refactor(imap): make select_folder() accept non-optional folder

If no folder should be selected,
`maybe_close_folder()` can be called directly.

src/download.rs

@@ -184,7 +184,7 @@ impl Session {
             bail!("Attempt to fetch UID 0");
         }
 
-        self.select_folder(context, Some(folder)).await?;
+        self.select_folder(context, folder).await?;
 
         // we are connected, and the folder is selected
         info!(context, "Downloading message {}/{} fully...", folder, uid);

src/imap.rs

@@ -838,7 +838,7 @@ impl Session {
         // Collect pairs of UID and Message-ID.
         let mut msgs = BTreeMap::new();
 
-        self.select_folder(context, Some(folder)).await?;
+        self.select_folder(context, folder).await?;
 
         let mut list = self
             .uid_fetch("1:*", RFC724MID_UID)
@@ -1039,7 +1039,7 @@ impl Session {
             // MOVE/DELETE operations. This does not result in multiple SELECT commands
             // being sent because `select_folder()` does nothing if the folder is already
             // selected.
-            self.select_folder(context, Some(folder)).await?;
+            self.select_folder(context, folder).await?;
 
             // Empty target folder name means messages should be deleted.
             if target.is_empty() {
@@ -1087,7 +1087,7 @@ impl Session {
             .await?;
 
         for (folder, rowid_set, uid_set) in UidGrouper::from(rows) {
-            self.select_folder(context, Some(&folder))
+            self.select_folder(context, &folder)
                 .await
                 .context("failed to select folder")?;
 
@@ -1131,7 +1131,7 @@ impl Session {
             return Ok(());
         }
 
-        self.select_folder(context, Some(folder))
+        self.select_folder(context, folder)
             .await
             .context("failed to select folder")?;
 
@@ -1563,7 +1563,7 @@ impl Session {
     ) -> Result<Option<&'a str>> {
         // Close currently selected folder if needed.
         // We are going to select folders using low-level EXAMINE operations below.
-        self.select_folder(context, None).await?;
+        self.maybe_close_folder(context).await?;
 
         for folder in folders {
             info!(context, "Looking for MVBOX-folder \"{}\"...", &folder);

src/imap/idle.rs

@@ -29,7 +29,7 @@ impl Session {
     ) -> Result<Self> {
         use futures::future::FutureExt;
 
-        self.select_folder(context, Some(folder)).await?;
+        self.select_folder(context, folder).await?;
 
         if self.server_sent_unsolicited_exists(context)? {
             return Ok(self);

src/imap/select_folder.rs

@@ -55,15 +55,13 @@ impl ImapSession {
     pub(crate) async fn select_folder(
         &mut self,
         context: &Context,
-        folder: Option<&str>,
+        folder: &str,
     ) -> Result<NewlySelected> {
         // if there is a new folder and the new folder is equal to the selected one, there's nothing to do.
         // if there is _no_ new folder, we continue as we might want to expunge below.
-        if let Some(folder) = folder {
+        if let Some(selected_folder) = &self.selected_folder {
-            if let Some(selected_folder) = &self.selected_folder {
+            if folder == selected_folder {
-                if folder == selected_folder {
+                return Ok(NewlySelected::No);
-                    return Ok(NewlySelected::No);
-                }
             }
         }
 
@@ -71,34 +69,30 @@ impl ImapSession {
         self.maybe_close_folder(context).await?;
 
         // select new folder
-        if let Some(folder) = folder {
+        let res = if self.can_condstore() {
-            let res = if self.can_condstore() {
+            self.select_condstore(folder).await
-                self.select_condstore(folder).await
-            } else {
-                self.select(folder).await
-            };
-
-            // <https://tools.ietf.org/html/rfc3501#section-6.3.1>
-            // says that if the server reports select failure we are in
-            // authenticated (not-select) state.
-
-            match res {
-                Ok(mailbox) => {
-                    self.selected_folder = Some(folder.to_string());
-                    self.selected_mailbox = Some(mailbox);
-                    Ok(NewlySelected::Yes)
-                }
-                Err(async_imap::error::Error::ConnectionLost) => Err(Error::ConnectionLost),
-                Err(async_imap::error::Error::Validate(_)) => {
-                    Err(Error::BadFolderName(folder.to_string()))
-                }
-                Err(async_imap::error::Error::No(response)) => {
-                    Err(Error::NoFolder(folder.to_string(), response))
-                }
-                Err(err) => Err(Error::Other(err.to_string())),
-            }
         } else {
-            Ok(NewlySelected::No)
+            self.select(folder).await
+        };
+
+        // <https://tools.ietf.org/html/rfc3501#section-6.3.1>
+        // says that if the server reports select failure we are in
+        // authenticated (not-select) state.
+
+        match res {
+            Ok(mailbox) => {
+                self.selected_folder = Some(folder.to_string());
+                self.selected_mailbox = Some(mailbox);
+                Ok(NewlySelected::Yes)
+            }
+            Err(async_imap::error::Error::ConnectionLost) => Err(Error::ConnectionLost),
+            Err(async_imap::error::Error::Validate(_)) => {
+                Err(Error::BadFolderName(folder.to_string()))
+            }
+            Err(async_imap::error::Error::No(response)) => {
+                Err(Error::NoFolder(folder.to_string(), response))
+            }
+            Err(err) => Err(Error::Other(err.to_string())),
         }
     }
 
@@ -108,7 +102,7 @@ impl ImapSession {
         context: &Context,
         folder: &str,
     ) -> anyhow::Result<NewlySelected> {
-        match self.select_folder(context, Some(folder)).await {
+        match self.select_folder(context, folder).await {
             Ok(newly_selected) => Ok(newly_selected),
             Err(err) => match err {
                 Error::NoFolder(..) => {
@@ -118,7 +112,7 @@ impl ImapSession {
                         info!(context, "Couldn't select folder, then create() failed: {err:#}.");
                         // Need to recheck, could have been created in parallel.
                     }
-                    let select_res = self.select_folder(context, Some(folder)).await.with_context(|| format!("failed to select newely created folder {folder}"));
+                    let select_res = self.select_folder(context, folder).await.with_context(|| format!("failed to select newely created folder {folder}"));
                     if select_res.is_err() {
                         create_res?;
                     }