Auto-rename of db_dir/mainnet to db_dir/bitcoin

Since version 0.9 the `mainnet` subdir is called `bitcoin` we need to
rename it if auto reindex is specified to fulfill the purpose of auto
reindex. The logic in this change keeps the intention of disabled auto
reindex causing no changes.

src/bin/electrs.rs

@@ -2,9 +2,31 @@
 
 use anyhow::{Context, Result};
 use electrs::{server, Config, Rpc, Tracker};
+use std::{io, fs};
 
 fn main() -> Result<()> {
     let config = Config::from_args();
+
+    match (config.network, config.auto_reindex, config.db_path.parent()) {
+        (bitcoin::Network::Bitcoin, true, Some(db_parent)) => {
+            let old_dir = db_parent.join("mainnet");
+            match fs::rename(&old_dir, &config.db_path) {
+                Ok(()) => (),
+                Err(error) if error.kind() == io::ErrorKind::NotFound => (),
+                Err(error) => return Err(error).with_context(|| format!("failed to rename the old directory ({}) to {}", old_dir.display(), config.db_path.display())),
+            }
+        },
+        (bitcoin::Network::Bitcoin, false, Some(db_parent)) => {
+            let old_dir = db_parent.join("mainnet");
+            match fs::metadata(&old_dir) {
+                Ok(_) => anyhow::bail!("The old directory {} exists but auto reindex was disabled", old_dir.display()),
+                Err(error) if error.kind() == io::ErrorKind::NotFound => (),
+                Err(error) => return Err(error).with_context(|| format!("failed to check whether the old directory ({}) exists", old_dir.display())),
+            }
+        },
+        _ => (),
+    }
+
     let rpc = Rpc::new(&config, Tracker::new(&config)?)?;
     if config.sync_once {
         return Ok(());