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Damian Gryski
4fcf03414c
Go 1.27 promoted "generic methods" (methods with their own type
parameters, independent of any type parameters on the receiver) out
of the GenericMethods experiment, e.g.:
func (r *Rand) N[Int intType](n Int) Int
Boxing a value of a type with such a method into an interface caused
tinygo to panic while building the runtime type's method table:
getTypeCode -> getMethodSetValue -> getTypeCodeName
getTypeCodeName's type switch has no case for *types.TypeParam, and a
generic method's Signature carries the method's own type parameters
in its parameter/result types (e.g. "Int" above), so encoding it into
a type code name panicked with "unknown type: <param name>".
This affected any package using math/rand/v2.Rand.N, including much of
the math/rand/v2 test suite, since printing or otherwise boxing a
*Rand into an interface is common.
Upstream reflect deliberately excludes generic methods from
Type.NumMethod()/Type.Method() (they can't be instantiated implicitly,
and a generic method can never satisfy an interface method), so mirror
that behavior: add isGenericMethod, which checks whether a method's
Signature has its own type parameters, and skip such methods when
building the runtime method count, method set value, and method set
in compiler/interface.go.
Fixes a panic isolated to:
package main
type T struct{}
func (t T) M[X int](n X) X { return n }
func main() {
var t T
var i interface{} = t
_ = i
}