Inconsistent Behavior with len on Nil Array Pointer in tinygo

[Yeaseen]

The len function behaves inconsistently when applied to a nil array pointer in TinyGo compared to standard Go. While Go 1.24.1 returns the array length without a panic, TinyGo produces a runtime error when dereferencing a nil array pointer.

$ cat test.go
package main
func nilPtrToArray() *[2]byte {
        println("Some Activity")
        return nil
}
func main() {
        println(len(*nilPtrToArray()))

$ go version
go version go1.24.1 linux/amd64

$ go run test.go
Some Activity
2

$ tinygo run test.go
Some Activity
panic: runtime error at 0x0000000000203697: nil pointer dereference
[tinygo: panic at test.go:7:14]
failed to run compiled binary /tmp/tinygo782597653/main: signal: aborted

$ tinygo version
tinygo version 0.36.0 linux/amd64 (using go version go1.24.1 and LLVM version 19.1.2)

Expected Behavior

In Go, len(*nilPtrToArray()) should not result in a panic. Instead, it should return the length of the array type (in this case, 2), as the len function in Go does not evaluate the contents of the array but rather its static length. tinygo should replicate this behavior to maintain compatibility.

Analysis

The discrepancy likely stems from how tinygo handles nil pointer dereferencing in combination with len. In standard Go, dereferencing a nil pointer to an array solely for evaluating its length does not trigger a runtime error. tinygo, however, appears to strictly enforce pointer validity, leading to a nil pointer dereference panic.

[Yeaseen]

I think cap function also shows the same discrepancy.

func main() {
	println(cap(*nilPtrToArray()))
}

[aykevl]

I can confirm this issue.

[aykevl]

Looks like this is actually a bug in the golang.org/x/tools/go/ssa package. I'll see whether I can create a reproducer for the Go team.

[aykevl]

Reported the issue upstream: golang/go#72844

[Yeaseen]

@aykevl It looks like a Go compiler bug! Thank you for submitting the issue on upstream.