[PATCH 7/9] merge-ort: format messages slightly different for use in headers

["Elijah Newren via GitGitGadget" <gitgitgadget@xxxxxxxxx>]

From: Elijah Newren <newren@xxxxxxxxx>

We want to add an ability for users to run
    git show --remerge-diff $MERGE_COMMIT
or even
    git log -p --remerge-diff ...
and have git show the differences between where the merge machinery
would stop and what is recorded in merge commits.  However, in such
cases, stdout is not an appropriate location to dump conflict messages.
We instead want these messages to appear as headers in the subsequent
diff.  For them to work as headers, though, we need for any multiline
messages to replace newlines with both a newline and a space.  Add a new
flag to signal when we want these messages modified in such a fashion,
and use it in path_msg() to modify these messages this way.

Signed-off-by: Elijah Newren <newren@xxxxxxxxx>
---
 merge-ort.c       | 36 ++++++++++++++++++++++++++++++++++--
 merge-recursive.c |  3 +++
 merge-recursive.h |  1 +
 3 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/merge-ort.c b/merge-ort.c
index c4d6c5c81cc..0ae3e4ffa75 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -634,17 +634,46 @@ static void path_msg(struct merge_options *opt,
 		     const char *fmt, ...)
 {
 	va_list ap;
-	struct strbuf *sb = strmap_get(&opt->priv->output, path);
+	struct strbuf *sb, *dest;
+	struct strbuf tmp = STRBUF_INIT;
+
+	if (opt->record_conflict_msgs_as_headers && omittable_hint)
+		return; /* Do not record mere hints in tree */
+	sb = strmap_get(&opt->priv->output, path);
 	if (!sb) {
 		sb = xmalloc(sizeof(*sb));
 		strbuf_init(sb, 0);
 		strmap_put(&opt->priv->output, path, sb);
 	}
 
+	dest = (opt->record_conflict_msgs_as_headers ? &tmp : sb);
+
 	va_start(ap, fmt);
-	strbuf_vaddf(sb, fmt, ap);
+	strbuf_vaddf(dest, fmt, ap);
 	va_end(ap);
 
+	if (opt->record_conflict_msgs_as_headers) {
+		int i_sb = 0, i_tmp = 0;
+
+		/* Copy tmp to sb, adding spaces after newlines */
+		strbuf_grow(sb, 2*tmp.len); /* more than sufficient */
+		for (; i_tmp < tmp.len; i_tmp++, i_sb++) {
+			/* Copy next character from tmp to sb */
+			sb->buf[sb->len + i_sb] = tmp.buf[i_tmp];
+
+			/* If we copied a newline, add a space */
+			if (tmp.buf[i_tmp] == '\n')
+				sb->buf[++i_sb] = ' ';
+		}
+		/* Update length and ensure it's NUL-terminated */
+		sb->len += i_sb;
+		sb->buf[sb->len] = '\0';
+
+		/* Clean up tmp */
+		strbuf_release(&tmp);
+	}
+
+	/* Add final newline character to sb */
 	strbuf_addch(sb, '\n');
 }
 
@@ -4246,6 +4275,9 @@ void merge_switch_to_result(struct merge_options *opt,
 		struct string_list olist = STRING_LIST_INIT_NODUP;
 		int i;
 
+		if (opt->record_conflict_msgs_as_headers)
+			BUG("Either display conflict messages or record them as headers, not both");
+
 		trace2_region_enter("merge", "display messages", opt->repo);
 
 		/* Hack to pre-allocate olist to the desired size */
diff --git a/merge-recursive.c b/merge-recursive.c
index bc73c52dd84..c9ba7e904a6 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -3714,6 +3714,9 @@ static int merge_start(struct merge_options *opt, struct tree *head)
 
 	assert(opt->priv == NULL);
 
+	/* Not supported; option specific to merge-ort */
+	assert(!opt->record_conflict_msgs_as_headers);
+
 	/* Sanity check on repo state; index must match head */
 	if (repo_index_has_changes(opt->repo, head, &sb)) {
 		err(opt, _("Your local changes to the following files would be overwritten by merge:\n  %s"),
diff --git a/merge-recursive.h b/merge-recursive.h
index 0795a1d3ec1..ebfdb7f994e 100644
--- a/merge-recursive.h
+++ b/merge-recursive.h
@@ -46,6 +46,7 @@ struct merge_options {
 	/* miscellaneous control options */
 	const char *subtree_shift;
 	unsigned renormalize : 1;
+	unsigned record_conflict_msgs_as_headers : 1;
 
 	/* internal fields used by the implementation */
 	struct merge_options_internal *priv;
-- 
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