imprecise inference of underlying method called by kwfunc method causes unnecessary allocation

[jrevels]

Feel free to close if this is a dupe, but I really like this because of how tiny the MWE is:

julia> versioninfo()
Julia Version 1.1.0-DEV.843
Commit a0bc8fdb75 (2018-12-08 18:35 UTC)
Platform Info:
  OS: macOS (x86_64-apple-darwin17.5.0)
  CPU: Intel(R) Core(TM) i7-7920HQ CPU @ 3.10GHz
  WORD_SIZE: 64
  LIBM: libopenlibm
  LLVM: libLLVM-6.0.1 (ORCJIT, skylake)

julia> @noinline f(a, b; c::Bool=true, d::Float64=1.0) = a * b + c * d
f (generic function with 1 method)

julia> x, y = rand(2);

julia> f(x, y) # warmup
1.0256215120847518

julia> @allocated f(x, y) # sad allocation :(
64

julia> @code_typed f(x, y) # _1 is only inferred as Function, I'm assuming that makes codegen sad
CodeInfo(
1 ─ %1 = invoke Main.:(#f#3)(true::Bool, 1.0::Float64, _1::Function, _2::Float64, _3::Float64)::Float64
└──      return %1
) => Float64