merge-recursive: fix unclear and outright wrong comments

Commits 7c0a6c8e47 ("merge-recursive: move some definitions around to
clean up the header", 2019-08-17), and b4db8a2b76 ("merge-recursive:
remove useless parameter in merge_trees()", 2019-08-17) added some
useful documentation to the functions, but had a few places where the
new comments were unclear or even misleading.  Fix those comments.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-recursive.c

@@ -3529,8 +3529,9 @@ static struct commit_list *reverse_commit_list(struct commit_list *list)
 }
 
 /*
- * Merge the commits h1 and h2, return the resulting virtual
- * commit object and a flag indicating the cleanness of the merge.
+ * Merge the commits h1 and h2, returning a flag (int) indicating the
+ * cleanness of the merge.  Also, if opt->priv->call_depth, create a
+ * virtual commit and write its location to *result.
  */
 static int merge_recursive_internal(struct merge_options *opt,
 				    struct commit *h1,

merge-recursive.h

@@ -69,9 +69,8 @@ int parse_merge_opt(struct merge_options *opt, const char *s);
  *
  * Outputs:
  *   - See RETURN VALUES above
- *   - No commit is created
  *   - opt->repo->index has the new index
- *   - $GIT_INDEX_FILE is not updated
+ *   - new index NOT written to disk
  *   - The working tree is updated with results of the merge
  */
 int merge_trees(struct merge_options *opt,
@@ -81,7 +80,7 @@ int merge_trees(struct merge_options *opt,
 
 /*
  * merge_recursive is like merge_trees() but with recursive ancestor
- * consolidation and, if the commit is clean, creation of a commit.
+ * consolidation.
  *
  * NOTE: empirically, about a decade ago it was determined that with more
  *       than two merge bases, optimal behavior was found when the
@@ -91,9 +90,9 @@ int merge_trees(struct merge_options *opt,
  *
  * Outputs:
  *   - See RETURN VALUES above
- *   - If merge is clean, a commit is created and its address written to *result
+ *   - *result is treated as scratch space for temporary recursive merges
  *   - opt->repo->index has the new index
- *   - $GIT_INDEX_FILE is not updated
+ *   - new index NOT written to disk
  *   - The working tree is updated with results of the merge
  */
 int merge_recursive(struct merge_options *opt,
@@ -109,9 +108,9 @@ int merge_recursive(struct merge_options *opt,
  *
  * Outputs:
  *   - See RETURN VALUES above
- *   - If merge is clean, a commit is created and its address written to *result
+ *   - *result is treated as scratch space for temporary recursive merges
  *   - opt->repo->index has the new index
- *   - $GIT_INDEX_FILE is updated
+ *   - new index also written to $GIT_INDEX_FILE on disk
  *   - The working tree is updated with results of the merge
  */
 int merge_recursive_generic(struct merge_options *opt,