
@@ -0,0 +1,33 @@
+// Copyright 2018 Guillaume Pinot (@TeXitoi) <texitoi@texitoi.eu>,
+// Kevin Knapp (@kbknapp) <kbknapp@gmail.com>, and
+// Andrew Hobden (@hoverbear) <andrew@hoverbear.org>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+//
+// This work was derived from Structopt (https://github.com/TeXitoi/structopt)
+// commit#ea76fa1b1b273e65e3b0b1046643715b49bec51f which is licensed under the
+// MIT/Apache 2.0 license.
+
+use clap::Clap;
+
+// Tests that clap_derive properly detects an `Option` field
+// that results from a macro expansion
+#[test]
+fn use_option() {
+    macro_rules! expand_ty {
+        ($name:ident: $ty:ty) => {
+            #[derive(Clap)]
+            struct Outer {
+                #[clap(short, long)]
+                #[allow(dead_code)]
+                $name: $ty,
+            }
+        };
+    }
+
+    expand_ty!(my_field: Option<String>);
+}