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5b89670a31
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.
95 lines
2.3 KiB
Go
95 lines
2.3 KiB
Go
// 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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