LuaLaTeX Problem with Greek language

Question

I'm trying to typeset this code with LuaLaTeX:

\documentclass{article}
\usepackage[greek]{babel}
\usepackage{fontspec}
\setmainfont[Ligatures=TeX]{Gentium Plus}
\parindent=0pt
\begin{document}
Α α Α α
Β β  Β β
Γ γ  Γ γ
Δ δ  Δ δ
Ε ε  Ε ε
Ζ ζ  Ζ ζ
Η η  Η η
Θ θ  Θ θ
Ι ι  Ι ι
Κ κ  Κ κ
Λ λ  Λ λ
Μ μ  Μ μ
Ν ν  Ν ν
Ξ ξ  Ξ ξ
Ο ο  Ο ο
Π π  Π π
Ρ ρ  Ρ ρ
Σ σ  Σ σ
Τ τ  Τ τ
Υ υ  Υ υ
Φ φ  Φ φ
Χ χ  Χ χ
Ψ ψ  Ψ ψ
Ω ω  Ω ω
\end{document}

However, I get this warning:

LaTeX Font Warning: Some font shapes were not available, defaults substituted.

and an empty page (except for the page number at the bottom). (I'm using Gentium Plus here, but other fonts I've tested give me the same error.)

If I comment out the second line from above (\usepackage[greek]{babel}) everything works fine.

Any ideas on what's going on here?

(I'm using LuaTeX, Version 0.95.0 (TeX Live 2016) on MacTeX 2016.)

Answer 1

It works fine if you load fontspec before babel. The greek module checks the active font encoding.

\documentclass{article}
\usepackage{fontspec}
\usepackage[greek]{babel}

\setmainfont[Ligatures=TeX]{Gentium Plus}
\parindent=0pt
\begin{document}
Α α Α α
Β β  Β β
Γ γ  Γ γ
Δ δ  Δ δ
Ε ε  Ε ε
Ζ ζ  Ζ ζ
Η η  Η η
Θ θ  Θ θ
Ι ι  Ι ι
Κ κ  Κ κ
Λ λ  Λ λ
Μ μ  Μ μ
Ν ν  Ν ν
Ξ ξ  Ξ ξ
Ο ο  Ο ο
Π π  Π π
Ρ ρ  Ρ ρ
Σ σ  Σ σ
Τ τ  Τ τ
Υ υ  Υ υ
Φ φ  Φ φ
Χ χ  Χ χ
Ψ ψ  Ψ ψ
Ω ω  Ω ω
\end{document}