Remove Connection path field

Use sqlite3_db_filename instead.
Pros: memory footprint, absolute path
Cons: one cannot make the disctinction between multiple memory
databases anymore (like file:one.db?mode=memory and
file:another.db?mode=memory).

src/lib.rs

@@ -62,7 +62,7 @@ use std::ffi::{CStr, CString};
 use std::fmt;
 use std::os::raw::{c_char, c_int};
 
-use std::path::{Path, PathBuf};
+use std::path::Path;
 use std::result;
 use std::str;
 use std::sync::atomic::Ordering;
@@ -330,7 +330,6 @@ impl DatabaseName<'_> {
 pub struct Connection {
     db: RefCell<InnerConnection>,
     cache: StatementCache,
-    path: Option<PathBuf>,
 }
 
 unsafe impl Send for Connection {}
@@ -427,7 +426,6 @@ impl Connection {
         InnerConnection::open_with_flags(&c_path, flags, None).map(|db| Connection {
             db: RefCell::new(db),
             cache: StatementCache::with_capacity(STATEMENT_CACHE_DEFAULT_CAPACITY),
-            path: Some(path.as_ref().to_path_buf()),
         })
     }
 
@@ -452,7 +450,6 @@ impl Connection {
         InnerConnection::open_with_flags(&c_path, flags, Some(&c_vfs)).map(|db| Connection {
             db: RefCell::new(db),
             cache: StatementCache::with_capacity(STATEMENT_CACHE_DEFAULT_CAPACITY),
-            path: Some(path.as_ref().to_path_buf()),
         })
     }
 
@@ -580,12 +577,23 @@ impl Connection {
 
     /// Returns the path to the database file, if one exists and is known.
     ///
+    /// Returns `Some("")` for a temporary or in-memory database.
+    ///
     /// Note that in some cases [PRAGMA
     /// database_list](https://sqlite.org/pragma.html#pragma_database_list) is
     /// likely to be more robust.
     #[inline]
-    pub fn path(&self) -> Option<&Path> {
-        self.path.as_deref()
+    pub fn path(&self) -> Option<&str> {
+        unsafe {
+            let db = self.handle();
+            let db_name = DatabaseName::Main.as_cstring().unwrap();
+            let db_filename = ffi::sqlite3_db_filename(db, db_name.as_ptr());
+            if db_filename.is_null() {
+                None
+            } else {
+                CStr::from_ptr(db_filename).to_str().ok()
+            }
+        }
     }
 
     /// Attempts to free as much heap memory as possible from the database
@@ -915,12 +923,10 @@ impl Connection {
     /// This function is unsafe because improper use may impact the Connection.
     #[inline]
     pub unsafe fn from_handle(db: *mut ffi::sqlite3) -> Result<Connection> {
-        let db_path = db_filename(db);
         let db = InnerConnection::new(db, false);
         Ok(Connection {
             db: RefCell::new(db),
             cache: StatementCache::with_capacity(STATEMENT_CACHE_DEFAULT_CAPACITY),
-            path: db_path,
         })
     }
 
@@ -973,7 +979,7 @@ impl Connection {
 impl fmt::Debug for Connection {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("Connection")
-            .field("path", &self.path)
+            .field("path", &self.path())
             .finish()
     }
 }
@@ -1164,16 +1170,6 @@ impl InterruptHandle {
     }
 }
 
-unsafe fn db_filename(db: *mut ffi::sqlite3) -> Option<PathBuf> {
-    let db_name = DatabaseName::Main.as_cstring().unwrap();
-    let db_filename = ffi::sqlite3_db_filename(db, db_name.as_ptr());
-    if db_filename.is_null() {
-        None
-    } else {
-        CStr::from_ptr(db_filename).to_str().ok().map(PathBuf::from)
-    }
-}
-
 #[cfg(doctest)]
 doc_comment::doctest!("../README.md");
 
@@ -1275,6 +1271,21 @@ mod test {
         db.close().unwrap();
     }
 
+    #[test]
+    fn test_path() -> Result<()> {
+        let tmp = tempfile::tempdir().unwrap();
+        let db = Connection::open("")?;
+        assert_eq!(Some(""), db.path());
+        let db = Connection::open_in_memory()?;
+        assert_eq!(Some(""), db.path());
+        let db = Connection::open("file:dummy.db?mode=memory&cache=shared")?;
+        assert_eq!(Some(""), db.path());
+        let path = tmp.path().join("file.db");
+        let db = Connection::open(path)?;
+        assert!(db.path().map(|p| p.ends_with("file.db")).unwrap_or(false));
+        Ok(())
+    }
+
     #[test]
     fn test_open_failure() {
         let filename = "no_such_file.db";