emacs: error decrypting s/mime

[Alexander Adolf <alexander.adolf@condition-alpha.com>]

Dear Notmuch Developers,

I have trouble getting going with S/MIME.

Emacs version: GNU Emacs 27.1 (build 1, x86_64-apple-darwin18.7.0, NS
appkit-1671.60 Version 10.14.6 (Build 18G95)) of 2020-08-12

notmuch version: notmuch 0.31+2~gd127b16
(brew install notmuch --head)

gpgsm version: gpgsm (GnuPG) 2.2.23
libgcrypt 1.8.6
libksba 1.4.0

When I send an encrypted and signed message to myself, the sending works
as expected.

When I open the message in emacs from a notmuch search, the gnupg
password agent pops up, and asks for the passphrase for my secret
key. Once the password agent dialogue is finished (I entered the
passphrase), emacs switches to a notmuch-show buffer with the
message. The body part of the message however only shows "[ smime.p7m:
application/pkcs7-mime ]", nothing else.

I then hit the "$" key twice to turn processing for cryptographic MIME
parts off, and on again. After the second "$", the gnupg password agent
comes up again. I enter the passphrase, and the following appears in the
notmuch-show buffer:

---------------------------- Begin Quote -----------------------------
!!! Bodypart handler `notmuch-show-insert-part-*/*' threw an error:
!!! Wrong type argument: char-or-string-p, ((:id 2 :sigstatus ((:status "good" :fingerprint "142AFE91C66D710592AF9D90A1385D251FEC65B7" :created 1599693325 :expires 1631218144 :userid "1.2.840.113549.1.9.1=#616C6578616E6465722E61646F6C6640636F6E646974696F6E2D616C7068612E636F6D,CN=Alexander Adolf,O=Condition-ALPHA Digital Broadcast Technology Consulting,L=Munich,C=DE")) :content-type "multipart/signed" :content ((:id 3 :content-type "multipart/mixed" :content ((:id 4 :content-type "text/plain" :content-disposition "inline" :content "Earlier patches have moved the handling of wash fake inline patch
parts to insert-bodypart so we can drop the function
notmuch-show-insert-part-inline-patch-fake-part
"))) (:id 5 :content-type "application/pkcs7-signature" :content-disposition "attachment" :filename "smime.p7s" :content-transfer-encoding "base64" :content-length 4478))))
----------------------------- End Quote ------------------------------

The actual message content seems to have been decrypted ok (it shows up
as the text/plain part in the dumped function arguments). Also, I can
open the message without problems in the Apple Mail.app that ships with
macOS (shows the same decrypted content, and a good signature).


Many thanks and looking forward to your thoughts,

  --alexander