Support the immutable option on SQLite connections (#1289)

Co-authored-by: Austin Bonander <austin@launchbadge.com>

sqlx-core/src/sqlite/connection/establish.rs

@@ -29,8 +29,6 @@ pub(crate) async fn establish(options: &SqliteConnectOptions) -> Result<SqliteCo
         })?
         .to_owned();
 
-    filename.push('\0');
-
     // By default, we connect to an in-memory database.
     // [SQLITE_OPEN_NOMUTEX] will instruct [sqlite3_open_v2] to return an error if it
     // cannot satisfy our wish for a thread-safe, lock-free connection object
@@ -55,6 +53,13 @@ pub(crate) async fn establish(options: &SqliteConnectOptions) -> Result<SqliteCo
         SQLITE_OPEN_PRIVATECACHE
     };
 
+    if options.immutable {
+        filename = format!("file:{}?immutable=true", filename);
+        flags |= libsqlite3_sys::SQLITE_OPEN_URI;
+    }
+
+    filename.push('\0');
+
     let busy_timeout = options.busy_timeout;
 
     let handle = blocking!({

sqlx-core/src/sqlite/options/mod.rs

@@ -63,6 +63,7 @@ pub struct SqliteConnectOptions {
     pub(crate) synchronous: SqliteSynchronous,
     pub(crate) auto_vacuum: SqliteAutoVacuum,
     pub(crate) page_size: u32,
+    pub(crate) immutable: bool,
 }
 
 impl Default for SqliteConnectOptions {
@@ -88,6 +89,7 @@ impl SqliteConnectOptions {
             synchronous: SqliteSynchronous::Full,
             auto_vacuum: Default::default(),
             page_size: 4096,
+            immutable: false,
         }
     }
 
@@ -191,6 +193,11 @@ impl SqliteConnectOptions {
         self
     }
 
+    pub fn immutable(mut self, immutable: bool) -> Self {
+        self.immutable = immutable;
+        self
+    }
+  
     /// Sets the log settings.
     ///
     /// # Example

sqlx-core/src/sqlite/options/parse.rs

@@ -94,6 +94,20 @@ impl FromStr for SqliteConnectOptions {
                         }
                     },
 
+                    "immutable" => match &*value {
+                        "true" | "1" => {
+                            options.immutable = true;
+                        }
+                        "false" | "0" => {
+                            options.immutable = false;
+                        }
+                        _ => {
+                            return Err(Error::Configuration(
+                                format!("unknown value {:?} for `immutable`", value).into(),
+                            ));
+                        }
+                    },
+
                     _ => {
                         return Err(Error::Configuration(
                             format!(