reflect.SliceHeader expects incorrect field types

[bjatkin]

The following code does not compile correctly when using the tinygo compiler

package main

import (
	"fmt"
	"reflect"
	"unsafe"
)

func main() {
	a := []int{0, 1, 2, 3, 4}
	b := reflect.SliceHeader{
		Data: uintptr(unsafe.Pointer(&a[0])),

		Len: len(a),
		Cap: len(a),
	}

	fmt.Println(b)
}

when running tinygo run . I get the following output

main.go:14:8: cannot use len(a) (value of type int) as uintptr value in struct literal
main.go:15:8: cannot use len(a) (value of type int) as uintptr value in struct literal

surprisingly however, when I change the types of the Len and Cap fields to uintptrs, the code complies successfully and runs correctly.

func main() {
	a := []int{0, 1, 2, 3, 4}
	b := reflect.SliceHeader{
		Data: uintptr(unsafe.Pointer(&a[0])),

		Len: uintptr(len(a)),
		Cap: uintptr(len(a)),
	}

	fmt.Println(b)
}

This new code however, will not compile when using the go compiler as the SliceHeader type expects ints for it's length and capacity.

runninggo run . with this version of the code results in the following error

./main.go:14:8: cannot use uintptr(len(a)) (value of type uintptr) as type int in struct literal
./main.go:15:8: cannot use uintptr(len(a)) (value of type uintptr) as type int in struct literal

I believe the behavior of the go compiler is correct here and the tinygo compiler should be updated to expect int values for the Len and Cap fields in the reflect.SliceHeader type.

I'm using tinygo version 0.26.0

tinygo version 0.26.0 linux/amd64 (using go version go1.19 and LLVM version 14.0.0)

[dgryski]

Yes. Please see #1284 .

[bjatkin]

I appreciate the context. I will port my code to instead use the new unsafe.Slice() function introduced in 1.17