Fix assertion failure in FlakeRef::to_string()

src/libexpr/primops/fetchGit.cc

@@ -39,6 +39,7 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
                files. */
 
             GitInfo gitInfo;
+            gitInfo.ref = "HEAD";
             gitInfo.rev = "0000000000000000000000000000000000000000";
             gitInfo.shortRev = std::string(gitInfo.rev, 0, 7);
 
@@ -67,7 +68,6 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
 
         // clean working tree, but no ref or rev specified.  Use 'HEAD'.
         rev = chomp(runProgram("git", true, { "-C", uri, "rev-parse", "HEAD" }));
-        ref = "HEAD"s;
     }
 
     if (!ref) ref = "HEAD"s;
@@ -127,6 +127,7 @@ GitInfo exportGit(ref<Store> store, const std::string & uri,
 
     // FIXME: check whether rev is an ancestor of ref.
     GitInfo gitInfo;
+    gitInfo.ref = *ref;
     gitInfo.rev = rev != "" ? rev : chomp(readFile(localRefFile));
     gitInfo.shortRev = std::string(gitInfo.rev, 0, 7);
 

src/libexpr/primops/fetchGit.hh

@@ -9,6 +9,7 @@ namespace nix {
 struct GitInfo
 {
     Path storePath;
+    std::string ref;
     std::string rev;
     std::string shortRev;
     std::optional<uint64_t> revCount;

src/libexpr/primops/flake.cc

@@ -237,8 +237,8 @@ static FlakeSourceInfo fetchFlake(EvalState & state, const FlakeRef flakeRef, bo
         info.storePath = gitInfo.storePath;
         info.rev = Hash(gitInfo.rev, htSHA1);
         info.revCount = gitInfo.revCount;
+        info.flakeRef.ref = gitInfo.ref;
         info.flakeRef.rev = info.rev;
-        // FIXME: ensure info.flakeRef.ref is set.
         return info;
     }
 

src/libexpr/primops/flakeref.cc

@@ -128,7 +128,7 @@ std::string FlakeRef::to_string() const
     }
 
     else if (auto refData = std::get_if<FlakeRef::IsGit>(&data)) {
-        assert(ref || !rev);
+        assert(!rev || ref);
         string = refData->uri;
     }