mvn2nix VS haskell-te

My problem is, that to install java-debug, I need to clone its repository and run ./mvnw clean install in the cloned repo. But this does not work, because 1. when writing a flake to install it using stdenv.mkderivation and maven as a buildDepend, I have no internet and ./mvnw clean install fails. 2. using mvn2nix's nix run github:fzakaria/mvn2nix#mvn2nix results in a Failed to execute goals [[package]]. Exit code: 1.

You won't be replacing Ant or Ivy, your nix derivations will use them to build your software. I couldn't find an ivy2nix project, but I think Ivy uses Maven underneath, so you could look at https://github.com/fzakaria/mvn2nix to get some ideas.

Yes, to get Nixpkgs it's much faster to use `fetchTarball`.

You're right that `builtins.fetchTarball` is faster than `builtins.fetchGit` (due to the ridiculous amount of commits in the Nixpkgs repo). I like to keep such definitions in a single, company-wide/project-agnostic git repo (what the Nix Pills series calls the "repository pattern"), and have individual projects import them via `builtins.fetchGit`.

Many years ago we didn't have `builtins.fetchGit`, so had to use the 'fetchgit' function from Nixpkgs instead. That created a chicken-and-egg situation if we wanted to take the Nixpkgs version from some other git repo; hence needing to "bootstrap" via `(import { config = {}; }).fetchgit`, and cross our fingers that `NIX_PATH` wasn't set to some crazy value (which, of course, I would inevitably do... https://github.com/Warbo/haskell-te/blob/24475a229908caa3447... )

Note that we need `config = {};` when importing Nixpkgs to avoid an impurity which tries to read files in $HOME. More recent versions of Nixpkgs also need `overlays = [];` to avoid another impurity (looks like this changed at Nixpkgs 17.03, according to https://github.com/Warbo/nix-helpers/blob/master/nixpkgs.nix )