From 6eb58e2c549411b43550e26ebff7d11acf300002 Mon Sep 17 00:00:00 2001
From: Patrick Walton <pcwalton@mimiga.net>
Date: Mon, 28 Mar 2016 15:52:05 -0700
Subject: [PATCH] layout: Only take nonnegative margins into account when
 estimating inline placement of floats.

Otherwise, the heuristics can pass even when there are no floats,
causing block formatting contexts to be speculated to be flowing around
floats that don't exist!

Closes #10237.
---
 components/layout/floats.rs                   | 32 +++++++++++--------
 tests/wpt/mozilla/meta/MANIFEST.json          | 24 ++++++++++++++
 ...speculation_negative_inline_margins_a.html | 30 +++++++++++++++++
 ...eculation_negative_inline_margins_ref.html | 29 +++++++++++++++++
 4 files changed, 101 insertions(+), 14 deletions(-)
 create mode 100644 tests/wpt/mozilla/tests/css/float_speculation_negative_inline_margins_a.html
 create mode 100644 tests/wpt/mozilla/tests/css/float_speculation_negative_inline_margins_ref.html

diff --git a/components/layout/floats.rs b/components/layout/floats.rs
index e3ae4716e53..a31d7461db0 100644
--- a/components/layout/floats.rs
+++ b/components/layout/floats.rs
@@ -459,8 +459,8 @@ impl SpeculatedFloatPlacement {
         }
     }
 
-    /// Given the speculated inline size of the floats in for this flow, computes the speculated
-    /// inline size of the floats out for this flow.
+    /// Given the speculated inline size of the floats out for this flow's last child, computes the
+    /// speculated inline size of the floats out for this flow.
     pub fn compute_floats_out(&mut self, flow: &mut Flow) {
         if flow.is_block_like() {
             let block_flow = flow.as_block();
@@ -470,10 +470,10 @@ impl SpeculatedFloatPlacement {
                 if self.left > Au(0) || self.right > Au(0) {
                     let speculated_inline_content_edge_offsets =
                         block_flow.fragment.guess_inline_content_edge_offsets();
-                    if self.left > Au(0) {
+                    if self.left > Au(0) && speculated_inline_content_edge_offsets.start > Au(0) {
                         self.left = self.left + speculated_inline_content_edge_offsets.start
                     }
-                    if self.right > Au(0) {
+                    if self.right > Au(0) && speculated_inline_content_edge_offsets.end > Au(0) {
                         self.right = self.right + speculated_inline_content_edge_offsets.end
                     }
                 }
@@ -507,16 +507,20 @@ impl SpeculatedFloatPlacement {
         let speculated_inline_content_edge_offsets =
             parent_block_flow.fragment.guess_inline_content_edge_offsets();
 
-        if placement.left > speculated_inline_content_edge_offsets.start {
-            placement.left = placement.left - speculated_inline_content_edge_offsets.start
-        } else {
-            placement.left = Au(0)
-        };
-        if placement.right > speculated_inline_content_edge_offsets.end {
-            placement.right = placement.right - speculated_inline_content_edge_offsets.end
-        } else {
-            placement.right = Au(0)
-        };
+        if speculated_inline_content_edge_offsets.start > Au(0) {
+            placement.left = if placement.left > speculated_inline_content_edge_offsets.start {
+                placement.left - speculated_inline_content_edge_offsets.start
+            } else {
+                Au(0)
+            }
+        }
+        if speculated_inline_content_edge_offsets.end > Au(0) {
+            placement.right = if placement.right > speculated_inline_content_edge_offsets.end {
+                placement.right - speculated_inline_content_edge_offsets.end
+            } else {
+                Au(0)
+            }
+        }
 
         placement
     }
diff --git a/tests/wpt/mozilla/meta/MANIFEST.json b/tests/wpt/mozilla/meta/MANIFEST.json
index 947e3ae93a5..8b24f561ea3 100644
--- a/tests/wpt/mozilla/meta/MANIFEST.json
+++ b/tests/wpt/mozilla/meta/MANIFEST.json
@@ -1484,6 +1484,18 @@
             "url": "/_mozilla/css/float_right_intrinsic_width_a.html"
           }
         ],
+        "css/float_speculation_negative_inline_margins_a.html": [
+          {
+            "path": "css/float_speculation_negative_inline_margins_a.html",
+            "references": [
+              [
+                "/_mozilla/css/float_speculation_negative_inline_margins_ref.html",
+                "=="
+              ]
+            ],
+            "url": "/_mozilla/css/float_speculation_negative_inline_margins_a.html"
+          }
+        ],
         "css/float_table_a.html": [
           {
             "path": "css/float_table_a.html",
@@ -7822,6 +7834,18 @@
           "url": "/_mozilla/css/float_right_intrinsic_width_a.html"
         }
       ],
+      "css/float_speculation_negative_inline_margins_a.html": [
+        {
+          "path": "css/float_speculation_negative_inline_margins_a.html",
+          "references": [
+            [
+              "/_mozilla/css/float_speculation_negative_inline_margins_ref.html",
+              "=="
+            ]
+          ],
+          "url": "/_mozilla/css/float_speculation_negative_inline_margins_a.html"
+        }
+      ],
       "css/float_table_a.html": [
         {
           "path": "css/float_table_a.html",
diff --git a/tests/wpt/mozilla/tests/css/float_speculation_negative_inline_margins_a.html b/tests/wpt/mozilla/tests/css/float_speculation_negative_inline_margins_a.html
new file mode 100644
index 00000000000..383ec5b5552
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/float_speculation_negative_inline_margins_a.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title></title>
+<link rel="match" href="float_speculation_negative_inline_margins_ref.html">
+<style>
+  * {
+    margin: 0;
+    padding: 0;
+    font-size: 0;
+  }
+  .red {
+    left: 50%;
+    position: absolute;
+    top: 40px;
+    width: 480px;
+    margin-left: -240px;
+    background: red;
+  }
+  .green {
+    display: block;
+    width: 410px;
+    height: 34px;
+    line-height: 34px;
+    background: green;
+    border: none
+  }
+</style>
+
+<div class="red"><input class="green"></div>
+
diff --git a/tests/wpt/mozilla/tests/css/float_speculation_negative_inline_margins_ref.html b/tests/wpt/mozilla/tests/css/float_speculation_negative_inline_margins_ref.html
new file mode 100644
index 00000000000..db43f561b89
--- /dev/null
+++ b/tests/wpt/mozilla/tests/css/float_speculation_negative_inline_margins_ref.html
@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title></title>
+<style>
+  * {
+    margin: 0;
+    padding: 0;
+    font-size: 0;
+  }
+  .red {
+    left: 50%;
+    position: absolute;
+    top: 40px;
+    width: 480px;
+    margin-left: -240px;
+    background: red;
+  }
+  .green {
+    display: block;
+    width: 410px;
+    height: 34px;
+    line-height: 34px;
+    background: green;
+    border: none
+  }
+</style>
+
+<div class="red"><div class="green"></div>
+