Docs falsely state that `lazy-trees` are enabled by default

[erikarvstedt]

Docs:

Lazy trees are currently stable in Determinate Nix and enabled by default for all users.

But lazy-trees is disabled by default in the current version (3.15.2).
Also, github:DeterminateSystems/determinate#nixosModules.default doesn't enable lazy-trees in nix.conf.

To check that lazy-trees is off by default, ensure that nix.conf doesn't enable it and then run:

# Create tmp flake
mkdir -p /tmp/tmpflake
echo '{ outputs = _: { lib.a = "a"; }; }' > /tmp/tmpflake/flake.nix
touch /tmp/tmpflake/mydummyfile.tmp
(cd /tmp/tmpflake && git init && git add . && git commit -m init)

nix eval /tmp/tmpflake#lib.a

# Check that flake src was copied
ls /nix/store/*/mydummyfile.tmp

[grahamc]

This default probably should be improved in nix-src itself, but this is true for users of Determinate Nix which specifically includes running the determinate-nixd daemon. The daemon always writes out a nix.conf which enables lazy-trees.

[erikarvstedt]

My user story was:

• See docs page
• Get curious about det-nix
• Try out locally in shell.
  Because lazy-trees is a client feature, not a daemon feature, I assumed the default was implemented in the client. Which, I think, is a reasonable assumption.

[grahamc]

Makes sense, thanks! I'll file a ticket internally too