Merge branch 'en/remerge-diff'

"git log --remerge-diff" shows the difference from mechanical merge
result and the result that is actually recorded in a merge commit.

* en/remerge-diff:
  diff-merges: avoid history simplifications when diffing merges
  merge-ort: mark conflict/warning messages from inner merges as omittable
  show, log: include conflict/warning messages in --remerge-diff headers
  diff: add ability to insert additional headers for paths
  merge-ort: format messages slightly different for use in headers
  merge-ort: mark a few more conflict messages as omittable
  merge-ort: capture and print ll-merge warnings in our preferred fashion
  ll-merge: make callers responsible for showing warnings
  log: clean unneeded objects during `log --remerge-diff`
  show, log: provide a --remerge-diff capability

1 files changed, 50 insertions, 5 deletions

diff --git a/merge-ort.c b/merge-ort.c
index d455fca7d2..d85b1cd99e 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -634,17 +634,51 @@ 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 headers */
+	if (opt->record_conflict_msgs_as_headers && opt->priv->call_depth)
+		return; /* Do not record inner merge issues in headers */
+	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;
+
+		/* Start with the specified prefix */
+		if (opt->msg_header_prefix)
+			strbuf_addf(sb, "%s ", opt->msg_header_prefix);
+
+		/* Copy tmp to sb, adding spaces after newlines */
+		strbuf_grow(sb, sb->len + 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';
+
+		strbuf_release(&tmp);
+	}
+
+	/* Add final newline character to sb */
 	strbuf_addch(sb, '\n');
 }
 
@@ -1743,7 +1777,7 @@ static int merge_3way(struct merge_options *opt,
 	mmfile_t orig, src1, src2;
 	struct ll_merge_options ll_opts = {0};
 	char *base, *name1, *name2;
-	int merge_status;
+	enum ll_merge_result merge_status;
 
 	if (!opt->priv->attr_index.initialized)
 		initialize_attr_index(opt);
@@ -1787,6 +1821,10 @@ static int merge_3way(struct merge_options *opt,
 	merge_status = ll_merge(result_buf, path, &orig, base,
 				&src1, name1, &src2, name2,
 				&opt->priv->attr_index, &ll_opts);
+	if (merge_status == LL_MERGE_BINARY_CONFLICT)
+		path_msg(opt, path, 0,
+			 "warning: Cannot merge binary files: %s (%s vs. %s)",
+			 path, name1, name2);
 
 	free(base);
 	free(name1);
@@ -2416,7 +2454,7 @@ static void apply_directory_rename_modifications(struct merge_options *opt,
 		 */
 		ci->path_conflict = 1;
 		if (pair->status == 'A')
-			path_msg(opt, new_path, 0,
+			path_msg(opt, new_path, 1,
 				 _("CONFLICT (file location): %s added in %s "
 				   "inside a directory that was renamed in %s, "
 				   "suggesting it should perhaps be moved to "
@@ -2424,7 +2462,7 @@ static void apply_directory_rename_modifications(struct merge_options *opt,
 				 old_path, branch_with_new_path,
 				 branch_with_dir_rename, new_path);
 		else
-			path_msg(opt, new_path, 0,
+			path_msg(opt, new_path, 1,
 				 _("CONFLICT (file location): %s renamed to %s "
 				   "in %s, inside a directory that was renamed "
 				   "in %s, suggesting it should perhaps be "
@@ -4259,6 +4297,9 @@ 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 */
@@ -4360,6 +4401,9 @@ static void merge_start(struct merge_options *opt, struct merge_result *result)
 	assert(opt->recursive_variant >= MERGE_VARIANT_NORMAL &&
 	       opt->recursive_variant <= MERGE_VARIANT_THEIRS);
 
+	if (opt->msg_header_prefix)
+		assert(opt->record_conflict_msgs_as_headers);
+
 	/*
 	 * detect_renames, verbosity, buffer_output, and obuf are ignored
 	 * fields that were used by "recursive" rather than "ort" -- but
@@ -4560,6 +4604,7 @@ redo:
 	trace2_region_leave("merge", "process_entries", opt->repo);
 
 	/* Set return values */
+	result->path_messages = &opt->priv->output;
 	result->tree = parse_tree_indirect(&working_tree_oid);
 	/* existence of conflicted entries implies unclean */
 	result->clean &= strmap_empty(&opt->priv->conflicted);