Use finalizers to detect unclosed connections.

README.md

@@ -59,7 +59,7 @@ As a work around for other Unixes, you can use [`nolock=1`](https://www.sqlite.o
   - [ ] snapshots
   - [ ] session extension
   - [ ] resumable bulk update
-  - [ ] shared cache mode
+  - [ ] shared-cache mode
   - [ ] unlock-notify
 - [ ] custom SQL functions
 - [ ] custom VFSes

blob.go

@@ -8,7 +8,6 @@ import "io"
 type ZeroBlob int64
 
 // Blob is a handle to an open BLOB.
-//
 // It implements [io.ReadWriteSeeker] for incremental BLOB I/O.
 //
 // https://www.sqlite.org/c3ref/blob.html

conn.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"math"
 	"net/url"
+	"runtime"
 	"strings"
 	"sync/atomic"
 	"unsafe"
@@ -30,8 +31,8 @@ type Conn struct {
 }
 
 // Open calls [OpenFlags] with [OPEN_READWRITE], [OPEN_CREATE] and [OPEN_URI].
-func Open(filename string) (conn *Conn, err error) {
-	return OpenFlags(filename, OPEN_READWRITE|OPEN_CREATE|OPEN_URI)
+func Open(filename string) (*Conn, error) {
+	return openFlags(filename, OPEN_READWRITE|OPEN_CREATE|OPEN_URI)
 }
 
 // OpenFlags opens an SQLite database file as specified by the filename argument.
@@ -41,7 +42,11 @@ func Open(filename string) (conn *Conn, err error) {
 //	sqlite3.Open("file:demo.db?_pragma=busy_timeout(10000)&_pragma=locking_mode(normal)")
 //
 // https://www.sqlite.org/c3ref/open.html
-func OpenFlags(filename string, flags OpenFlag) (conn *Conn, err error) {
+func OpenFlags(filename string, flags OpenFlag) (*Conn, error) {
+	return openFlags(filename, flags)
+}
+
+func openFlags(filename string, flags OpenFlag) (conn *Conn, err error) {
 	ctx := context.Background()
 	module, err := sqlite3.instantiateModule(ctx)
 	if err != nil {
@@ -50,6 +55,8 @@ func OpenFlags(filename string, flags OpenFlag) (conn *Conn, err error) {
 	defer func() {
 		if conn == nil {
 			module.Close(ctx)
+		} else {
+			runtime.SetFinalizer(conn, finalizer[Conn](3))
 		}
 	}()
 
@@ -109,6 +116,7 @@ func (c *Conn) Close() error {
 	}
 
 	c.handle = 0
+	runtime.SetFinalizer(c, nil)
 	return c.mem.mod.Close(c.ctx)
 }
 
@@ -133,9 +141,11 @@ func (c *Conn) MustPrepare(sql string) *Stmt {
 		panic(err)
 	}
 	if s == nil {
+		s.Close()
 		panic(emptyErr)
 	}
 	if !emptyStatement(tail) {
+		s.Close()
 		panic(tailErr)
 	}
 	return s

error.go

@@ -1,6 +1,7 @@
 package sqlite3
 
 import (
+	"fmt"
 	"runtime"
 	"strconv"
 	"strings"
@@ -215,3 +216,11 @@ func assertErr() errorString {
 	}
 	return errorString(msg)
 }
+
+func finalizer[T any](skip int) func(*T) {
+	msg := fmt.Sprintf("sqlite3: %T not closed", new(T))
+	if _, file, line, ok := runtime.Caller(skip + 1); ok && skip >= 0 {
+		msg += " (" + file + ":" + strconv.Itoa(line) + ")"
+	}
+	return func(*T) { panic(errorString(msg)) }
+}

tests/tx_test.go

@@ -29,6 +29,7 @@ func TestConn_Transaction_exec(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
+		defer stmt.Close()
 		if stmt.Step() {
 			return stmt.ColumnInt(0)
 		}
@@ -117,6 +118,7 @@ func TestConn_Transaction_panic(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
+		defer stmt.Close()
 		if stmt.Step() {
 			got := stmt.ColumnInt(0)
 			if got != 1 {
@@ -275,6 +277,7 @@ func TestConn_Savepoint_exec(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
+		defer stmt.Close()
 		if stmt.Step() {
 			return stmt.ColumnInt(0)
 		}
@@ -361,6 +364,7 @@ func TestConn_Savepoint_panic(t *testing.T) {
 		if err != nil {
 			t.Fatal(err)
 		}
+		defer stmt.Close()
 		if stmt.Step() {
 			got := stmt.ColumnInt(0)
 			if got != 1 {