Reproduction of nix evaluation failure

fine.nix

let
  system = "aarch64-darwin";
in
{
  foo.foo = "foo";
  foo.bar = "bar";
}

repro-first.nix

let
  system = "aarch64-darwin";
in
{
  ${system}.foo = "foo";
  ${system}.bar = "bar";
}

repro-second.nix

let
  system = "aarch64-darwin";
in
{
  foo.${system}.foo = "foo";
  foo.${system}.bar = "bar";
}

repro.sh

#!/bin/sh

for file in repro-first.nix repro-second.nix fine.nix; do
  echo "nix eval --file $file --json | jq"
  nix eval --file $file --json | jq
done