Panic when using pointer-type map as environment #825
Description
📝Bug Description
The conf.Env() function panics when passed a pointer to a map (e.g., *map[string]any ) instead of a direct map value.
However, from the code perspective, the pointer type is intended to be supported.
// file: conf/env.go
// line: 25
...
v := reflect.ValueOf(env)
d := deref.Value(v)
...
// file: internal/deref/deref.go
// line: 39
func Value(v reflect.Value) reflect.Value {
for v.Kind() == reflect.Ptr || v.Kind() == reflect.Interface {
if v.IsNil() {
return v
}
v = v.Elem()
}
return v
}🌍 Environment
- expr version : Latest (master branch)
- Go version : 1.24
- OS : All platforms
🔄 Steps to Reproduce
package main
import (
"github.com/expr-lang/expr"
)
func main() {
m := map[string]any{"foo": 42}
env := &m
_, err := expr.Compile("foo > 0", expr.Env(env))
if err != nil {
panic(err)
}
}✅ Expected Behavior
The function should handle pointer-to-map types gracefully by properly dereferencing the pointer before performing map operations. 🎯
❌ Actual Behavior
panic: reflect: call of reflect.Value.Len on ptr to non-array Value
goroutine 1 [running]:
reflect.Value.lenNonSlice({0x1011f8ca0?, 0x140000a4378?, 0x1400009c998?})
/usr/local/go/src/reflect/value.go:1780 +0x220
reflect.Value.Len(...)
/usr/local/go/src/reflect/value.go:1761
github.com/expr-lang/expr/conf.Env({0x1011f8ca0, 0x140000a4378})
/Users/bytedance/go/pkg/mod/github.com/expr-lang/expr@v1.17.6/conf/env.go:38 +0x208
github.com/expr-lang/expr/conf.(*Config).WithEnv(0x140000de000, {0x1011f8ca0?, 0x140000a4378?})
/Users/bytedance/go/pkg/mod/github.com/expr-lang/expr@v1.17.6/conf/config.go:64 +0x58
main.main.Env.func1(0x101219660?)
/Users/bytedance/go/pkg/mod/github.com/expr-lang/expr@v1.17.6/expr.go:31 +0x24
github.com/expr-lang/expr.Compile({0x101187670, 0x7}, {0x1400009cf08, 0x1, 0x1400005c738?})
/Users/bytedance/go/pkg/mod/github.com/expr-lang/expr@v1.17.6/expr.go:211 +0x17c
main.main()
/Users/bytedance/projects/go/rule/main.go:12 +0xc8
exit status 2
🔍 Root Cause Analysis
In conf/env.go , lines 38-43, the code uses:
- v.Len() ❌ fails on pointer types
- v.MapKeys() ❌ fails on pointer types
- v.MapIndex(key) ❌ fails on pointer types
The fix is to use the dereferenced value d (from deref.Value(v) ) for these operations. 💡
I have a working implementation ready that addresses this issue. Would you like me to submit a PR for this fix?