Detect normalized-out boldness in headings

Fixes #113 by looking for headings with a mix of children with normal/400 weight and no set weight, then updating the children with no set weight to be bold.

lib/css.js

@@ -104,6 +104,18 @@ function getResolvedStyleProperty(propertyName, node, ancestors) {
   return getResolvedStyleProperty(propertyName, parent, parentAncestors);
 }
 
+/**
+ * Set a local style property on a node. Later calls to look up the node's
+ * styles or resolved styles will use the new property value.
+ * @param {string} propertyName
+ * @param {string} propertyValue
+ * @param {RehypeNode} node
+ */
+function setStyleProperty(propertyName, propertyValue, node) {
+  const style = getNodeStyle(node);
+  style[propertyName] = propertyValue;
+}
+
 /**
  * Get an object with properties representing a node's fully resolved styles,
  * including anything inherited from ancestors.
@@ -120,5 +132,9 @@ export function resolveNodeStyle(node, ancestors) {
       }
       return target[property];
     },
+    set(_target, property, value, _receiver) {
+      setStyleProperty(property, value, node);
+      return value;
+    },
   });
 }

lib/fix-google-html.js

@@ -61,6 +61,8 @@ const blockElements = new Set([
   'ul',
 ]);
 
+const headingElements = new Set(['h1', 'h2', 'h3', 'h4', 'h5', 'h6']);
+
 // These elements convert to Markdown nodes that can't start or end with spaces.
 // For example, you can't start emphasis with a space: `This * is emphasized*`.
 const spaceSensitiveElements = new Set(['em', 'strong']);
@@ -72,6 +74,7 @@ const isSpaceSensitive = (node) =>
   node && spaceSensitiveElements.has(node.tagName);
 const isCell = (node) => node.tagName === 'th' || node.tagName === 'td';
 const isAnchor = (node) => node.tagName === 'a';
+const isHeading = (node) => headingElements.has(node?.tagName);
 
 const spaceAtStartPattern = /^(\s+)/;
 const spaceAtEndPattern = /(\s+)$/;
@@ -667,13 +670,60 @@ function fixInternalLinks(node, sliceClip) {
   );
 }
 
+/**
+ * Mark spans of bold-formatted text in headings as bold.
+ *
+ * In some browsers, spans of bold-formatted text in a heading get their
+ * bold-ness normalized out (because the heading itself is bold, so the
+ * bold-ness of text in it can be inherited from the heading itself). This
+ * isn't universal, though, since not all browsers format headings as bold by
+ * default (they also may not all do the same normalizations), so we can't just
+ * infer that text without a `font-weight` is bold.
+ *
+ * Instead, this looks for a heading with children that are a mix of explicit
+ * font-weight and non-explicit font-weight, and adds font-weights back to the
+ * ones that are missing. This means that *all* bold won't get marked up as
+ * bold, which could be good or bad depending on your perspective.
+ *
+ * @param {RehypeNode} node Fix the tree below this node
+ */
+function fixBoldInHeadings(node) {
+  visitParents(node, isHeading, (node, parents) => {
+    const childrenParents = [...parents, node];
+    let hasNormalChildren = false;
+    let hasBoldChildren = false;
+    let unknownChildrenStyles = [];
+
+    // For Google Docs, we are only concerned about immediate children.
+    for (const child of node.children) {
+      const style = resolveNodeStyle(child, childrenParents);
+
+      const weight = style['font-weight'];
+      if (!weight) {
+        unknownChildrenStyles.push(style);
+      } else if (weight === 'bold' || weight === '700') {
+        hasBoldChildren = true;
+      } else if (weight === 'normal' || weight === '400') {
+        hasNormalChildren = true;
+      }
+    }
+
+    if (hasNormalChildren && !hasBoldChildren) {
+      for (const style of unknownChildrenStyles) {
+        style['font-weight'] = '700';
+      }
+    }
+  });
+}
+
 /**
  * A rehype plugin to clean up the HTML of a Google Doc. .This applies to the
  * live HTML of Doc, as when you copy and paste it; not *exported* HTML (it
  * might apply there, too; I haven’t looked into it).
  */
 export default function fixGoogleHtml() {
   return (tree, _file) => {
+    fixBoldInHeadings(tree);
     unInlineStyles(tree);
     createCodeBlocks(tree);
     moveSpaceOutsideSensitiveChildren(tree);