CSS: Make `offsetHeight( true )`, etc. include negative margins

This regressed in gh-3656 as the added logic to include scroll gutters
in `.innerWidth()` / `.innerHeight()` didn't take negative margins into
account. This broke handling of negative margins in
`.offsetHeight( true )` and `.offsetWidth( true )`. To fix it, calculate
margin delta separately and only add it after the scroll gutter
adjustment logic.

Fixes gh-3982
Closes gh-5234
Ref gh-3656

1 files changed, 6 insertions, 3 deletions

diff --git a/src/css.js b/src/css.js
index 29dca0e42..a69ad1730 100644
--- a/src/css.js
+++ b/src/css.js
@@ -46,7 +46,8 @@ function setPositiveNumber( _elem, value, subtract ) {
 function boxModelAdjustment( elem, dimension, box, isBorderBox, styles, computedVal ) {
 	var i = dimension === "width" ? 1 : 0,
 		extra = 0,
-		delta = 0;
+		delta = 0,
+		marginDelta = 0;
 
 	// Adjustment may not be necessary
 	if ( box === ( isBorderBox ? "border" : "content" ) ) {
@@ -56,8 +57,10 @@ function boxModelAdjustment( elem, dimension, box, isBorderBox, styles, computed
 	for ( ; i < 4; i += 2 ) {
 
 		// Both box models exclude margin
+		// Count margin delta separately to only add it after scroll gutter adjustment.
+		// This is needed to make negative margins work with `outerHeight( true )` (gh-3982).
 		if ( box === "margin" ) {
-			delta += jQuery.css( elem, box + cssExpand[ i ], true, styles );
+			marginDelta += jQuery.css( elem, box + cssExpand[ i ], true, styles );
 		}
 
 		// If we get here with a content-box, we're seeking "padding" or "border" or "margin"
@@ -108,7 +111,7 @@ function boxModelAdjustment( elem, dimension, box, isBorderBox, styles, computed
 		) ) || 0;
 	}
 
-	return delta;
+	return delta + marginDelta;
 }
 
 function getWidthOrHeight( elem, dimension, extra ) {