log: load decorations with --simplify-by-decoration

It's possible to specify --simplify-by-decoration but not --decorate. In
this case we do respect the simplification, but we don't actually show
any decorations. However, it works by lazy-loading the decorations when
needed; this is discussed in more detail in 0cc7380 (log-tree: call
load_ref_decorations() in get_name_decoration(), 2019-09-08).

This works for basic cases, but will fail to respect any --decorate-refs
option (or its variants). Those are handled only when cmd_log_init()
loads the ref decorations up front, which is only when --decorate is
specified explicitly (or as of the previous commit, when the userformat
asks for %d or similar).

We can solve this by making sure to load the decorations if we're going
to simplify using them but they're not otherwise going to be displayed.

The new test shows a simple case that fails without this patch. Note
that we expect two commits in the output: the one we asked for by
--decorate-refs, and the initial commit. The latter is just a quirk of
how --simplify-by-decoration works. Arguably it may be a bug, but it's
unrelated to this patch (which is just about the loading of the
decorations; you get the same behavior before this patch with an
explicit --decorate).

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

builtin/log.c

@@ -262,7 +262,7 @@ static void cmd_log_init_finish(int argc, const char **argv, const char *prefix,
 		}
 	}
 
-	if (decoration_style) {
+	if (decoration_style || rev->simplify_by_decoration) {
 		const struct string_list *config_exclude =
 			repo_config_get_value_multi(the_repository,
 						    "log.excludeDecoration");
@@ -274,7 +274,8 @@ static void cmd_log_init_finish(int argc, const char **argv, const char *prefix,
 						   item->string);
 		}
 
-		rev->show_decorations = 1;
+		if (decoration_style)
+			rev->show_decorations = 1;
 
 		load_ref_decorations(&decoration_filter, decoration_style);
 	}

t/t4202-log.sh

@@ -974,6 +974,21 @@ test_expect_success 'implied decorate does not override option' '
 	test_cmp expect actual
 '
 
+test_expect_success 'decorate-refs and simplify-by-decoration without output' '
+	cat >expect <<-\EOF &&
+	side-2
+	initial
+	EOF
+	# Do not just use a --format without %d here; we want to
+	# make sure that we did not accidentally turn on displaying
+	# the decorations, too. And that requires one of the regular
+	# formats.
+	git log --decorate-refs="*side-2" --oneline \
+		--simplify-by-decoration >actual.raw &&
+	sed "s/^[0-9a-f]* //" <actual.raw >actual &&
+	test_cmp expect actual
+'
+
 test_expect_success 'log.decorate config parsing' '
 	git log --oneline --decorate=full >expect.full &&
 	git log --oneline --decorate=short >expect.short &&