feat: add --dry-run mode to Rust implementation

Add comprehensive dry-run functionality to the Rust implementation that allows
users to test their configuration without making any changes to CouchDB:

- Added --dry-run/-n command line flag with clap argument parsing
- Extended CommandLineArgs struct with dry_run field
- Updated bash completion script to include new flag
- Comprehensive dry-run logic throughout sync coordinator:
  - Skip database creation with informative logging
  - Skip sync metadata retrieval and use config fallback
  - Skip deleted message handling in sync mode
  - Skip message and attachment storage with detailed simulation
  - Skip sync metadata updates with summary information
- Enhanced summary output to clearly indicate dry-run vs normal mode
- Updated all tests to include new dry_run field
- Maintains all IMAP operations for realistic mail discovery testing

This brings the Rust implementation to feature parity with the Go version
for safe configuration testing as identified in ANALYSIS.md.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

rust/src/cli.rs

@@ -28,6 +28,11 @@ pub fn parse_command_line() -> CommandLineArgs {
             .help("Maximum number of messages to process per mailbox per run (0 = no limit)")
             .value_parser(clap::value_parser!(u32))
             .action(ArgAction::Set))
+        .arg(Arg::new("dry-run")
+            .short('n')
+            .long("dry-run")
+            .help("Show what would be done without making any changes")
+            .action(ArgAction::SetTrue))
         .arg(Arg::new("generate-bash-completion")
             .long("generate-bash-completion")
             .help("Generate bash completion script and exit")
@@ -44,6 +49,7 @@ pub fn parse_command_line() -> CommandLineArgs {
     CommandLineArgs {
         config_path: matches.get_one::<String>("config").map(|s| s.clone()),
         max_messages: matches.get_one::<u32>("max-messages").copied(),
+        dry_run: matches.get_flag("dry-run"),
         generate_bash_completion: matches.get_flag("generate-bash-completion"),
         help: false, // Using clap's built-in help
     }
@@ -83,7 +89,7 @@ _{}_completions() {{
 
     if [[ $cur == -* ]]; then
         # Complete with available options
-        local opts="-c --config -m --max-messages -h --help --generate-bash-completion"
+        local opts="-c --config -m --max-messages -n --dry-run -h --help --generate-bash-completion"
         COMPREPLY=($(compgen -W "$opts" -- "$cur"))
         return
     fi

rust/src/config.rs

@@ -107,6 +107,7 @@ impl MailSource {
 pub struct CommandLineArgs {
     pub config_path: Option<String>,
     pub max_messages: Option<u32>,
+    pub dry_run: bool,
     pub generate_bash_completion: bool,
     pub help: bool,
 }
@@ -283,6 +284,7 @@ mod tests {
         let args = CommandLineArgs {
             config_path: None,
             max_messages: None,
+            dry_run: false,
             generate_bash_completion: false,
             help: false,
         };

rust/src/main.rs

@@ -36,6 +36,10 @@ async fn run(args: mail2couch::config::CommandLineArgs) -> Result<()> {
         info!("Maximum messages per mailbox: unlimited");
     }
 
+    if args.dry_run {
+        info!("🔍 DRY-RUN MODE: No changes will be made to CouchDB");
+    }
+
     // Display configuration summary
     print_config_summary(&config);
 

rust/src/sync.rs

@@ -119,8 +119,12 @@ impl SyncCoordinator {
         let db_name = generate_database_name(&source.name, &source.user);
         info!("Using database: {}", db_name);
 
-        // Create database if it doesn't exist
+        // Create database if it doesn't exist (skip in dry-run mode)
+        if !self.args.dry_run {
             self.couch_client.create_database(&db_name).await?;
+        } else {
+            info!("🔍 DRY-RUN: Would create database {}", db_name);
+        }
 
         // Connect to IMAP server
         let mut imap_client = ImapClient::connect(source.clone()).await?;
@@ -212,8 +216,9 @@ impl SyncCoordinator {
         let mailbox_info = imap_client.select_mailbox(mailbox).await?;
         debug!("Selected mailbox {}: {} messages", mailbox, mailbox_info.exists);
 
-        // Get last sync metadata
+        // Get last sync metadata (skip in dry-run mode)
-        let since_date = match self.couch_client.get_sync_metadata(db_name, mailbox).await {
+        let since_date = if !self.args.dry_run {
+            match self.couch_client.get_sync_metadata(db_name, mailbox).await {
                 Ok(metadata) => {
                     info!("  Found sync metadata, last sync: {}", metadata.last_sync_time);
                     Some(metadata.last_sync_time)
@@ -228,6 +233,16 @@ impl SyncCoordinator {
                                 .ok()
                         })
                 }
+            }
+        } else {
+            info!("  🔍 DRY-RUN: Would check for sync metadata");
+            // In dry-run mode, use config since date if available
+            source.message_filter.since.as_ref()
+                .and_then(|since_str| {
+                    DateTime::parse_from_str(&format!("{} 00:00:00 +0000", since_str), "%Y-%m-%d %H:%M:%S %z")
+                        .map(|dt| dt.with_timezone(&Utc))
+                        .ok()
+                })
         };
 
         // Search for messages using server-side IMAP SEARCH with keyword filtering when possible
@@ -257,9 +272,10 @@ impl SyncCoordinator {
         };
         info!("  Found {} messages matching search criteria", message_uids.len());
 
-        // Handle sync mode - check for deleted messages
+        // Handle sync mode - check for deleted messages (skip in dry-run mode)
         let mut messages_deleted = 0;
         if source.mode == "sync" {
+            if !self.args.dry_run {
                 messages_deleted = self.handle_deleted_messages(db_name, mailbox, &message_uids).await
                     .unwrap_or_else(|e| {
                         warn!("  Failed to handle deleted messages: {}", e);
@@ -269,6 +285,9 @@ impl SyncCoordinator {
                 if messages_deleted > 0 {
                     info!("  🗑️  Deleted {} messages that no longer exist on server", messages_deleted);
                 }
+            } else {
+                info!("  🔍 DRY-RUN: Would check for deleted messages in sync mode");
+            }
         }
 
         if message_uids.is_empty() {
@@ -312,7 +331,8 @@ impl SyncCoordinator {
             // Extract UID before moving the document
             let uid_str = mail_doc.source_uid.clone();
 
-            // Store the message document first
+            // Store the message document first (skip in dry-run mode)
+            if !self.args.dry_run {
                 match self.couch_client.store_mail_document(db_name, mail_doc).await {
                     Ok(doc_id) => {
                         messages_stored += 1;
@@ -347,10 +367,26 @@ impl SyncCoordinator {
                         messages_skipped += 1;
                     }
                 }
+            } else {
+                // In dry-run mode, simulate successful storage
+                messages_stored += 1;
+                debug!("  🔍 DRY-RUN: Would store message {} (Subject: {})", 
+                    uid_str, mail_doc.subject);
+                
+                if !attachments.is_empty() {
+                    debug!("  🔍 DRY-RUN: Would store {} attachments", attachments.len());
                 }
                 
-        // Update sync metadata
+                // Parse UID from source_uid
+                if let Ok(uid) = uid_str.parse::<u32>() {
+                    last_uid = Some(last_uid.map_or(uid, |prev: u32| prev.max(uid)));
+                }
+            }
+        }
+
+        // Update sync metadata (skip in dry-run mode)
         if let Some(uid) = last_uid {
+            if !self.args.dry_run {
                 let sync_metadata = SyncMetadata::new(
                     mailbox.to_string(),
                     start_time,
@@ -361,6 +397,9 @@ impl SyncCoordinator {
                 if let Err(e) = self.couch_client.store_sync_metadata(db_name, &sync_metadata).await {
                     warn!("  Failed to store sync metadata: {}", e);
                 }
+            } else {
+                info!("  🔍 DRY-RUN: Would update sync metadata (last UID: {}, {} messages)", uid, messages_stored);
+            }
         }
 
         Ok(MailboxSyncResult {
@@ -422,7 +461,11 @@ impl SyncCoordinator {
 
     /// Print summary of sync results
     pub fn print_sync_summary(&self, results: &[SourceSyncResult]) {
+        if self.args.dry_run {
+            info!("\n🔍 DRY-RUN completed!");
+        } else {
             info!("\n🎉 Synchronization completed!");
+        }
         info!("{}", "=".repeat(50));
 
         let mut total_sources = 0;
@@ -434,6 +477,15 @@ impl SyncCoordinator {
             total_mailboxes += result.mailboxes_processed;
             total_messages += result.total_messages;
 
+            if self.args.dry_run {
+                info!(
+                    "📧 {}: {} mailboxes, {} messages found (database: {})",
+                    result.source_name,
+                    result.mailboxes_processed,
+                    result.total_messages,
+                    result.database
+                );
+            } else {
                 info!(
                     "📧 {}: {} mailboxes, {} messages (database: {})",
                     result.source_name,
@@ -442,16 +494,28 @@ impl SyncCoordinator {
                     result.database
                 );
             }
+        }
 
         info!("{}", "=".repeat(50));
+        if self.args.dry_run {
+            info!(
+                "📊 DRY-RUN Total: {} sources, {} mailboxes, {} messages found",
+                total_sources, total_mailboxes, total_messages
+            );
+        } else {
             info!(
                 "📊 Total: {} sources, {} mailboxes, {} messages",
                 total_sources, total_mailboxes, total_messages
             );
+        }
 
         if let Some(max) = self.args.max_messages {
             info!("⚠️  Message limit was applied: {} per mailbox", max);
         }
+
+        if self.args.dry_run {
+            info!("🔍 No changes were made to CouchDB");
+        }
     }
 }
 
@@ -493,6 +557,7 @@ mod tests {
         let args = CommandLineArgs {
             config_path: None,
             max_messages: Some(10),
+            dry_run: false,
             generate_bash_completion: false,
             help: false,
         };