feat(whitespace): handle whitespace-only changes

If there is no difference between the logical structure of the JSON,
then try to minimize file thrashing by picking a consistent winner.
- If ours and theirs are identical, use that (should be no conflict)
- Otherwise, use base (minimize whitespace-only changes to JSON file)

Author: timshadel

bin/git-json-merge

@@ -20,10 +20,16 @@ function mergeJson (oursJson, baseJson, theirsJson) {
 	var ours = JSON.parse(oursJson);
 	var base = JSON.parse(baseJson);
 	var theirs = JSON.parse(theirsJson);
-	var newOurs = merge(ours, base, theirs);
-	var newOursJson = JSON.stringify(newOurs, null, newOursIndent);
-
-	return newOursJson;
+	var diff = xdiff.diff3(ours, base, theirs);
+	if (diff) {
+		var newOurs = xdiff.patch(base, diff);
+		var newOursJson = JSON.stringify(newOurs, null, newOursIndent);
+		return newOursJson;
+	} else if (oursJson === theirsJson) {
+		return oursJson;
+	} else {
+		return baseJson;
+	}
 }
 
 function merge (ours, base, theirs) {

lib/git-json-merge.js

@@ -32,6 +32,31 @@ describe('gitJsonMerge', function () {
 		describeStripBomTest('[{"id":1,\uFEFF"field":"Foo"}]', '[{"id":1,\uFEFF"field":"Foo"}]');
 		describeStripBomTest('\uFEFF[{"id":1,"field":"Foo"}]\uFEFF', '[{"id":1,"field":"Foo"}]\uFEFF');
 	});
+
+	describe('Keep common string.', function() {
+		// All are identical
+		describeStringEquivalence(
+			'[{"id":1,"field":"Foo"}]',
+			'[{"id":1,"field":"Foo"}]',
+			'[{"id":1,"field":"Foo"}]',
+			'[{"id":1,"field":"Foo"}]'
+		);
+		// Ours and theirs have identical whitespace-only changes
+		describeStringEquivalence(
+			'[\n  {"id": 1,"field":"Foo"\n}\n]',
+			'[\n  {"id":1,"field":"Foo"}\n]',
+			'[\n  {"id": 1,"field":"Foo"\n}\n]',
+			'[\n  {"id": 1,"field":"Foo"\n}\n]'
+		);
+		// Ours and theirs have diverging whitespace-only changes
+		describeStringEquivalence(
+			'[{"id":1,"field":  "Foo"}]',
+			'[\n  {"id":1,"field":"Foo"}\n]',
+			'[\n  {"id": 1,"field":"Foo"\n}\n]',
+			'[\n  {"id":1,"field":"Foo"}\n]'
+		);
+	});
+
 });
 
 function toString (object) {
@@ -85,3 +110,13 @@ function describeStripBomTest (str, expected)  {
 		})
 	});
 }
+
+function describeStringEquivalence (ours, base, theirs, expected)  {
+	describe('given arguments of ' + toString(ours) + ' as ours, ' + toString(base) + ' as base and '  + toString(theirs) + ' as theirs', function () {
+		var actual = gitJsonMerge.mergeJson(ours, base, theirs);
+
+		it('should return ' + toString(expected), function () {
+			expect(actual).to.deep.equal(expected);
+		})
+	});
+}