blame: allow "blame file" in the middle of a conflicted merge

"git blame file" has always meant "find the origin of each line of
the file in the history leading to HEAD, oh by the way, blame the
lines that are modified locally to the working tree".

This teaches "git blame" that during a conflicted merge, some
uncommitted changes may have come from the other history that is
being merged.

The verify_working_tree_path() function introduced in the previous
patch to notice a typo in the filename (primarily on case insensitive
filesystems) has been updated to allow a filename that does not exist
in HEAD (i.e. the tip of our history) as long as it exists one of the
commits being merged, so that a "we deleted, the other side modified"
case tracks the history of the file in the history of the other side.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 70 insertions, 25 deletions

diff --git a/builtin/blame.c b/builtin/blame.c
index 83683b8287..449880e802 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -2044,17 +2044,53 @@ static int git_blame_config(const char *var, const char *value, void *cb)
 	return git_default_config(var, value, cb);
 }
 
-static void verify_working_tree_path(unsigned char *head_sha1, const char *path)
+static void verify_working_tree_path(struct commit *work_tree, const char *path)
 {
-	unsigned char blob_sha1[20];
-	unsigned mode;
+	struct commit_list *parents;
 
-	if (!resolve_ref_unsafe("HEAD", head_sha1, 1, NULL))
-		die("no such ref: HEAD");
-	if (get_tree_entry(head_sha1, path, blob_sha1, &mode))
-		die("no such path '%s' in HEAD", path);
-	if (sha1_object_info(blob_sha1, NULL) != OBJ_BLOB)
-		die("path '%s' in HEAD is not a blob", path);
+	for (parents = work_tree->parents; parents; parents = parents->next) {
+		const unsigned char *commit_sha1 = parents->item->object.sha1;
+		unsigned char blob_sha1[20];
+		unsigned mode;
+
+		if (!get_tree_entry(commit_sha1, path, blob_sha1, &mode) &&
+		    sha1_object_info(blob_sha1, NULL) == OBJ_BLOB)
+			return;
+	}
+	die("no such path '%s' in HEAD", path);
+}
+
+static struct commit_list **append_parent(struct commit_list **tail, const unsigned char *sha1)
+{
+	struct commit *parent;
+
+	parent = lookup_commit_reference(sha1);
+	if (!parent)
+		die("no such commit %s", sha1_to_hex(sha1));
+	return &commit_list_insert(parent, tail)->next;
+}
+
+static void append_merge_parents(struct commit_list **tail)
+{
+	int merge_head;
+	const char *merge_head_file = git_path("MERGE_HEAD");
+	struct strbuf line = STRBUF_INIT;
+
+	merge_head = open(merge_head_file, O_RDONLY);
+	if (merge_head < 0) {
+		if (errno == ENOENT)
+			return;
+		die("cannot open '%s' for reading", merge_head_file);
+	}
+
+	while (!strbuf_getwholeline_fd(&line, merge_head, '\n')) {
+		unsigned char sha1[20];
+		if (line.len < 40 || get_sha1_hex(line.buf, sha1))
+			die("unknown line in '%s': %s", merge_head_file, line.buf);
+		tail = append_parent(tail, sha1);
+	}
+	close(merge_head);
+	strbuf_release(&line);
 }
 
 /*
@@ -2067,6 +2103,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 {
 	struct commit *commit;
 	struct origin *origin;
+	struct commit_list **parent_tail, *parent;
 	unsigned char head_sha1[20];
 	struct strbuf buf = STRBUF_INIT;
 	const char *ident;
@@ -2074,19 +2111,38 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	int size, len;
 	struct cache_entry *ce;
 	unsigned mode;
-
-	verify_working_tree_path(head_sha1, path);
+	struct strbuf msg = STRBUF_INIT;
 
 	time(&now);
 	commit = xcalloc(1, sizeof(*commit));
-	commit->parents = xcalloc(1, sizeof(*commit->parents));
-	commit->parents->item = lookup_commit_reference(head_sha1);
 	commit->object.parsed = 1;
 	commit->date = now;
 	commit->object.type = OBJ_COMMIT;
+	parent_tail = &commit->parents;
+
+	if (!resolve_ref_unsafe("HEAD", head_sha1, 1, NULL))
+		die("no such ref: HEAD");
+
+	parent_tail = append_parent(parent_tail, head_sha1);
+	append_merge_parents(parent_tail);
+	verify_working_tree_path(commit, path);
 
 	origin = make_origin(commit, path);
 
+	ident = fmt_ident("Not Committed Yet", "not.committed.yet", NULL, 0);
+	strbuf_addstr(&msg, "tree 0000000000000000000000000000000000000000\n");
+	for (parent = commit->parents; parent; parent = parent->next)
+		strbuf_addf(&msg, "parent %s\n",
+			    sha1_to_hex(parent->item->object.sha1));
+	strbuf_addf(&msg,
+		    "author %s\n"
+		    "committer %s\n\n"
+		    "Version of %s from %s\n",
+		    ident, ident, path,
+		    (!contents_from ? path :
+		     (!strcmp(contents_from, "-") ? "standard input" : contents_from)));
+	commit->buffer = strbuf_detach(&msg, NULL);
+
 	if (!contents_from || strcmp("-", contents_from)) {
 		struct stat st;
 		const char *read_from;
@@ -2123,7 +2179,6 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	}
 	else {
 		/* Reading from stdin */
-		contents_from = "standard input";
 		mode = 0;
 		if (strbuf_read(&buf, 0, 0) < 0)
 			die_errno("failed to read from stdin");
@@ -2167,16 +2222,6 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 	 */
 	cache_tree_invalidate_path(active_cache_tree, path);
 
-	commit->buffer = xmalloc(400);
-	ident = fmt_ident("Not Committed Yet", "not.committed.yet", NULL, 0);
-	snprintf(commit->buffer, 400,
-		"tree 0000000000000000000000000000000000000000\n"
-		"parent %s\n"
-		"author %s\n"
-		"committer %s\n\n"
-		"Version of %s from %s\n",
-		sha1_to_hex(head_sha1),
-		ident, ident, path, contents_from ? contents_from : path);
 	return commit;
 }
 
diff --git a/t/t8004-blame-with-conflicts.sh b/t/t8004-blame-with-conflicts.sh
index b4a260a0fc..9c353ab222 100755
--- a/t/t8004-blame-with-conflicts.sh
+++ b/t/t8004-blame-with-conflicts.sh
@@ -67,7 +67,7 @@ test_expect_success \
 '
 
 test_expect_success 'blame does not crash with conflicted file in stages 1,3' '
-	test_must_fail git blame file1
+	git blame file1
 '
 
 test_done