populate flake-input: fail on failures, reuse the store, leave out replaced inputs

Delivering flakes and flake inputs gets more robust:

- With fetchOnTarget, the inputs get collected before the pipeline that
  links them, so populate fails if the target can't fetch one, instead of
  linking the flake without its inputs and succeeding.
- What the lock file pins gets taken from the store if it's there: the
  store path is the one of a directory named source with the locked hash,
  which nix-store --print-fixed-path computes.  builtins.fetchTree
  contacts where the input comes from even then, so redeploying unchanged
  sources fails without that if a server is unreachable.
- With fetchOnTarget, a delivered input that is itself locked to a local
  path the target lacks fails with populate's error naming the input, like
  its inputs do.
- Inputs that get drawn from other sources are left out, with all they
  pin: Nix archives an empty flake in their place.  So nothing gets
  fetched, copied, and rooted that no evaluation uses, and a pin that is
  unreachable doesn't matter if it gets replaced anyway.
- flake-input sources get the option requireInputs.  By default,
  populating fails if the inputs that the input's own lock file pins
  can't be delivered, e.g. because the lock file lacks an input its
  flake.nix has.  With false, populate warns and delivers the input with
  what Nix locks now, or else without its inputs.

A remote flake that the target fetches entirely on its own collects its
inputs like everything else does.  The Nix function finding its
subdirectory moves next to the jq programs.

New edge cases cover each of these.

1 files changed, 102 insertions, 0 deletions

diff --git a/tests/fixtures.sh b/tests/fixtures.sh
index 3839c1d..d9d8b2b 100755
--- a/tests/fixtures.sh
+++ b/tests/fixtures.sh
@@ -359,3 +359,105 @@ cat > /fixtures/patches/bad.patch <<'PATCH'
 -nothing like this
 +anything
 PATCH
+
+# broken: a flake with an input that can't be fetched anymore.
+mkdir /fixtures/www/src/vanishing
+cat > /fixtures/www/src/vanishing/flake.nix <<'NIX'
+{ outputs = _: { who = "vanishing"; }; }
+NIX
+tarball vanishing
+mkdir /fixtures/broken
+cat > /fixtures/broken/flake.nix <<NIX
+{
+  inputs.vanishing.url = "$url/vanishing.tar.gz";
+  outputs = { vanishing, ... }: { msg = "broken:\${vanishing.who}"; };
+}
+NIX
+(cd /fixtures/broken && nix flake lock)
+
+# pinned, usepinned: a tarball flake whose own lock file pins an input that
+# can't be fetched anymore, and a flake that draws that input from its own
+# input instead, so nothing it evaluates needs the pin.
+mkdir /fixtures/www/src/pinned
+cat > /fixtures/www/src/pinned/flake.nix <<NIX
+{
+  inputs.inner.url = "$url/vanishing.tar.gz";
+  outputs = { inner, ... }: { greeting = "pinned+\${inner.who}"; };
+}
+NIX
+(cd /fixtures/www/src/pinned && nix flake lock)
+tarball pinned
+mkdir /fixtures/usepinned
+cat > /fixtures/usepinned/flake.nix <<NIX
+{
+  inputs.inner.url = "$url/inner.tar.gz";
+  inputs.dep.url = "$url/pinned.tar.gz";
+  inputs.dep.inputs.inner.follows = "inner";
+  outputs = { dep, ... }: { msg = "usepinned:\${dep.greeting}"; };
+}
+NIX
+(cd /fixtures/usepinned && nix flake lock)
+rm /fixtures/www/vanishing.tar.gz
+
+# stale, usestale: a tarball flake whose lock file lacks an input its
+# flake.nix has, and a flake with it as input, whose own lock file is
+# complete.
+mkdir /fixtures/www/src/stale
+cat > /fixtures/www/src/stale/flake.nix <<NIX
+{
+  inputs.inner.url = "$url/inner.tar.gz";
+  outputs = { inner, ... }: { greeting = "stale+\${inner.who}"; };
+}
+NIX
+(cd /fixtures/www/src/stale && nix flake lock)
+cat > /fixtures/www/src/stale/flake.nix <<NIX
+{
+  inputs.inner.url = "$url/inner.tar.gz";
+  inputs.extra.url = "$url/inner2.tar.gz";
+  outputs = { inner, extra, ... }: { greeting = "stale+\${inner.who}+\${extra.who}"; };
+}
+NIX
+tarball stale
+mkdir /fixtures/usestale
+cat > /fixtures/usestale/flake.nix <<NIX
+{
+  inputs.dep.url = "$url/stale.tar.gz";
+  outputs = { dep, ... }: { msg = "usestale:\${dep.greeting}"; };
+}
+NIX
+(cd /fixtures/usestale && nix flake lock)
+
+# offline: a flake with an input of its own, which the tests make
+# unreachable between deploys.
+mkdir /fixtures/www/src/gap
+cat > /fixtures/www/src/gap/flake.nix <<'NIX'
+{ outputs = _: { who = "gap"; }; }
+NIX
+tarball gap
+mkdir /fixtures/offline
+cat > /fixtures/offline/flake.nix <<NIX
+{
+  inputs.gap.url = "$url/gap.tar.gz";
+  outputs = { gap, ... }: { msg = "offline:\${gap.who}"; };
+}
+NIX
+(cd /fixtures/offline && nix flake lock)
+
+# c3: a flake with an input, to draw another flake's input from.
+mkdir /fixtures/c3
+cat > /fixtures/c3/flake.nix <<NIX
+{
+  inputs.z.url = "$url/inner.tar.gz";
+  outputs = { z, ... }: { who = "c3(\${z.who})"; };
+}
+NIX
+(cd /fixtures/c3 && nix flake lock)
+
+# filtered-parent, filtered-parent-link: like filtered, but the filter file
+# applies to a subdirectory, which is what gets synced.
+mkdir -p /fixtures/filtered-parent/sub
+printf -- '- garbage\n' > /fixtures/filtered-parent/.rsync-filter
+echo keep > /fixtures/filtered-parent/sub/keep
+echo garbage > /fixtures/filtered-parent/sub/garbage
+ln -s filtered-parent /fixtures/filtered-parent-link
+chown -h nobody /fixtures/filtered-parent-link