sync: select destination read-write so PERMANENTFLAGS is real (flags were dropped)

src/imap/client.rs

@@ -60,6 +60,9 @@ pub struct SelectInfo {
     pub exists: u32,
     pub uidvalidity: Option<u32>,
     pub permanent_flags: Option<Vec<String>>,
+    /// EXAMINE / [READ-ONLY]: PERMANENTFLAGS is then empty and says nothing
+    /// about what APPEND will keep.
+    pub read_only: bool,
 }
 
 impl SelectInfo {
@@ -67,6 +70,7 @@ impl SelectInfo {
     pub fn accepts_flag(&self, f: &str) -> bool {
         match &self.permanent_flags {
             None => true,
+            Some(_) if self.read_only => true,
             Some(p) => {
                 p.iter().any(|x| x.eq_ignore_ascii_case(f)) || (!f.starts_with('\\') && p.iter().any(|x| x == "\\*"))
             }
@@ -426,7 +430,10 @@ impl Client {
         let mut args = vec![Arg::Raw(format!("{verb} "))];
         args.push(mailbox_arg(wire));
         let r = self.run(args, &format!("{verb} {wire}")).await?;
-        let mut info = SelectInfo::default();
+        let mut info = SelectInfo {
+            read_only: readonly || r.status.code.as_deref().is_some_and(|c| c.eq_ignore_ascii_case("READ-ONLY")),
+            ..Default::default()
+        };
         for u in &r.untagged {
             if let Some(s) = u.status() {
                 if let Some(code) = s.code {
@@ -673,5 +680,8 @@ mod tests {
         assert!(!s.accepts_flag("\\Flagged"));
         let s = SelectInfo { permanent_flags: Some(vec!["\\Seen".into()]), ..Default::default() };
         assert!(!s.accepts_flag("$Forwarded"));
+        // EXAMINE: PERMANENTFLAGS () is meaningless for APPEND
+        let s = SelectInfo { permanent_flags: Some(vec![]), read_only: true, ..Default::default() };
+        assert!(s.accepts_flag("\\Seen"));
     }
 }