From 8d66f5f1107fe87f70ea24ade045720235cc31fa Mon Sep 17 00:00:00 2001
From: regnat <rg@regnat.ovh>
Date: Wed, 21 Apr 2021 17:33:21 +0200
Subject: [PATCH] Make `nix shell` fallback to static outputs when needed

In case of pure input-addressed derivations, the build loop doesn't
guaranty that the realisations are stored in the db (if the output paths
are already there or can be substituted, the realisations won't be
registered). This caused `nix shell` to fail in some cases because it
was assuming that the realisations were always existing.

A better (but more involved) fix would probably to ensure that we always
register the realisations, but in the meantime this patches the surface
issue.

Fix #4721
---
 src/libcmd/installables.cc | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/libcmd/installables.cc b/src/libcmd/installables.cc
index e15addfae..39162a662 100644
--- a/src/libcmd/installables.cc
+++ b/src/libcmd/installables.cc
@@ -736,9 +736,18 @@ std::set<RealisedPath> toRealisedPaths(
                                     output.first);
                             auto outputId = DrvOutput{outputHashes.at(output.first), output.first};
                             auto realisation = store->queryRealisation(outputId);
-                            if (!realisation)
-                                throw Error("cannot operate on an output of unbuilt content-addresed derivation '%s'", outputId.to_string());
-                            res.insert(RealisedPath{*realisation});
+                            if (!realisation) {
+                                // TODO: remove this check once #4725 is fixed
+                                // as we’ll have the guaranty that if
+                                // `output.second` exists, then the realisation
+                                // will be there too
+                                if (output.second)
+                                    res.insert(*output.second);
+                                else
+                                    throw Error("cannot operate on an output of unbuilt content-addresed derivation '%s'", outputId.to_string());
+                            } else {
+                                res.insert(RealisedPath{*realisation});
+                            }
                         }
                         else {
                             // If ca-derivations isn't enabled, behave as if