cmd/compile: incorrect program produces "invalid syntax tree" error

[griesemer]

package main

func main() {
	var value = new(Demo)
	UseFunc[value.(type)]()
}

type Demo struct{}

func UseFunc[T any]() {}

produces 3 errors:

./prog.go:4:6: value declared and not used
./prog.go:5:10: value.(type) is not a type
./prog.go:5:10: invalid syntax tree: use of .(type) outside type switch

Only the 2nd error should be presented.

From #58608.

[gopherbot]

Change https://go.dev/cl/470015 mentions this issue: go/types, types2: avoid unused variable error in invalid x.(type) expression

[griesemer]

The above CL reduces the number of follow-on errors to 1 (for 2 errors total). Good enough for now. Marking as backlog.