incorrect dispatch with invoke on methods with default arguments

[skariel]

see image below, this works correctly if no keyword arguments are used. This is causing the current test failures of #9575

[simonster]

This makes some sort of sense based on the implementation of default arguments. f(i::Number, o::Int64=1) = println("Number") is eventually lowered to:

f(i::Number, o::Int64) = println("Number")
f(i::Number) = f(i, 1)

which is why f above has 4 methods, not 2. So invoke calls f(::Number), but then f(::Number) dispatches to f(::Int64, ::Int64) instead of f(::Number, ::Int64). I think there has been some discussion of this in another issue but I can't find it. We could potentially lower to:

f(i::Number, o::Int64) = println("Number")
f(i::Number) = invoke(f, (Number, Int64), i)

although we'd need #9642 for this to perform well, and it would be a breaking change, since a different method would be called for:

f(i::Int64, o::Int64) = println("Int64")
f(i::Number, o::Int64=1) = println("Number")
f(1)

For #9575 it seems like the tests that use invoke could be changed to pass the default arguments so that the appropriate method gets dispatched.

[vtjnash]

i believe @simonster's solution is correct. might need to search back through the issues to make sure there wasn't specific concerns with it. i think the previous concern was that it would change the behavior of:

f(x::Int, y::String=2) = 1
f(x::Int, y) = 2

which is valid under the current rules (where f(1) would return 1)

[skariel]

@simonster good point, I changed the test it works now.

[JeffBezanson]

More or less a duplicate of #7357. In that issue the solution of lowering default arguments to use invoke is mentioned.

[JeffBezanson]

Closing as dup.