TinyGo Panics on Nil Pointer Dereference in Map Lookup, Unlike Standard Go

[Yeaseen]

TinyGo incorrectly panics on a nil pointer dereference when accessing a struct field from a map lookup, while standard Go handles the same code without errors. This inconsistency suggests that TinyGo does not optimize nil pointer access in maps the same way as the Go compiler does.

$ cat test.go
package main
import "fmt"
type thing struct {
        field int
}
func main() {
        m := map[string]*thing{}
        t, ok := m["abc"]
        valid := t.field >= 0

        if !ok || !valid {
                fmt.Printf("got: %v\n", t)
                t = &thing{field: 0}
                m["abc"] = t
        }

        t.field += 3
        fmt.Println(t.field)
}

$ go version
go version go1.24.1 linux/amd64

$ go run test.go
got: <nil>
3

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

$ tinygo run test.go
panic: runtime error at 0x000000000021261d: nil pointer dereference
[tinygo: panic at /usr/local/lib/tinygo/src/runtime/scheduler_cooperative.go]
failed to run compiled binary /tmp/tinygo4289749700/main: signal: aborted

[aykevl]

Actually the panic looks correct to me: t is nil so t.field is a nil pointer dereference.
Might be another bug in the Go compiler?

[aykevl]

Here you go: golang/go#72918
Pretty sure this is actually a bug in the Go compiler.

...how do you find these edge cases? This is the second one in a short time.

[aykevl]

Ok, this is indeed a bug in the Go compiler. Not a TinyGo bug.

The reproducer is very similar to golang/go#72860. I guess it originated from the same source?

[Yeaseen]

@aykevl Yeah. I believe so. I just found the discrepancy in the outputs between tinygo and go.