Ability to checkout from an index

Author: tiennou

ObjectiveGit/GTRepository.h

@@ -526,6 +526,15 @@ typedef NS_ENUM(NSInteger, GTRepositoryStateType) {
 /// Returns YES if operation was successful, NO otherwise
 - (BOOL)checkoutReference:(GTReference *)targetReference options:(nullable GTCheckoutOptions *)options error:(NSError **)error;
 
+/// Checkout an index
+///
+/// index   - The index to checkout. Must not be nil.
+/// options - The checkout options to use. Can be nil.
+/// error   - The error if one occurred. Can be NULL.
+///
+/// Returns YES if operation was successful, NO otherwise
+- (BOOL)checkoutIndex:(GTIndex *)index options:(nullable GTCheckoutOptions *)options error:(NSError **)error;
+
 /// Flush the gitattributes cache.
 - (void)flushAttributesCache;
 

ObjectiveGit/GTRepository.m

@@ -831,6 +831,15 @@ - (BOOL)checkoutReference:(GTReference *)targetReference options:(GTCheckoutOpti
 	return [self moveHEADToReference:targetReference error:error];
 }
 
+- (BOOL)checkoutIndex:(GTIndex *)index options:(GTCheckoutOptions *)options error:(NSError **)error {
+	int gitError = git_checkout_index(self.git_repository, index.git_index, options.git_checkoutOptions);
+	if (gitError < GIT_OK) {
+		if (error != NULL) *error = [NSError git_errorFor:gitError description:@"Failed to checkout index."];
+		return NO;
+	}
+	return YES;
+}
+
 - (void)flushAttributesCache {
 	git_attr_cache_flush(self.git_repository);
 }