From a572c9433330ea307a3b5c83db2357d6ca55f8e0 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Thu, 12 Jun 2025 20:19:19 +0200
Subject: [PATCH] Fix deep overrides

An override like

  inputs.foo.inputs.bar.inputs.nixpkgs.follows = "nixpkgs";

implicitly set `inputs.foo.inputs.bar` to `flake:bar`, which led to an
unexpected error like

  error: cannot find flake 'flake:bar' in the flake registries

We now no longer create a parent override (like for `foo.bar` in the
example above) if it doesn't set an explicit ref or follows
attribute. We only recursively apply its child overrides.

Fixes https://github.com/NixOS/nix/issues/8325, https://github.com/DeterminateSystems/nix-src/issues/95, https://github.com/NixOS/nix/issues/12083, https://github.com/NixOS/nix/issues/5790.
---
 src/libflake/flake.cc | 35 ++++++++++++++++++++---------------
 1 file changed, 20 insertions(+), 15 deletions(-)

diff --git a/src/libflake/flake.cc b/src/libflake/flake.cc
index 31328abde..5570422a3 100644
--- a/src/libflake/flake.cc
+++ b/src/libflake/flake.cc
@@ -85,7 +85,6 @@ static void parseFlakeInputAttr(
 
 static FlakeInput parseFlakeInput(
     EvalState & state,
-    std::string_view inputName,
     Value * value,
     const PosIdx pos,
     const InputAttrPath & lockRootAttrPath,
@@ -155,9 +154,6 @@ static FlakeInput parseFlakeInput(
             input.ref = parseFlakeRef(state.fetchSettings, *url, {}, true, input.isFlake, true);
     }
 
-    if (!input.follows && !input.ref)
-        input.ref = FlakeRef::fromAttrs(state.fetchSettings, {{"type", "indirect"}, {"id", std::string(inputName)}});
-
     return input;
 }
 
@@ -185,7 +181,6 @@ static std::pair<std::map<FlakeId, FlakeInput>, fetchers::Attrs> parseFlakeInput
         } else {
             inputs.emplace(inputName,
                 parseFlakeInput(state,
-                    inputName,
                     inputAttr.value,
                     inputAttr.pos,
                     lockRootAttrPath,
@@ -467,18 +462,27 @@ LockedFlake lockFlake(
 
             /* Get the overrides (i.e. attributes of the form
                'inputs.nixops.inputs.nixpkgs.url = ...'). */
-            for (auto & [id, input] : flakeInputs) {
+            std::function<void(const FlakeInput & input, const InputAttrPath & prefix)> addOverrides;
+            addOverrides = [&](const FlakeInput & input, const InputAttrPath & prefix)
+            {
                 for (auto & [idOverride, inputOverride] : input.overrides) {
-                    auto inputAttrPath(inputAttrPathPrefix);
-                    inputAttrPath.push_back(id);
+                    auto inputAttrPath(prefix);
                     inputAttrPath.push_back(idOverride);
-                    overrides.emplace(inputAttrPath,
-                        OverrideTarget {
-                            .input = inputOverride,
-                            .sourcePath = sourcePath,
-                            .parentInputAttrPath = inputAttrPathPrefix
-                        });
+                    if (inputOverride.ref || inputOverride.follows)
+                        overrides.emplace(inputAttrPath,
+                            OverrideTarget {
+                                .input = inputOverride,
+                                .sourcePath = sourcePath,
+                                .parentInputAttrPath = inputAttrPathPrefix
+                            });
+                    addOverrides(inputOverride, inputAttrPath);
                 }
+            };
+
+            for (auto & [id, input] : flakeInputs) {
+                auto inputAttrPath(inputAttrPathPrefix);
+                inputAttrPath.push_back(id);
+                addOverrides(input, inputAttrPath);
             }
 
             /* Check whether this input has overrides for a
@@ -534,7 +538,8 @@ LockedFlake lockFlake(
                         continue;
                     }
 
-                    assert(input.ref);
+                    if (!input.ref)
+                        input.ref = FlakeRef::fromAttrs(state.fetchSettings, {{"type", "indirect"}, {"id", std::string(id)}});
 
                     auto overridenParentPath =
                         input.ref->input.isRelative()