Adds attachment support through the mail gem. Notmuch-Attach headers
list files which are added to the message before sending.

Files are added by constructing a new post-processed transport Mail
object using the Notmuch-Attach header and the original Mail object. Any
attachments added (say by hand, or by some other method) to the
pre-transport message are preserved.

Adds a helper which prompts for an attachment (with filename completion)
and adds the header for you (bound to ,a).
---
 vim/notmuch.vim | 45 ++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 42 insertions(+), 3 deletions(-)

diff --git a/vim/notmuch.vim b/vim/notmuch.vim
index bea30f8..09685c3 100644
--- a/vim/notmuch.vim
+++ b/vim/notmuch.vim
@@ -45,6 +45,7 @@ let g:notmuch_show_maps = {
 
 let g:notmuch_compose_maps = {
 	\ ',s':		'compose_send()',
+	\ ',a':		'compose_attach()',
 	\ ',q':		'compose_quit()',
 	\ }
 
@@ -84,6 +85,20 @@ function! s:compose_quit()
 	call s:kill_this_buffer()
 endfunction
 
+function! s:compose_attach()
+ruby << EOF
+	raise "Attachment support unavailable." unless NotmuchHeaders.include?("Attach")
+EOF
+	let attachment = input('attach: ', '~/', 'file')
+ruby << EOF
+	r, c = $curwin.cursor
+	non_help_lines = (1..$curbuf.count).reject { |i| $curbuf[i].start_with?("Notmuch-Help: ") }
+	attachment = File.expand_path(VIM::evaluate('attachment'))
+	$curbuf.append(non_help_lines[0] - 1, "Notmuch-Attach: #{attachment}")
+	$curwin.cursor = [r + 1, c]
+EOF
+endfunction
+
 function! s:compose_send()
 	let b:compose_done = 1
 	let fname = expand('%')
@@ -91,18 +106,39 @@ function! s:compose_send()
 ruby << EOF
 	# Generate proper mail to send
 	text = []
+	attachments = []
 	eval_nm_headers = true
 	VIM::evaluate('getline(0, \'$\')').each do |line|
 		unless eval_nm_headers and NotmuchHeaders.any? { |h| line.start_with?("Notmuch-#{h}: ") }
 			text << line
 			eval_nm_headers = false
+		else
+			if line.start_with?("Notmuch-Attach: ")
+				attachments << line["Notmuch-Attach: ".length..-1]
+			end
 		end
 	end
 	fname = VIM::evaluate('fname')
 	transport = Mail.new(text.join("\n"))
 	transport.message_id = generate_message_id
 	transport.charset = 'utf-8'
-	File.write(fname, transport.to_s)
+
+	transport_fin = Mail.new do
+		transport.header_fields.reject do |f|
+			[
+				"Content-Type",
+				"Content-Transfer-Encoding",
+			].include?(f.name)
+		end.each do |f|
+			header[f.name] = f.value
+		end
+		transport.attachments.each { |a| add_file(:filename => a.filename, :mime_type => a.mime_type, :content => a.decoded) }
+		attachments.each { |a| add_file(a) }
+
+		body (transport.find_first_text || transport).body.to_s
+	end
+
+	File.write(fname, transport_fin.to_s)
 EOF
 
 	let cmdtxt = g:notmuch_sendmail . ' -t -f ' . s:reply_from . ' < ' . fname
@@ -489,7 +525,9 @@ ruby << EOF
 	$messages = []
 	$mail_installed = defined?(Mail)
 
-	NotmuchHeaders = ["Help"]
+	NotmuchHeaders = ["Help",
+		$mail_installed && "Attach",
+	].select { |s| s.is_a?(String) }
 
 	def get_config_item(item)
 		result = ''
@@ -557,9 +595,10 @@ ruby << EOF
 		help_lines = [
 			'Notmuch-Help: Type in your message here; to help you use these bindings:',
 			'Notmuch-Help:   ,s    - send the message',
+			NotmuchHeaders.include?("Attach") && 'Notmuch-Help:   ,a    - prompt for attachment',
 			'Notmuch-Help:   ,q    - abort the message',
 			"Notmuch-Help: Magic Notmuch- headers (removed on send): #{NotmuchHeaders.join(", ")}.",
-			]
+		].select { |s| s.is_a?(String) }
 
 		dir = File.expand_path('~/.notmuch/compose')
 		FileUtils.mkdir_p(dir)
-- 
2.7.3