[css-flexbox-1] Fix intrinsic size algo to better match the layout algo. #7189

Author: tabatkins

css-flexbox-1/Overview.bs

@@ -2908,38 +2908,52 @@ Flex Container Intrinsic Main Sizes</h4>
 			For each <a>flex item</a>,
 			subtract its outer <a>flex base size</a> from its [[#intrinsic-item-contributions|max-content contribution]] size.
 			If that result is positive,
-			divide by its <a>flex grow factor</a> floored at 1;
+			divide by its <a>flex grow factor</a>;
 			if negative,
-			divide by its <a>scaled flex shrink factor</a>
-			having floored the <a>flex shrink factor</a> at 1.
-			This is the item's <var>max-content flex fraction</var>.
+			divide by its <a>scaled flex shrink factor</a>.
+			This is the item's <var>desired flex fraction</var>.
 
 		<li>
 			Place all <a>flex items</a> into lines of infinite length.
-
-		<li>
 			Within each line,
-			find the largest <var>max-content flex fraction</var>
+			find the greatest (most positive)
+			<var>desired flex fraction</var>
 			among all the <a>flex items</a>.
+			This is the line’s <var>chosen flex fraction</var>.
+
+		<li>
+			If the sum of the line’s <a>flex grow factors</a>
+			(<a>flex shrink factors</a>,
+			if the <var>chosen flex fraction</var> is negative)
+			is less than 1,
+			multiply the <var>chosen flex fraction</var> by that sum.
+
+		<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)
-			and the chosen <var>max-content flex fraction</var>,
+			(<a>scaled flex shrink factor</a>, if shrinking)
+			and the <var>chosen flex fraction</var>,
 			then clamp that result by the <a>max main size</a>
 			floored by the <a>min main size</a>.
 
 		<li>
-			The <a>flex container</a>’s <a>max-content size</a> is the
-			largest sum of the afore-calculated sizes of all items within a single line.
+			The <a>flex container</a>’s <a>max-content size</a> is
+			the largest sum (among all the lines)
+			of the afore-calculated sizes of all items within a single line.
 	</ol>
 
 	The <strong><a>min-content</a> <a>main size</a></strong> of a <em><a>single-line</a></em> flex container
 	is calculated identically to the <a>max-content</a> <a>main size</a>,
 	except that the <a>flex items</a>’ [[#intrinsic-item-contributions|min-content contributions]] are used
 	instead of their [[#intrinsic-item-contributions|max-content contributions]].
+
 	However, for a <em><a>multi-line</a></em> container,
-	it is simply the largest [[#intrinsic-item-contributions|min-content contribution]]
+	the [=min-content=] [=main size=] is simply the largest [[#intrinsic-item-contributions|min-content contribution]]
 	of all the non-[=collapsed=] <a>flex items</a> in the <a>flex container</a>.
+	For this purpose,
+	each item's contribution
+	is capped by the item’s [=flex base size=] if the item is not growable,
+	and floored by the item’s [=flex base size=] if the item is not shrinkable.
 
 	<details class=note>
 		<summary>Implications of this algorithm when the sum of flex is less than 1</summary>
@@ -3008,17 +3022,13 @@ Flex Item Intrinsic Size Contributions</h4>
 	is the larger of its <em>outer</em> <a>min-content size</a>
 	and outer <a>preferred size</a>
 	if that is not ''width/auto'',
-	clamped by its <a>flex base size</a> as a maximum (if it is not growable)
-	and/or as a minimum (if it is not shrinkable),
-	and then further clamped by its <a lt="min main size">min</a>/<a>max main size</a>.
+	clamped by its <a lt="min main size">min</a>/<a>max main size</a>.
 
 	The <strong>main-size <a>max-content contribution</a> of a <a>flex item</a></strong>
 	is the larger of its <em>outer</em> <a>max-content size</a>
 	and outer <a>preferred size</a>
 	if that is not ''width/auto'',
-	clamped by its <a>flex base size</a> as a maximum (if it is not growable)
-	and/or as a minimum (if it is not shrinkable),
-	and then further clamped by its <a lt="min main size">min</a>/<a>max main size</a>.
+	clamped by its <a lt="min main size">min</a>/<a>max main size</a>.
 
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