Subject: [PATCH] Simplified merge logic

From: "Seija K. via GitGitGadget" <[email-masked]>
Date: Sun, 08 Nov 2020 21:37:36 +0000

From: pi1024e <[email-masked]>

commit: Avoid extraneous boolean checking by simplifying the if statements.
Signed-off-by: Seija <[email-masked]>
---
    Simplified merge logic
    
    The logic for the merging is somewhat confusing. So I simplified it to
    be equivalent. I tested all my changes to ensure in practice they work.
    
    The first thing I did was test out which branch would occur for every
    possible value of 
    
    remoteheads->nextcommon->nextoption_commitBranchTTTATTFATFTATFFAFTTCFTFC
    FFTBFFFAUsing this truth table, I was able to deduce that if the second
    branch ran, the if statement for the first branch was false. Taking the
    inverse, it was then found many of the checks were redundant, so the if
    statement was rewritten to have each branch run under the same exact
    conditions, except each value is evaluated as little as possible.
    
    I hope you can approve of this and show me how to send it.
    
    Thank you.

Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-911%2Fpi1024e%2Fmerge-cleanup-v1
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-911/pi1024e/merge-cleanup-v1
Pull-Request: https://github.com/git/git/pull/911

 builtin/merge.c | 85 ++++++++++++++++++++++---------------------------
 1 file changed, 38 insertions(+), 47 deletions(-)

diff --git a/builtin/merge.c b/builtin/merge.c
index 4c133402a6..9664da6031 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -853,9 +853,8 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 	if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg",
 			    git_path_merge_msg(the_repository), "merge", NULL))
 		abort_commit(remoteheads, NULL);
-	if (0 < option_edit) {
-		if (launch_editor(git_path_merge_msg(the_repository), NULL, NULL))
-			abort_commit(remoteheads, NULL);
+	if (0 < option_edit && launch_editor(git_path_merge_msg(the_repository), NULL, NULL)) {
+		abort_commit(remoteheads, NULL);
 	}
 
 	if (!no_verify && run_commit_hook(0 < option_edit, get_index_file(),
@@ -1213,7 +1212,7 @@ static int merging_a_throwaway_tag(struct commit *commit)
 	if (!merge_remote_util(commit) ||
 	    !merge_remote_util(commit)->obj ||
 	    merge_remote_util(commit)->obj->type != OBJ_TAG)
-		return is_throwaway_tag;
+		return 0;
 
 	/*
 	 * Now we know we are merging a tag object.  Are we downstream
@@ -1459,13 +1458,12 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 			fast_forward = FF_NO;
 	}
 
-	if (!use_strategies) {
-		if (!remoteheads)
-			; /* already up-to-date */
-		else if (!remoteheads->next)
-			add_strategies(pull_twohead, DEFAULT_TWOHEAD);
-		else
+	if (!use_strategies && remoteheads) {
+		/* not up-to-date */
+		if (remoteheads->next)
 			add_strategies(pull_octopus, DEFAULT_OCTOPUS);
+		else
+			add_strategies(pull_twohead, DEFAULT_TWOHEAD);
 	}
 
 	for (i = 0; i < use_strategies_nr; i++) {
@@ -1475,15 +1473,15 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 			allow_trivial = 0;
 	}
 
-	if (!remoteheads)
-		; /* already up-to-date */
-	else if (!remoteheads->next)
-		common = get_merge_bases(head_commit, remoteheads->item);
-	else {
-		struct commit_list *list = remoteheads;
-		commit_list_insert(head_commit, &list);
-		common = get_octopus_merge_bases(list);
-		free(list);
+	if (remoteheads) {
+		/* not up-to-date */
+		if (remoteheads->next) {
+			struct commit_list *list = remoteheads;
+			commit_list_insert(head_commit, &list);
+			common = get_octopus_merge_bases(list);
+			free(list);
+		} else
+			common = get_merge_bases(head_commit, remoteheads->item);
 	}
 
 	update_ref("updating ORIG_HEAD", "ORIG_HEAD",
@@ -1542,31 +1540,7 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 		finish(head_commit, remoteheads, &commit->object.oid, msg.buf);
 		remove_merge_branch_state(the_repository);
 		goto done;
-	} else if (!remoteheads->next && common->next)
-		;
-		/*
-		 * We are not doing octopus and not fast-forward.  Need
-		 * a real merge.
-		 */
-	else if (!remoteheads->next && !common->next && option_commit) {
-		/*
-		 * We are not doing octopus, not fast-forward, and have
-		 * only one common.
-		 */
-		refresh_cache(REFRESH_QUIET);
-		if (allow_trivial && fast_forward != FF_ONLY) {
-			/* See if it is really trivial. */
-			git_committer_info(IDENT_STRICT);
-			printf(_("Trying really trivial in-index merge...\n"));
-			if (!read_tree_trivial(&common->item->object.oid,
-					       &head_commit->object.oid,
-					       &remoteheads->item->object.oid)) {
-				ret = merge_trivial(head_commit, remoteheads);
-				goto done;
-			}
-			printf(_("Nope.\n"));
-		}
-	} else {
+	} else if (remoteheads->next || (!common->next && !option_commit)) {
 		/*
 		 * An octopus.  If we can reach all the remote we are up
 		 * to date.
@@ -1592,6 +1566,24 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 			finish_up_to_date(_("Already up to date. Yeeah!"));
 			goto done;
 		}
+	} else if (!common->next) {
+		/*
+		 * We are not doing octopus, not fast-forward, and have
+		 * only one common.
+		 */
+		refresh_cache(REFRESH_QUIET);
+		if (allow_trivial && fast_forward != FF_ONLY) {
+			/* See if it is really trivial. */
+			git_committer_info(IDENT_STRICT);
+			printf(_("Trying really trivial in-index merge...\n"));
+			if (!read_tree_trivial(&common->item->object.oid,
+					       &head_commit->object.oid,
+					       &remoteheads->item->object.oid)) {
+				ret = merge_trivial(head_commit, remoteheads);
+				goto done;
+			}
+			printf(_("Nope.\n"));
+		}
 	}
 
 	if (fast_forward == FF_ONLY)
@@ -1685,9 +1677,8 @@ int cmd_merge(int argc, const char **argv, const char *prefix)
 				use_strategies[0]->name);
 		ret = 2;
 		goto done;
-	} else if (best_strategy == wt_strategy)
-		; /* We already have its result in the working tree. */
-	else {
+	} else if (best_strategy != wt_strategy) {
+		/* We do not have its result in the working tree. */
 		printf(_("Rewinding the tree to pristine...\n"));
 		restore_state(&head_commit->object.oid, &stash);
 		printf(_("Using the %s to prepare resolving by hand.\n"),

base-commit: 7f7ebe054af6d831b999d6c2241b9227c4e4e08d
-- 
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