#5662: Implement fast-forward to upstream.

plugins/vcs/Algorithm.h

@@ -135,6 +135,12 @@ inline void syncWithRemote(const std::shared_ptr<Repository>& repository)
         repository->pushToTrackedRemote();
         return;
     }
+
+    if (status.strategy == RequiredMergeStrategy::FastForward)
+    {
+        repository->fastForwardToTrackedRemote();
+        return;
+    }
 
     if (!repository->isReadyForMerge())
     {

plugins/vcs/Reference.h

@@ -3,6 +3,7 @@
 #include <string>
 #include <memory>
 #include <git2.h>
+#include "GitException.h"
 
 namespace vcs
 {
@@ -62,6 +63,20 @@ class Reference final
         return upstream != nullptr ? std::make_shared<Reference>(upstream) : Ptr();
     }
 
+    // Create a new reference with the same name as the given reference but a
+    // different OID target. The new reference will be written to disk, overwriting the given reference.
+    void setTarget(git_oid* oid)
+    {
+        git_reference* newTargetRef;
+        auto error = git_reference_set_target(&newTargetRef, _reference, oid, "Reference set to new target by DarkRadiant");
+        GitException::ThrowOnError(error);
+
+        // Swap the wrapped reference pointer, release the old one
+        git_reference_free(_reference);
+
+        _reference = newTargetRef;
+    }
+
     ~Reference()
     {
         git_reference_free(_reference);

plugins/vcs/Repository.cpp

@@ -150,6 +150,45 @@ void Repository::pushToTrackedRemote()
     remote->push(*getHead()); // getHead will succeed because getTrackedRemote did
 }
 
+void Repository::fastForwardToTrackedRemote()
+{
+    auto head = getHead();
+    if (!head) throw GitException("Could not retrieve HEAD reference from repository");
+
+    auto upstream = head->getUpstream();
+    if (!upstream) throw GitException("No tracked remote branch configured");
+
+    // Lookup the target object
+    git_oid targetOid;
+    git_reference_name_to_id(&targetOid, _repository, upstream->getName().c_str());
+
+    git_object* target;
+    auto error = git_object_lookup(&target, _repository, &targetOid, GIT_OBJECT_COMMIT);
+    GitException::ThrowOnError(error);
+
+    rMessage() << "Fast-fowarding " << head->getName() << " to upstream " << upstream->getName() << std::endl;
+
+    try
+    {
+        // Checkout the result so the workdir is in the expected state
+        git_checkout_options checkoutOptions = GIT_CHECKOUT_OPTIONS_INIT;
+        checkoutOptions.checkout_strategy = GIT_CHECKOUT_SAFE;
+
+        error = git_checkout_tree(_repository, target, &checkoutOptions);
+        GitException::ThrowOnError(error);
+
+        // Move the target reference to the target OID
+        head->setTarget(&targetOid);
+
+        rMessage() << "Fast-foward done, " << head->getName() << " is now at " << Reference::OidToString(&targetOid) << std::endl;
+    }
+    catch (const GitException& ex)
+    {
+        git_object_free(target);
+        throw ex;
+    }
+}
+
 RefSyncStatus Repository::getSyncStatusOfBranch(const Reference& reference)
 {
     RefSyncStatus status;

plugins/vcs/Repository.h

@@ -51,6 +51,9 @@ class Repository final
     // Performs a fetch from the remote the current branch is tracking
     void fetchFromTrackedRemote();
 
+    // Fast-forwards the current head to the tracked remote branch
+    void fastForwardToTrackedRemote();
+
     // Pushes the current head to its tracked remote branch
     void pushToTrackedRemote();
 

plugins/vcs/ui/VcsStatus.cpp

@@ -18,6 +18,7 @@
 #include "../GitModule.h"
 #include "../Diff.h"
 #include "../GitException.h"
+#include "../Algorithm.h"
 
 namespace vcs
 {
@@ -232,7 +233,7 @@ void VcsStatus::performSync(std::shared_ptr<git::Repository> repository)
 {
     try
     {
-        repository->pushToTrackedRemote();
+        syncWithRemote(repository);
         setRemoteStatus(git::analyseRemoteStatus(repository));
     }
     catch (git::GitException& ex)