IMAP: fix delete_all against a readonly connection

Closes #1206

CHANGELOG.rdoc

@@ -14,6 +14,7 @@ Bugs:
 * Fix transfer encoding when message encoding is blank. (jakubonty, saks)
 * Fix 7bit/base64 content transfer encoding mismatch. (ahorek)
 * Fix UTF-8 attachment filename quoting. (ahorek)
+* Fix `delete_all` using a readonly IMAP connection. (kimromi)
 
 
 == Version 2.7.0 (2017-10-31)

lib/mail/network/retriever_methods/imap.rb

@@ -121,7 +121,7 @@ def delete_all(mailbox='INBOX')
       mailbox = Net::IMAP.encode_utf7(mailbox)
 
       start do |imap|
-        imap.examine(mailbox)
+        imap.select(mailbox)
         imap.uid_search(['ALL']).each do |uid|
           imap.uid_store(uid, "+FLAGS", [Net::IMAP::DELETED])
         end

spec/mail/network/retriever_methods/imap_spec.rb

@@ -190,6 +190,7 @@
       expect(Net::IMAP).to receive(:encode_utf7).once
       Mail.delete_all
 
+      expect(MockIMAP.readonly?).to be_falsey
       expect(MockIMAP.examples.size).to eq 0
     end
   end

spec/spec_helper.rb

@@ -241,6 +241,7 @@ def initialize(rfc822, number, flag)
 class MockIMAP
   @@connection = false
   @@mailbox = nil
+  @@readonly = false
   @@marked_for_deletion = []
   @@default_examples = {
     :default => (0..19).map do |i|
@@ -270,10 +271,12 @@ def disconnect
 
   def select(mailbox)
     @@mailbox = mailbox
+    @@readonly = false
   end
 
   def examine(mailbox)
     select(mailbox)
+    @@readonly = true
   end
 
   def uid_search(keys, charset = nil)
@@ -298,6 +301,7 @@ def expunge
   end
 
   def self.mailbox; @@mailbox end    # test only
+  def self.readonly?; @@readonly end # test only
 
   def self.disconnected?; @@connection == false end
   def      disconnected?; @@connection == false end