From 5f362303687a78160fe809467d0cc11657b4135b Mon Sep 17 00:00:00 2001
From: Lexi Mattick <lexi.mattick@neuralink.com>
Date: Thu, 11 Jul 2024 16:18:24 -0700
Subject: [PATCH] Eval cache: fix cache regressions

- Fix eval cache not being persisted in `nix develop` (since #10570)
- Fallback to flake path so the eval cache isn't disabled for flakes evaluated by a relative `path:` (since #10149, #10176)
- Don't attempt to commit cache transaction if there is no active transaction, which will spew errors in edge cases
- Drive-by: trivial typo fix
---
 src/libcmd/installable-value.hh | 2 +-
 src/libexpr/eval-cache.cc       | 2 +-
 src/libflake/flake/flake.cc     | 6 ++++--
 src/nix/develop.cc              | 4 ++++
 4 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/libcmd/installable-value.hh b/src/libcmd/installable-value.hh
index f300d392bb52..798cb5e1a00f 100644
--- a/src/libcmd/installable-value.hh
+++ b/src/libcmd/installable-value.hh
@@ -66,7 +66,7 @@ struct ExtraPathInfoValue : ExtraPathInfo
 };
 
 /**
- * An Installable which corresponds a Nix langauge value, in addition to
+ * An Installable which corresponds a Nix language value, in addition to
  * a collection of \ref DerivedPath "derived paths".
  */
 struct InstallableValue : Installable
diff --git a/src/libexpr/eval-cache.cc b/src/libexpr/eval-cache.cc
index 2630c34d5637..5085fedc2f05 100644
--- a/src/libexpr/eval-cache.cc
+++ b/src/libexpr/eval-cache.cc
@@ -95,7 +95,7 @@ struct AttrDb
     {
         try {
             auto state(_state->lock());
-            if (!failed)
+            if (!failed && state->txn->active)
                 state->txn->commit();
             state->txn.reset();
         } catch (...) {
diff --git a/src/libflake/flake/flake.cc b/src/libflake/flake/flake.cc
index 6f47b5992298..6dcdd96d1d2d 100644
--- a/src/libflake/flake/flake.cc
+++ b/src/libflake/flake/flake.cc
@@ -947,8 +947,10 @@ std::optional<Fingerprint> LockedFlake::getFingerprint(ref<Store> store) const
 {
     if (lockFile.isUnlocked()) return std::nullopt;
 
-    auto fingerprint = flake.lockedRef.input.getFingerprint(store);
-    if (!fingerprint) return std::nullopt;
+    auto fingerprint = flake.lockedRef.input.getFingerprint(store)
+        // Fingerprints are null for relative path references so we use
+        // the flake path as a fallback to avoid losing caching.
+        .value_or(flake.path.to_string());
 
     *fingerprint += fmt(";%s;%s", flake.lockedRef.subdir, lockFile);
 
diff --git a/src/nix/develop.cc b/src/nix/develop.cc
index 6bd3dc9efc6a..b89de5d5c1d7 100644
--- a/src/nix/develop.cc
+++ b/src/nix/develop.cc
@@ -697,6 +697,10 @@ struct CmdDevelop : Common, MixEnvironment
             }
         }
 
+        // Release our references to eval caches to ensure they are persisted to disk, because
+        // we are about to exec out of this process without running C++ destructors.
+        getEvalState()->evalCaches.clear();
+
         runProgramInStore(store, UseLookupPath::Use, shell, args, buildEnvironment.getSystem());
 #endif
     }