Minimize whitespace dirty diffs in existing headings, tables, lists

* For existing and edited headings, tables, lists, this patch examines
  the original source for the node and where there is leading/trailing
  whitespace, adds back at most 1 whitespace char.

* So, this doesn't preserve all whitespace or avoid all normalization.
  * this doesn't look for comments or other rendering transparent nodes.
  * this doesn't try to preserve multiple whitespace characters
  * this doesn't try to preserve trailing whitepace for a <td>/<th> that
    is the last element in a wikitext line.

* The blacklist changes are all improvements.

Bug: T195486
Change-Id: Ib571806a765e7306e1dbbf26c293998030aff0c1

lib/html2wt/DOMHandlers.js

@@ -60,6 +60,52 @@ function isRecognizedSpanWrapper(type) {
 	}) !== undefined;
 }
 
+function getLeadingSpace(state, node, newEltDefault, fc) {
+	let space = '';
+	if (DU.isNewElt(node)) {
+		if (!fc) {
+			fc = node.firstChild;
+		}
+		if (fc && (!DU.isText(fc) || !fc.nodeValue.match(/^\s/))) {
+			space = newEltDefault;
+		}
+	} else if (state.selserMode) {
+		const dsr = DU.getDataParsoid(node).dsr;
+		if (Util.isValidDSR(dsr, true)) {
+			const offset = dsr[0] + dsr[2];
+			space = offset < (dsr[1] - dsr[3]) ? state.getOrigSrc(offset, offset + 1) : '';
+			if (!/[ \t]/.test(space)) {
+				space = '';
+			}
+		}
+	}
+	return space;
+}
+
+function getTrailingSpace(state, node, newEltDefault) {
+	let space = '';
+	if (DU.isNewElt(node)) {
+		const lc = node.lastChild;
+		if (lc && (!DU.isText(lc) || !lc.nodeValue.match(/\s$/))) {
+			space = newEltDefault;
+		}
+	} else if (state.selserMode) {
+		const dsr = DU.getDataParsoid(node).dsr;
+		if (Util.isValidDSR(dsr, true)) {
+			const offset = dsr[1] - dsr[3] - 1;
+			// The > instead of >= is to deal with an edge case
+			// = = where that single space is captured by the
+			// getLeadingSpace case above
+			space = offset > (dsr[0] + dsr[2]) ? state.getOrigSrc(offset, offset + 1) : '';
+			if (!/[ \t]/.test(space)) {
+				space = '';
+			}
+		}
+	}
+
+	return space;
+}
+
 function buildHeadingHandler(headingWT) {
 	return {
 		forceSOL: true,
@@ -69,14 +115,10 @@ function buildHeadingHandler(headingWT) {
 				// Skip fallback ID if present.
 				fc = fc.nextSibling;
 			}
+
 			// For new elements, for prettier wikitext serialization,
 			// emit a space after the last '=' char.
-			var space = '';
-			if (DU.isNewElt(node)) {
-				if (fc && (!DU.isText(fc) || !fc.nodeValue.match(/^\s/))) {
-					space = ' ';
-				}
-			}
+			let space = getLeadingSpace(state, node, ' ', fc);
 			state.emitChunk(headingWT + space, node);
 			state.singleLineContext.enforce();
 
@@ -89,13 +131,7 @@ function buildHeadingHandler(headingWT) {
 
 			// For new elements, for prettier wikitext serialization,
 			// emit a space before the first '=' char.
-			space = '';
-			if (DU.isNewElt(node)) {
-				var lc = node.lastChild;
-				if (lc && (!DU.isText(lc) || !lc.nodeValue.match(/\s$/))) {
-					space = ' ';
-				}
-			}
+			space = getTrailingSpace(state, node, ' ');
 			state.emitChunk(space + headingWT, node);
 			state.singleLineContext.pop();
 		}),
@@ -138,13 +174,7 @@ function getListBullets(state, node) {
 
 	// For new elements, for prettier wikitext serialization,
 	// emit a space after the last bullet (if required)
-	var space = '';
-	if (DU.isNewElt(node)) {
-		var fc = node.firstChild;
-		if (fc && (!DU.isText(fc) || !fc.nodeValue.match(/^\s/))) {
-			space = ' ';
-		}
-	}
+	var space = getLeadingSpace(state, node, ' ');
 
 	var dp, nodeName, parentName;
 	var res = '';
@@ -794,12 +824,13 @@ var tagHandlers = JSUtils.mapObject({
 					.replace(/{{!}}{{!}}/, '{{!}}');
 			}
 
+			const thTag = yield serializeTableTag(startTagSrc, attrSepSrc, state, node, wrapperUnmodified);
+			const inWideTH = /!!|\|\||^{{!}}{{!}}/.test(thTag);
+			const trailingSpace = inWideTH ? getTrailingSpace(state, DU.previousNonDeletedSibling(node), '') : '';
+			const leadingSpace = getLeadingSpace(state, node, '');
 			// If the HTML for the first th is not enclosed in a tr-tag,
 			// we start a new line.  If not, tr will have taken care of it.
-			WTSUtils.emitStartTag(
-				yield serializeTableTag(
-					startTagSrc, attrSepSrc, state, node, wrapperUnmodified
-				),
+			WTSUtils.emitStartTag(trailingSpace + thTag + leadingSpace,
 				node,
 				state
 			);
@@ -862,8 +893,10 @@ var tagHandlers = JSUtils.mapObject({
 				startTagSrc, attrSepSrc,
 				state, node, wrapperUnmodified
 			);
-			var inWideTD = (tdTag.length > 1);
-			WTSUtils.emitStartTag(tdTag, node, state);
+			var inWideTD = /\|\||^{{!}}{{!}}/.test(tdTag);
+			const trailingSpace = inWideTD ? getTrailingSpace(state, DU.previousNonDeletedSibling(node), '') : '';
+			const leadingSpace = getLeadingSpace(state, node, '');
+			WTSUtils.emitStartTag(trailingSpace + tdTag + leadingSpace, node, state);
 			var tdHandler = state.serializer.wteHandlers.tdHandler
 				.bind(state.serializer.wteHandlers, node, inWideTD);
 

lib/utils/Util.js

@@ -1350,10 +1350,11 @@ var Util = {
 			(cp >= 0x10000 && cp <= 0x10ffff);
 	},
 
-	isValidDSR: function(dsr) {
+	isValidDSR: function(dsr, all) {
+		const isValidOffset = n => typeof (n) === 'number' && n >= 0;
 		return dsr &&
-			typeof (dsr[0]) === 'number' && dsr[0] >= 0 &&
-			typeof (dsr[1]) === 'number' && dsr[1] >= 0;
+			isValidOffset(dsr[0]) && isValidOffset(dsr[1]) &&
+			(!all || (isValidOffset(dsr[2]) && isValidOffset(dsr[3])));
 	},
 
 	/**