Remove masterlist update loading and rollback

LOOT's ability to roll back to a working masterlist version hasn't been
exercised in years, as our CI testing has gotten better at catching
issues before they reach users.

Coupling updating a masterlist with loading it also complicates the
introduction of a common prelude, so given the very low usefulness of
the functionality it's best to drop it entirely .

include/loot/database_interface.h

@@ -95,8 +95,7 @@ public:
    *  @details Uses Git to update the given masterlist to a given remote.
    *           If the masterlist doesn't exist, this will create it. This
    *           function also initialises a Git repository in the given
-   *           masterlist's parent folder. If the masterlist was not already
-   *           up-to-date, it will be re-loaded, but not re-evaluated.
+   *           masterlist's parent folder.
    *
    *           If a Git repository is already present, it will be used to
    *           perform a diff-only update, but if for any reason a
@@ -120,8 +119,7 @@ public:
    *         check their repositories to see which is the latest release branch.
    *  @returns `true` if the masterlist was updated. `false` if no update was
    *           necessary, ie. it was already up-to-date. If `true`, the
-   *           masterlist will have been re-loaded, but will need to be
-   *           re-evaluated separately.
+   *           masterlist will need to be re-loaded and re-evaluated separately.
    */
   virtual bool UpdateMasterlist(const std::filesystem::path& masterlist_path,
                                 const std::string& remote_url,

src/api/api_database.cpp

@@ -95,13 +95,7 @@ bool ApiDatabase::UpdateMasterlist(const std::filesystem::path& masterlistPath,
                                 masterlistPath.u8string() +
                                 "\" does not have a valid parent directory.");
 
-  Masterlist masterlist;
-  if (masterlist.Update(masterlistPath, remoteURL, remoteBranch)) {
-    masterlist_ = masterlist;
-    return true;
-  }
-
-  return false;
+  return Masterlist::Update(masterlistPath, remoteURL, remoteBranch);
 }
 
 MasterlistInfo ApiDatabase::GetMasterlistRevision(

src/api/helpers/git_helper.cpp

@@ -346,33 +346,6 @@ void GitHelper::CheckoutNewBranch(const std::string& remote,
   data_.reference = nullptr;
 }
 
-void GitHelper::CheckoutRevision(const std::string& revision) {
-  if (data_.repo == nullptr)
-    throw GitStateError(
-        "Cannot checkout revision for repository that has not been opened.");
-  else if (data_.object != nullptr)
-    throw GitStateError(
-        "Cannot fetch repository updates, object memory already allocated.");
-
-  // Get an object ID for 'HEAD^'.
-  Call(git_revparse_single(&data_.object, data_.repo, revision.c_str()));
-  const git_oid* oid = git_object_id(data_.object);
-
-  // Detach HEAD to HEAD~1. This will roll back HEAD by one commit each time it
-  // is called.
-  Call(git_repository_set_head_detached(data_.repo, oid));
-
-  // Checkout the new HEAD.
-  auto logger = getLogger();
-  if (logger) {
-    logger->trace("Performing a Git checkout of HEAD.");
-  }
-  Call(git_checkout_head(data_.repo, &data_.checkout_options));
-
-  git_object_free(data_.object);
-  data_.object = nullptr;
-}
-
 void GitHelper::DeleteBranch(const std::string& branch) {
   if (data_.repo == nullptr) {
     throw GitStateError(

src/api/helpers/git_helper.h

@@ -47,7 +47,6 @@ public:
   void Fetch(const std::string& remote);
 
   void CheckoutNewBranch(const std::string& remote, const std::string& branch);
-  void CheckoutRevision(const std::string& revision);
 
   // Deletes the branch, detaching HEAD if it's currently set to the branch.
   void DeleteBranch(const std::string& branch);

src/api/masterlist.cpp

@@ -150,25 +150,7 @@ bool Masterlist::Update(const std::filesystem::path& path,
   }
 
   // Now whether the repository was cloned or updated, the working directory
-  // contains the latest masterlist. Try parsing it: on failure, detach the HEAD
-  // back one commit and try again.
-  while (true) {
-    try {
-      this->Load(path);
-
-      return true;
-    } catch (std::exception& e) {
-      if (logger) {
-        logger->error("Masterlist parsing failed. Masterlist revision {}: {}",
-                      git.GetHeadCommitId(true),
-                      e.what());
-      }
-      git.CheckoutRevision("HEAD^");
-    }
-  }
-
-  // This should never be reached as git.CheckoutRevision() will throw if it
-  // tries to go one back from the start of history.
+  // contains the latest masterlist.
   return true;
 }
 }

src/api/masterlist.h

@@ -34,7 +34,7 @@
 namespace loot {
 class Masterlist : public MetadataList {
 public:
-  bool Update(const std::filesystem::path& path,
+  static bool Update(const std::filesystem::path& path,
               const std::string& repoURL,
               const std::string& repoBranch);