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mirror of https://github.com/go-gitea/gitea.git synced 2024-12-23 09:44:33 +01:00
gitea/modules/templates/eval/eval_test.go
wxiaoguang 5b89670a31
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.
2023-04-07 21:25:49 +08:00

95 lines
2.3 KiB
Go

// Copyright 2023 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT
package eval
import (
"math"
"strings"
"testing"
"github.com/stretchr/testify/assert"
)
func tokens(s string) (a []any) {
for _, v := range strings.Fields(s) {
a = append(a, v)
}
return a
}
func TestEval(t *testing.T) {
n, err := Expr(0, "/", 0.0)
assert.NoError(t, err)
assert.True(t, math.IsNaN(n.Value.(float64)))
_, err = Expr(nil)
assert.ErrorContains(t, err, "unsupported token type")
_, err = Expr([]string{})
assert.ErrorContains(t, err, "unsupported token type")
_, err = Expr(struct{}{})
assert.ErrorContains(t, err, "unsupported token type")
cases := []struct {
expr string
want any
}{
{"-1", int64(-1)},
{"1 + 2", int64(3)},
{"3 - 2 + 4", int64(5)},
{"1 + 2 * 3", int64(7)},
{"1 + ( 2 * 3 )", int64(7)},
{"( 1 + 2 ) * 3", int64(9)},
{"( 1 + 2.0 ) / 3", float64(1)},
{"sum( 1 , 2 , 3 , 4 )", int64(10)},
{"100 + sum( 1 , 2 + 3 , 0.0 ) / 2", float64(103)},
{"100 * 5 / ( 5 + 15 )", int64(25)},
{"9 == 5", int64(0)},
{"5 == 5", int64(1)},
{"9 != 5", int64(1)},
{"5 != 5", int64(0)},
{"9 > 5", int64(1)},
{"5 > 9", int64(0)},
{"5 >= 9", int64(0)},
{"9 >= 9", int64(1)},
{"9 < 5", int64(0)},
{"5 < 9", int64(1)},
{"9 <= 5", int64(0)},
{"5 <= 5", int64(1)},
{"1 and 2", int64(1)}, // Golang template definition: non-zero values are all truth
{"1 and 0", int64(0)},
{"0 and 0", int64(0)},
{"1 or 2", int64(1)},
{"1 or 0", int64(1)},
{"0 or 1", int64(1)},
{"0 or 0", int64(0)},
{"not 2 == 1", int64(1)},
{"not not ( 9 < 5 )", int64(0)},
}
for _, c := range cases {
n, err := Expr(tokens(c.expr)...)
if assert.NoError(t, err, "expr: %s", c.expr) {
assert.Equal(t, c.want, n.Value)
}
}
bads := []struct {
expr string
errMsg string
}{
{"0 / 0", "integer divide by zero"},
{"1 +", "num stack is empty"},
{"+ 1", "num stack is empty"},
{"( 1", "incomplete sub-expression"},
{"1 )", "op stack is empty"}, // can not find the corresponding open bracket after the stack becomes empty
{"1 , 2", "expect 1 value as final result"},
{"( 1 , 2 )", "too many values in one bracket"},
{"1 a 2", "unknown operator"},
}
for _, c := range bads {
_, err = Expr(tokens(c.expr)...)
assert.ErrorContains(t, err, c.errMsg, "expr: %s", c.expr)
}
}