Fix git merge editor for renames (microsoft#209542)

Author: alexr00

extensions/git/src/commands.ts

@@ -711,10 +711,13 @@ export class CommandCenter {
 		}
 
 		try {
-			const [head, rebaseOrMergeHead] = await Promise.all([
+			const [head, rebaseOrMergeHead, diffBetween] = await Promise.all([
 				repo.getCommit('HEAD'),
-				isRebasing ? repo.getCommit('REBASE_HEAD') : repo.getCommit('MERGE_HEAD')
+				isRebasing ? repo.getCommit('REBASE_HEAD') : repo.getCommit('MERGE_HEAD'),
+				await repo.diffBetween(isRebasing ? 'REBASE_HEAD' : 'MERGE_HEAD', 'HEAD')
 			]);
+			const diffFile = diffBetween?.find(diff => diff.uri.fsPath === uri.fsPath);
+
 			// ours (current branch and commit)
 			current.detail = head.refNames.map(s => s.replace(/^HEAD ->/, '')).join(', ');
 			current.description = '$(git-commit) ' + head.hash.substring(0, 7);
@@ -723,7 +726,11 @@ export class CommandCenter {
 			// theirs
 			incoming.detail = rebaseOrMergeHead.refNames.join(', ');
 			incoming.description = '$(git-commit) ' + rebaseOrMergeHead.hash.substring(0, 7);
-			incoming.uri = toGitUri(uri, rebaseOrMergeHead.hash);
+			if (diffFile) {
+				incoming.uri = toGitUri(diffFile.originalUri, rebaseOrMergeHead.hash);
+			} else {
+				incoming.uri = toGitUri(uri, rebaseOrMergeHead.hash);
+			}
 
 		} catch (error) {
 			// not so bad, can continue with just uris