[experiment] add alternative wasm sqlite3 implementation available via build-tag (#2863)

This allows for building GoToSocial with [SQLite transpiled to WASM](https://github.com/ncruces/go-sqlite3) and accessed through [Wazero](https://wazero.io/).

vendor/github.com/ncruces/go-sqlite3/func.go

@@ -0,0 +1,214 @@
+package sqlite3
+
+import (
+	"context"
+	"sync"
+
+	"github.com/ncruces/go-sqlite3/internal/util"
+	"github.com/tetratelabs/wazero/api"
+)
+
+// CollationNeeded registers a callback to be invoked
+// whenever an unknown collation sequence is required.
+//
+// https://sqlite.org/c3ref/collation_needed.html
+func (c *Conn) CollationNeeded(cb func(db *Conn, name string)) error {
+	var enable uint64
+	if cb != nil {
+		enable = 1
+	}
+	r := c.call("sqlite3_collation_needed_go", uint64(c.handle), enable)
+	if err := c.error(r); err != nil {
+		return err
+	}
+	c.collation = cb
+	return nil
+}
+
+// AnyCollationNeeded uses [Conn.CollationNeeded] to register
+// a fake collating function for any unknown collating sequence.
+// The fake collating function works like BINARY.
+//
+// This can be used to load schemas that contain
+// one or more unknown collating sequences.
+func (c *Conn) AnyCollationNeeded() {
+	c.call("sqlite3_anycollseq_init", uint64(c.handle), 0, 0)
+}
+
+// CreateCollation defines a new collating sequence.
+//
+// https://sqlite.org/c3ref/create_collation.html
+func (c *Conn) CreateCollation(name string, fn func(a, b []byte) int) error {
+	defer c.arena.mark()()
+	namePtr := c.arena.string(name)
+	funcPtr := util.AddHandle(c.ctx, fn)
+	r := c.call("sqlite3_create_collation_go",
+		uint64(c.handle), uint64(namePtr), uint64(funcPtr))
+	return c.error(r)
+}
+
+// CreateFunction defines a new scalar SQL function.
+//
+// https://sqlite.org/c3ref/create_function.html
+func (c *Conn) CreateFunction(name string, nArg int, flag FunctionFlag, fn ScalarFunction) error {
+	defer c.arena.mark()()
+	namePtr := c.arena.string(name)
+	funcPtr := util.AddHandle(c.ctx, fn)
+	r := c.call("sqlite3_create_function_go",
+		uint64(c.handle), uint64(namePtr), uint64(nArg),
+		uint64(flag), uint64(funcPtr))
+	return c.error(r)
+}
+
+// ScalarFunction is the type of a scalar SQL function.
+// Implementations must not retain arg.
+type ScalarFunction func(ctx Context, arg ...Value)
+
+// CreateWindowFunction defines a new aggregate or aggregate window SQL function.
+// If fn returns a [WindowFunction], then an aggregate window function is created.
+// If fn returns an [io.Closer], it will be called to free resources.
+//
+// https://sqlite.org/c3ref/create_function.html
+func (c *Conn) CreateWindowFunction(name string, nArg int, flag FunctionFlag, fn func() AggregateFunction) error {
+	defer c.arena.mark()()
+	call := "sqlite3_create_aggregate_function_go"
+	namePtr := c.arena.string(name)
+	funcPtr := util.AddHandle(c.ctx, fn)
+	if _, ok := fn().(WindowFunction); ok {
+		call = "sqlite3_create_window_function_go"
+	}
+	r := c.call(call,
+		uint64(c.handle), uint64(namePtr), uint64(nArg),
+		uint64(flag), uint64(funcPtr))
+	return c.error(r)
+}
+
+// AggregateFunction is the interface an aggregate function should implement.
+//
+// https://sqlite.org/appfunc.html
+type AggregateFunction interface {
+	// Step is invoked to add a row to the current window.
+	// The function arguments, if any, corresponding to the row being added, are passed to Step.
+	// Implementations must not retain arg.
+	Step(ctx Context, arg ...Value)
+
+	// Value is invoked to return the current (or final) value of the aggregate.
+	Value(ctx Context)
+}
+
+// WindowFunction is the interface an aggregate window function should implement.
+//
+// https://sqlite.org/windowfunctions.html
+type WindowFunction interface {
+	AggregateFunction
+
+	// Inverse is invoked to remove the oldest presently aggregated result of Step from the current window.
+	// The function arguments, if any, are those passed to Step for the row being removed.
+	// Implementations must not retain arg.
+	Inverse(ctx Context, arg ...Value)
+}
+
+// OverloadFunction overloads a function for a virtual table.
+//
+// https://sqlite.org/c3ref/overload_function.html
+func (c *Conn) OverloadFunction(name string, nArg int) error {
+	defer c.arena.mark()()
+	namePtr := c.arena.string(name)
+	r := c.call("sqlite3_overload_function",
+		uint64(c.handle), uint64(namePtr), uint64(nArg))
+	return c.error(r)
+}
+
+func destroyCallback(ctx context.Context, mod api.Module, pApp uint32) {
+	util.DelHandle(ctx, pApp)
+}
+
+func collationCallback(ctx context.Context, mod api.Module, pArg, pDB, eTextRep, zName uint32) {
+	if c, ok := ctx.Value(connKey{}).(*Conn); ok && c.handle == pDB && c.collation != nil {
+		name := util.ReadString(mod, zName, _MAX_NAME)
+		c.collation(c, name)
+	}
+}
+
+func compareCallback(ctx context.Context, mod api.Module, pApp, nKey1, pKey1, nKey2, pKey2 uint32) uint32 {
+	fn := util.GetHandle(ctx, pApp).(func(a, b []byte) int)
+	return uint32(fn(util.View(mod, pKey1, uint64(nKey1)), util.View(mod, pKey2, uint64(nKey2))))
+}
+
+func funcCallback(ctx context.Context, mod api.Module, pCtx, pApp, nArg, pArg uint32) {
+	args := getFuncArgs()
+	defer putFuncArgs(args)
+	db := ctx.Value(connKey{}).(*Conn)
+	fn := util.GetHandle(db.ctx, pApp).(ScalarFunction)
+	callbackArgs(db, args[:nArg], pArg)
+	fn(Context{db, pCtx}, args[:nArg]...)
+}
+
+func stepCallback(ctx context.Context, mod api.Module, pCtx, pAgg, pApp, nArg, pArg uint32) {
+	args := getFuncArgs()
+	defer putFuncArgs(args)
+	db := ctx.Value(connKey{}).(*Conn)
+	callbackArgs(db, args[:nArg], pArg)
+	fn, _ := callbackAggregate(db, pAgg, pApp)
+	fn.Step(Context{db, pCtx}, args[:nArg]...)
+}
+
+func finalCallback(ctx context.Context, mod api.Module, pCtx, pAgg, pApp uint32) {
+	db := ctx.Value(connKey{}).(*Conn)
+	fn, handle := callbackAggregate(db, pAgg, pApp)
+	fn.Value(Context{db, pCtx})
+	util.DelHandle(ctx, handle)
+}
+
+func valueCallback(ctx context.Context, mod api.Module, pCtx, pAgg uint32) {
+	db := ctx.Value(connKey{}).(*Conn)
+	fn := util.GetHandle(db.ctx, pAgg).(AggregateFunction)
+	fn.Value(Context{db, pCtx})
+}
+
+func inverseCallback(ctx context.Context, mod api.Module, pCtx, pAgg, nArg, pArg uint32) {
+	args := getFuncArgs()
+	defer putFuncArgs(args)
+	db := ctx.Value(connKey{}).(*Conn)
+	callbackArgs(db, args[:nArg], pArg)
+	fn := util.GetHandle(db.ctx, pAgg).(WindowFunction)
+	fn.Inverse(Context{db, pCtx}, args[:nArg]...)
+}
+
+func callbackAggregate(db *Conn, pAgg, pApp uint32) (AggregateFunction, uint32) {
+	if pApp == 0 {
+		handle := util.ReadUint32(db.mod, pAgg)
+		return util.GetHandle(db.ctx, handle).(AggregateFunction), handle
+	}
+
+	// We need to create the aggregate.
+	fn := util.GetHandle(db.ctx, pApp).(func() AggregateFunction)()
+	handle := util.AddHandle(db.ctx, fn)
+	if pAgg != 0 {
+		util.WriteUint32(db.mod, pAgg, handle)
+	}
+	return fn, handle
+}
+
+func callbackArgs(db *Conn, arg []Value, pArg uint32) {
+	for i := range arg {
+		arg[i] = Value{
+			c:      db,
+			handle: util.ReadUint32(db.mod, pArg+ptrlen*uint32(i)),
+		}
+	}
+}
+
+var funcArgsPool sync.Pool
+
+func putFuncArgs(p *[_MAX_FUNCTION_ARG]Value) {
+	funcArgsPool.Put(p)
+}
+
+func getFuncArgs() *[_MAX_FUNCTION_ARG]Value {
+	if p := funcArgsPool.Get(); p == nil {
+		return new([_MAX_FUNCTION_ARG]Value)
+	} else {
+		return p.(*[_MAX_FUNCTION_ARG]Value)
+	}
+}