Improve our ability to override default parameters #11704
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(this is a blocker for #11671) |
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I think we want to go the other way: make default arguments inline (and hence final). Without that step we won't be able to get any of the other desired improvements of default arguments. So, is this change really necessary? |
It's necessary to get the scala.js tests to pass with #11671. This change improves compatibility with Scala 2 in general but does not change anything fundamentally, we already allow overrides for default parameters, this change just avoid seemingly arbitrary situations where this fails with a puzzling error message. So getting this change in won't have any impact on our future plans with default parameters. |
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Also, independent of overrides, this change is good because it avoids breaking unnecessary breaks to binary compatibility, right now: class A {
def foo(param: X = new Y): X = param
}will generate a default getter whose return type is |
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- Replace rhsType/widenRhs by typedAheadRhs/rhsType to avoid computing rhsProto twice - Rename rhsProto to defaultParamType and move the wildcard handling to rhsType (this will be useful in the next commit)
Don't just use the type of the rhs of the default getter as its inferred type, this can be more precise than the type of the corresponding parameter and prevent seemingly valid overrides.
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This is needed to compile geny in the community build which does:
def count(f: A => Boolean = ((_: Any) => true))
This happened to work before the previous commit because the inferred
type of the getter was `Any => Boolean`.
Crucially, we can only disable variance checking for default getters
whose result type matches the parameter type of the method, see
default-getter-variance.scala for a detailed justification of why this
is safe.
This fixes lets us get rid of an unjustified usage of
`@uncheckedVariance` when desugaring case classes.
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This is now green after fixing some community build issues. |
It looks like this bug got fixed in scala#11704!
It looks like this bug got fixed in scala#11704!
Don't just use the type of the rhs of the default getter as its inferred
type, this can be more precise than the type of the corresponding
parameter and prevent seemingly valid overrides.