From 408fcc6584ca598533a0f8c9012d60450db148a8 Mon Sep 17 00:00:00 2001
From: tv <tv@krebsco.de>
Date: Thu, 12 Nov 2026 02:33:43 +0000
Subject: populate: place overrides on sources with generated flakes correctly

An override below an input drawn from a source that has a generated
flake itself got placed on that generated flake, which has no such
input, so Nix ignored it with a warning.  Generated flakes have their
source as input of the same name, so the override goes below that.

An edge case overrides an input of a source with a generated flake.
---
 pkgs/populate/default.nix |  3 +++
 tests/fixtures.sh         | 17 +++++++++++++++++
 tests/scenarios.nix       | 16 ++++++++++++++++
 3 files changed, 36 insertions(+)

diff --git a/pkgs/populate/default.nix b/pkgs/populate/default.nix
index 7a52ca9..06197b6 100644
--- a/pkgs/populate/default.nix
+++ b/pkgs/populate/default.nix
@@ -89,6 +89,9 @@ let
         rest = if parent == null then x.path else drop (length parent) x.path;
       in
         "inputs.${toJSON base}" +
+        # A source with a generated flake has itself as input therein.
+        optionalString (parent != null && generated ? ${base})
+          ".inputs.${toJSON base}" +
         concatMapStrings (name: ".inputs.${toJSON name}") rest +
         ".follows = ${toJSON x.source};";
     in /* sh */ ''
diff --git a/tests/fixtures.sh b/tests/fixtures.sh
index 9813c8f..8222b13 100755
--- a/tests/fixtures.sh
+++ b/tests/fixtures.sh
@@ -216,6 +216,23 @@ cat > /fixtures/rel/flake.nix <<'NIX'
 NIX
 (cd /fixtures/rel && nix flake lock && git init -q && commit rel)
 
+# two, c1, c2: a flake with two inputs, and two flakes to draw them from.
+mkdir /fixtures/two /fixtures/c1 /fixtures/c2
+cat > /fixtures/two/flake.nix <<NIX
+{
+  inputs.p.url = "$url/inner.tar.gz";
+  inputs.q.url = "$url/inner.tar.gz";
+  outputs = { p, q, ... }: { greeting = "two:\${p.who}+\${q.who}"; };
+}
+NIX
+(cd /fixtures/two && nix flake lock)
+cat > /fixtures/c1/flake.nix <<'NIX'
+{ outputs = _: { who = "c1"; }; }
+NIX
+cat > /fixtures/c2/flake.nix <<'NIX'
+{ outputs = _: { who = "c2"; }; }
+NIX
+
 # noflake: a directory without flake.nix.
 mkdir /fixtures/noflake
 echo noflake > /fixtures/noflake/README
diff --git a/tests/scenarios.nix b/tests/scenarios.nix
index 307e521..5dd44db 100644
--- a/tests/scenarios.nix
+++ b/tests/scenarios.nix
@@ -867,6 +867,22 @@ assert !(krops.isLocalTarget (targets.remote "/"));
         }
       ];
     }))
+    (s "override-generated" {
+      phases = twice {
+        sources = {
+          x.flake = {
+            flake = "/fixtures/top"; inherit fetchOnTarget;
+            inputs.dep = { follows = "b"; inputs.q.follows = "c2"; };
+          };
+          b.file = { path = "/fixtures/two"; inputs.p.follows = "c1"; };
+          c1.file = "/fixtures/c1";
+          c2.file = "/fixtures/c2";
+        };
+        check = ''
+          expect_eq msg "$(nix_eval_online "$T"/.populate/flakes/x#msg)" top:two:c1+c2,sub
+        '';
+      };
+    })
   ] ++ lib.optional (targetKind == "local")
     # The target has the path the input is locked to.
     (s "uselocal" {
-- 
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