Lazy flake input fetching #2920
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As long as the flake input is locked, it is now only fetched when it
is evaluated (e.g. "nixpkgs" is fetched when
"inputs.nixpkgs.<something>" is evaluated).
This required adding an "id" attribute to the members of "inputs" in
lockfiles, e.g.
"inputs": {
"nixpkgs/release-19.03": {
"id": "nixpkgs",
"inputs": {},
"narHash": "sha256-eYtxncIMFVmOHaHBtTdPGcs/AnJqKqA6tHCm0UmPYQU=",
"nonFlakeInputs": {},
"uri": "github:edolstra/nixpkgs/e9d5882bb861dc48f8d46960e7c820efdbe8f9c1"
}
}
because the flake ID needs to be known beforehand to construct the
"inputs" attrset.
Fixes #2913.
Also use nlohmann::json range-based for.
Unfortunately this doesn't work. Maybe we should keep separate roots for each path.
Also add a proper test for non-flake inputs.
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Just a heads up that I moved flake-related files from |
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Flake inputs are now fetched lazily. That is, as long as a flake is locked by the top-level lockfile, it won't be fetched unless it's actually needed (i.e.
inputs.<foo>is evaluated).Note that this required a change to the lockfile format: we now store the flake ID of inputs, because this is needed before the flake is fetched to construct the
inputsattrset.Other changes:
Moved some lockfile-related stuff to
lockfile.{cc,hh}. There's also some funky multiple inheritance going on now to factor out some common code between flake and non-flake inputs and between top-level and non-top-level flakes.resolveFlake()now avoids fetching the top-level flake twice.