1 files changed, 130 insertions, 0 deletions
diff --git a/tools/diff.py b/tools/diff.py
new file mode 100644
index 000000000..860a6b051
--- /dev/null
+++ b/tools/diff.py
@@ -0,0 +1,130 @@
+#!/usr/bin/env python3
+##  Copyright (c) 2012 The WebM project authors. All Rights Reserved.
+##
+##  Use of this source code is governed by a BSD-style license
+##  that can be found in the LICENSE file in the root of the source
+##  tree. An additional intellectual property rights grant can be found
+##  in the file PATENTS.  All contributing project authors may
+##  be found in the AUTHORS file in the root of the source tree.
+##
+"""Classes for representing diff pieces."""
+
+__author__ = "jkoleszar@google.com"
+
+import re
+
+
+class DiffLines(object):
+    """A container for one half of a diff."""
+
+    def __init__(self, filename, offset, length):
+        self.filename = filename
+        self.offset = offset
+        self.length = length
+        self.lines = []
+        self.delta_line_nums = []
+
+    def Append(self, line):
+        l = len(self.lines)
+        if line[0] != " ":
+            self.delta_line_nums.append(self.offset + l)
+        self.lines.append(line[1:])
+        assert l+1 <= self.length
+
+    def Complete(self):
+        return len(self.lines) == self.length
+
+    def __contains__(self, item):
+        return item >= self.offset and item <= self.offset + self.length - 1
+
+
+class DiffHunk(object):
+    """A container for one diff hunk, consisting of two DiffLines."""
+
+    def __init__(self, header, file_a, file_b, start_a, len_a, start_b, len_b):
+        self.header = header
+        self.left = DiffLines(file_a, start_a, len_a)
+        self.right = DiffLines(file_b, start_b, len_b)
+        self.lines = []
+
+    def Append(self, line):
+        """Adds a line to the DiffHunk and its DiffLines children."""
+        if line[0] == "-":
+            self.left.Append(line)
+        elif line[0] == "+":
+            self.right.Append(line)
+        elif line[0] == " ":
+            self.left.Append(line)
+            self.right.Append(line)
+        elif line[0] == "\\":
+            # Ignore newline messages from git diff.
+            pass
+        else:
+            assert False, ("Unrecognized character at start of diff line "
+                           "%r" % line[0])
+        self.lines.append(line)
+
+    def Complete(self):
+        return self.left.Complete() and self.right.Complete()
+
+    def __repr__(self):
+        return "DiffHunk(%s, %s, len %d)" % (
+            self.left.filename, self.right.filename,
+            max(self.left.length, self.right.length))
+
+
+def ParseDiffHunks(stream):
+    """Walk a file-like object, yielding DiffHunks as they're parsed."""
+
+    file_regex = re.compile(r"(\+\+\+|---) (\S+)")
+    range_regex = re.compile(r"@@ -(\d+)(,(\d+))? \+(\d+)(,(\d+))?")
+    hunk = None
+    while True:
+        line = stream.readline()
+        if not line:
+            break
+
+        if hunk is None:
+            # Parse file names
+            diff_file = file_regex.match(line)
+            if diff_file:
+              if line.startswith("---"):
+                  a_line = line
+                  a = diff_file.group(2)
+                  continue
+              if line.startswith("+++"):
+                  b_line = line
+                  b = diff_file.group(2)
+                  continue
+
+            # Parse offset/lengths
+            diffrange = range_regex.match(line)
+            if diffrange:
+                if diffrange.group(2):
+                    start_a = int(diffrange.group(1))
+                    len_a = int(diffrange.group(3))
+                else:
+                    start_a = 1
+                    len_a = int(diffrange.group(1))
+
+                if diffrange.group(5):
+                    start_b = int(diffrange.group(4))
+                    len_b = int(diffrange.group(6))
+                else:
+                    start_b = 1
+                    len_b = int(diffrange.group(4))
+
+                header = [a_line, b_line, line]
+                hunk = DiffHunk(header, a, b, start_a, len_a, start_b, len_b)
+        else:
+            # Add the current line to the hunk
+            hunk.Append(line)
+
+            # See if the whole hunk has been parsed. If so, yield it and prepare
+            # for the next hunk.
+            if hunk.Complete():
+                yield hunk
+                hunk = None
+
+    # Partial hunks are a parse error
+    assert hunk is None