From 9d0e7f089b14037cc6ceb0db135b19a3086b51b4 Mon Sep 17 00:00:00 2001
From: Nathaniel McCallum <nathaniel@profian.com>
Date: Tue, 8 Feb 2022 17:57:25 -0500
Subject: [PATCH] Fix length calculation for explicit tags

When deriving `Choice`, the existing macros emit incorrect length
calculation code when explicit tags are used.

Signed-off-by: Nathaniel McCallum <nathaniel@profian.com>
---
 der/derive/src/choice/variant.rs | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/der/derive/src/choice/variant.rs b/der/derive/src/choice/variant.rs
index e9841cb99..486cdf9fa 100644
--- a/der/derive/src/choice/variant.rs
+++ b/der/derive/src/choice/variant.rs
@@ -67,8 +67,22 @@ impl ChoiceVariant {
     /// Derive a match arm for the impl body for `der::EncodeValue::value_len`.
     pub(super) fn to_value_len_tokens(&self) -> TokenStream {
         let ident = &self.ident;
-        quote! {
-            Self::#ident(variant) => variant.value_len(),
+
+        match self.attrs.context_specific {
+            Some(tag_number) => {
+                let tag_number = tag_number.to_tokens();
+                let tag_mode = self.attrs.tag_mode.to_tokens();
+
+                quote! {
+                    Self::#ident(variant) => ::der::asn1::ContextSpecificRef {
+                        tag_number: #tag_number,
+                        tag_mode: #tag_mode,
+                        value: variant,
+                    }.value_len(),
+                }
+            }
+
+            _ => quote! { Self::#ident(variant) => variant.value_len(), },
         }
     }