tests: add tests about diff quality

These show the differences between bdiff and xdiff.

Differential Revision: https://phab.mercurial-scm.org/D2604

tests/test-diff-antipatience.t

@@ -0,0 +1,91 b''
+#testcases bdiff xdiff
+
+#if xdiff
+#require xdiff
+  $ cat >> $HGRCPATH <<EOF
+  > [experimental]
+  > xdiff = true
+  > EOF
+#endif
+
+Test case that makes use of the weakness of patience diff algorithm
+
+  $ hg init
+  >>> open('a', 'wb').write(b'\n'.join(list(b'a' + b'x' * 10 + b'u' + b'x' * 30 + b'a\n')))
+  $ hg commit -m 1 -A a
+  >>> open('a', 'wb').write(b'\n'.join(list(b'b' + b'x' * 30 + b'u' + b'x' * 10 + b'b\n')))
+#if xdiff
+  $ hg diff
+  diff -r f0aeecb49805 a
+  --- a/a	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
+  @@ -1,4 +1,4 @@
+  -a
+  +b
+   x
+   x
+   x
+  @@ -9,7 +9,6 @@
+   x
+   x
+   x
+  -u
+   x
+   x
+   x
+  @@ -30,6 +29,7 @@
+   x
+   x
+   x
+  +u
+   x
+   x
+   x
+  @@ -40,5 +40,5 @@
+   x
+   x
+   x
+  -a
+  +b
+   
+#else
+  $ hg diff
+  diff -r f0aeecb49805 a
+  --- a/a	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
+  @@ -1,15 +1,4 @@
+  -a
+  -x
+  -x
+  -x
+  -x
+  -x
+  -x
+  -x
+  -x
+  -x
+  -x
+  -u
+  +b
+   x
+   x
+   x
+  @@ -40,5 +29,16 @@
+   x
+   x
+   x
+  -a
+  +u
+  +x
+  +x
+  +x
+  +x
+  +x
+  +x
+  +x
+  +x
+  +x
+  +x
+  +b
+   
+#endif

tests/test-diff-indent-heuristic.t

@@ -0,0 +1,339 b''
+#testcases bdiff xdiff
+
+#if xdiff
+#require xdiff
+  $ cat >> $HGRCPATH <<EOF
+  > [experimental]
+  > xdiff = true
+  > EOF
+#endif
+
+  $ hg init
+
+  $ cat > a.c <<'EOF'
+  > /*
+  >  * This function returns 1.
+  >  */
+  > int f() {
+  >   return 1;
+  > }
+  > /*
+  >  * This function returns 2.
+  >  */
+  > int g() {
+  >   return 2;
+  > }
+  > /*
+  >  * This function returns 3.
+  >  */
+  > int h() {
+  >   return 3;
+  > }
+  > EOF
+
+  $ cat > b.c <<'EOF'
+  > if (x) {
+  >    do_something();
+  > }
+  > 
+  > if (y) {
+  >    do_something_else();
+  > }
+  > EOF
+
+  $ cat > c.rb <<'EOF'
+  > #!ruby
+  > ["foo", "bar", "baz"].map do |i|
+  >   i.upcase
+  > end
+  > EOF
+
+  $ cat > d.py <<'EOF'
+  > try:
+  >     import foo
+  > except ImportError:
+  >     pass
+  > try:
+  >     import bar
+  > except ImportError:
+  >     pass
+  > EOF
+
+The below two files are taken from git: t/t4061-diff-indent.sh
+
+  $ cat > spaces.txt <<'EOF'
+  > 1
+  > 2
+  > a
+  > 
+  > b
+  > 3
+  > 4
+  > EOF
+
+  $ cat > functions.c <<'EOF'
+  > 1
+  > 2
+  > /* function */
+  > foo() {
+  >     foo
+  > }
+  > 
+  > 3
+  > 4
+  > EOF
+
+  $ hg commit -m 1 -A . -q
+
+  $ cat > a.c <<'EOF'
+  > /*
+  >  * This function returns 1.
+  >  */
+  > int f() {
+  >   return 1;
+  > }
+  > /*
+  >  * This function returns 3.
+  >  */
+  > int h() {
+  >   return 3;
+  > }
+  > EOF
+
+  $ cat > b.c <<'EOF'
+  > if (x) {
+  >    do_something();
+  > }
+  > 
+  > if (y) {
+  >    do_another_thing();
+  > }
+  > 
+  > if (y) {
+  >    do_something_else();
+  > }
+  > EOF
+
+  $ cat > c.rb <<'EOF'
+  > #!ruby
+  > ["foo", "bar", "baz"].map do |i|
+  >   i
+  > end
+  > ["foo", "bar", "baz"].map do |i|
+  >   i.upcase
+  > end
+  > EOF
+
+  $ cat > d.py <<'EOF'
+  > try:
+  >     import foo
+  > except ImportError:
+  >     pass
+  > try:
+  >     import baz
+  > except ImportError:
+  >     pass
+  > try:
+  >     import bar
+  > except ImportError:
+  >     pass
+  > EOF
+
+  $ cat > spaces.txt <<'EOF'
+  > 1
+  > 2
+  > a
+  > 
+  > b
+  > a
+  > 
+  > b
+  > 3
+  > 4
+  > EOF
+
+  $ cat > functions.c <<'EOF'
+  > 1
+  > 2
+  > /* function */
+  > bar() {
+  >     foo
+  > }
+  > 
+  > /* function */
+  > foo() {
+  >     foo
+  > }
+  > 
+  > 3
+  > 4
+  > EOF
+
+#if xdiff
+  $ hg diff --git
+  diff --git a/a.c b/a.c
+  --- a/a.c
+  +++ b/a.c
+  @@ -4,12 +4,6 @@
+   int f() {
+     return 1;
+   }
+  -/*
+  - * This function returns 2.
+  - */
+  -int g() {
+  -  return 2;
+  -}
+   /*
+    * This function returns 3.
+    */
+  diff --git a/b.c b/b.c
+  --- a/b.c
+  +++ b/b.c
+  @@ -2,6 +2,10 @@
+      do_something();
+   }
+   
+  +if (y) {
+  +   do_another_thing();
+  +}
+  +
+   if (y) {
+      do_something_else();
+   }
+  diff --git a/c.rb b/c.rb
+  --- a/c.rb
+  +++ b/c.rb
+  @@ -1,4 +1,7 @@
+   #!ruby
+  +["foo", "bar", "baz"].map do |i|
+  +  i
+  +end
+   ["foo", "bar", "baz"].map do |i|
+     i.upcase
+   end
+  diff --git a/d.py b/d.py
+  --- a/d.py
+  +++ b/d.py
+  @@ -2,6 +2,10 @@
+       import foo
+   except ImportError:
+       pass
+  +try:
+  +    import baz
+  +except ImportError:
+  +    pass
+   try:
+       import bar
+   except ImportError:
+  diff --git a/functions.c b/functions.c
+  --- a/functions.c
+  +++ b/functions.c
+  @@ -1,5 +1,10 @@
+   1
+   2
+  +/* function */
+  +bar() {
+  +    foo
+  +}
+  +
+   /* function */
+   foo() {
+       foo
+  diff --git a/spaces.txt b/spaces.txt
+  --- a/spaces.txt
+  +++ b/spaces.txt
+  @@ -2,6 +2,9 @@
+   2
+   a
+   
+  +b
+  +a
+  +
+   b
+   3
+   4
+#else
+  $ hg diff --git
+  diff --git a/a.c b/a.c
+  --- a/a.c
+  +++ b/a.c
+  @@ -5,12 +5,6 @@
+     return 1;
+   }
+   /*
+  - * This function returns 2.
+  - */
+  -int g() {
+  -  return 2;
+  -}
+  -/*
+    * This function returns 3.
+    */
+   int h() {
+  diff --git a/b.c b/b.c
+  --- a/b.c
+  +++ b/b.c
+  @@ -3,5 +3,9 @@
+   }
+   
+   if (y) {
+  +   do_another_thing();
+  +}
+  +
+  +if (y) {
+      do_something_else();
+   }
+  diff --git a/c.rb b/c.rb
+  --- a/c.rb
+  +++ b/c.rb
+  @@ -1,4 +1,7 @@
+   #!ruby
+   ["foo", "bar", "baz"].map do |i|
+  +  i
+  +end
+  +["foo", "bar", "baz"].map do |i|
+     i.upcase
+   end
+  diff --git a/d.py b/d.py
+  --- a/d.py
+  +++ b/d.py
+  @@ -3,6 +3,10 @@
+   except ImportError:
+       pass
+   try:
+  +    import baz
+  +except ImportError:
+  +    pass
+  +try:
+       import bar
+   except ImportError:
+       pass
+  diff --git a/functions.c b/functions.c
+  --- a/functions.c
+  +++ b/functions.c
+  @@ -1,6 +1,11 @@
+   1
+   2
+   /* function */
+  +bar() {
+  +    foo
+  +}
+  +
+  +/* function */
+   foo() {
+       foo
+   }
+  diff --git a/spaces.txt b/spaces.txt
+  --- a/spaces.txt
+  +++ b/spaces.txt
+  @@ -3,5 +3,8 @@
+   a
+   
+   b
+  +a
+  +
+  +b
+   3
+   4
+#endif

tests/hghave.py

@@ -1,710 +1,719 b''
 from __future__ import absolute_import
 
 import errno
 import os
 import re
 import socket
 import stat
 import subprocess
 import sys
 import tempfile
 
 tempprefix = 'hg-hghave-'
 
 checks = {
     "true": (lambda: True, "yak shaving"),
     "false": (lambda: False, "nail clipper"),
 }
 
 def check(name, desc):
     """Registers a check function for a feature."""
     def decorator(func):
         checks[name] = (func, desc)
         return func
     return decorator
 
 def checkvers(name, desc, vers):
     """Registers a check function for each of a series of versions.
 
     vers can be a list or an iterator"""
     def decorator(func):
         def funcv(v):
             def f():
                 return func(v)
             return f
         for v in vers:
             v = str(v)
             f = funcv(v)
             checks['%s%s' % (name, v.replace('.', ''))] = (f, desc % v)
         return func
     return decorator
 
 def checkfeatures(features):
     result = {
         'error': [],
         'missing': [],
         'skipped': [],
     }
 
     for feature in features:
         negate = feature.startswith('no-')
         if negate:
             feature = feature[3:]
 
         if feature not in checks:
             result['missing'].append(feature)
             continue
 
         check, desc = checks[feature]
         try:
             available = check()
         except Exception:
             result['error'].append('hghave check failed: %s' % feature)
             continue
 
         if not negate and not available:
             result['skipped'].append('missing feature: %s' % desc)
         elif negate and available:
             result['skipped'].append('system supports %s' % desc)
 
     return result
 
 def require(features):
     """Require that features are available, exiting if not."""
     result = checkfeatures(features)
 
     for missing in result['missing']:
         sys.stderr.write('skipped: unknown feature: %s\n' % missing)
     for msg in result['skipped']:
         sys.stderr.write('skipped: %s\n' % msg)
     for msg in result['error']:
         sys.stderr.write('%s\n' % msg)
 
     if result['missing']:
         sys.exit(2)
 
     if result['skipped'] or result['error']:
         sys.exit(1)
 
 def matchoutput(cmd, regexp, ignorestatus=False):
     """Return the match object if cmd executes successfully and its output
     is matched by the supplied regular expression.
     """
     r = re.compile(regexp)
     try:
         p = subprocess.Popen(
             cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     except OSError as e:
         if e.errno != errno.ENOENT:
             raise
         ret = -1
     ret = p.wait()
     s = p.stdout.read()
     return (ignorestatus or not ret) and r.search(s)
 
 @check("baz", "GNU Arch baz client")
 def has_baz():
     return matchoutput('baz --version 2>&1', br'baz Bazaar version')
 
 @check("bzr", "Canonical's Bazaar client")
 def has_bzr():
     try:
         import bzrlib
         import bzrlib.bzrdir
         import bzrlib.errors
         import bzrlib.revision
         import bzrlib.revisionspec
         bzrlib.revisionspec.RevisionSpec
         return bzrlib.__doc__ is not None
     except (AttributeError, ImportError):
         return False
 
 @checkvers("bzr", "Canonical's Bazaar client >= %s", (1.14,))
 def has_bzr_range(v):
     major, minor = v.split('.')[0:2]
     try:
         import bzrlib
         return (bzrlib.__doc__ is not None
                 and bzrlib.version_info[:2] >= (int(major), int(minor)))
     except ImportError:
         return False
 
 @check("chg", "running with chg")
 def has_chg():
     return 'CHGHG' in os.environ
 
 @check("cvs", "cvs client/server")
 def has_cvs():
     re = br'Concurrent Versions System.*?server'
     return matchoutput('cvs --version 2>&1', re) and not has_msys()
 
 @check("cvs112", "cvs client/server 1.12.* (not cvsnt)")
 def has_cvs112():
     re = br'Concurrent Versions System \(CVS\) 1.12.*?server'
     return matchoutput('cvs --version 2>&1', re) and not has_msys()
 
 @check("cvsnt", "cvsnt client/server")
 def has_cvsnt():
     re = br'Concurrent Versions System \(CVSNT\) (\d+).(\d+).*\(client/server\)'
     return matchoutput('cvsnt --version 2>&1', re)
 
 @check("darcs", "darcs client")
 def has_darcs():
     return matchoutput('darcs --version', br'\b2\.([2-9]|\d{2})', True)
 
 @check("mtn", "monotone client (>= 1.0)")
 def has_mtn():
     return matchoutput('mtn --version', br'monotone', True) and not matchoutput(
         'mtn --version', br'monotone 0\.', True)
 
 @check("eol-in-paths", "end-of-lines in paths")
 def has_eol_in_paths():
     try:
         fd, path = tempfile.mkstemp(dir='.', prefix=tempprefix, suffix='\n\r')
         os.close(fd)
         os.remove(path)
         return True
     except (IOError, OSError):
         return False
 
 @check("execbit", "executable bit")
 def has_executablebit():
     try:
         EXECFLAGS = stat.S_IXUSR | stat.S_IXGRP | stat.S_IXOTH
         fh, fn = tempfile.mkstemp(dir='.', prefix=tempprefix)
         try:
             os.close(fh)
             m = os.stat(fn).st_mode & 0o777
             new_file_has_exec = m & EXECFLAGS
             os.chmod(fn, m ^ EXECFLAGS)
             exec_flags_cannot_flip = ((os.stat(fn).st_mode & 0o777) == m)
         finally:
             os.unlink(fn)
     except (IOError, OSError):
         # we don't care, the user probably won't be able to commit anyway
         return False
     return not (new_file_has_exec or exec_flags_cannot_flip)
 
 @check("icasefs", "case insensitive file system")
 def has_icasefs():
     # Stolen from mercurial.util
     fd, path = tempfile.mkstemp(dir='.', prefix=tempprefix)
     os.close(fd)
     try:
         s1 = os.stat(path)
         d, b = os.path.split(path)
         p2 = os.path.join(d, b.upper())
         if path == p2:
             p2 = os.path.join(d, b.lower())
         try:
             s2 = os.stat(p2)
             return s2 == s1
         except OSError:
             return False
     finally:
         os.remove(path)
 
 @check("fifo", "named pipes")
 def has_fifo():
     if getattr(os, "mkfifo", None) is None:
         return False
     name = tempfile.mktemp(dir='.', prefix=tempprefix)
     try:
         os.mkfifo(name)
         os.unlink(name)
         return True
     except OSError:
         return False
 
 @check("killdaemons", 'killdaemons.py support')
 def has_killdaemons():
     return True
 
 @check("cacheable", "cacheable filesystem")
 def has_cacheable_fs():
     from mercurial import util
 
     fd, path = tempfile.mkstemp(dir='.', prefix=tempprefix)
     os.close(fd)
     try:
         return util.cachestat(path).cacheable()
     finally:
         os.remove(path)
 
 @check("lsprof", "python lsprof module")
 def has_lsprof():
     try:
         import _lsprof
         _lsprof.Profiler # silence unused import warning
         return True
     except ImportError:
         return False
 
 def gethgversion():
     m = matchoutput('hg --version --quiet 2>&1', br'(\d+)\.(\d+)')
     if not m:
         return (0, 0)
     return (int(m.group(1)), int(m.group(2)))
 
 @checkvers("hg", "Mercurial >= %s",
             list([(1.0 * x) / 10 for x in range(9, 99)]))
 def has_hg_range(v):
     major, minor = v.split('.')[0:2]
     return gethgversion() >= (int(major), int(minor))
 
 @check("hg08", "Mercurial >= 0.8")
 def has_hg08():
     if checks["hg09"][0]():
         return True
     return matchoutput('hg help annotate 2>&1', '--date')
 
 @check("hg07", "Mercurial >= 0.7")
 def has_hg07():
     if checks["hg08"][0]():
         return True
     return matchoutput('hg --version --quiet 2>&1', 'Mercurial Distributed SCM')
 
 @check("hg06", "Mercurial >= 0.6")
 def has_hg06():
     if checks["hg07"][0]():
         return True
     return matchoutput('hg --version --quiet 2>&1', 'Mercurial version')
 
 @check("gettext", "GNU Gettext (msgfmt)")
 def has_gettext():
     return matchoutput('msgfmt --version', br'GNU gettext-tools')
 
 @check("git", "git command line client")
 def has_git():
     return matchoutput('git --version 2>&1', br'^git version')
 
 def getgitversion():
     m = matchoutput('git --version 2>&1', br'git version (\d+)\.(\d+)')
     if not m:
         return (0, 0)
     return (int(m.group(1)), int(m.group(2)))
 
 # https://github.com/git-lfs/lfs-test-server
 @check("lfs-test-server", "git-lfs test server")
 def has_lfsserver():
     exe = 'lfs-test-server'
     if has_windows():
         exe = 'lfs-test-server.exe'
     return any(
         os.access(os.path.join(path, exe), os.X_OK)
         for path in os.environ["PATH"].split(os.pathsep)
     )
 
 @checkvers("git", "git client (with ext::sh support) version >= %s", (1.9,))
 def has_git_range(v):
     major, minor = v.split('.')[0:2]
     return getgitversion() >= (int(major), int(minor))
 
 @check("docutils", "Docutils text processing library")
 def has_docutils():
     try:
         import docutils.core
         docutils.core.publish_cmdline # silence unused import
         return True
     except ImportError:
         return False
 
 def getsvnversion():
     m = matchoutput('svn --version --quiet 2>&1', br'^(\d+)\.(\d+)')
     if not m:
         return (0, 0)
     return (int(m.group(1)), int(m.group(2)))
 
 @checkvers("svn", "subversion client and admin tools >= %s", (1.3, 1.5))
 def has_svn_range(v):
     major, minor = v.split('.')[0:2]
     return getsvnversion() >= (int(major), int(minor))
 
 @check("svn", "subversion client and admin tools")
 def has_svn():
     return matchoutput('svn --version 2>&1', br'^svn, version') and \
         matchoutput('svnadmin --version 2>&1', br'^svnadmin, version')
 
 @check("svn-bindings", "subversion python bindings")
 def has_svn_bindings():
     try:
         import svn.core
         version = svn.core.SVN_VER_MAJOR, svn.core.SVN_VER_MINOR
         if version < (1, 4):
             return False
         return True
     except ImportError:
         return False
 
 @check("p4", "Perforce server and client")
 def has_p4():
     return (matchoutput('p4 -V', br'Rev\. P4/') and
             matchoutput('p4d -V', br'Rev\. P4D/'))
 
 @check("symlink", "symbolic links")
 def has_symlink():
     if getattr(os, "symlink", None) is None:
         return False
     name = tempfile.mktemp(dir='.', prefix=tempprefix)
     try:
         os.symlink(".", name)
         os.unlink(name)
         return True
     except (OSError, AttributeError):
         return False
 
 @check("hardlink", "hardlinks")
 def has_hardlink():
     from mercurial import util
     fh, fn = tempfile.mkstemp(dir='.', prefix=tempprefix)
     os.close(fh)
     name = tempfile.mktemp(dir='.', prefix=tempprefix)
     try:
         util.oslink(fn, name)
         os.unlink(name)
         return True
     except OSError:
         return False
     finally:
         os.unlink(fn)
 
 @check("hardlink-whitelisted", "hardlinks on whitelisted filesystems")
 def has_hardlink_whitelisted():
     from mercurial import util
     try:
         fstype = util.getfstype('.')
     except OSError:
         return False
     return fstype in util._hardlinkfswhitelist
 
 @check("rmcwd", "can remove current working directory")
 def has_rmcwd():
     ocwd = os.getcwd()
     temp = tempfile.mkdtemp(dir='.', prefix=tempprefix)
     try:
         os.chdir(temp)
         # On Linux, 'rmdir .' isn't allowed, but the other names are okay.
         # On Solaris and Windows, the cwd can't be removed by any names.
         os.rmdir(os.getcwd())
         return True
     except OSError:
         return False
     finally:
         os.chdir(ocwd)
         # clean up temp dir on platforms where cwd can't be removed
         try:
             os.rmdir(temp)
         except OSError:
             pass
 
 @check("tla", "GNU Arch tla client")
 def has_tla():
     return matchoutput('tla --version 2>&1', br'The GNU Arch Revision')
 
 @check("gpg", "gpg client")
 def has_gpg():
     return matchoutput('gpg --version 2>&1', br'GnuPG')
 
 @check("gpg2", "gpg client v2")
 def has_gpg2():
     return matchoutput('gpg --version 2>&1', br'GnuPG[^0-9]+2\.')
 
 @check("gpg21", "gpg client v2.1+")
 def has_gpg21():
     return matchoutput('gpg --version 2>&1', br'GnuPG[^0-9]+2\.(?!0)')
 
 @check("unix-permissions", "unix-style permissions")
 def has_unix_permissions():
     d = tempfile.mkdtemp(dir='.', prefix=tempprefix)
     try:
         fname = os.path.join(d, 'foo')
         for umask in (0o77, 0o07, 0o22):
             os.umask(umask)
             f = open(fname, 'w')
             f.close()
             mode = os.stat(fname).st_mode
             os.unlink(fname)
             if mode & 0o777 != ~umask & 0o666:
                 return False
         return True
     finally:
         os.rmdir(d)
 
 @check("unix-socket", "AF_UNIX socket family")
 def has_unix_socket():
     return getattr(socket, 'AF_UNIX', None) is not None
 
 @check("root", "root permissions")
 def has_root():
     return getattr(os, 'geteuid', None) and os.geteuid() == 0
 
 @check("pyflakes", "Pyflakes python linter")
 def has_pyflakes():
     return matchoutput("sh -c \"echo 'import re' 2>&1 | pyflakes\"",
                        br"<stdin>:1: 're' imported but unused",
                        True)
 
 @check("pylint", "Pylint python linter")
 def has_pylint():
     return matchoutput("pylint --help",
                        br"Usage:  pylint",
                        True)
 
 @check("clang-format", "clang-format C code formatter")
 def has_clang_format():
     return matchoutput("clang-format --help",
                        br"^OVERVIEW: A tool to format C/C\+\+[^ ]+ code.")
 
 @check("jshint", "JSHint static code analysis tool")
 def has_jshint():
     return matchoutput("jshint --version 2>&1", br"jshint v")
 
 @check("pygments", "Pygments source highlighting library")
 def has_pygments():
     try:
         import pygments
         pygments.highlight # silence unused import warning
         return True
     except ImportError:
         return False
 
 @check("outer-repo", "outer repo")
 def has_outer_repo():
     # failing for other reasons than 'no repo' imply that there is a repo
     return not matchoutput('hg root 2>&1',
                            br'abort: no repository found', True)
 
 @check("ssl", "ssl module available")
 def has_ssl():
     try:
         import ssl
         ssl.CERT_NONE
         return True
     except ImportError:
         return False
 
 @check("sslcontext", "python >= 2.7.9 ssl")
 def has_sslcontext():
     try:
         import ssl
         ssl.SSLContext
         return True
     except (ImportError, AttributeError):
         return False
 
 @check("defaultcacerts", "can verify SSL certs by system's CA certs store")
 def has_defaultcacerts():
     from mercurial import sslutil, ui as uimod
     ui = uimod.ui.load()
     return sslutil._defaultcacerts(ui) or sslutil._canloaddefaultcerts
 
 @check("defaultcacertsloaded", "detected presence of loaded system CA certs")
 def has_defaultcacertsloaded():
     import ssl
     from mercurial import sslutil, ui as uimod
 
     if not has_defaultcacerts():
         return False
     if not has_sslcontext():
         return False
 
     ui = uimod.ui.load()
     cafile = sslutil._defaultcacerts(ui)
     ctx = ssl.create_default_context()
     if cafile:
         ctx.load_verify_locations(cafile=cafile)
     else:
         ctx.load_default_certs()
 
     return len(ctx.get_ca_certs()) > 0
 
 @check("tls1.2", "TLS 1.2 protocol support")
 def has_tls1_2():
     from mercurial import sslutil
     return 'tls1.2' in sslutil.supportedprotocols
 
 @check("windows", "Windows")
 def has_windows():
     return os.name == 'nt'
 
 @check("system-sh", "system() uses sh")
 def has_system_sh():
     return os.name != 'nt'
 
 @check("serve", "platform and python can manage 'hg serve -d'")
 def has_serve():
     return True
 
 @check("test-repo", "running tests from repository")
 def has_test_repo():
     t = os.environ["TESTDIR"]
     return os.path.isdir(os.path.join(t, "..", ".hg"))
 
 @check("tic", "terminfo compiler and curses module")
 def has_tic():
     try:
         import curses
         curses.COLOR_BLUE
         return matchoutput('test -x "`which tic`"', br'')
     except ImportError:
         return False
 
 @check("msys", "Windows with MSYS")
 def has_msys():
     return os.getenv('MSYSTEM')
 
 @check("aix", "AIX")
 def has_aix():
     return sys.platform.startswith("aix")
 
 @check("osx", "OS X")
 def has_osx():
     return sys.platform == 'darwin'
 
 @check("osxpackaging", "OS X packaging tools")
 def has_osxpackaging():
     try:
         return (matchoutput('pkgbuild', br'Usage: pkgbuild ', ignorestatus=1)
                 and matchoutput(
                     'productbuild', br'Usage: productbuild ',
                     ignorestatus=1)
                 and matchoutput('lsbom', br'Usage: lsbom', ignorestatus=1)
                 and matchoutput(
                     'xar --help', br'Usage: xar', ignorestatus=1))
     except ImportError:
         return False
 
 @check('linuxormacos', 'Linux or MacOS')
 def has_linuxormacos():
     # This isn't a perfect test for MacOS. But it is sufficient for our needs.
     return sys.platform.startswith(('linux', 'darwin'))
 
 @check("docker", "docker support")
 def has_docker():
     pat = br'A self-sufficient runtime for'
     if matchoutput('docker --help', pat):
         if 'linux' not in sys.platform:
             # TODO: in theory we should be able to test docker-based
             # package creation on non-linux using boot2docker, but in
             # practice that requires extra coordination to make sure
             # $TESTTEMP is going to be visible at the same path to the
             # boot2docker VM. If we figure out how to verify that, we
             # can use the following instead of just saying False:
             # return 'DOCKER_HOST' in os.environ
             return False
 
         return True
     return False
 
 @check("debhelper", "debian packaging tools")
 def has_debhelper():
     # Some versions of dpkg say `dpkg', some say 'dpkg' (` vs ' on the first
     # quote), so just accept anything in that spot.
     dpkg = matchoutput('dpkg --version',
                        br"Debian .dpkg' package management program")
     dh = matchoutput('dh --help',
                      br'dh is a part of debhelper.', ignorestatus=True)
     dh_py2 = matchoutput('dh_python2 --help',
                          br'other supported Python versions')
     # debuild comes from the 'devscripts' package, though you might want
     # the 'build-debs' package instead, which has a dependency on devscripts.
     debuild = matchoutput('debuild --help',
                           br'to run debian/rules with given parameter')
     return dpkg and dh and dh_py2 and debuild
 
 @check("debdeps",
        "debian build dependencies (run dpkg-checkbuilddeps in contrib/)")
 def has_debdeps():
     # just check exit status (ignoring output)
     path = '%s/../contrib/debian/control' % os.environ['TESTDIR']
     return matchoutput('dpkg-checkbuilddeps %s' % path, br'')
 
 @check("demandimport", "demandimport enabled")
 def has_demandimport():
     # chg disables demandimport intentionally for performance wins.
     return ((not has_chg()) and os.environ.get('HGDEMANDIMPORT') != 'disable')
 
 @check("py3k", "running with Python 3.x")
 def has_py3k():
     return 3 == sys.version_info[0]
 
 @check("py3exe", "a Python 3.x interpreter is available")
 def has_python3exe():
     return 'PYTHON3' in os.environ
 
 @check("py3pygments", "Pygments available on Python 3.x")
 def has_py3pygments():
     if has_py3k():
         return has_pygments()
     elif has_python3exe():
         # just check exit status (ignoring output)
         py3 = os.environ['PYTHON3']
         return matchoutput('%s -c "import pygments"' % py3, br'')
     return False
 
 @check("pure", "running with pure Python code")
 def has_pure():
     return any([
         os.environ.get("HGMODULEPOLICY") == "py",
         os.environ.get("HGTEST_RUN_TESTS_PURE") == "--pure",
     ])
 
 @check("slow", "allow slow tests (use --allow-slow-tests)")
 def has_slow():
     return os.environ.get('HGTEST_SLOW') == 'slow'
 
 @check("hypothesis", "Hypothesis automated test generation")
 def has_hypothesis():
     try:
         import hypothesis
         hypothesis.given
         return True
     except ImportError:
         return False
 
 @check("unziplinks", "unzip(1) understands and extracts symlinks")
 def unzip_understands_symlinks():
     return matchoutput('unzip --help', br'Info-ZIP')
 
 @check("zstd", "zstd Python module available")
 def has_zstd():
     try:
         import mercurial.zstd
         mercurial.zstd.__version__
         return True
     except ImportError:
         return False
 
 @check("devfull", "/dev/full special file")
 def has_dev_full():
     return os.path.exists('/dev/full')
 
 @check("virtualenv", "Python virtualenv support")
 def has_virtualenv():
     try:
         import virtualenv
         virtualenv.ACTIVATE_SH
         return True
     except ImportError:
         return False
 
 @check("fsmonitor", "running tests with fsmonitor")
 def has_fsmonitor():
     return 'HGFSMONITOR_TESTS' in os.environ
 
 @check("fuzzywuzzy", "Fuzzy string matching library")
 def has_fuzzywuzzy():
     try:
         import fuzzywuzzy
         fuzzywuzzy.__version__
         return True
     except ImportError:
         return False
 
 @check("clang-libfuzzer", "clang new enough to include libfuzzer")
 def has_clang_libfuzzer():
     mat = matchoutput('clang --version', b'clang version (\d)')
     if mat:
         # libfuzzer is new in clang 6
         return int(mat.group(1)) > 5
     return False
+
+@check("xdiff", "xdiff algorithm")
+def has_xdiff():
+    try:
+        from mercurial import policy
+        bdiff = policy.importmod('bdiff')
+        return bdiff.xdiffblocks('', '') == [(0, 0, 0, 0)]
+    except (ImportError, AttributeError) as ex:
+        return False