[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/tetratelabs/wazero/internal/wasm/host.go

@@ -0,0 +1,179 @@
+package wasm
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/tetratelabs/wazero/api"
+	"github.com/tetratelabs/wazero/internal/wasmdebug"
+)
+
+type HostFuncExporter interface {
+	ExportHostFunc(*HostFunc)
+}
+
+// HostFunc is a function with an inlined type, used for NewHostModule.
+// Any corresponding FunctionType will be reused or added to the Module.
+type HostFunc struct {
+	// ExportName is the only value returned by api.FunctionDefinition.
+	ExportName string
+
+	// Name is equivalent to the same method on api.FunctionDefinition.
+	Name string
+
+	// ParamTypes is equivalent to the same method on api.FunctionDefinition.
+	ParamTypes []ValueType
+
+	// ParamNames is equivalent to the same method on api.FunctionDefinition.
+	ParamNames []string
+
+	// ResultTypes is equivalent to the same method on api.FunctionDefinition.
+	ResultTypes []ValueType
+
+	// ResultNames is equivalent to the same method on api.FunctionDefinition.
+	ResultNames []string
+
+	// Code is the equivalent function in the SectionIDCode.
+	Code Code
+}
+
+// WithGoModuleFunc returns a copy of the function, replacing its Code.GoFunc.
+func (f *HostFunc) WithGoModuleFunc(fn api.GoModuleFunc) *HostFunc {
+	ret := *f
+	ret.Code.GoFunc = fn
+	return &ret
+}
+
+// NewHostModule is defined internally for use in WASI tests and to keep the code size in the root directory small.
+func NewHostModule(
+	moduleName string,
+	exportNames []string,
+	nameToHostFunc map[string]*HostFunc,
+	enabledFeatures api.CoreFeatures,
+) (m *Module, err error) {
+	if moduleName != "" {
+		m = &Module{NameSection: &NameSection{ModuleName: moduleName}}
+	} else {
+		return nil, errors.New("a module name must not be empty")
+	}
+
+	if exportCount := uint32(len(nameToHostFunc)); exportCount > 0 {
+		m.ExportSection = make([]Export, 0, exportCount)
+		m.Exports = make(map[string]*Export, exportCount)
+		if err = addFuncs(m, exportNames, nameToHostFunc, enabledFeatures); err != nil {
+			return
+		}
+	}
+
+	m.IsHostModule = true
+	// Uses the address of *wasm.Module as the module ID so that host functions can have each state per compilation.
+	// Downside of this is that compilation cache on host functions (trampoline codes for Go functions and
+	// Wasm codes for Wasm-implemented host functions) are not available and compiles each time. On the other hand,
+	// compilation of host modules is not costly as it's merely small trampolines vs the real-world native Wasm binary.
+	// TODO: refactor engines so that we can properly cache compiled machine codes for host modules.
+	m.AssignModuleID([]byte(fmt.Sprintf("@@@@@@@@%p", m)), // @@@@@@@@ = any 8 bytes different from Wasm header.
+		nil, false)
+	return
+}
+
+func addFuncs(
+	m *Module,
+	exportNames []string,
+	nameToHostFunc map[string]*HostFunc,
+	enabledFeatures api.CoreFeatures,
+) (err error) {
+	if m.NameSection == nil {
+		m.NameSection = &NameSection{}
+	}
+	moduleName := m.NameSection.ModuleName
+
+	for _, k := range exportNames {
+		hf := nameToHostFunc[k]
+		if hf.Name == "" {
+			hf.Name = k // default name to export name
+		}
+		switch hf.Code.GoFunc.(type) {
+		case api.GoModuleFunction, api.GoFunction:
+			continue // already parsed
+		}
+
+		// Resolve the code using reflection
+		hf.ParamTypes, hf.ResultTypes, hf.Code, err = parseGoReflectFunc(hf.Code.GoFunc)
+		if err != nil {
+			return fmt.Errorf("func[%s.%s] %w", moduleName, k, err)
+		}
+
+		// Assign names to the function, if they exist.
+		params := hf.ParamTypes
+		if paramNames := hf.ParamNames; paramNames != nil {
+			if paramNamesLen := len(paramNames); paramNamesLen != len(params) {
+				return fmt.Errorf("func[%s.%s] has %d params, but %d params names", moduleName, k, paramNamesLen, len(params))
+			}
+		}
+
+		results := hf.ResultTypes
+		if resultNames := hf.ResultNames; resultNames != nil {
+			if resultNamesLen := len(resultNames); resultNamesLen != len(results) {
+				return fmt.Errorf("func[%s.%s] has %d results, but %d results names", moduleName, k, resultNamesLen, len(results))
+			}
+		}
+	}
+
+	funcCount := uint32(len(exportNames))
+	m.NameSection.FunctionNames = make([]NameAssoc, 0, funcCount)
+	m.FunctionSection = make([]Index, 0, funcCount)
+	m.CodeSection = make([]Code, 0, funcCount)
+
+	idx := Index(0)
+	for _, name := range exportNames {
+		hf := nameToHostFunc[name]
+		debugName := wasmdebug.FuncName(moduleName, name, idx)
+		typeIdx, typeErr := m.maybeAddType(hf.ParamTypes, hf.ResultTypes, enabledFeatures)
+		if typeErr != nil {
+			return fmt.Errorf("func[%s] %v", debugName, typeErr)
+		}
+		m.FunctionSection = append(m.FunctionSection, typeIdx)
+		m.CodeSection = append(m.CodeSection, hf.Code)
+
+		export := hf.ExportName
+		m.ExportSection = append(m.ExportSection, Export{Type: ExternTypeFunc, Name: export, Index: idx})
+		m.Exports[export] = &m.ExportSection[len(m.ExportSection)-1]
+		m.NameSection.FunctionNames = append(m.NameSection.FunctionNames, NameAssoc{Index: idx, Name: hf.Name})
+
+		if len(hf.ParamNames) > 0 {
+			localNames := NameMapAssoc{Index: idx}
+			for i, n := range hf.ParamNames {
+				localNames.NameMap = append(localNames.NameMap, NameAssoc{Index: Index(i), Name: n})
+			}
+			m.NameSection.LocalNames = append(m.NameSection.LocalNames, localNames)
+		}
+		if len(hf.ResultNames) > 0 {
+			resultNames := NameMapAssoc{Index: idx}
+			for i, n := range hf.ResultNames {
+				resultNames.NameMap = append(resultNames.NameMap, NameAssoc{Index: Index(i), Name: n})
+			}
+			m.NameSection.ResultNames = append(m.NameSection.ResultNames, resultNames)
+		}
+		idx++
+	}
+	return nil
+}
+
+func (m *Module) maybeAddType(params, results []ValueType, enabledFeatures api.CoreFeatures) (Index, error) {
+	if len(results) > 1 {
+		// Guard >1.0 feature multi-value
+		if err := enabledFeatures.RequireEnabled(api.CoreFeatureMultiValue); err != nil {
+			return 0, fmt.Errorf("multiple result types invalid as %v", err)
+		}
+	}
+	for i := range m.TypeSection {
+		t := &m.TypeSection[i]
+		if t.EqualsSignature(params, results) {
+			return Index(i), nil
+		}
+	}
+
+	result := m.SectionElementCount(SectionIDType)
+	m.TypeSection = append(m.TypeSection, FunctionType{Params: params, Results: results})
+	return result, nil
+}