| # Copyright 2016 The Chromium Authors. All rights reserved. |
| # Use of this source code is governed by a BSD-style license that can be |
| # found in the LICENSE file. |
| |
| """Utility for outputting a HTML diff of two multi-line strings. |
| |
| The main purpose of this utility is to show the difference between |
| text baselines (-expected.txt files) and actual text results. |
| |
| Note, in the standard library module difflib, there is also a HtmlDiff class, |
| although it outputs a larger and more complex HTML table than we need. |
| """ |
| |
| import difflib |
| |
| _TEMPLATE = """<html> |
| <head> |
| <style>.del { background: #faa; } .add { background: #afa; }</style> |
| </head> |
| <body> |
| <pre>%s</pre> |
| </body> |
| </html> |
| """ |
| |
| |
| def html_diff(a_text, b_text): |
| """Returns a diff between two strings as HTML.""" |
| # Diffs can be between multiple text files of different encodings |
| # so we always want to deal with them as byte arrays, not unicode strings. |
| assert isinstance(a_text, str) |
| assert isinstance(b_text, str) |
| a_lines = a_text.splitlines(True) |
| b_lines = b_text.splitlines(True) |
| return _TEMPLATE % html_diff_body(a_lines, b_lines) |
| |
| |
| def html_diff_body(a_lines, b_lines): |
| matcher = difflib.SequenceMatcher(None, a_lines, b_lines) |
| output = [] |
| for tag, a_start, a_end, b_start, b_end in matcher.get_opcodes(): |
| a_chunk = ''.join(a_lines[a_start:a_end]) |
| b_chunk = ''.join(b_lines[b_start:b_end]) |
| output.append(_format_chunk(tag, a_chunk, b_chunk)) |
| return ''.join(output) |
| |
| |
| def _format_chunk(tag, a_chunk, b_chunk): |
| if tag == 'delete': |
| return _format_delete(a_chunk) |
| if tag == 'insert': |
| return _format_insert(b_chunk) |
| if tag == 'replace': |
| return _format_delete(a_chunk) + _format_insert(b_chunk) |
| assert tag == 'equal' |
| return a_chunk |
| |
| |
| def _format_insert(chunk): |
| return '<span class="add">%s</span>' % chunk |
| |
| |
| def _format_delete(chunk): |
| return '<span class="del">%s</span>' % chunk |
