Use a general Eval function for expressions in templates. (#23927)
One of the proposals in #23328 This PR introduces a simple expression calculator (templates/eval/eval.go), it can do basic expression calculations. Many untested template helper functions like `Mul` `Add` can be replaced by this new approach. Then these `Add` / `Mul` / `percentage` / `Subtract` / `DiffStatsWidth` could all use this `Eval`. And it provides enhancements for Golang templates, and improves readability. Some examples: ---- * Before: `{{Add (Mul $glyph.Row 12) 12}}` * After: `{{Eval $glyph.Row "*" 12 "+" 12}}` ---- * Before: `{{if lt (Add $i 1) (len $.Topics)}}` * After: `{{if Eval $i "+" 1 "<" (len $.Topics)}}` ## FAQ ### Why not use an existing expression package? We need a highly customized expression engine: * do the calculation on the fly, without pre-compiling * deal with int/int64/float64 types, to make the result could be used in Golang template. * make the syntax could be used in the Golang template directly * do not introduce too much complex or strange syntax, we just need a simple calculator. * it needs to strictly follow Golang template's behavior, for example, Golang template treats all non-zero values as truth, but many 3rd packages don't do so. ### What's the benefit? * Developers don't need to add more `Add`/`Mul`/`Sub`-like functions, they were getting more and more. Now, only one `Eval` is enough for all cases. * The new code reads better than old `{{Add (Mul $glyph.Row 12) 12}}`, the old one isn't familiar to most procedural programming developers (eg, the Golang expression syntax). * The `Eval` is fully covered by tests, many old `Add`/`Mul`-like functions were never tested. ### The performance? It doesn't use `reflect`, it doesn't need to parse or compile when used in Golang template, the performance is as fast as native Go template. ### Is it too complex? Could it be unstable? The expression calculator program is a common homework for computer science students, and it's widely used as a teaching and practicing purpose for developers. The algorithm is pretty well-known. The behavior can be clearly defined, it is stable.wip
wxiaoguang
GitHub
parent
ecf34fcd89
commit
5b89670a31
@ -0,0 +1,344 @@
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// Copyright 2023 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package eval
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import (
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"fmt"
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"strconv"
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"strings"
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"code.gitea.io/gitea/modules/util"
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)
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type Num struct {
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Value any // int64 or float64, nil on error
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}
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var opPrecedence = map[string]int{
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// "(": 1, this is for low precedence like function calls, they are handled separately
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"or": 2,
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"and": 3,
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"not": 4,
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"==": 5, "!=": 5, "<": 5, "<=": 5, ">": 5, ">=": 5,
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"+": 6, "-": 6,
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"*": 7, "/": 7,
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}
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type stack[T any] struct {
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name string
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elems []T
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}
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func (s *stack[T]) push(t T) {
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s.elems = append(s.elems, t)
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}
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func (s *stack[T]) pop() T {
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if len(s.elems) == 0 {
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panic(s.name + " stack is empty")
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}
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t := s.elems[len(s.elems)-1]
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s.elems = s.elems[:len(s.elems)-1]
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return t
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}
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func (s *stack[T]) peek() T {
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if len(s.elems) == 0 {
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panic(s.name + " stack is empty")
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}
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return s.elems[len(s.elems)-1]
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}
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type operator string
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type eval struct {
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stackNum stack[Num]
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stackOp stack[operator]
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funcMap map[string]func([]Num) Num
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}
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func newEval() *eval {
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e := &eval{}
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e.stackNum.name = "num"
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e.stackOp.name = "op"
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return e
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}
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func toNum(v any) (Num, error) {
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switch v := v.(type) {
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case string:
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if strings.Contains(v, ".") {
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n, err := strconv.ParseFloat(v, 64)
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if err != nil {
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return Num{n}, err
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}
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return Num{n}, nil
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}
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n, err := strconv.ParseInt(v, 10, 64)
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if err != nil {
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return Num{n}, err
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}
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return Num{n}, nil
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case float32, float64:
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n, _ := util.ToFloat64(v)
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return Num{n}, nil
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default:
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n, err := util.ToInt64(v)
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if err != nil {
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return Num{n}, err
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}
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return Num{n}, nil
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}
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}
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func truth(b bool) int64 {
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if b {
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return int64(1)
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}
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return int64(0)
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}
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func applyOp2Generic[T int64 | float64](op operator, n1, n2 T) Num {
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switch op {
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case "+":
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return Num{n1 + n2}
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case "-":
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return Num{n1 - n2}
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case "*":
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return Num{n1 * n2}
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case "/":
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return Num{n1 / n2}
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case "==":
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return Num{truth(n1 == n2)}
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case "!=":
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return Num{truth(n1 != n2)}
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case "<":
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return Num{truth(n1 < n2)}
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case "<=":
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return Num{truth(n1 <= n2)}
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case ">":
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return Num{truth(n1 > n2)}
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case ">=":
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return Num{truth(n1 >= n2)}
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case "and":
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t1, _ := util.ToFloat64(n1)
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t2, _ := util.ToFloat64(n2)
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return Num{truth(t1 != 0 && t2 != 0)}
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case "or":
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t1, _ := util.ToFloat64(n1)
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t2, _ := util.ToFloat64(n2)
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return Num{truth(t1 != 0 || t2 != 0)}
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}
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panic("unknown operator: " + string(op))
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}
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func applyOp2(op operator, n1, n2 Num) Num {
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float := false
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if _, ok := n1.Value.(float64); ok {
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float = true
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} else if _, ok = n2.Value.(float64); ok {
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float = true
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}
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if float {
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f1, _ := util.ToFloat64(n1.Value)
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f2, _ := util.ToFloat64(n2.Value)
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return applyOp2Generic(op, f1, f2)
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}
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return applyOp2Generic(op, n1.Value.(int64), n2.Value.(int64))
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}
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func toOp(v any) (operator, error) {
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if v, ok := v.(string); ok {
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return operator(v), nil
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}
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return "", fmt.Errorf(`unsupported token type "%T"`, v)
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}
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func (op operator) hasOpenBracket() bool {
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return strings.HasSuffix(string(op), "(") // it's used to support functions like "sum("
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}
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func (op operator) isComma() bool {
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return op == ","
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}
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func (op operator) isCloseBracket() bool {
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return op == ")"
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}
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type ExprError struct {
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msg string
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tokens []any
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err error
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}
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func (err ExprError) Error() string {
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sb := strings.Builder{}
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sb.WriteString(err.msg)
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sb.WriteString(" [ ")
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for _, token := range err.tokens {
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_, _ = fmt.Fprintf(&sb, `"%v" `, token)
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}
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sb.WriteString("]")
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if err.err != nil {
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sb.WriteString(": ")
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sb.WriteString(err.err.Error())
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}
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return sb.String()
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}
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func (err ExprError) Unwrap() error {
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return err.err
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}
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func (e *eval) applyOp() {
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op := e.stackOp.pop()
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if op == "not" {
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num := e.stackNum.pop()
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i, _ := util.ToInt64(num.Value)
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e.stackNum.push(Num{truth(i == 0)})
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} else if op.hasOpenBracket() || op.isCloseBracket() || op.isComma() {
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panic(fmt.Sprintf("incomplete sub-expression with operator %q", op))
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} else {
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num2 := e.stackNum.pop()
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num1 := e.stackNum.pop()
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e.stackNum.push(applyOp2(op, num1, num2))
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}
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}
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func (e *eval) exec(tokens ...any) (ret Num, err error) {
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defer func() {
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if r := recover(); r != nil {
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rErr, ok := r.(error)
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if !ok {
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rErr = fmt.Errorf("%v", r)
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}
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err = ExprError{"invalid expression", tokens, rErr}
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}
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}()
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for _, token := range tokens {
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n, err := toNum(token)
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if err == nil {
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e.stackNum.push(n)
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continue
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}
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op, err := toOp(token)
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if err != nil {
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return Num{}, ExprError{"invalid expression", tokens, err}
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}
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switch {
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case op.hasOpenBracket():
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e.stackOp.push(op)
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case op.isCloseBracket(), op.isComma():
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var stackTopOp operator
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for len(e.stackOp.elems) > 0 {
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stackTopOp = e.stackOp.peek()
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if stackTopOp.hasOpenBracket() || stackTopOp.isComma() {
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break
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}
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e.applyOp()
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}
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if op.isCloseBracket() {
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nums := []Num{e.stackNum.pop()}
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for !e.stackOp.peek().hasOpenBracket() {
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stackTopOp = e.stackOp.pop()
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if !stackTopOp.isComma() {
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return Num{}, ExprError{"bracket doesn't match", tokens, nil}
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}
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nums = append(nums, e.stackNum.pop())
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}
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for i, j := 0, len(nums)-1; i < j; i, j = i+1, j-1 {
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nums[i], nums[j] = nums[j], nums[i] // reverse nums slice, to get the right order for arguments
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}
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stackTopOp = e.stackOp.pop()
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fn := string(stackTopOp[:len(stackTopOp)-1])
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if fn == "" {
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if len(nums) != 1 {
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return Num{}, ExprError{"too many values in one bracket", tokens, nil}
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}
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e.stackNum.push(nums[0])
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} else if f, ok := e.funcMap[fn]; ok {
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e.stackNum.push(f(nums))
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} else {
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return Num{}, ExprError{"unknown function: " + fn, tokens, nil}
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}
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} else {
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e.stackOp.push(op)
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}
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default:
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for len(e.stackOp.elems) > 0 && len(e.stackNum.elems) > 0 {
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stackTopOp := e.stackOp.peek()
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if stackTopOp.hasOpenBracket() || stackTopOp.isComma() || precedence(stackTopOp, op) < 0 {
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break
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}
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e.applyOp()
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}
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e.stackOp.push(op)
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}
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}
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for len(e.stackOp.elems) > 0 && !e.stackOp.peek().isComma() {
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e.applyOp()
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}
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if len(e.stackNum.elems) != 1 {
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return Num{}, ExprError{fmt.Sprintf("expect 1 value as final result, but there are %d", len(e.stackNum.elems)), tokens, nil}
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}
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return e.stackNum.pop(), nil
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}
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func precedence(op1, op2 operator) int {
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p1 := opPrecedence[string(op1)]
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p2 := opPrecedence[string(op2)]
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if p1 == 0 {
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panic("unknown operator precedence: " + string(op1))
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} else if p2 == 0 {
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panic("unknown operator precedence: " + string(op2))
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}
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return p1 - p2
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}
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func castFloat64(nums []Num) bool {
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hasFloat := false
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for _, num := range nums {
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if _, hasFloat = num.Value.(float64); hasFloat {
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break
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}
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}
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if hasFloat {
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for i, num := range nums {
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if _, ok := num.Value.(float64); !ok {
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f, _ := util.ToFloat64(num.Value)
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nums[i] = Num{f}
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}
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}
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}
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return hasFloat
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}
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func fnSum(nums []Num) Num {
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if castFloat64(nums) {
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var sum float64
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for _, num := range nums {
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sum += num.Value.(float64)
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}
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return Num{sum}
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}
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var sum int64
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for _, num := range nums {
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sum += num.Value.(int64)
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}
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return Num{sum}
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}
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// Expr evaluates the given expression tokens and returns the result.
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// It supports the following operators: +, -, *, /, and, or, not, ==, !=, >, >=, <, <=.
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// Non-zero values are treated as true, zero values are treated as false.
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// If no error occurs, the result is either an int64 or a float64.
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// If all numbers are integer, the result is an int64, otherwise if there is any float number, the result is a float64.
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func Expr(tokens ...any) (Num, error) {
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e := newEval()
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e.funcMap = map[string]func([]Num) Num{"sum": fnSum}
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return e.exec(tokens...)
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}
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@ -0,0 +1,94 @@
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// Copyright 2023 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package eval
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import (
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"math"
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"strings"
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"testing"
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"github.com/stretchr/testify/assert"
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)
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func tokens(s string) (a []any) {
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for _, v := range strings.Fields(s) {
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a = append(a, v)
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}
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return a
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}
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func TestEval(t *testing.T) {
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n, err := Expr(0, "/", 0.0)
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assert.NoError(t, err)
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assert.True(t, math.IsNaN(n.Value.(float64)))
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_, err = Expr(nil)
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assert.ErrorContains(t, err, "unsupported token type")
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_, err = Expr([]string{})
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assert.ErrorContains(t, err, "unsupported token type")
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_, err = Expr(struct{}{})
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assert.ErrorContains(t, err, "unsupported token type")
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cases := []struct {
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expr string
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want any
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}{
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{"-1", int64(-1)},
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{"1 + 2", int64(3)},
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{"3 - 2 + 4", int64(5)},
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{"1 + 2 * 3", int64(7)},
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{"1 + ( 2 * 3 )", int64(7)},
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{"( 1 + 2 ) * 3", int64(9)},
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{"( 1 + 2.0 ) / 3", float64(1)},
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{"sum( 1 , 2 , 3 , 4 )", int64(10)},
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{"100 + sum( 1 , 2 + 3 , 0.0 ) / 2", float64(103)},
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{"100 * 5 / ( 5 + 15 )", int64(25)},
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{"9 == 5", int64(0)},
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{"5 == 5", int64(1)},
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{"9 != 5", int64(1)},
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{"5 != 5", int64(0)},
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{"9 > 5", int64(1)},
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{"5 > 9", int64(0)},
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{"5 >= 9", int64(0)},
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{"9 >= 9", int64(1)},
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{"9 < 5", int64(0)},
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{"5 < 9", int64(1)},
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{"9 <= 5", int64(0)},
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{"5 <= 5", int64(1)},
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{"1 and 2", int64(1)}, // Golang template definition: non-zero values are all truth
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{"1 and 0", int64(0)},
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{"0 and 0", int64(0)},
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{"1 or 2", int64(1)},
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{"1 or 0", int64(1)},
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{"0 or 1", int64(1)},
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{"0 or 0", int64(0)},
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{"not 2 == 1", int64(1)},
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{"not not ( 9 < 5 )", int64(0)},
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}
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for _, c := range cases {
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n, err := Expr(tokens(c.expr)...)
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if assert.NoError(t, err, "expr: %s", c.expr) {
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assert.Equal(t, c.want, n.Value)
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}
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}
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bads := []struct {
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expr string
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errMsg string
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}{
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{"0 / 0", "integer divide by zero"},
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{"1 +", "num stack is empty"},
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{"+ 1", "num stack is empty"},
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{"( 1", "incomplete sub-expression"},
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{"1 )", "op stack is empty"}, // can not find the corresponding open bracket after the stack becomes empty
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{"1 , 2", "expect 1 value as final result"},
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{"( 1 , 2 )", "too many values in one bracket"},
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{"1 a 2", "unknown operator"},
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}
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for _, c := range bads {
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_, err = Expr(tokens(c.expr)...)
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assert.ErrorContains(t, err, c.errMsg, "expr: %s", c.expr)
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}
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}
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@ -1,4 +1,4 @@
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{{Add .file.Addition .file.Deletion}}
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<span class="diff-stats-bar gt-mx-3" data-tooltip-content="{{.root.locale.Tr "repo.diff.stats_desc_file" (Add .file.Addition .file.Deletion) .file.Addition .file.Deletion | Str2html}}">
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{{Eval .file.Addition "+" .file.Deletion}}
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<span class="diff-stats-bar gt-mx-3" data-tooltip-content="{{.root.locale.Tr "repo.diff.stats_desc_file" (Eval .file.Addition "+" .file.Deletion) .file.Addition .file.Deletion | Str2html}}">
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<div class="diff-stats-add-bar" style="width: {{DiffStatsWidth .file.Addition .file.Deletion}}%"></div>
|
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</span>
|
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Reference in New Issue