runtime(gpg): Mark dangerous use-embedded-filename with WarningMsg

The syntax highlighter is likely to encourage people to use the listed
commands.

But `use-embedded-filename` is a dangerous option that can cause GnuPG
to write arbitrary data to arbitrary files whenever GnuPG encounters
malicious data.

GnuPG upstream explicitly warns against using this option:

https://dev.gnupg.org/T4500
https://dev.gnupg.org/T6972

However, since this is a valid option, we cannot just drop it from the
syntax script. Instead, let's mark it with the WarningMsg highlighting
to make it obvious, that this option is different (and should not be
used for security reasons).

closes: #13961

Co-authored-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Signed-off-by:  Christian Brabandt <cb@256bit.org>
diff --git a/runtime/syntax/gpg.vim b/runtime/syntax/gpg.vim
index c7f3584..2728ecf 100644
--- a/runtime/syntax/gpg.vim
+++ b/runtime/syntax/gpg.vim
@@ -1,9 +1,13 @@
 " Vim syntax file
 " Language:		gpg(1) configuration file
+" Maintainer: This file is looking for a maintainer!
 " Previous Maintainer:	Nikolai Weibull <now@bitwi.se>
-" Latest Revision:	2010-10-14
-" Updated:		2023-01-23 @ObserverOfTime: added a couple of keywords
+" Latest Revision:	2024-02-11
+" Updated:		
+"     2023-01-23 @ObserverOfTime: added a couple of keywords
 "			2023-03-21 Todd Zullinger <tmz@pobox.com>: sync with gnupg-2.4.0
+"			2024-02-10 Daniel Kahn Gillmor <dkg@fifthhorseman.net>:
+"			           mark use-embedded-filename as warning for security reasons
 
 if exists("b:current_syntax")
   finish
@@ -21,7 +25,7 @@
 
 syn match   gpgID	contained display '\<\(0x\)\=\x\{8,}\>'
 
-syn match   gpgBegin	display '^' skipwhite nextgroup=gpgComment,gpgOption,gpgCommand
+syn match   gpgBegin	display '^' skipwhite nextgroup=gpgComment,gpgOption,gpgOptionDeprecated,gpgCommand
 
 syn keyword gpgCommand	contained skipwhite nextgroup=gpgArg
 			\ change-passphrase check-sig check-signatures
@@ -41,6 +45,7 @@
 			\ quick-set-expire quick-set-primary-uid quick-sign-key
 			\ quick-update-pref receive-keys recv-keys refresh-keys
 			\ search-keys show-key show-keys sign-key tofu-policy
+
 syn keyword gpgCommand	contained skipwhite nextgroup=gpgArgError
 			\ card-edit card-status change-pin check-trustdb
 			\ clear-sign clearsign dearmor dearmour decrypt
@@ -97,6 +102,7 @@
 			\ trusted-key trust-model try-secret-key ttyname
 			\ ttytype ungroup user verify-options weak-digest
 			\ xauthority
+
 syn keyword gpgOption	contained skipwhite nextgroup=gpgArgError
 			\ allow-freeform-uid allow-multiple-messages
 			\ allow-multisig-verification allow-non-selfsigned-uid
@@ -145,7 +151,7 @@
 			\ no-sk-comments no-skip-hidden-recipients
 			\ no-symkey-cache not-dash-escaped no-textmode
 			\ no-throw-keyids no-tty no-use-agent
-			\ no-use-embedded-filename no-utf8-strings no-verbose
+			\ no-utf8-strings no-verbose
 			\ no-version only-sign-text-ids openpgp
 			\ override-compliance-check pgp6 pgp7 pgp8
 			\ preserve-permissions print-dane-records quiet
@@ -155,7 +161,7 @@
 			\ show-notation show-photos show-policy-url
 			\ show-session-key sk-comments skip-hidden-recipients
 			\ skip-verify textmode throw-keyids try-all-secrets
-			\ unwrap use-agent use-embedded-filename use-keyboxd
+			\ unwrap use-agent use-keyboxd
 			\ use-only-openpgp-card utf8-strings verbose version
 			\ warranty with-colons with-fingerprint
 			\ with-icao-spelling with-key-data with-keygrip
@@ -164,6 +170,10 @@
 			\ with-subkey-fingerprints with-tofu-info with-wkd-hash
 			\ yes
 
+" depcrated for security reasons
+syn keyword gpgOptionDeprecated	contained skipwhite nextgroup=gpgArgError
+      \ use-embedded-filename no-use-embedded-filename
+
 syn match   gpgArg	contained display '\S\+\(\s\+\S\+\)*' contains=gpgID
 syn match   gpgArgError contained display '\S\+\(\s\+\S\+\)*'
 
@@ -171,6 +181,7 @@
 hi def link gpgTodo	Todo
 hi def link gpgID	Number
 hi def link gpgOption	Keyword
+hi def link gpgOptionDeprecated	WarningMsg
 hi def link gpgCommand	Error
 hi def link gpgArgError	Error