[css-flexbox][css-grid] Fix calculation of intrinsic sizes of grid/flex containers when tracks/items flex factors sum to less than one. #1735

Author: fantasai

css-flexbox/Overview.bs

@@ -2809,9 +2809,18 @@ Flex Container Intrinsic Main Sizes</h4>
 			Within each line,
 			find the largest <var>max-content flex fraction</var>
 			among all the <a>flex items</a>.
+			If the sum of the <a>flex grow factors</a>
+			(<a>flex shrink factors</a>,
+			if the largest <var>max-content flex fraction</var> was negative)
+			on that line is less than one,
+			divide each <a>flex grow factor</a> (<a>flex shrink factor</a>)
+			by that sum to rescale their total to one.
+
+		<li>
 			Add each item’s <a>flex base size</a>
-			to the product of its <a>flex grow factor</a>
-			(or <a>scaled flex shrink factor</a>, if the chosen <var>max-content flex fraction</var> was negative)
+			to the product of its <em>rescaled</em> <a>flex grow factor</a>
+			(or <em>rescaled</em> <a>scaled flex shrink factor</a>,
+			if the chosen <var>max-content flex fraction</var> was negative)
 			and the chosen <var>max-content flex fraction</var>,
 			then clamp that result by the <a>max main size property</a>
 			floored by the <a>min main size property</a>.

css-flexbox/issues-cr-20160526.bsi

@@ -392,8 +392,10 @@ Issue 42.
 Summary:  Intrinsic sizing with ∑flex < 1 is broken
 From:     fantasai
 Comment:  https://github.com/w3c/csswg-drafts/issues/1735
-Open:     =WG= Resolve.
+Response: https://github.com/w3c/csswg-drafts/issues/1735#issuecomment-329218845
+Open:     Accepted
 Resolved: Bugfix
+Verified: =dholbert= Review.
 ----
 Issue 43.
 Summary:  Rename “Implied Minimum Size” section to “Automatic Minimum Size”
@@ -408,5 +410,13 @@ Summary:  Confusion over content size vs transferred size of images.
 From:     AmeliaBR
 Comment:  https://github.com/w3c/csswg-drafts/issues/694
 Response: https://github.com/w3c/csswg-drafts/issues/694#issuecomment-315920507
-Closed:   OutOfScope, refiled as https://github.com/w3c/csswg-drafts/issues/1609
+Closed:   OutOfScope
+Note:     Refiled as https://github.com/w3c/csswg-drafts/issues/1609
+----
+Issue 45.
+Summary:  Clarify sentence construction in finding max-content flex fraction
+From:     Alan Stearns
+Comment:  https://github.com/w3c/csswg-drafts/issues/1803
+Response: https://github.com/w3c/csswg-drafts/issues/1803#issuecomment-329247658
+Closed:   Editorial
 ----

css-grid/Overview.bs

@@ -905,15 +905,16 @@ Sizing Grid Containers</h3>
 	<span class="note">The block layout spec should probably define this,
 	but it isn't written yet.</span>
 
-	The <a>max-content size</a> of a <a>grid container</a> is
+	The <a>max-content size</a> (<a>min-content size</a>) of a <a>grid container</a> is
 	the sum of the <a>grid container’s</a> track sizes (including gutters)
 	in the appropriate axis,
-	when the grid is sized under a <a>max-content constraint</a>.
-
-	The <a>min-content size</a> of a <a>grid container</a> is
-	the sum of the <a>grid container’s</a> track sizes (including gutters)
-	in the appropriate axis,
-	when the grid is sized under a <a>min-content constraint</a>.
+	when the grid is sized under a <a>max-content constraint</a> (<a>min-content constraint</a>).
+	However, if the sum of the <a>flex factors</a> of the <a>flexible tracks</a>
+	is less than one,
+	then instead calculate the flexible tracks’ sizes
+	using <em>rescaled</em> flex factors--
+	each track’s <a>flex factor</a> divided by the sum of all the tracks’ flex factors</a>--
+	in place of their actual flex factors.
 
 
 <!--
@@ -1692,6 +1693,9 @@ Flexible Lengths: the ''fr'' unit</h4>
 	A <dfn export>flexible length</dfn> or <dfn><<flex>></dfn> is a dimension
 	with the <dfn value for="<flex>" lt="fr|fr unit">fr</dfn> unit,
 	which represents a fraction of the <a>leftover space</a> in the <a>grid container</a>.
+	Tracks sized with ''fr'' units are called <dfn>flexible tracks</dfn>
+	as they flex in response to <a>leftover space</a>
+	similar to how <a>flex items</a> fill space in a <a>flex container</a>.
 
 	Note: <<flex>> values are not <<length>>s
 	(nor are they compatible with <<length>>s, like some <<percentage>> values),
@@ -4254,6 +4258,25 @@ Major Changes</h4>
 Significant Adjustments and Fixes</h4>
 
 	<ul>
+		<li id="change-2016-flex-max-content">
+			Corrected max-content contributions of flexible tracks
+			to handle cases where the sum of the flex factors is less than one.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/1735">Issue 1735</a>)
+			<blockquote>
+				<p>
+				The <a>max-content size</a> (<a>min-content size</a>) of a <a>grid container</a> is
+				the sum of the <a>grid container’s</a> track sizes (including gutters)
+				in the appropriate axis,
+				when the grid is sized under a <a>max-content constraint</a> (<a>min-content constraint</a>).
+				<ins>However, if the sum of the <a>flex factors</a> of the <a>flexible tracks</a>
+				is less than one,
+				then instead calculate the flexible tracks’ sizes
+				using <em>rescaled</em> flex factors--
+				each track’s <a>flex factor</a> divided by the sum of all the tracks’ flex factors</a>--
+				in place of their actual flex factors.</ins>
+				</p>
+			</blockquote>
+
 		<li id="change-2016-flex-clamping-indefinite">
 			Applied flex factor clamping to 1 also to indefinite case
 			(<a href="https://drafts.csswg.org/css-grid-1/issues-cr-2016#issue-26">Issue 26</a>,