compiler: fix interface calls for big underlying values

When the underlying value of an interface does not fit in a pointer, a
pointer to the value was correctly inserted in the heap. However, the
receiving method still assumed it got the underlying value instead of a
pointer to it leading to a crash.

This commit inserts wrapper functions for method calls on interfaces.

The bug wasn't obvious as on a 64-bit system, the underlying value was
almost always put directly in the interface. However, it led to a crash
on the AVR platform where pointer are (usually) just 16 bits making it
far more likely that underlying values cannot be directly stored in an
interface.

1 files changed, 87 insertions, 0 deletions

diff --git a/testdata/interface.go b/testdata/interface.go
new file mode 100644
index 000000000..f24a995fa
--- /dev/null
+++ b/testdata/interface.go
@@ -0,0 +1,87 @@
+package main
+
+func main() {
+	thing := &Thing{"foo"}
+	println("thing:", thing.String())
+	thing.Print()
+	printItf(5)
+	printItf(byte('x'))
+	printItf("foo")
+	printItf(*thing)
+	printItf(thing)
+	printItf(Stringer(thing))
+	printItf(Number(3))
+	array := Array([4]uint32{1, 7, 11, 13})
+	printItf(array)
+	s := Stringer(thing)
+	println("Stringer.String():", s.String())
+	var itf interface{} = s
+	println("Stringer.(*Thing).String():", itf.(Stringer).String())
+}
+
+func printItf(val interface{}) {
+	switch val := val.(type) {
+	case Doubler:
+		println("is Doubler:", val.Double())
+	case Tuple:
+		println("is Tuple:", val.Nth(0), val.Nth(1), val.Nth(2), val.Nth(3))
+		val.Print()
+	case int:
+		println("is int:", val)
+	case byte:
+		println("is byte:", val)
+	case string:
+		println("is string:", val)
+	case Thing:
+		println("is Thing:", val.String())
+	case *Thing:
+		println("is *Thing:", val.String())
+	case Foo:
+		println("is Foo:", val)
+	default:
+		println("is ?")
+	}
+}
+
+type Thing struct {
+	name string
+}
+
+func (t Thing) String() string {
+	return t.name
+}
+
+func (t Thing) Print() {
+	println("Thing.Print:", t.name)
+}
+
+type Stringer interface {
+	String() string
+}
+
+type Foo int
+
+type Number int
+
+func (n Number) Double() int {
+	return int(n) * 2
+}
+
+type Doubler interface {
+	Double() int
+}
+
+type Tuple interface {
+	Nth(int) uint32
+	Print()
+}
+
+type Array [4]uint32
+
+func (a Array) Nth(n int) uint32 {
+	return a[n]
+}
+
+func (a Array) Print() {
+	println("Array len:", len(a))
+}