Resolve relative size rendering error in inspector (#23804)

Summary:
Currently, when relative sizes are given in margin or padding stylings (be it a percentage or an auto measure), the inspector crashes, due to frame rendering not properly handling those kinds of measurements. This PR adds a resolution step for them:

* Percentages are evaluated relative to the window size.
* I decided to simply not render `auto` margins/paddings, due to the complexities involved (e.g. when the margin is between multiple elements with relative sizes).

Since the inspector does not crash anymore on relative sizes on paddings or margins, I believe that this addresses #17496.

Fixes #17496

[General] [Fixed] - Fix inspector rendering of relative margins and paddings
Pull Request resolved: #23804

Differential Revision: D14437273

Pulled By: cpojer

fbshipit-source-id: c9f0f71a2e1b2399a2b2148cef2124787703ead3

Author: Georgios Andreadis

Libraries/Inspector/ElementBox.js

@@ -14,15 +14,16 @@ const BorderBox = require('BorderBox');
 const React = require('React');
 const StyleSheet = require('StyleSheet');
 const View = require('View');
+const Dimensions = require('Dimensions');
 
 const flattenStyle = require('flattenStyle');
 const resolveBoxStyle = require('resolveBoxStyle');
 
 class ElementBox extends React.Component<$FlowFixMeProps> {
   render() {
     const style = flattenStyle(this.props.style) || {};
-    const margin = resolveBoxStyle('margin', style);
-    const padding = resolveBoxStyle('padding', style);
+    let margin = resolveBoxStyle('margin', style);
+    let padding = resolveBoxStyle('padding', style);
 
     const frameStyle = {...this.props.frame};
     const contentStyle = {
@@ -31,6 +32,8 @@ class ElementBox extends React.Component<$FlowFixMeProps> {
     };
 
     if (margin != null) {
+      margin = resolveRelativeSizes(margin);
+
       frameStyle.top -= margin.top;
       frameStyle.left -= margin.left;
       frameStyle.height += margin.top + margin.bottom;
@@ -51,6 +54,8 @@ class ElementBox extends React.Component<$FlowFixMeProps> {
     }
 
     if (padding != null) {
+      padding = resolveRelativeSizes(padding);
+
       contentStyle.width -= padding.left + padding.right;
       contentStyle.height -= padding.top + padding.bottom;
     }
@@ -82,4 +87,51 @@ const styles = StyleSheet.create({
   },
 });
 
+type Style = {
+  top: number,
+  right: number,
+  bottom: number,
+  left: number,
+};
+
+/**
+ * Resolves relative sizes (percentages and auto) in a style object.
+ *
+ * @param style the style to resolve
+ * @return a modified copy
+ */
+function resolveRelativeSizes(style: $ReadOnly<Style>): Style {
+  let resolvedStyle = Object.assign({}, style);
+  resolveSizeInPlace(resolvedStyle, 'top', 'height');
+  resolveSizeInPlace(resolvedStyle, 'right', 'width');
+  resolveSizeInPlace(resolvedStyle, 'bottom', 'height');
+  resolveSizeInPlace(resolvedStyle, 'left', 'width');
+  return resolvedStyle;
+}
+
+/**
+ * Resolves the given size of a style object in place.
+ *
+ * @param style the style object to modify
+ * @param direction the direction to resolve (e.g. 'top')
+ * @param dimension the window dimension that this direction belongs to (e.g. 'height')
+ */
+function resolveSizeInPlace(
+  style: Style,
+  direction: string,
+  dimension: string,
+) {
+  if (style[direction] !== null && typeof style[direction] === 'string') {
+    if (style[direction].indexOf('%') !== -1) {
+      style[direction] =
+        (parseFloat(style[direction]) / 100.0) *
+        Dimensions.get('window')[dimension];
+    }
+    if (style[direction] === 'auto') {
+      // Ignore auto sizing in frame drawing due to complexity of correctly rendering this
+      style[direction] = 0;
+    }
+  }
+}
+
 module.exports = ElementBox;