From 801cb161319148bca4c6d4e9daea0ccea1953b2e Mon Sep 17 00:00:00 2001
From: John Ericson <John.Ericson@Obsidian.Systems>
Date: Mon, 24 Nov 2025 23:27:00 -0500
Subject: [PATCH] Simplify `nix develop` "gathering derivation environment"

Before, had some funny logic with an unnecessary is CA enabled branch,
and erroneous use of the comma operator. Now, take advantage of the new
`Derivation::fillInOutputPaths` to fill in input addresses (and output
path env vars) in a much-more lightweight manner.

Also, fix `nix develop` on fixed-output derivations so that weird things
don't happen when we have that experimental feature enabled.

As a slight behavior change, if the original derivation was
content-addressing this one will be too, but I really don't think that
matters --- if anything, it is a slight improvement for users that have
already opted into content-addressing anyways.
---
 src/nix/develop.cc            | 36 +++++++++++++++++------------------
 tests/functional/nix-shell.sh |  8 +++-----
 2 files changed, 20 insertions(+), 24 deletions(-)

diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index 1eff735da..68ff3fcf9 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -272,26 +272,24 @@ static StorePath getDerivationEnvironment(ref<Store> store, ref<Store> evalStore
     drv.name += "-env";
     drv.env.emplace("name", drv.name);
     drv.inputSrcs.insert(std::move(getEnvShPath));
-    if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations)) {
-        for (auto & output : drv.outputs) {
-            output.second = DerivationOutput::Deferred{}, drv.env[output.first] = hashPlaceholder(output.first);
-        }
-    } else {
-        for (auto & output : drv.outputs) {
-            output.second = DerivationOutput::Deferred{};
-            drv.env[output.first] = "";
-        }
-        auto hashesModulo = hashDerivationModulo(*evalStore, drv, true);
-
-        for (auto & output : drv.outputs) {
-            Hash h = hashesModulo.hashes.at(output.first);
-            auto outPath = store->makeOutputPath(output.first, h, drv.name);
-            output.second = DerivationOutput::InputAddressed{
-                .path = outPath,
-            };
-            drv.env[output.first] = store->printStorePath(outPath);
-        }
+    for (auto & [outputName, output] : drv.outputs) {
+        std::visit(
+            overloaded{
+                [&](const DerivationOutput::InputAddressed &) {
+                    output = DerivationOutput::Deferred{};
+                    drv.env[outputName] = "";
+                },
+                [&](const DerivationOutput::CAFixed &) {
+                    output = DerivationOutput::Deferred{};
+                    drv.env[outputName] = "";
+                },
+                [&](const auto &) {
+                    // Do nothing for other types (CAFloating, Deferred, Impure)
+                },
+            },
+            output.raw);
     }
+    drv.fillInOutputPaths(*evalStore);
 
     auto shellDrvPath = writeDerivation(*evalStore, drv);
 
diff --git a/tests/functional/nix-shell.sh b/tests/functional/nix-shell.sh
index 2ff994c99..418857987 100755
--- a/tests/functional/nix-shell.sh
+++ b/tests/functional/nix-shell.sh
@@ -280,8 +280,6 @@ assert (!(args ? inNixShell));
 EOF
 nix-shell "$TEST_ROOT"/shell-ellipsis.nix --run "true"
 
-if [[ -z ${NIX_TESTS_CA_BY_DEFAULT:-} ]]; then
-  # `nix develop` should also work with fixed-output derivations
-  # shellcheck disable=SC2016
-  nix develop -f "$shellDotNix" fixed -c bash -c '[[ -n $stdenv ]]'
-fi
+# `nix develop` should also work with fixed-output derivations
+# shellcheck disable=SC2016
+nix develop -f "$shellDotNix" fixed -c bash -c '[[ -n $stdenv ]]'