Compute NAR hash for Git archive flakes if --no-trust-tarballs-from-git-forges

src/libfetchers/github.cc

@@ -299,6 +299,13 @@ struct GitArchiveInputScheme : InputScheme
             false,
             "«" + input.to_string() + "»");
 
+        if (!input.settings->trustTarballsFromGitForges)
+            // FIXME: computing the NAR hash here is wasteful if
+            // copyInputToStore() is just going to hash/copy it as
+            // well.
+            input.attrs.insert_or_assign("narHash",
+                accessor->hashPath(CanonPath::root).to_string(HashFormat::SRI, true));
+
         return {accessor, input};
     }