Gracefully accept invalid newStart in hunks, same as patch(1) does.

Author: Artyom Skrobov

src/patch/apply.js

@@ -79,10 +79,11 @@ export function applyPatch(source, uniDiff, options = {}) {
   }
 
   // Apply patch hunks
+  let diffOffset = 0;
   for (let i = 0; i < hunks.length; i++) {
     let hunk = hunks[i],
-        toPos = hunk.offset + hunk.newStart - 1;
-    if (hunk.newLines == 0) { toPos++; }
+        toPos = hunk.oldStart + hunk.offset + diffOffset - 1;
+    diffOffset += hunk.newLines - hunk.oldLines;
 
     for (let j = 0; j < hunk.lines.length; j++) {
       let line = hunk.lines[j],

test/patch/apply.js

@@ -416,6 +416,51 @@ describe('patch/apply', function() {
           + 'line5\n');
     });
 
+    it('should succeed when 1st hunk specifies invalid newStart', function() {
+      expect(applyPatch(
+          'line1\n'
+          + 'line2\n'
+          + 'line3\n'
+          + 'line5\n',
+
+          '--- test\theader1\n'
+          + '+++ test\theader2\n'
+          + '@@ -1,2 +2,3 @@\n'
+          + ' line3\n'
+          + '+line4\n'
+          + ' line5\n'))
+        .to.equal(
+          'line1\n'
+          + 'line2\n'
+          + 'line3\n'
+          + 'line4\n'
+          + 'line5\n');
+    });
+
+    it('should succeed when 2nd hunk specifies invalid newStart', function() {
+      expect(applyPatch(
+          'line1\n'
+          + 'line2\n'
+          + 'line3\n'
+          + 'line5\n',
+
+          '--- test\theader1\n'
+          + '+++ test\theader2\n'
+          + '@@ -1,3 +1,2 @@\n'
+          + ' line1\n'
+          + '-line2\n'
+          + ' line3\n'
+          + '@@ -3,2 +3,3 @@\n'
+          + ' line3\n'
+          + '+line4\n'
+          + ' line5\n'))
+        .to.equal(
+          'line1\n'
+          + 'line3\n'
+          + 'line4\n'
+          + 'line5\n');
+    });
+
     it('should erase a file', function() {
       expect(applyPatch(
           'line1\n'