test: add alloc@zpos-4x-domino-fail

This test makes sure composited layers make layers underneath fall back to
composition too, in a transitive manner. That is, if plane A is under plane B
which is itself under plane C, plane A falling back to composition means that
both planes B and C fall back to composition too (even if C isn't directly
underneath A).

test/meson.build

@@ -33,6 +33,7 @@ alloc_tests = [
 	#'zpos-3x-disjoint',
 	'zpos-4x-intersect-partial',
 	#'zpos-4x-disjoint',
+	'zpos-4x-domino-fail',
 ]
 
 foreach name : alloc_tests

test/test_alloc.c

@@ -327,6 +327,47 @@ static struct test_case tests[] = {
 			},
 		},
 	},
+	{
+		.name = "zpos-4x-domino-fail",
+		/* A layer on top falls back to composition. There is a layer at
+		 * zpos=2 which doesn't overlap and could be mapped to a plane,
+		 * however another layer at zpos=3 overlaps both and prevents
+		 * all layers from being mapped to a plane. */
+		.layers = {
+			{
+				.width = 1920,
+				.height = 1080,
+				.zpos = 1,
+				.compat = { PRIMARY_PLANE },
+				.result = PRIMARY_PLANE,
+			},
+			{
+				.width = 100,
+				.height = 100,
+				.zpos = 4,
+				.compat = { NULL },
+				.result = NULL,
+			},
+			{
+				.x = 100,
+				.y = 100,
+				.width = 100,
+				.height = 100,
+				.zpos = 2,
+				.compat = FIRST_4_PLANES,
+				.result = NULL,
+			},
+			{
+				.x = 50,
+				.y = 50,
+				.width = 100,
+				.height = 100,
+				.zpos = 3,
+				.compat = FIRST_4_PLANES,
+				.result = NULL,
+			},
+		},
+	},
 };
 
 static void run_test(struct test_layer *test_layers)