support for reverse patching, Fixes #10

Author: Thomas Grainger

tests/test_apply.py

@@ -7,6 +7,15 @@
 import unittest
 
 
+def _apply(src, diff_text, reverse=False, use_patch=False):
+    diff = next(wtp.parse_patch(diff_text))
+    return wtp.apply.apply_diff(diff, src, reverse, use_patch)
+
+
+def _apply_r(src, diff_text, reverse=True, use_patch=False):
+    return _apply(src, diff_text, reverse, use_patch)
+
+
 class ApplyTestSuite(unittest.TestCase):
     """Basic test cases."""
 
@@ -27,38 +36,29 @@ def test_diff_default(self):
         with open('tests/casefiles/diff-default.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
-
-        new_text = wtp.apply.apply_diff(diff, self.lao)
-        self.assertEqual(new_text, self.tzu)
+        self.assertEqual(_apply(self.lao, diff_text), self.tzu)
+        self.assertEqual(_apply_r(self.tzu, diff_text), self.lao)
 
     def test_diff_context(self):
         with open('tests/casefiles/diff-context.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
-
-        new_text = wtp.apply.apply_diff(diff, self.lao)
-        self.assertEqual(new_text, self.tzu)
+        self.assertEqual(_apply(self.lao, diff_text), self.tzu)
+        self.assertEqual(_apply_r(self.tzu, diff_text), self.lao)
 
     def test_diff_unified(self):
         with open('tests/casefiles/diff-unified.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
-
-        new_text = wtp.apply.apply_diff(diff, self.lao)
-
-        self.assertEqual(new_text, self.tzu)
+        self.assertEqual(_apply(self.lao, diff_text), self.tzu)
+        self.assertEqual(_apply_r(self.tzu, diff_text), self.lao)
 
     def test_diff_unified_bad(self):
         with open('tests/casefiles/diff-unified-bad.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
-
         with assert_raises(exceptions.ApplyException) as ec:
-            wtp.apply.apply_diff(diff, self.lao)
+            _apply(self.lao, diff_text)
 
         e = ec.exception
         e_str = str(e)
@@ -71,10 +71,8 @@ def test_diff_unified_bad2(self):
         with open('tests/casefiles/diff-unified-bad2.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
-
         with assert_raises(exceptions.ApplyException) as ec:
-            wtp.apply.apply_diff(diff, self.lao)
+            _apply(self.lao, diff_text)
 
         e = ec.exception
         e_str = str(e)
@@ -87,10 +85,8 @@ def test_diff_unified_bad_backward(self):
         with open('tests/casefiles/diff-unified-bad2.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
-
         with assert_raises(exceptions.ApplyException) as ec:
-            wtp.apply.apply_diff(diff, self.tzu)
+            _apply(self.tzu, diff_text)
 
         e = ec.exception
         e_str = str(e)
@@ -103,10 +99,8 @@ def test_diff_unified_bad_empty_source(self):
         with open('tests/casefiles/diff-unified-bad2.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
-
         with assert_raises(exceptions.ApplyException) as ec:
-            wtp.apply.apply_diff(diff, '')
+            _apply('', diff_text)
 
         e = ec.exception
         e_str = str(e)
@@ -119,39 +113,42 @@ def test_diff_unified_patchutil(self):
         with open('tests/casefiles/diff-unified.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
+        self.assertEqual(
+            _apply(self.lao, diff_text, use_patch=True),
+            (self.tzu, None),
+        )
+        self.assertEqual(
+            _apply_r(self.tzu, diff_text, use_patch=True),
+            (self.lao, None),
+        )
 
-        new_text = wtp.apply.apply_diff(diff, self.lao, use_patch=True)
+        new_text = _apply(self.lao, diff_text, use_patch=True)
         self.assertEqual(new_text, (self.tzu, None))
 
+        def _do_apply():
+            return _apply([''] + self.lao, diff_text, use_patch=True)
+
         self.assertRaises(
             exceptions.ApplyException,
-            wtp.apply.apply_diff,
-            diff,
-            [''] + self.lao,
-            use_patch=True,
+            _do_apply,
         )
 
     def test_diff_rcs(self):
         with open('tests/casefiles/diff-rcs.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
+        new_text = _apply(self.lao, diff_text)
 
-        new_text = wtp.apply.apply_diff(diff, self.lao)
         self.assertEqual(new_text, self.tzu)
 
     def test_diff_ed(self):
-        self.maxDiff = None
         with open('tests/casefiles/diff-ed.diff') as f:
             diff_text = f.read()
 
-        diff = next(wtp.parse_patch(diff_text))
-
-        new_text = wtp.apply.apply_diff(diff, self.lao)
+        new_text = _apply(self.lao, diff_text)
         self.assertEqual(self.tzu, new_text)
 
-        new_text = wtp.apply.apply_diff(diff, self.lao, use_patch=True)
+        new_text = _apply(self.lao, diff_text, use_patch=True)
         self.assertEqual(new_text, (self.tzu, None))
 
 

whatthepatch/apply.py

@@ -25,7 +25,7 @@ def apply_patch(diffs):
             f.write(new_text)
 
 
-def _apply_diff_with_subprocess(diff, lines):
+def _apply_diff_with_subprocess(diff, lines, reverse=False):
     # call out to patch program
     patchexec = which('patch')
     if not patchexec:
@@ -43,6 +43,7 @@ def _apply_diff_with_subprocess(diff, lines):
         f.write(diff.text)
 
     args = [patchexec,
+            '--reverse' if reverse else '--forward',
             '--quiet',
             '-o', newfilepath,
             '-i', patchfilepath,
@@ -72,18 +73,30 @@ def _apply_diff_with_subprocess(diff, lines):
     return lines, rejlines
 
 
-def apply_diff(diff, text, use_patch=False):
+def _reverse(changes):
+    def _reverse_change(c):
+        return c._replace(
+            old=c.new,
+            new=c.old,
+        )
+
+    return [_reverse_change(c) for c in changes]
+
+
+def apply_diff(diff, text, reverse=False, use_patch=False):
     try:
         lines = text.splitlines()
     except AttributeError:
         lines = list(text)
 
     if use_patch:
-        return _apply_diff_with_subprocess(diff, lines)
+        return _apply_diff_with_subprocess(diff, lines, reverse)
 
     n_lines = len(lines)
+
+    changes = _reverse(diff.changes) if reverse else diff.changes
     # check that the source text matches the context of the diff
-    for old, new, hunk, line in diff.changes:
+    for old, new, hunk, line in changes:
         # might have to check for line is None here for ed scripts
         if old is not None and line is not None:
             if old > n_lines:
@@ -108,7 +121,7 @@ def apply_diff(diff, text, use_patch=False):
     r = 0
     i = 0
 
-    for old, new, hunk, line in diff.changes:
+    for old, new, hunk, line in changes:
         if old is not None and new is None:
             del lines[old-1-r+i]
             r += 1