From 2f95386dbbdce2b530d19d4f3916ae984c471013 Mon Sep 17 00:00:00 2001
From: Fedor <fedor@mail.ru>
Date: Mon, 20 May 2019 09:01:07 +0300
Subject: [PATCH] Handle the special case of a flex frame being the absolute
 containing block correctly from the CSS align code

---
 layout/generic/nsAbsoluteContainingBlock.cpp  | 28 +++++++++++---
 ...ion-absolute-containing-block-001-ref.html | 27 +++++++++++++
 ...osition-absolute-containing-block-001.html | 30 +++++++++++++++
 ...ion-absolute-containing-block-002-ref.html | 27 +++++++++++++
 ...osition-absolute-containing-block-002.html | 38 +++++++++++++++++++
 .../w3c-css/submitted/flexbox/reftest.list    |  4 ++
 6 files changed, 148 insertions(+), 6 deletions(-)
 create mode 100644 layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001-ref.html
 create mode 100644 layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001.html
 create mode 100644 layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002-ref.html
 create mode 100644 layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002.html

diff --git a/layout/generic/nsAbsoluteContainingBlock.cpp b/layout/generic/nsAbsoluteContainingBlock.cpp
index 7c48aae92..e3c847d01 100644
--- a/layout/generic/nsAbsoluteContainingBlock.cpp
+++ b/layout/generic/nsAbsoluteContainingBlock.cpp
@@ -409,14 +409,30 @@ OffsetToAlignedStaticPos(const ReflowInput& aKidReflowInput,
                         ? GetOrthogonalAxis(aAbsPosCBAxis)
                         : aAbsPosCBAxis);
 
+  const bool placeholderContainerIsContainingBlock =
+    aPlaceholderContainer == aKidReflowInput.mCBReflowInput->mFrame;
+
   nsIAtom* parentType = aPlaceholderContainer->GetType();
   LogicalSize alignAreaSize(pcWM);
   if (parentType == nsGkAtoms::flexContainerFrame) {
-    // The alignment container is the flex container's content box:
-    alignAreaSize = aPlaceholderContainer->GetLogicalSize(pcWM);
-    LogicalMargin pcBorderPadding =
-      aPlaceholderContainer->GetLogicalUsedBorderAndPadding(pcWM);
-    alignAreaSize -= pcBorderPadding.Size(pcWM);
+    // We store the frame rect in FinishAndStoreOverflow, which runs _after_
+    // reflowing the absolute frames, so handle the special case of the frame
+    // being the actual containing block here, by getting the size from
+    // aAbsPosCBSize.
+    //
+    // The alignment container is the flex container's content box.
+    if (placeholderContainerIsContainingBlock) {
+      alignAreaSize = aAbsPosCBSize.ConvertTo(pcWM, aAbsPosCBWM);
+      // aAbsPosCBSize is the padding-box, so substract the padding to get the
+      // content box.
+      alignAreaSize -=
+        aPlaceholderContainer->GetLogicalUsedPadding(pcWM).Size(pcWM);
+    } else {
+      alignAreaSize = aPlaceholderContainer->GetLogicalSize(pcWM);
+      LogicalMargin pcBorderPadding =
+        aPlaceholderContainer->GetLogicalUsedBorderAndPadding(pcWM);
+      alignAreaSize -= pcBorderPadding.Size(pcWM);
+    }
   } else if (parentType == nsGkAtoms::gridContainerFrame) {
     // This abspos elem's parent is a grid container. Per CSS Grid 10.1 & 10.2:
     //  - If the grid container *also* generates the abspos containing block (a
@@ -424,7 +440,7 @@ OffsetToAlignedStaticPos(const ReflowInput& aKidReflowInput,
     // the alignment container, too. (And its size is aAbsPosCBSize.)
     //  - Otherwise, we use the grid's padding box as the alignment container.
     // https://drafts.csswg.org/css-grid/#static-position
-    if (aPlaceholderContainer == aKidReflowInput.mCBReflowInput->mFrame) {
+    if (placeholderContainerIsContainingBlock) {
       // The alignment container is the grid area that we're using as the
       // absolute containing block.
       alignAreaSize = aAbsPosCBSize.ConvertTo(pcWM, aAbsPosCBWM);
diff --git a/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001-ref.html b/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001-ref.html
new file mode 100644
index 000000000..08eec8691
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001-ref.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<html><head>
+<meta http-equiv="content-type" content="text/html; charset=UTF-8"><title>CSS Test Reference</title>
+<meta charset="utf-8">
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
+<style>
+.parent {
+  position: fixed;
+  top: 0;
+  left: 0;
+  display: block;
+  width: 200px;
+  height: 200px;
+  background: yellow;
+}
+
+.child {
+  position: absolute;
+  left: 50px;
+  top: 50px;
+  width: 100px;
+  height: 100px;
+  background: green;
+}
+</style>
+</head><body><div class="parent"><div class="child"></div></div>
+</body></html>
\ No newline at end of file
diff --git a/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001.html b/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001.html
new file mode 100644
index 000000000..5f623cb84
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<html><head>
+<meta http-equiv="content-type" content="text/html; charset=UTF-8"><title>CSS Test: Absolutely positioned children of flex container with CSS align</title>
+<meta charset="utf-8">
+<link rel="help" href="https://drafts.csswg.org/css-flexbox/#abspos-items">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1386654">
+<link rel="match" href="https://hg.mozilla.org/mozilla-central/raw-file/6538de3b6137/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-001-ref.html">
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
+<style>
+.parent {
+  position: fixed;
+  top: 0;
+  left: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 200px;
+  height: 200px;
+  background: yellow;
+}
+
+.child {
+  position: absolute;
+  width: 100px;
+  height: 100px;
+  background: green;
+}
+</style>
+</head><body><div class="parent"><div class="child"></div></div>
+</body></html>
\ No newline at end of file
diff --git a/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002-ref.html b/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002-ref.html
new file mode 100644
index 000000000..df730047b
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002-ref.html
@@ -0,0 +1,27 @@
+<!DOCTYPE html>
+<html><head>
+<meta http-equiv="content-type" content="text/html; charset=UTF-8"><title>CSS Test Reference</title>
+<meta charset="utf-8">
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
+<style>
+.parent {
+  position: fixed;
+  top: 0;
+  left: 0;
+  display: block;
+  width: 200px;
+  height: 200px;
+  background: yellow;
+}
+
+.child {
+  position: absolute;
+  left: 60px;
+  top: 60px;
+  width: 100px;
+  height: 100px;
+  background: green;
+}
+</style>
+</head><body><div class="parent"><div class="child"></div></div>
+</body></html>
\ No newline at end of file
diff --git a/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002.html b/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002.html
new file mode 100644
index 000000000..9e89c5ad0
--- /dev/null
+++ b/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<html><head>
+<meta http-equiv="content-type" content="text/html; charset=UTF-8"><title>CSS Test: Absolutely positioned children of flex container with CSS align</title>
+<meta charset="utf-8">
+<link rel="help" href="https://drafts.csswg.org/css-flexbox/#abspos-items">
+<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1386654">
+<link rel="match" href="https://hg.mozilla.org/mozilla-central/raw-file/6538de3b6137/layout/reftests/w3c-css/submitted/flexbox/position-absolute-containing-block-002-ref.html">
+<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
+<style>
+.parent {
+  position: fixed;
+  top: 0;
+  left: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  width: 180px;
+  height: 180px;
+
+  /* Expand the background area to 200px, without touching the content-box,
+     which is what flex absolute children should be aligned relative to. */
+  border-top: 5px solid yellow;
+  padding-top: 15px;
+  border-left: 5px solid yellow;
+  padding-left: 15px;
+
+  background: yellow;
+}
+
+.child {
+  position: absolute;
+  width: 100px;
+  height: 100px;
+  background: green;
+}
+</style>
+</head><body><div class="parent"><div class="child"></div></div>
+</body></html>
\ No newline at end of file
diff --git a/layout/reftests/w3c-css/submitted/flexbox/reftest.list b/layout/reftests/w3c-css/submitted/flexbox/reftest.list
index fd8bfccc9..3df75aee6 100644
--- a/layout/reftests/w3c-css/submitted/flexbox/reftest.list
+++ b/layout/reftests/w3c-css/submitted/flexbox/reftest.list
@@ -211,3 +211,7 @@ fails == flexbox-min-height-auto-002b.html flexbox-min-height-auto-002-ref.html
 == flexbox-single-line-clamp-1.html flexbox-single-line-clamp-1-ref.html
 == flexbox-single-line-clamp-2.html flexbox-single-line-clamp-2-ref.html
 == flexbox-single-line-clamp-3.html flexbox-single-line-clamp-3-ref.html
+
+# Flexbox as an absolute containing block.
+== position-absolute-containing-block-001.html position-absolute-containing-block-001-ref.html
+== position-absolute-containing-block-002.html position-absolute-containing-block-002-ref.html