From f69931552b8db1e9a098d0bd939c326dfee0a278 Mon Sep 17 00:00:00 2001
From: Patrick Walton <pcwalton@mimiga.net>
Date: Thu, 7 Apr 2016 10:47:31 -0700
Subject: [PATCH] =?UTF-8?q?layout:=20Disallow=20margins=20from=20collapsin?=
 =?UTF-8?q?g=20through=20block=20formatting=20contexts=20per=20CSS=202.1?=
 =?UTF-8?q?=20=C2=A7=208.3.1.?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Closes #10449.
---
 components/layout/block.rs                    |  2 +-
 .../html4/margin-collapse-009.htm.ini         |  3 --
 tests/wpt/mozilla/meta/MANIFEST.json          | 24 ++++++++++++++
 ..._formatting_context_margin_collapse_a.html | 28 +++++++++++++++++
 ...ormatting_context_margin_collapse_ref.html | 31 +++++++++++++++++++
 5 files changed, 84 insertions(+), 4 deletions(-)
 delete mode 100644 tests/wpt/metadata-css/css21_dev/html4/margin-collapse-009.htm.ini
 create mode 100644 tests/wpt/mozilla/tests/css/block_formatting_context_margin_collapse_a.html
 create mode 100644 tests/wpt/mozilla/tests/css/block_formatting_context_margin_collapse_ref.html

diff --git a/components/layout/block.rs b/components/layout/block.rs
index 4f69a9487d8..fa91b847b20 100644
--- a/components/layout/block.rs
+++ b/components/layout/block.rs
@@ -1751,7 +1751,7 @@ impl Flow for BlockFlow {
                 self.base.position.size.block = self.fragment.border_box.size.block;
             }
             None
-        } else if self.is_root() || self.base.flags.is_float() || self.is_inline_block() {
+        } else if self.is_root() || self.formatting_context_type() != FormattingContextType::None {
             // Root element margins should never be collapsed according to CSS § 8.3.1.
             debug!("assign_block_size: assigning block_size for root flow {:?}",
                    flow::base(self).debug_id());
diff --git a/tests/wpt/metadata-css/css21_dev/html4/margin-collapse-009.htm.ini b/tests/wpt/metadata-css/css21_dev/html4/margin-collapse-009.htm.ini
deleted file mode 100644
index 6627a225d8a..00000000000
--- a/tests/wpt/metadata-css/css21_dev/html4/margin-collapse-009.htm.ini
+++ /dev/null
@@ -1,3 +0,0 @@
-[margin-collapse-009.htm]
-  type: reftest
-  expected: FAIL
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 69c05eaecdc..121842c43ff 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -579,6 +579,18 @@
             "url": "/_mozilla/css/block_formatting_context_float_placement_a.html"
           }
         ],
+        "css/block_formatting_context_margin_collapse_a.html": [
+          {
+            "path": "css/block_formatting_context_margin_collapse_a.html",
+            "references": [
+              [
+                "/_mozilla/css/block_formatting_context_margin_collapse_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/block_formatting_context_margin_collapse_a.html"
+          }
+        ],
         "css/block_formatting_context_max_width_a.html": [
           {
             "path": "css/block_formatting_context_max_width_a.html",
@@ -7193,6 +7205,18 @@
           "url": "/_mozilla/css/block_formatting_context_float_placement_a.html"
         }
       ],
+      "css/block_formatting_context_margin_collapse_a.html": [
+        {
+          "path": "css/block_formatting_context_margin_collapse_a.html",
+          "references": [
+            [
+              "/_mozilla/css/block_formatting_context_margin_collapse_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/block_formatting_context_margin_collapse_a.html"
+        }
+      ],
       "css/block_formatting_context_max_width_a.html": [
         {
           "path": "css/block_formatting_context_max_width_a.html",
diff --git a/tests/wpt/mozilla/tests/css/block_formatting_context_margin_collapse_a.html b/tests/wpt/mozilla/tests/css/block_formatting_context_margin_collapse_a.html
new file mode 100644
index 00000000000..787505d08c2
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/block_formatting_context_margin_collapse_a.html
@@ -0,0 +1,28 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title></title>
+<link rel="match" href="block_formatting_context_margin_collapse_ref.html">
+<style>
+html, body {
+    margin: 0;
+    padding: 0;
+}
+main {
+    height: 300px;
+    width: 250px;
+    background-image: linear-gradient(to bottom, red, blue);
+    overflow: hidden;
+    background: blue;
+}
+
+div {
+    margin-top: 200px;
+    height: 200px;
+    width: 200px;
+    overflow: hidden;
+    background: green;
+}
+
+</style>
+<main><div></div></main>
+
diff --git a/tests/wpt/mozilla/tests/css/block_formatting_context_margin_collapse_ref.html b/tests/wpt/mozilla/tests/css/block_formatting_context_margin_collapse_ref.html
new file mode 100644
index 00000000000..3dfb8717acf
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/block_formatting_context_margin_collapse_ref.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title></title>
+<style>
+html, body {
+    margin: 0;
+    padding: 0;
+}
+main {
+    height: 300px;
+    width: 250px;
+    background-image: linear-gradient(to bottom, red, blue);
+    background: blue;
+    position: absolute;
+    top: 0;
+    left: 0;
+}
+
+div {
+    position: absolute;
+    top: 200px;
+    left: 0;
+    height: 100px;
+    width: 200px;
+    background: green;
+}
+
+</style>
+<main><div></div></main>
+
+