graph API: fix bug in graph_is_interesting()

Previously, graph_is_interesting() did not behave quite the same way as
the code in get_revision().  As a result, it would sometimes think
commits were uninteresting, even though get_revision() would return
them.  This resulted in incorrect lines in the graph output.

This change creates a get_commit_action() function, which
graph_is_interesting() and simplify_commit() both now use to determine
if a commit will be shown.  It is identical to the old simplify_commit()
behavior, except that it never calls rewrite_parents().

This problem was reported by Santi Béjar.  The following command
would exhibit the problem before, but now works correctly:

  git log --graph --simplify-by-decoration --oneline v1.6.3.3

Previously git graph did not display the output for this command
correctly between f29ac4f1 and 66996ecc, among other places.
Signed-off-by: NAdam Simpkins <simpkins@facebook.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

graph.c

@@ -286,9 +286,10 @@ static int graph_is_interesting(struct git_graph *graph, struct commit *commit)
 	}
 
 	/*
-	 * Uninteresting and pruned commits won't be printed
+	 * Otherwise, use get_commit_action() to see if this commit is
+	 * interesting
 	 */
-	return (commit->object.flags & (UNINTERESTING | TREESAME)) ? 0 : 1;
+	return get_commit_action(graph->revs, commit) == commit_show;
 }
 
 static struct commit_list *next_interesting_parent(struct git_graph *graph,

revision.c

@@ -1664,7 +1664,7 @@ static inline int want_ancestry(struct rev_info *revs)
 	return (revs->rewrite_parents || revs->children.name);
 }
 
-enum commit_action simplify_commit(struct rev_info *revs, struct commit *commit)
+enum commit_action get_commit_action(struct rev_info *revs, struct commit *commit)
 {
 	if (commit->object.flags & SHOWN)
 		return commit_ignore;
@@ -1692,12 +1692,23 @@ enum commit_action simplify_commit(struct rev_info *revs, struct commit *commit)
 			if (!commit->parents || !commit->parents->next)
 				return commit_ignore;
 		}
-		if (want_ancestry(revs) && rewrite_parents(revs, commit) < 0)
-			return commit_error;
 	}
 	return commit_show;
 }
 
+enum commit_action simplify_commit(struct rev_info *revs, struct commit *commit)
+{
+	enum commit_action action = get_commit_action(revs, commit);
+
+	if (action == commit_show &&
+	    !revs->show_all &&
+	    revs->prune && revs->dense && want_ancestry(revs)) {
+		if (rewrite_parents(revs, commit) < 0)
+			return commit_error;
+	}
+	return action;
+}
+
 static struct commit *get_revision_1(struct rev_info *revs)
 {
 	if (!revs->commits)

revision.h

@@ -165,6 +165,7 @@ enum commit_action {
 	commit_error
 };
 
+extern enum commit_action get_commit_action(struct rev_info *revs, struct commit *commit);
 extern enum commit_action simplify_commit(struct rev_info *revs, struct commit *commit);
 
 #endif

t/t6015-rev-list-show-all-parents.sh

+#!/bin/sh
+
+test_description='--show-all --parents does not rewrite TREESAME commits'
+
+. ./test-lib.sh
+
+test_expect_success 'set up --show-all --parents test' '
+	test_commit one foo.txt &&
+	commit1=`git rev-list -1 HEAD` &&
+	test_commit two bar.txt &&
+	commit2=`git rev-list -1 HEAD` &&
+	test_commit three foo.txt &&
+	commit3=`git rev-list -1 HEAD`
+	'
+
+test_expect_success '--parents rewrites TREESAME parents correctly' '
+	echo $commit3 $commit1 > expected &&
+	echo $commit1 >> expected &&
+	git rev-list --parents HEAD -- foo.txt > actual &&
+	test_cmp expected actual
+	'
+
+test_expect_success '--parents --show-all does not rewrites TREESAME parents' '
+	echo $commit3 $commit2 > expected &&
+	echo $commit2 $commit1 >> expected &&
+	echo $commit1 >> expected &&
+	git rev-list --parents --show-all HEAD -- foo.txt > actual &&
+	test_cmp expected actual
+	'
+
+test_done