salix/salix.go

515 lines
13 KiB
Go

/*
* Salix - Go templating engine
* Copyright (C) 2023 Elara Musayelyan
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package salix
import (
"errors"
"fmt"
"html"
"io"
"reflect"
"sync"
"go.elara.ws/salix/ast"
)
var (
ErrNoSuchFunc = errors.New("no such function")
ErrNoSuchVar = errors.New("no such variable")
ErrNoSuchMethod = errors.New("no such method")
ErrNoSuchField = errors.New("no such field")
ErrNoSuchTag = errors.New("no such tag")
ErrNotOperatorNonBool = errors.New("not operator cannot be used on a non-bool value")
ErrParamNumMismatch = errors.New("incorrect parameter amount")
ErrIncorrectParamType = errors.New("incorrect parameter type for function")
ErrEndTagWithoutStart = errors.New("end tag without a start tag")
ErrIncorrectIndexType = errors.New("incorrect index type")
ErrIndexOutOfRange = errors.New("index out of range")
ErrMapIndexNotFound = errors.New("map index not found")
ErrMapInvalidIndexType = errors.New("invalid map index type")
ErrFuncTooManyReturns = errors.New("template functions can only have two return values")
ErrFuncNoReturns = errors.New("template functions must return at least one value")
ErrFuncSecondReturnType = errors.New("the second return value of a template function must be an error")
ErrTernaryCondBool = errors.New("ternary condition must be a boolean")
)
// HTML represents unescaped HTML strings
type HTML string
// Template represents a Salix template
type Template struct {
ns *Namespace
name string
ast []ast.Node
escapeHTML bool
tags map[string]Tag
vars map[string]reflect.Value
macroMtx sync.Mutex
macros map[string][]ast.Node
}
// WithVarMap returns a copy of the template with its variable map set to m.
func (t *Template) WithVarMap(m map[string]any) *Template {
newTmpl := &Template{
ns: t.ns,
name: t.name,
ast: t.ast,
escapeHTML: t.escapeHTML,
tags: t.tags,
vars: map[string]reflect.Value{},
}
if m != nil {
for k, v := range m {
newTmpl.vars[k] = reflect.ValueOf(v)
}
}
return newTmpl
}
// WithTagMap returns a copy of the template with its tag map set to m.
func (t *Template) WithTagMap(m map[string]Tag) *Template {
// Make sure the tag map is never nil to avoid panics
if m == nil {
m = map[string]Tag{}
}
return &Template{
ns: t.ns,
name: t.name,
ast: t.ast,
escapeHTML: t.escapeHTML,
tags: m,
vars: t.vars,
}
}
// WithEscapeHTML returns a copy of the template with HTML escaping enabled or disabled.
// The HTML escaping functionality is NOT context-aware.
// Using the HTML type allows you to get around the escaping if needed.
func (t *Template) WithEscapeHTML(b bool) *Template {
t.escapeHTML = true
return &Template{
ns: t.ns,
name: t.name,
ast: t.ast,
escapeHTML: b,
tags: t.tags,
vars: t.vars,
}
}
// Execute executes a parsed template and writes
// the result to w.
func (t *Template) Execute(w io.Writer) error {
// Create a new template to give each execution
// its own macros
tmpl := &Template{
ns: t.ns,
name: t.name,
ast: t.ast,
escapeHTML: t.escapeHTML,
tags: t.tags,
vars: t.vars,
macros: map[string][]ast.Node{},
}
return tmpl.execute(w, t.ast, nil)
}
func (t *Template) execute(w io.Writer, nodes []ast.Node, local map[string]any) error {
for i := 0; i < len(nodes); i++ {
switch node := nodes[i].(type) {
case ast.Text:
_, err := w.Write(node.Data)
if err != nil {
return t.posError(node, "%w", err)
}
case ast.Tag:
newOffset, err := t.execTag(node, w, nodes, i, local)
if err != nil {
return err
}
i = newOffset
case ast.EndTag:
// We should never see an end tag here because it
// should be taken care of by execTag, so if we do,
// return an error because execTag was never called,
// which means there was no start tag.
return ErrEndTagWithoutStart
case ast.ExprTag:
v, err := t.getValue(node.Value, local)
if err != nil {
return err
}
_, err = io.WriteString(w, t.toString(v))
if err != nil {
return err
}
}
}
return nil
}
func (t *Template) toString(v any) string {
if h, ok := v.(HTML); ok {
return string(h)
} else if t.escapeHTML {
return html.EscapeString(fmt.Sprint(v))
}
return fmt.Sprint(v)
}
// getBlock gets all the nodes in the input, up to the end tag with the given name
func (t *Template) getBlock(nodes []ast.Node, offset, startLine int, name string) []ast.Node {
var out []ast.Node
tagAmount := 1
for i := offset; i < len(nodes); i++ {
switch node := nodes[i].(type) {
case ast.Tag:
// If we encounter another tag with the same name,
// increment tagAmount so that we know that the next
// end tag isn't the end of this tag.
if node.Name.Value == name {
tagAmount++
}
out = append(out, node)
case ast.EndTag:
if node.Name.Value == name {
tagAmount--
}
// Once tagAmount is zero (all the tags of the same name
// have been closed with an end tag), we can return
// the nodes we've accumulated.
if tagAmount == 0 {
return out
} else {
out = append(out, node)
}
default:
out = append(out, node)
}
}
return out
}
// getValue gets a Go value from an AST node
func (t *Template) getValue(node ast.Node, local map[string]any) (any, error) {
switch node := node.(type) {
case ast.Value:
return t.unwrapASTValue(node, local)
case ast.Ident:
val, err := t.getVar(node, local)
if err != nil {
return nil, err
}
return val.Interface(), nil
case ast.String:
return node.Value, nil
case ast.Float:
return node.Value, nil
case ast.Integer:
return node.Value, nil
case ast.Bool:
return node.Value, nil
case ast.Expr:
return t.evalExpr(node, local)
case ast.FuncCall:
return t.execFuncCall(node, local)
case ast.Index:
return t.getIndex(node, local)
case ast.FieldAccess:
return t.getField(node, local)
case ast.MethodCall:
return t.execMethodCall(node, local)
case ast.Ternary:
return t.evalTernary(node, local)
case ast.VariableOr:
return t.evalVariableOr(node, local)
default:
return nil, nil
}
}
// unwrapASTValue unwraps an ast.Value node into its underlying value
func (t *Template) unwrapASTValue(node ast.Value, local map[string]any) (any, error) {
v, err := t.getValue(node.Node, local)
if err != nil {
return nil, err
}
if node.Not {
rval := reflect.ValueOf(v)
if rval.Kind() != reflect.Bool {
return nil, ErrNotOperatorNonBool
}
return !rval.Bool(), nil
}
return v, err
}
// getVar tries to get a variable from the local map. If it's not found,
// it'll try the global variable map. If it doesn't exist in either map,
// it will return an error.
func (t *Template) getVar(id ast.Ident, local map[string]any) (reflect.Value, error) {
if local != nil {
v, ok := local[id.Value]
if ok {
return reflect.ValueOf(v), nil
}
}
v, ok := t.vars[id.Value]
if ok {
return v, nil
}
v, ok = t.ns.getVar(id.Value)
if ok {
return v, nil
}
v, ok = globalVars[id.Value]
if ok {
return v, nil
}
return reflect.Value{}, t.posError(id, "%w: %s", ErrNoSuchVar, id.Value)
}
func (t *Template) getTag(name string) (Tag, bool) {
tag, ok := t.tags[name]
if ok {
return tag, true
}
tag, ok = t.ns.getTag(name)
if ok {
return tag, true
}
tag, ok = globalTags[name]
if ok {
return tag, true
}
return nil, false
}
// execTag executes a tag
func (t *Template) execTag(node ast.Tag, w io.Writer, nodes []ast.Node, i int, local map[string]any) (newOffset int, err error) {
tag, ok := t.getTag(node.Name.Value)
if !ok {
return 0, t.posError(node, "%w: %s", ErrNoSuchTag, node.Name.Value)
}
var block []ast.Node
if node.HasBody {
block = t.getBlock(nodes, i+1, node.Position.Line, node.Name.Value)
i += len(block) + 1
}
tc := &TagContext{w, t, local}
err = tag.Run(tc, block, node.Params)
if err != nil {
return 0, err
}
return i, nil
}
// execFuncCall executes a function call
func (t *Template) execFuncCall(fc ast.FuncCall, local map[string]any) (any, error) {
fn, err := t.getVar(fc.Name, local)
if err != nil {
return nil, t.posError(fc, "%w: %s", ErrNoSuchFunc, fc.Name.Value)
}
return t.execFunc(fn, fc, fc.Params, local)
}
// getIndex tries to evaluate an ast.Index node by indexing the underlying value.
func (t *Template) getIndex(i ast.Index, local map[string]any) (any, error) {
val, err := t.getValue(i.Value, local)
if err != nil {
return nil, err
}
index, err := t.getValue(i.Index, local)
if err != nil {
return nil, err
}
rval := reflect.ValueOf(val)
rindex := reflect.ValueOf(index)
switch rval.Kind() {
case reflect.Slice, reflect.Array:
intType := reflect.TypeOf(0)
if rindex.CanConvert(intType) {
rindex = rindex.Convert(intType)
} else {
return nil, ErrIncorrectIndexType
}
intIndex := rindex.Interface().(int)
if intIndex < rval.Len() {
return rval.Index(intIndex).Interface(), nil
} else {
return nil, t.posError(i, "%w: %d", ErrIndexOutOfRange, intIndex)
}
case reflect.Map:
if rindex.CanConvert(rval.Type().Key()) {
rindex = rindex.Convert(rval.Type().Key())
} else {
return nil, t.posError(i, "%w: %T (expected %s)", ErrMapInvalidIndexType, index, rval.Type().Key())
}
if out := rval.MapIndex(rindex); out.IsValid() {
return out.Interface(), nil
} else {
return nil, t.posError(i, "%w: %q", ErrMapIndexNotFound, index)
}
}
return nil, nil
}
// getField tries to get a struct field from the underlying value
func (t *Template) getField(fa ast.FieldAccess, local map[string]any) (any, error) {
val, err := t.getValue(fa.Value, local)
if err != nil {
return nil, err
}
rval := reflect.ValueOf(val)
field := rval.FieldByName(fa.Name.Value)
if !field.IsValid() {
return nil, t.posError(fa, "%w: %s", ErrNoSuchField, fa.Name.Value)
}
return field.Interface(), nil
}
// execMethodCall executes a method call on the underlying value
func (t *Template) execMethodCall(mc ast.MethodCall, local map[string]any) (any, error) {
val, err := t.getValue(mc.Value, local)
if err != nil {
return nil, err
}
rval := reflect.ValueOf(val)
mtd := rval.MethodByName(mc.Name.Value)
if !mtd.IsValid() {
return nil, t.posError(mc, "%w: %s", ErrNoSuchMethod, mc.Name.Value)
}
return t.execFunc(mtd, mc, mc.Params, local)
}
// execFunc executes a function call
func (t *Template) execFunc(fn reflect.Value, node ast.Node, args []ast.Node, local map[string]any) (any, error) {
fnType := fn.Type()
if fnType.NumIn() != len(args) {
return nil, t.posError(node, "%w: %d (expected %d)", ErrParamNumMismatch, len(args), fnType.NumIn())
}
if err := validateFunc(fnType); err != nil {
return nil, t.posError(node, "%w", err)
}
params := make([]reflect.Value, fnType.NumIn())
for i, arg := range args {
paramVal, err := t.getValue(arg, local)
if err != nil {
return nil, err
}
params[i] = reflect.ValueOf(paramVal)
if params[i].CanConvert(fnType.In(i)) {
params[i] = params[i].Convert(fnType.In(i))
} else {
return nil, t.posError(node, "%w", ErrIncorrectParamType)
}
}
ret := fn.Call(params)
if len(ret) == 1 {
retv := ret[0].Interface()
if err, ok := retv.(error); ok {
return nil, err
}
return ret[0].Interface(), nil
} else {
return ret[0].Interface(), ret[1].Interface().(error)
}
}
func (t *Template) evalTernary(tr ast.Ternary, local map[string]any) (any, error) {
condVal, err := t.getValue(tr.Condition, local)
if err != nil {
return nil, t.posError(tr.Condition, "%w", ErrTernaryCondBool)
}
cond, ok := condVal.(bool)
if !ok {
return nil, errors.New("ternary condition must be a boolean")
}
if cond {
return t.getValue(tr.IfTrue, local)
} else {
return t.getValue(tr.Else, local)
}
}
func (t *Template) evalVariableOr(vo ast.VariableOr, local map[string]any) (any, error) {
val, err := t.getVar(vo.Variable, local)
if err != nil {
return t.getValue(vo.Or, local)
}
return val.Interface(), nil
}
func (t *Template) posError(n ast.Node, format string, v ...any) error {
return ast.PosError(n, t.name, format, v...)
}
func validateFunc(t reflect.Type) error {
numOut := t.NumOut()
if numOut > 2 {
return ErrFuncTooManyReturns
} else if numOut == 0 {
return ErrFuncNoReturns
}
if numOut == 2 {
if !t.Out(1).Implements(reflect.TypeOf(error(nil))) {
return ErrFuncSecondReturnType
}
}
return nil
}