From c5ae41d8be6eb391ae39de9cce58b5e6b9e8085b Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Tue, 30 Apr 2024 16:39:34 +0200
Subject: [PATCH] Copy roots to the store as /nix/store/<hash1>-<hash2>-source

When you have a attribute like

  src = ./.;

the root of the flake should produce a store path
/nix/store/<hash1>-<hash2>-source, because before lazy trees, the
basename of the tree in the store was /nix/store/<hash2>-source. Even
though that was really a bug, we do need to mimic this behaviour so we
don't change evaluation results.
---
 src/libexpr/eval.cc | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 8e9e0c56083..ca61c33d438 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -2431,7 +2431,16 @@ StorePath EvalState::copyPathToStore(NixStringContext & context, const SourcePat
                 *store,
                 path.resolveSymlinks(),
                 settings.readOnlyMode ? FetchMode::DryRun : FetchMode::Copy,
-                path.baseName(),
+                /* For backwards compatibility, if the path is the
+                   root of a tree, we need to construct a
+                   "double-copied" store path like
+                   /nix/store/<hash1>-<hash2>-source. We don't need to
+                   materialize /nix/store/<hash2>-source
+                   though. Still, this requires reading/hashing the
+                   path twice. */
+                path.path.isRoot()
+                ? store->computeStorePath("source", *path.accessor, path.path).first.to_string()
+                : path.baseName(),
                 FileIngestionMethod::Recursive,
                 nullptr,
                 repair);