Revert "Revert "Merge pull request #6621 from Kha/nested-follows""

This reverts commit a8b3d777fbdaf0b732f129e5be62cd2a1227674b.

This undoes the revert of PR#6621, which allows nested `follows`, i.e.

    {
      inputs = {
        foo.url = "github:bar/foo";
        foo.inputs.bar.inputs.nixpkgs = "nixpkgs";
      };
    }

does the expected thing now. This is useful to avoid the 1000 instances
of nixpkgs problem without having each flake in the dependency tree to
expose all of its transitive dependencies for modification.

This was in fact part of Nix before and the C++ changes applied w/o
conflicts. However, it got reverted then because people didn't want to
merge lazy-trees against it which was supposed to be merged soon back in
October 2022.

Fixes: https://git.lix.systems/lix-project/lix/issues/201

Change-Id: I5ddef914135b695717b2ef88862d57ced5e7aa3c

1 files changed, 21 insertions, 0 deletions

diff --git a/doc/manual/rl-next/fix-nested-follows.md b/doc/manual/rl-next/fix-nested-follows.md
new file mode 100644
index 000000000..d4a381ba4
--- /dev/null
+++ b/doc/manual/rl-next/fix-nested-follows.md
@@ -0,0 +1,21 @@
+---
+synopsis: Fix nested flake input `follows`
+prs: 6621
+cls: 994
+---
+
+Previously nested-input overrides were ignored; that is, the following did not
+override anything, in spite of the `nix3-flake` manual documenting it working:
+
+```
+{
+  inputs = {
+    foo.url = "github:bar/foo";
+    foo.inputs.bar.inputs.nixpkgs = "nixpkgs";
+  };
+}
+```
+
+This is useful to avoid the 1000 instances of nixpkgs problem without having
+each flake in the dependency tree to expose all of its transitive dependencies
+for modification.