[gtk-doc] common.py: start porting common.py from perl

[Stefan Sauer <stefkost src gnome org>]

commit 6e5bb3ca8d95e6af189574522338ea48072b7dfa
Author: Stefan Sauer <ensonic users sf net>
Date:   Sun Apr 2 21:58:16 2017 +0200

    common.py: start porting common.py from perl
    
    Add a first function with a test.

 Makefile.am            |    2 +
 gtkdoc/common.py       |   59 ++++++++++++++++++++++++++++++++++++++++++++++++
 tests/Makefile.am      |    2 +-
 tests/gtkdoc-common.py |   18 ++++++++++++++
 4 files changed, 80 insertions(+), 1 deletions(-)
---
diff --git a/Makefile.am b/Makefile.am
index baab3cb..f7f16fc 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -38,6 +38,7 @@ pylibdatadir = $(datadir)/gtk-doc/python/gtkdoc
 pylibdata_DATA = \
   gtkdoc/__init__.py \
   gtkdoc/check.py \
+  gtkdoc/common.py \
   gtkdoc/config.py \
   gtkdoc/mkhtml.py \
   gtkdoc/mkman.py \
@@ -81,6 +82,7 @@ CLEANFILES = \
   gtkdoc-rebasec \
   gtkdoc/__init__.pyc \
   gtkdoc/check.pyc \
+  gtkdoc/common.pyc \
   gtkdoc/config.pyc \
   gtkdoc/mkhtml.pyc \
   gtkdoc/mkman.pyc \
diff --git a/gtkdoc/common.py b/gtkdoc/common.py
new file mode 100644
index 0000000..0bfb966
--- /dev/null
+++ b/gtkdoc/common.py
@@ -0,0 +1,59 @@
+#!/usr/bin/python -w
+# -*- python -*-
+#
+# gtk-doc - GTK DocBook documentation generator.
+# Copyright (C) 2001  Damon Chaplin
+#               2007-2016  Stefan Sauer
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+#
+
+import logging, os
+
+
+def UpdateFileIfChanged(old_file, new_file, make_backup):
+    """Compares the old version of the file with the new version and if the
+    file has changed it moves the new version into the old versions place. This
+    is used so we only change files if needed, so we can do proper dependency
+    tracking.
+
+    Args:
+        old_file (string): The pathname of the old file.
+        new_file (string): The pathname of the new version of the file.
+        make_backup (bool) True if a backup of the old file should be kept.
+                           It will have the .bak suffix added to the file name.
+
+    Returns:
+        bool: It returns False if the file hasn't changed, and True if it has.
+    """
+
+    logging.debug("Comparing %s with %s...", old_file, new_file);
+
+    if os.path.exists(old_file):
+        old_contents = open(old_file, 'rb').read()
+        new_contents = open(new_file, 'rb').read()
+        if old_contents == new_contents:
+            return False
+
+        if make_backup:
+            backupname = old_file + '.bak'
+            if os.path.exists(backupname):
+                os.unlink(backupname)
+            os.rename(old_file, backupname)
+        else:
+            os.unlink(old_file)
+
+    os.rename(new_file, old_file)
+    return True
diff --git a/tests/Makefile.am b/tests/Makefile.am
index f5c41ef..1a7b303 100644
--- a/tests/Makefile.am
+++ b/tests/Makefile.am
@@ -6,7 +6,7 @@ if BUILD_TESTS
 
 TESTS = \
   gtkdoc-common.t gtkdoc-fixxref.t gtkdoc-mkdb.t gtkdoc-scan.t \
-  gtkdoc-check.py \
+  gtkdoc-check.py gtkdoc-common.py \
   tools.sh gobject.sh bugs.sh annotations.sh fail.sh empty.sh sanity.sh \
   program.sh
 TESTS_ENVIRONMENT = \
diff --git a/tests/gtkdoc-common.py b/tests/gtkdoc-common.py
new file mode 100755
index 0000000..722ae5a
--- /dev/null
+++ b/tests/gtkdoc-common.py
@@ -0,0 +1,18 @@
+#!/usr/bin/env python
+
+import mock, os, unittest
+
+from gtkdoc import common
+
+class TestCommon(unittest.TestCase):
+
+    @mock.patch('os.path.exists')
+    @mock.patch('os.rename')
+    def test_UpdateFileIfChanged_NoOldFile(self, os_rename, os_path_exists):
+        os_path_exists.return_value = False
+        res = common.UpdateFileIfChanged('/foo', '/bar', False)
+        os_rename.assert_called_with('/bar', '/foo')
+        self.assertTrue(res)
+
+if __name__ == '__main__':
+    unittest.main()