FEATURE: IMAP delete email sync for group inboxes (#10392)

Adds functionality to reflect topic delete in Discourse to IMAP inbox (Gmail only for now) and reflecting Gmail deletes in Discourse.

Adding lots of tests, various refactors and code improvements.

When Discourse topic is destroyed in PostDestroyer mark the topic incoming email as imap_sync: true, and do the opposite when post is recovered.

spec/lib/imap/providers/generic_spec.rb

@@ -16,6 +16,13 @@ RSpec.describe Imap::Providers::Generic do
       }
     )
   end
+  let(:dummy_mailboxes) do
+    [
+      Net::IMAP::MailboxList.new([], "/", "All Mail"),
+      Net::IMAP::MailboxList.new([:Noselect], "/", "Other"),
+      Net::IMAP::MailboxList.new([:Trash], "/", "Bin")
+    ]
+  end
 
   let(:imap_stub) { stub }
   before do
@@ -29,6 +36,101 @@ RSpec.describe Imap::Providers::Generic do
     end
   end
 
+  describe "#list_mailboxes" do
+    before do
+      imap_stub.expects(:list).with('', '*').returns(dummy_mailboxes)
+    end
+
+    it "does not return any mailboxes with the Noselect attribute" do
+      expect(provider.list_mailboxes).not_to include("Other")
+    end
+
+    it "filters by the provided attribute" do
+      expect(provider.list_mailboxes(:Trash)).to eq(["Bin"])
+    end
+
+    it "lists all mailboxes names" do
+      expect(provider.list_mailboxes).to eq(["All Mail", "Bin"])
+    end
+  end
+
+  describe "#trash_mailbox" do
+
+    before do
+      imap_stub.expects(:list).with('', '*').returns(dummy_mailboxes)
+      Discourse.cache.delete("imap_trash_mailbox_#{provider.account_digest}")
+    end
+
+    it "returns the mailbox with the special-use attribute \Trash" do
+      expect(provider.trash_mailbox).to eq("Bin")
+    end
+
+    it "caches the result based on the account username and server for 30 mins" do
+      provider.trash_mailbox
+      provider.expects(:list_mailboxes).never
+      provider.trash_mailbox
+    end
+  end
+
+  describe "#find_trashed_by_message_ids" do
+    before do
+      provider.stubs(:trash_mailbox).returns("Bin")
+      imap_stub.stubs(:examine).with("Inbox").twice
+      imap_stub.stubs(:responses).returns({ 'UIDVALIDITY' => [1] })
+      imap_stub.stubs(:examine).with("Bin")
+      imap_stub.stubs(:responses).returns({ 'UIDVALIDITY' => [9] })
+      provider.expects(:emails).with([4, 6], ['UID', 'ENVELOPE']).returns(
+        [
+          {
+            'ENVELOPE' => stub(message_id: "<h4786x34@test.com>"),
+            'UID' => 4
+          },
+          {
+            'ENVELOPE' => stub(message_id: "<f349xj84@test.com>"),
+            'UID' => 6
+          }
+        ]
+      )
+    end
+
+    let(:message_ids) do
+      [
+        "h4786x34@test.com",
+        "dvsfuf39@test.com",
+        "f349xj84@test.com"
+      ]
+    end
+
+    it "sends the message-id search in the correct format and returns the trashed emails and UIDVALIDITY" do
+      provider.open_mailbox("Inbox")
+      imap_stub.expects(:uid_search).with(
+        "OR OR HEADER Message-ID '<h4786x34@test.com>' HEADER Message-ID '<dvsfuf39@test.com>' HEADER Message-ID '<f349xj84@test.com>'"
+
+      ).returns([4, 6])
+      resp = provider.find_trashed_by_message_ids(message_ids)
+
+      expect(resp.trashed_emails.map(&:message_id)).to match_array(['h4786x34@test.com', 'f349xj84@test.com'])
+      expect(resp.trash_uid_validity).to eq(9)
+    end
+  end
+
+  describe "#trash" do
+    it "stores the \Deleted flag on the UID and expunges" do
+      provider.stubs(:can?).with('MOVE').returns(false)
+      provider.expects(:store).with(78, 'FLAGS', [], ['\Deleted'])
+      imap_stub.expects(:expunge)
+      provider.trash(78)
+    end
+
+    context "if the server supports MOVE" do
+      it "calls trash_move which is implemented by the provider" do
+        provider.stubs(:can?).with('MOVE').returns(true)
+        provider.expects(:trash_move).with(78)
+        provider.trash(78)
+      end
+    end
+  end
+
   describe "#uids" do
     it "can search with from and to" do
       imap_stub.expects(:uid_search).once.with("UID 5:9")