libgit2 · alehed · May 28, 2017 · Jun 5, 2017 · Jun 5, 2017 · Jul 9, 2017
diff --git a/ObjectiveGit/GTRepository+Merging.h b/ObjectiveGit/GTRepository+Merging.h
@@ -52,7 +52,7 @@ typedef NS_OPTIONS(NSInteger, GTMergeAnalysis) {
 /// will point to an error describing what happened).
 - (BOOL)mergeBranchIntoCurrentBranch:(GTBranch *)fromBranch withError:(NSError **)error;
 
-/// Analyze which merge to perform.
+/// Analyze which merge to perform from the branch to HEAD
 ///
 /// analysis   - The resulting analysis.
 /// fromBranch - The branch to merge from.
@@ -62,6 +62,17 @@ typedef NS_OPTIONS(NSInteger, GTMergeAnalysis) {
 /// will point to an error describing what happened).
 - (BOOL)analyzeMerge:(GTMergeAnalysis *)analysis fromBranch:(GTBranch *)fromBranch error:(NSError **)error;
 
+/// Analyze which merge to perform between two branches
+///
+/// analysis   - The resulting analysis.
+/// fromBranch - The branch to merge from.
+/// toBranch   - The branch to merge into
+/// error      - The error if one occurred. Can be NULL.
+///
+/// Returns YES if the analysis was successful, NO otherwise (and `error`, if provided,
+/// will point to an error describing what happened).
+- (BOOL)analyzeMerge:(GTMergeAnalysis *)analysis fromBranch:(GTBranch *)fromBranch toBranch:(GTBranch *)toBranch error:(NSError **)error;
+
 @end
 
 NS_ASSUME_NONNULL_END
diff --git a/ObjectiveGit/GTRepository+Merging.m b/ObjectiveGit/GTRepository+Merging.m
@@ -208,4 +208,34 @@ - (BOOL)analyzeMerge:(GTMergeAnalysis *)analysis fromBranch:(GTBranch *)fromBran
 	return YES;
 }
 
+- (BOOL)analyzeMerge:(GTMergeAnalysis *)analysis fromBranch:(GTBranch *)fromBranch toBranch:(GTBranch *)toBranch error:(NSError **)error {
+	NSParameterAssert(analysis != NULL);
+	NSParameterAssert(fromBranch != nil);
+	NSParameterAssert(toBranch != nil);
+
+	GTCommit *theirs = [toBranch targetCommitWithError:error];
+	GTCommit *ours = [fromBranch targetCommitWithError:error];
+	if (theirs == nil || ours == nil) {
+		return NO;
+	}
+
+	GTCommit *ancestor = [self mergeBaseBetweenFirstOID:theirs.OID secondOID:ours.OID error:NULL];
+
+	if (ours.SHA == nil && theirs.SHA == nil) {
+		*analysis = GTMergeAnalysisUnborn | 0;;
+	} else if (ours.SHA == nil && theirs.SHA != nil) {
+		*analysis = GTMergeAnalysisUnborn | GTMergeAnalysisFastForward;
+	} else if (ancestor.SHA == nil || theirs.SHA == nil) {
+		*analysis = GTMergeAnalysisNone | 0;
+	} else if ([ours.SHA isEqualToString:theirs.SHA] || [ancestor.SHA isEqualToString:theirs.SHA]) {
+		*analysis = GTMergeAnalysisUpToDate | 0;
+	} else if ([ancestor.SHA isEqualToString:ours.SHA]) {
+		*analysis = GTMergeAnalysisFastForward | GTMergeAnalysisNormal;
+	} else {
+		*analysis = GTMergeAnalysisNormal | 0;
+	}
+
+	return YES;
+}
+
 @end
diff --git a/ObjectiveGitTests/GTRepositorySpec.m b/ObjectiveGitTests/GTRepositorySpec.m
@@ -277,6 +277,113 @@
 	});
 });
 
+describe(@"analyzeMerge", ^{
+	it(@"should correctly recognize up-to-date merges", ^{
+		__block NSError *error = nil;
+		GTBranch *branch1 = [repository lookUpBranchWithName:@"new" type:GTBranchTypeLocal success:NULL error:&error];
+		expect(branch1).notTo(beNil());
+		expect(error).to(beNil());
+
+		GTBranch *branch2 = [repository lookUpBranchWithName:@"hi!" type:GTBranchTypeLocal success:NULL error:&error];
+		expect(branch2).notTo(beNil());
+		expect(error).to(beNil());
+
+		__block GTMergeAnalysis analysis = 0;
+		expect(@([repository analyzeMerge:&analysis fromBranch:branch2 toBranch:branch1 error:&error])).to(beTruthy());
+		expect(error).to(beNil());
+		expect(@(analysis)).to(equal(GTMergeAnalysisUpToDate | 0));
+	});
+
+	it(@"should correctly recognize fast-forward merges", ^{
+		__block NSError *error = nil;
+		GTBranch *masterBranch = [repository lookUpBranchWithName:@"master" type:GTBranchTypeLocal success:NULL error:&error];
+		expect(masterBranch).notTo(beNil());
+		expect(error).to(beNil());
+
+		GTBranch *otherBranch = [repository lookUpBranchWithName:@"other-branch" type:GTBranchTypeLocal success:NULL error:&error];
+		expect(otherBranch).notTo(beNil());
+		expect(error).to(beNil());
+
+		__block GTMergeAnalysis analysis = 0;
+		expect(@([repository analyzeMerge:&analysis fromBranch:otherBranch toBranch:masterBranch error:&error])).to(beTruthy());
+		expect(error).to(beNil());
+		expect(@(analysis)).to(equal(GTMergeAnalysisFastForward | GTMergeAnalysisNormal));
+	});
+
+	it(@"should correctly recognize 3-way merges", ^{
+		__block NSError *error = nil;
+		GTOID *oid1 = [GTOID oidWithSHA:@"3921db10e466211cb4d60b7f0e871667f318a7cd"];
+		GTBranch *branch1 = [repository createBranchNamed:@"branch1" fromOID:oid1 message:@"new branch 1" error:&error];
+		expect(branch1).notTo(beNil());
+		expect(error).to(beNil());
+
+		GTOID *oid2 = [GTOID oidWithSHA:@"47563e7aba76b656a43c04d30b3b6fbe76da6e81"];
+		GTBranch *branch2 = [repository createBranchNamed:@"branch2" fromOID:oid2 message:@"new branch 2" error:&error];
+		expect(branch2).notTo(beNil());
+		expect(error).to(beNil());
+
+		__block GTMergeAnalysis analysis = 0;
+		expect(@([repository analyzeMerge:&analysis fromBranch:branch1 toBranch:branch2 error:&error])).to(beTruthy());
+		expect(error).to(beNil());
+		expect(@(analysis)).to(equal(GTMergeAnalysisNormal | 0));
+	});
+
+	it(@"should correctly recognize unmergeable merges", ^{
+		__block NSError *error = nil;
+		GTBranch *masterBranch = [repository lookUpBranchWithName:@"master" type:GTBranchTypeLocal success:NULL error:&error];
+		expect(masterBranch).notTo(beNil());
+		expect(error).to(beNil());
+
+		NSURL *mainURL = [repository.fileURL URLByAppendingPathComponent:@"main.m"];
+		NSData *newMainContent = [@"This used to be main..." dataUsingEncoding:NSUTF8StringEncoding];
+		expect(@([[NSFileManager defaultManager] createFileAtPath:mainURL.path contents:newMainContent attributes:nil])).to(beTruthy());
+
+		GTIndex *index = [repository indexWithError:NULL];
+		expect(@([index addFile:mainURL.lastPathComponent error:NULL])).to(beTruthy());
+		GTCommit *unconnectedCommit = [repository createCommitWithTree:[index writeTree:NULL] message:@"unconnected commit" parents:[[NSArray alloc] init] updatingReferenceNamed:nil error:&error];
+		expect(unconnectedCommit).toNot(beNil());
+		expect(error).to(beNil());
+
+		GTBranch *unconnectedBranch = [repository createBranchNamed:@"unconnected" fromOID:unconnectedCommit.OID message:@"Create a new branch that has no common ancestor with head" error:&error];
+		expect(unconnectedBranch).notTo(beNil());
+		expect(error).to(beNil());
+
+		__block GTMergeAnalysis analysis = 0;
+		expect(@([repository analyzeMerge:&analysis fromBranch:masterBranch toBranch:unconnectedBranch error:&error])).to(beTruthy());
+		expect(error).to(beNil());
+		expect(@(analysis)).to(equal(GTMergeAnalysisNone | 0));
+	});
+
+	it(@"should correctly recognize unborn merges", ^{
+		__block NSError *error = nil;
+		GTRepository *repo = self.blankFixtureRepository;
+		expect(@(repo.isHEADUnborn)).to(beTruthy());
+
+		NSURL *mainURL = [repo.fileURL URLByAppendingPathComponent:@"main.m"];
+		NSData *newMainContent = [@"new main file" dataUsingEncoding:NSUTF8StringEncoding];
+		expect(@([[NSFileManager defaultManager] createFileAtPath:mainURL.path contents:newMainContent attributes:nil])).to(beTruthy());
+
+		GTIndex *index = [repo indexWithError:NULL];
+		expect(@([index addFile:mainURL.lastPathComponent error:NULL])).to(beTruthy());
+		GTTree *commitTree = [index writeTree:&error];
+		expect(commitTree).toNot(beNil());
+		expect(error).to(beNil());
+
+		GTCommit *initialCommit = [repo createCommitWithTree:commitTree message:@"initial commit" parents:[[NSArray alloc] init] updatingReferenceNamed:nil error:&error];
+		expect(initialCommit).toNot(beNil());
+		expect(error).to(beNil());
+
+		GTBranch *unrelatedNewMaster = [repo createBranchNamed:@"new_master" fromOID:initialCommit.OID message:@"create master" error:&error];
+		expect(unrelatedNewMaster).toNot(beNil());
+		expect(error).to(beNil());
+
+		__block GTMergeAnalysis analysis = 0;
+		expect(@([repo analyzeMerge:&analysis fromBranch:unrelatedNewMaster error:&error])).to(beTruthy());
+		expect(error).to(beNil());
+		expect(@(analysis)).to(equal(GTMergeAnalysisUnborn | GTMergeAnalysisFastForward));
+	});
+});
+
 describe(@"-allTagsWithError:", ^{
 	it(@"should return all tags", ^{
 		NSError *error = nil;