nix-prefetch-git: respect NETRC

This script needs to support being run both as part of a `fetchgit`
derivation and as a standalone, command-line tool.

The use of `$NIX_BUILD_TOP` only works when used in `fetchgit` but not when
invoked as a standalone tool. Instead we try to respect `$NETRC` so that
the command-line invocation behaves more like standard tools and the
`fetchgit` derivation can explicitly set `$NETRC` when `netrcPhase` is used
to avoid all ambiguity.

pkgs/build-support/fetchgit/default.nix

@@ -90,6 +90,7 @@ stdenvNoCC.mkDerivation {
     ${netrcPhase}
     # required that git uses the netrc file
     mv {,.}netrc
+    export NETRC=$PWD/.netrc
     export HOME=$PWD
   '';
 

pkgs/build-support/fetchgit/nix-prefetch-git

@@ -425,8 +425,8 @@ fi
 
 tmpHomePath="$(mktemp -d "${TMPDIR:-/tmp}/nix-prefetch-git-tmp-home-XXXXXXXXXX")"
 exit_handlers+=(remove_tmpHomePath)
+ln -s "${NETRC:-$HOME/.netrc}" "$tmpHomePath/.netrc"
 HOME="$tmpHomePath"
-ln -s "$NIX_BUILD_TOP/.netrc" "$HOME/"
 unset XDG_CONFIG_HOME
 export GIT_CONFIG_NOSYSTEM=1