cli/show: enable --decrypt=stash

Add fancy new feature, which makes "notmuch show" capable of actually
indexing messages that it just decrypted.

This enables a workflow where messages can come in in the background
and be indexed using "--decrypt=auto".  But when showing an encrypted
message for the first time, it gets automatically indexed.

This is something of a departure for "notmuch show" -- in particular,
because it requires read/write access to the database.  However, this
might be a common use case -- people get mail delivered and indexed in
the background, but only want access to their secret key to happen
when they're directly interacting with notmuch itself.

In such a scenario, they couldn't search newly-delivered, encrypted
messages, but they could search for them once they've read them.

Documentation of this new feature also uses a table form, similar to
that found in the description of index.decrypt in notmuch-config(1).

A notmuch UI that wants to facilitate this workflow while also
offering an interactive search interface might instead make use of
these additional commands while the user is at the console:

Count received encrypted messages (if > 0, there are some things we
haven't yet tried to index, and therefore can't yet search):

     notmuch count tag:encrypted and \
         not property:index.decryption=success and \
         not property:index.decryption=failure

Reindex those messages:

     notmuch reindex --try-decrypt=true tag:encrypted and \
         not property:index.decryption=success and \
         not property:index.decryption=failure

1 files changed, 18 insertions, 0 deletions

diff --git a/test/T357-index-decryption.sh b/test/T357-index-decryption.sh
index ad6c3616..c5435f4f 100755
--- a/test/T357-index-decryption.sh
+++ b/test/T357-index-decryption.sh
@@ -80,6 +80,24 @@ test_expect_equal \
     "$output" \
     "$expected"
 
+# show the message using stashing decryption
+test_begin_subtest "stash decryption during show"
+output=$(notmuch show --decrypt=stash tag:encrypted subject:002 | notmuch_show_part 3)
+expected='This is a test encrypted message with a wumpus.'
+test_expect_equal \
+    "$output" \
+    "$expected"
+
+test_begin_subtest "search should now find the contents"
+output=$(notmuch search wumpus)
+expected='thread:0000000000000003   2000-01-01 [1/1] Notmuch Test Suite; test encrypted message for cleartext index 002 (encrypted inbox unread)'
+if [ $NOTMUCH_HAVE_GMIME_SESSION_KEYS -eq 0 ]; then
+    test_subtest_known_broken
+fi
+test_expect_equal \
+    "$output" \
+    "$expected"
+
 # try reinserting it with decryption, should appear again, but now we
 # have two copies of the message:
 test_begin_subtest "message cleartext is present after reinserting with --decrypt=true"