From 1c7d0b716d1da05283b6c2cd9ee3e22553c7b0a0 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Thu, 2 Jun 2022 16:15:57 +0200
Subject: [PATCH] Give a better error message in case of unlocked inputs

---
 src/libexpr/flake/flake.cc    | 4 ++--
 src/libexpr/flake/lockfile.cc | 6 +++---
 src/libexpr/flake/lockfile.hh | 4 +++-
 3 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 658e06342..397ca4743 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -630,9 +630,9 @@ LockedFlake lockFlake(
 
             if (lockFlags.writeLockFile) {
                 if (auto sourcePath = topRef.input.getSourcePath()) {
-                    if (!newLockFile.isLocked()) {
+                    if (auto unlockedInput = newLockFile.isUnlocked()) {
                         if (fetchSettings.warnDirty)
-                            warn("will not write lock file of flake '%s' because it has an unlocked input", topRef);
+                            warn("will not write lock file of flake '%s' because it has an unlocked input ('%s')", topRef, *unlockedInput);
                     } else {
                         if (!lockFlags.updateLockFile)
                             throw Error("flake '%s' requires lock file changes but they're not allowed due to '--no-update-lock-file'", topRef);
diff --git a/src/libexpr/flake/lockfile.cc b/src/libexpr/flake/lockfile.cc
index ae67f8e61..7155f7371 100644
--- a/src/libexpr/flake/lockfile.cc
+++ b/src/libexpr/flake/lockfile.cc
@@ -197,7 +197,7 @@ void LockFile::write(const Path & path) const
     writeFile(path, fmt("%s\n", *this));
 }
 
-bool LockFile::isLocked() const
+std::optional<FlakeRef> LockFile::isUnlocked() const
 {
     std::unordered_set<std::shared_ptr<const Node>> nodes;
 
@@ -219,10 +219,10 @@ bool LockFile::isLocked() const
         if (node
             && !node->lockedRef.input.isLocked()
             && !node->lockedRef.input.isRelative())
-            return false;
+            return node->lockedRef;
     }
 
-    return true;
+    return {};
 }
 
 bool LockFile::operator ==(const LockFile & other) const
diff --git a/src/libexpr/flake/lockfile.hh b/src/libexpr/flake/lockfile.hh
index a4290c9e9..89b449dcf 100644
--- a/src/libexpr/flake/lockfile.hh
+++ b/src/libexpr/flake/lockfile.hh
@@ -60,7 +60,9 @@ struct LockFile
 
     void write(const Path & path) const;
 
-    bool isLocked() const;
+    /* Check whether this lock file has any unlocked inputs. If so,
+       return one. */
+    std::optional<FlakeRef> isUnlocked() const;
 
     bool operator ==(const LockFile & other) const;