[PATCH V2] update: fix edge-case with update.atomic-file and read-only files

[Boris Feld]

# HG changeset patch
# User Boris Feld <boris.feld at octobus.net>
# Date 1547128621 -3600
#      Thu Jan 10 14:57:01 2019 +0100
# Node ID d46392ed9a76773561c74c8df2063aaad4c3c952
# Parent  963462786f6e028563bcedc9008622e0f3b59c86
# EXP-Topic atomic-update-read-only
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r d46392ed9a76
update: fix edge-case with update.atomic-file and read-only files

We used to create the tempfile with the original file mode. That means
creating a read-only tempfile when the original file is read-only, which crash
if we need to write on the tempfile.

The file in the working directory ends up being writable with and without the
atomic update config, so the behavior is the same.

diff --git a/mercurial/util.py b/mercurial/util.py
--- a/mercurial/util.py
+++ b/mercurial/util.py
@@ -2045,7 +2045,7 @@ def splitpath(path):
     function if need.'''
     return path.split(pycompat.ossep)
 
-def mktempcopy(name, emptyok=False, createmode=None):
+def mktempcopy(name, emptyok=False, createmode=None, enforcewritable=False):
     """Create a temporary file with the same contents from name
 
     The permission bits are copied from the original file.
@@ -2062,6 +2062,15 @@ def mktempcopy(name, emptyok=False, crea
     # what we want.  If the original file already exists, just copy
     # its mode.  Otherwise, manually obey umask.
     copymode(name, temp, createmode)
+
+    # If the resulting temporary file needs to be writable enforce it now.
+    # createmode argument of copy mode is not used when the original file
+    # already exists so we need to do it outside of it
+    if enforcewritable:
+        oldstat = filestat.frompath(temp)
+        newstat = oldstat.stat.st_mode | stat.S_IWUSR
+        os.chmod(temp, newstat)
+
     if emptyok:
         return temp
     try:
@@ -2204,7 +2213,9 @@ class atomictempfile(object):
     def __init__(self, name, mode='w+b', createmode=None, checkambig=False):
         self.__name = name      # permanent name
         self._tempname = mktempcopy(name, emptyok=('w' in mode),
-                                    createmode=createmode)
+                                    createmode=createmode,
+                                    enforcewritable=('w' in mode))
+
         self._fp = posixfile(self._tempname, mode)
         self._checkambig = checkambig
 
diff --git a/tests/test-update-atomic.t b/tests/test-update-atomic.t
new file mode 100644
--- /dev/null
+++ b/tests/test-update-atomic.t
@@ -0,0 +1,142 @@
+#require execbit
+
+Checking that experimental.atomic-file works.
+
+  $ cat > $TESTTMP/show_mode.py <<EOF
+  > from __future__ import print_function
+  > import sys
+  > import os
+  > from stat import ST_MODE
+  > 
+  > for file_path in sys.argv[1:]:
+  >     file_stat = os.stat(file_path)
+  >     octal_mode = oct(file_stat[ST_MODE] & 0o777)
+  >     print("%s:%s" % (file_path, octal_mode))
+  > 
+  > EOF
+
+  $ hg init repo
+  $ cd repo
+
+  $ cat > .hg/showwrites.py <<EOF
+  > def uisetup(ui):
+  >   from mercurial import vfs
+  >   class newvfs(vfs.vfs):
+  >     def __call__(self, *args, **kwargs):
+  >       print('vfs open', args, sorted(list(kwargs.items())))
+  >       return super(newvfs, self).__call__(*args, **kwargs)
+  >   vfs.vfs = newvfs
+  > EOF
+
+  $ for v in a1 a2 b1 b2 c ro; do echo $v > $v; done
+  $ chmod +x b*
+  $ hg commit -Aqm _
+
+# We check that
+# - the changes are actually atomic
+# - that permissions are correct (all 4 cases of (executable before) * (executable after))
+# - that renames work, though they should be atomic anyway
+# - that it works when source files are read-only (but directories are read-write still)
+
+  $ for v in a1 a2 b1 b2 ro; do echo changed-$v > $v; done
+  $ chmod -x *1; chmod +x *2
+  $ hg rename c d
+  $ hg commit -qm _
+
+Check behavior without update.atomic-file
+
+  $ hg update -r 0 -q
+  $ hg update -r 1 --config extensions.showwrites=.hg/showwrites.py 2>&1 | grep "a1'.*wb"
+  ('vfs open', ('a1', 'wb'), [('atomictemp', False), ('backgroundclose', True)])
+
+  $ python $TESTTMP/show_mode.py *
+  a1:0644
+  a2:0755
+  b1:0644
+  b2:0755
+  d:0644
+  ro:0644
+
+Add a second revision for the ro file so we can test update when the file is
+present or not
+
+  $ echo "ro" > ro
+
+  $ hg commit -qm _
+
+Check behavior without update.atomic-file first
+
+  $ hg update -C -r 0 -q
+
+  $ hg update -r 1
+  6 files updated, 0 files merged, 1 files removed, 0 files unresolved
+
+  $ python $TESTTMP/show_mode.py *
+  a1:0644
+  a2:0755
+  b1:0644
+  b2:0755
+  d:0644
+  ro:0644
+
+Manually reset the mode of the read-only file
+
+  $ chmod a-w ro
+
+  $ python $TESTTMP/show_mode.py ro
+  ro:0444
+
+Now the file is present, try to update and check the permissions of the file
+
+  $ hg up -r 2
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+  $ python $TESTTMP/show_mode.py ro
+  ro:0644
+
+# The file which was read-only is now writable in the default behavior
+
+Check behavior with update.atomic-files
+
+
+  $ cat >> .hg/hgrc <<EOF
+  > [experimental]
+  > update.atomic-file = true
+  > EOF
+
+  $ hg update -C -r 0 -q
+  $ hg update -r 1 --config extensions.showwrites=.hg/showwrites.py 2>&1 | grep "a1'.*wb"
+  ('vfs open', ('a1', 'wb'), [('atomictemp', True), ('backgroundclose', True)])
+  $ hg st -A --rev 1
+  C a1
+  C a2
+  C b1
+  C b2
+  C d
+  C ro
+
+Check the file permission after update
+  $ python $TESTTMP/show_mode.py *
+  a1:0644
+  a2:0755
+  b1:0644
+  b2:0755
+  d:0644
+  ro:0644
+
+Manually reset the mode of the read-only file
+
+  $ chmod a-w ro
+
+  $ python $TESTTMP/show_mode.py ro
+  ro:0444
+
+Now the file is present, try to update and check the permissions of the file
+
+  $ hg update -r 2 --traceback
+  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+  $ python $TESTTMP/show_mode.py ro
+  ro:0644
+
+# The behavior is the same as without atomic update