[fix] Follow the file permission mode in the patch

patch_ng.py

@@ -273,6 +273,7 @@ def __init__(self):
     self.header = []
 
     self.type = None
+    self.filemode = None
 
   def __iter__(self):
     return iter(self.hunks)
@@ -290,6 +291,7 @@ def __init__(self, stream=None):
     self.name = None
     # patch set type - one of constants
     self.type = None
+    self.filemode = None
 
     # list of Patch objects
     self.items = []
@@ -660,6 +662,8 @@ def lineno(self):
     # ---- detect patch and patchset types ----
     for idx, p in enumerate(self.items):
       self.items[idx].type = self._detect_type(p)
+      if self.items[idx].type == GIT:
+        self.items[idx].filemode = self._detect_file_mode(p)
 
     types = set([p.type for p in self.items])
     if len(types) > 1:
@@ -706,13 +710,48 @@ def _detect_type(self, p):
         if p.header[idx].startswith(b"diff --git"):
           break
       if p.header[idx].startswith(b'diff --git a/'):
-        if (idx+1 < len(p.header)
-            and re.match(
-              b'(?:index \\w{4,40}\\.\\.\\w{4,40}(?: \\d{6})?|new file mode \\d+|deleted file mode \\d+)',
-              p.header[idx+1])):
-          if DVCS:
-            return GIT
-
+        git_indicators = []
+        for i in range(idx + 1, len(p.header)):
+          git_indicators.append(p.header[i])
+        for line in git_indicators:
+          if re.match(
+                  b'(?:index \\w{4,40}\\.\\.\\w{4,40}(?: \\d{6})?|new file mode \\d+|deleted file mode \\d+|old mode \\d+|new mode \\d+)',
+                  line):
+            if DVCS:
+              return GIT
+
+              # Additional check: look for mode change patterns
+              # "old mode XXXXX" followed by "new mode XXXXX"
+              has_old_mode = False
+              has_new_mode = False
+
+              for line in git_indicators:
+                if re.match(b'old mode \\d+', line):
+                  has_old_mode = True
+                elif re.match(b'new mode \\d+', line):
+                  has_new_mode = True
+
+              # If we have both old and new mode, it's definitely Git
+              if has_old_mode and has_new_mode and DVCS:
+                return GIT
+
+              # Check for similarity index (Git renames/copies)
+              for line in git_indicators:
+                if re.match(b'similarity index \\d+%', line):
+                  if DVCS:
+                    return GIT
+
+              # Check for rename patterns
+              for line in git_indicators:
+                if re.match(b'rename from .+', line) or re.match(b'rename to .+', line):
+                  if DVCS:
+                    return GIT
+
+              # Check for copy patterns
+              for line in git_indicators:
+                if re.match(b'copy from .+', line) or re.match(b'copy to .+', line):
+                  if DVCS:
+                    return GIT
     # HG check
     #
     #  - for plain HG format header is like "diff -r b2d9961ff1f5 filename"
@@ -735,6 +774,40 @@ def _detect_type(self, p):
 
     return PLAIN
 
+  def _detect_file_mode(self, p):
+    """ Detect the file mode listed in the patch header
+
+       INFO: Only working with Git-style patches
+    """
+    if len(p.header) > 1:
+      for idx in reversed(range(len(p.header))):
+        if p.header[idx].startswith(b"diff --git"):
+          break
+      if p.header[idx].startswith(b'diff --git a/'):
+        if idx + 1 < len(p.header):
+          # new file (e.g)
+          # diff --git a/quote.txt b/quote.txt
+          # new file mode 100755
+          match = re.match(b'new file mode (\\d+)', p.header[idx + 1])
+          if match:
+            return int(match.group(1), 8)
+          # changed mode (e.g)
+          # diff --git a/quote.txt b/quote.txt
+          # old mode 100755
+          # new mode 100644
+          if idx + 2 < len(p.header):
+            match = re.match(b'new mode (\\d+)', p.header[idx + 2])
+            if match:
+              return int(match.group(1), 8)
+    return None
+
+  def _apply_filemode(self, filepath, filemode):
+    if filemode is not None and stat.S_ISREG(filemode):
+      try:
+        only_file_permissions = filemode & 0o777
+        os.chmod(filepath, only_file_permissions)
+      except Exception as error:
+        warning(f"Could not set filemode {oct(filemode)} for {filepath}: {str(error)}")
 
   def _normalize_filenames(self):
     """ sanitize filenames, normalizing paths, i.e.:
@@ -752,6 +825,7 @@ def _normalize_filenames(self):
     for i,p in enumerate(self.items):
       if debugmode:
         debug("    patch type = %s" % p.type)
+        debug("    filemode = %s" % p.filemode)
         debug("    source = %s" % p.source)
         debug("    target = %s" % p.target)
       if p.type in (HG, GIT):
@@ -928,6 +1002,7 @@ def apply(self, strip=0, root=None, fuzz=False):
         hunks = [s.decode("utf-8") for s in item.hunks[0].text]
         new_file = "".join(hunk[1:] for hunk in hunks)
         save(target, new_file)
+        self._apply_filemode(target, item.filemode)
       elif "dev/null" in target:
         source = self.strip_path(source, root, strip)
         safe_unlink(source)
@@ -1059,6 +1134,7 @@ def apply(self, strip=0, root=None, fuzz=False):
         else:
           shutil.move(filenamen, backupname)
           if self.write_hunks(backupname if filenameo == filenamen else filenameo, filenamen, p.hunks):
+            self._apply_filemode(filenamen, p.filemode)
             info("successfully patched %d/%d:\t %s" % (i+1, total, filenamen))
             safe_unlink(backupname)
             if new == b'/dev/null':

tests/filepermission/create755.patch

@@ -0,0 +1,21 @@
+From 39fdfb57a112a3b00cc352b45d17aba4f0f58005 Mon Sep 17 00:00:00 2001
+From: John Doe <john.doe@mail.com>
+Date: Wed, 1 Oct 2025 12:39:25 +0200
+Subject: [PATCH] Add quotes.txt
+
+Signed-off-by: John Doe <john.doe@mail.com>
+---
+ quote.txt | 1 +
+ 1 file changed, 1 insertion(+)
+ create mode 100755 quote.txt
+
+diff --git a/quote.txt b/quote.txt
+new file mode 100755
+index 0000000000000000000000000000000000000000..cbfafe956ec35385f5b728daa390603ff71f1933
+--- /dev/null
++++ b/quote.txt
+@@ -0,0 +1 @@
++post malam segetem, serendum est.
+-- 
+2.51.0
+

tests/filepermission/update644.patch

@@ -0,0 +1,23 @@
+From 5f6ac26ddfe6ad80f76a1ec982abe95c11c7e947 Mon Sep 17 00:00:00 2001
+From: John Doe <john.doe@mail.com>
+Date: Wed, 1 Oct 2025 15:56:37 +0200
+Subject: [PATCH] Read only
+
+Signed-off-by: John Doe <john.doe@mail.com>
+---
+ quote.txt | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+ mode change 100755 => 100644 quote.txt
+
+diff --git a/quote.txt b/quote.txt
+old mode 100755
+new mode 100644
+index cbfafe956ec35385f5b728daa390603ff71f1933..155913b0aafa16e4b37278209e772e946cecb393
+--- a/quote.txt
++++ b/quote.txt
+@@ -1 +1 @@
+-post malam segetem, serendum est.
++praestat cautela quam medela.
+-- 
+2.51.0
+

tests/run_tests.py

@@ -37,6 +37,7 @@
 import shutil
 import unittest
 import stat
+import platform
 from os import listdir, chmod
 from os.path import abspath, dirname, exists, join, isdir, isfile
 from tempfile import mkdtemp
@@ -487,6 +488,39 @@ def test_apply_huge_patch(self):
         self.assertTrue(pto.apply(root=self.tmpdir))
 
 
+class TestPreserveFilePermissions(unittest.TestCase):
+
+    def setUp(self):
+        self.save_cwd = os.getcwd()
+        self.tmpdir = mkdtemp(prefix=self.__class__.__name__)
+        shutil.copytree(join(TESTS, 'filepermission'), join(self.tmpdir, 'filepermission'))
+
+    def tearDown(self):
+        os.chdir(self.save_cwd)
+        remove_tree_force(self.tmpdir)
+
+    @unittest.skipIf(platform.system() == "Windows", "File permission modes are not supported on Windows")
+    def test_handle_full_index_patch_format(self):
+        """Test that when file permission mode is listed in the patch,
+        the same should be applied to the target file after patching.
+        """
+
+        os.chdir(self.tmpdir)
+        pto = patch_ng.fromfile(join(self.tmpdir, 'filepermission', 'create755.patch'))
+        self.assertEqual(len(pto), 1)
+        self.assertEqual(pto.items[0].type, patch_ng.GIT)
+        self.assertEqual(pto.items[0].filemode, 0o100755)
+        self.assertTrue(pto.apply())
+        self.assertTrue(os.path.exists(join(self.tmpdir, 'quote.txt')))
+        self.assertEqual(os.stat(join(self.tmpdir, 'quote.txt')).st_mode, 0o755 | stat.S_IFREG)
+
+        pto = patch_ng.fromfile(join(self.tmpdir, 'filepermission', 'update644.patch'))
+        self.assertEqual(len(pto), 1)
+        self.assertEqual(pto.items[0].type, patch_ng.GIT)
+        self.assertEqual(pto.items[0].filemode, 0o100644)
+        self.assertTrue(pto.apply())
+        self.assertEqual(os.stat(join(self.tmpdir, 'quote.txt')).st_mode, 0o644 | stat.S_IFREG)
+
 class TestHelpers(unittest.TestCase):
     # unittest setting
     longMessage = True