rust-re2: add wrapper for calling Re2 from Rust

This assumes that Re2 is installed following Google's guide. I am not sure
how we want to integrate it in the project, but I think a follow-up patch would
be more appropriate for such work.
As it stands, *not* having Re2 installed results in a compilation error, which
is a problem as it breaks install compatibility. Hence, this is gated behind
a non-default `with-re2` compilation feature.

Differential Revision: https://phab.mercurial-scm.org/D7910

rust/hg-core/build.rs

@@ -0,0 +1,25 b''
+// build.rs
+//
+// Copyright 2020 Raphaël Gomès <[e-mail]>
+//
+// This software may be used and distributed according to the terms of the
+// GNU General Public License version 2 or any later version.
+
+#[cfg(feature = "with-re2")]
+use cc;
+
+#[cfg(feature = "with-re2")]
+fn compile_re2() {
+    cc::Build::new()
+        .cpp(true)
+        .flag("-std=c++11")
+        .file("src/re2/rust_re2.cpp")
+        .compile("librustre.a");
+
+    println!("cargo:rustc-link-lib=re2");
+}
+
+fn main() {
+    #[cfg(feature = "with-re2")]
+    compile_re2();
+}

rust/hg-core/src/re2/mod.rs

@@ -0,0 +1,21 b''
+/// re2 module
+///
+/// The Python implementation of Mercurial uses the Re2 regex engine when
+/// possible and if the bindings are installed, falling back to Python's `re`
+/// in case of unsupported syntax (Re2 is a non-backtracking engine).
+///
+/// Using it from Rust is not ideal. We need C++ bindings, a C++ compiler,
+/// Re2 needs to be installed... why not just use the `regex` crate?
+///
+/// Using Re2 from the Rust implementation guarantees backwards compatibility.
+/// We know it will work out of the box without needing to figure out the
+/// subtle differences in syntax. For example, `regex` currently does not
+/// support empty alternations (regex like `a||b`) which happens more often
+/// than we might think. Old benchmarks also showed worse performance from
+/// regex than with Re2, but the methodology and results were lost, so take
+/// this with a grain of salt.
+///
+/// The idea is to use Re2 for now as a temporary phase and then investigate
+/// how much work would be needed to use `regex`.
+mod re2;
+pub use re2::Re2;

rust/hg-core/src/re2/re2.rs

@@ -0,0 +1,66 b''
+/*
+re2.rs
+
+Rust FFI bindings to Re2.
+
+Copyright 2020 Valentin Gatien-Baron
+
+This software may be used and distributed according to the terms of the
+GNU General Public License version 2 or any later version.
+*/
+use libc::{c_int, c_void};
+
+type Re2Ptr = *const c_void;
+
+pub struct Re2(Re2Ptr);
+
+/// `re2.h` says:
+/// "An "RE2" object is safe for concurrent use by multiple threads."
+unsafe impl Sync for Re2 {}
+
+/// These bind to the C ABI in `rust_re2.cpp`.
+extern "C" {
+    fn rust_re2_create(data: *const u8, len: usize) -> Re2Ptr;
+    fn rust_re2_destroy(re2: Re2Ptr);
+    fn rust_re2_ok(re2: Re2Ptr) -> bool;
+    fn rust_re2_error(
+        re2: Re2Ptr,
+        outdata: *mut *const u8,
+        outlen: *mut usize,
+    ) -> bool;
+    fn rust_re2_match(
+        re2: Re2Ptr,
+        data: *const u8,
+        len: usize,
+        anchor: c_int,
+    ) -> bool;
+}
+
+impl Re2 {
+    pub fn new(pattern: &[u8]) -> Result<Re2, String> {
+        unsafe {
+            let re2 = rust_re2_create(pattern.as_ptr(), pattern.len());
+            if rust_re2_ok(re2) {
+                Ok(Re2(re2))
+            } else {
+                let mut data: *const u8 = std::ptr::null();
+                let mut len: usize = 0;
+                rust_re2_error(re2, &mut data, &mut len);
+                Err(String::from_utf8_lossy(std::slice::from_raw_parts(
+                    data, len,
+                ))
+                .to_string())
+            }
+        }
+    }
+
+    pub fn is_match(&self, data: &[u8]) -> bool {
+        unsafe { rust_re2_match(self.0, data.as_ptr(), data.len(), 1) }
+    }
+}
+
+impl Drop for Re2 {
+    fn drop(&mut self) {
+        unsafe { rust_re2_destroy(self.0) }
+    }
+}

rust/hg-core/src/re2/rust_re2.cpp

@@ -0,0 +1,49 b''
+/*
+rust_re2.cpp
+
+C ABI export of Re2's C++ interface for Rust FFI.
+
+Copyright 2020 Valentin Gatien-Baron
+
+This software may be used and distributed according to the terms of the
+GNU General Public License version 2 or any later version.
+*/
+
+#include <re2/re2.h>
+using namespace re2;
+
+extern "C" {
+	RE2* rust_re2_create(const char* data, size_t len) {
+		RE2::Options o;
+		o.set_encoding(RE2::Options::Encoding::EncodingLatin1);
+		o.set_log_errors(false);
+		o.set_max_mem(50000000);
+
+		return new RE2(StringPiece(data, len), o);
+	}
+
+	void rust_re2_destroy(RE2* re) {
+		delete re;
+	}
+
+	bool rust_re2_ok(RE2* re) {
+		return re->ok();
+	}
+
+	void rust_re2_error(RE2* re, const char** outdata, size_t* outlen) {
+		const std::string& e = re->error();
+		*outdata = e.data();
+		*outlen = e.length();
+	}
+
+	bool rust_re2_match(RE2* re, char* data, size_t len, int ianchor) {
+		const StringPiece sp = StringPiece(data, len);
+
+		RE2::Anchor anchor =
+			ianchor == 0 ? RE2::Anchor::UNANCHORED :
+			(ianchor == 1 ? RE2::Anchor::ANCHOR_START :
+			 RE2::Anchor::ANCHOR_BOTH);
+
+		return re->Match(sp, 0, len, anchor, NULL, 0);
+	}
+}

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rust/hg-core/Cargo.toml

@@ -1,25 +1,34 b''
 [package]
 name = "hg-core"
 version = "0.1.0"
 authors = ["Georges Racinet <[e-mail]>"]
 description = "Mercurial pure Rust core library, with no assumption on Python bindings (FFI)"
 edition = "2018"
+build = "build.rs"
 
 [lib]
 name = "hg"
 
 [dependencies]
 byteorder = "1.3.1"
 hex = "0.4.0"
 lazy_static = "1.3.0"
+libc = { version = "0.2.66", optional = true }
 memchr = "2.2.0"
 rand = "0.6.5"
 rand_pcg = "0.1.1"
 rayon = "1.3.0"
 regex = "1.1.0"
 twox-hash = "1.5.0"
 same-file = "1.0.6"
 
 [dev-dependencies]
 tempfile = "3.1.0"
-pretty_assertions = "0.6.1"
  No newline at end of file
+pretty_assertions = "0.6.1"
+
+[build-dependencies]
+cc = { version = "1.0.48", optional = true }
+
+[features]
+default = []
+with-re2 = ["cc", "libc"]

rust/hg-core/src/lib.rs

@@ -1,175 +1,177 b''
 // Copyright 2018-2020 Georges Racinet <[e-mail]>
 //           and Mercurial contributors
 //
 // This software may be used and distributed according to the terms of the
 // GNU General Public License version 2 or any later version.
 mod ancestors;
 pub mod dagops;
 pub use ancestors::{AncestorsIterator, LazyAncestors, MissingAncestors};
 mod dirstate;
 pub mod discovery;
 pub mod testing; // unconditionally built, for use from integration tests
 pub use dirstate::{
     dirs_multiset::{DirsMultiset, DirsMultisetIter},
     dirstate_map::DirstateMap,
     parsers::{pack_dirstate, parse_dirstate, PARENT_SIZE},
     status::{status, StatusResult},
     CopyMap, CopyMapIter, DirstateEntry, DirstateParents, EntryState,
     StateMap, StateMapIter,
 };
 mod filepatterns;
 pub mod matchers;
 pub mod revlog;
 pub use revlog::*;
+#[cfg(feature = "with-re2")]
+pub mod re2;
 pub mod utils;
 
 use crate::utils::hg_path::{HgPathBuf, HgPathError};
 pub use filepatterns::{
     parse_pattern_syntax, read_pattern_file, IgnorePattern,
     PatternFileWarning, PatternSyntax,
 };
 use std::collections::HashMap;
 use twox_hash::RandomXxHashBuilder64;
 
 pub type LineNumber = usize;
 
 /// Rust's default hasher is too slow because it tries to prevent collision
 /// attacks. We are not concerned about those: if an ill-minded person has
 /// write access to your repository, you have other issues.
 pub type FastHashMap<K, V> = HashMap<K, V, RandomXxHashBuilder64>;
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum DirstateParseError {
     TooLittleData,
     Overflow,
     CorruptedEntry(String),
     Damaged,
 }
 
 impl From<std::io::Error> for DirstateParseError {
     fn from(e: std::io::Error) -> Self {
         DirstateParseError::CorruptedEntry(e.to_string())
     }
 }
 
 impl ToString for DirstateParseError {
     fn to_string(&self) -> String {
         use crate::DirstateParseError::*;
         match self {
             TooLittleData => "Too little data for dirstate.".to_string(),
             Overflow => "Overflow in dirstate.".to_string(),
             CorruptedEntry(e) => format!("Corrupted entry: {:?}.", e),
             Damaged => "Dirstate appears to be damaged.".to_string(),
         }
     }
 }
 
 #[derive(Debug, PartialEq)]
 pub enum DirstatePackError {
     CorruptedEntry(String),
     CorruptedParent,
     BadSize(usize, usize),
 }
 
 impl From<std::io::Error> for DirstatePackError {
     fn from(e: std::io::Error) -> Self {
         DirstatePackError::CorruptedEntry(e.to_string())
     }
 }
 #[derive(Debug, PartialEq)]
 pub enum DirstateMapError {
     PathNotFound(HgPathBuf),
     EmptyPath,
     InvalidPath(HgPathError),
 }
 
 impl ToString for DirstateMapError {
     fn to_string(&self) -> String {
         match self {
             DirstateMapError::PathNotFound(_) => {
                 "expected a value, found none".to_string()
             }
             DirstateMapError::EmptyPath => "Overflow in dirstate.".to_string(),
             DirstateMapError::InvalidPath(e) => e.to_string(),
         }
     }
 }
 
 pub enum DirstateError {
     Parse(DirstateParseError),
     Pack(DirstatePackError),
     Map(DirstateMapError),
     IO(std::io::Error),
 }
 
 impl From<DirstateParseError> for DirstateError {
     fn from(e: DirstateParseError) -> Self {
         DirstateError::Parse(e)
     }
 }
 
 impl From<DirstatePackError> for DirstateError {
     fn from(e: DirstatePackError) -> Self {
         DirstateError::Pack(e)
     }
 }
 
 #[derive(Debug)]
 pub enum PatternError {
     Path(HgPathError),
     UnsupportedSyntax(String),
     UnsupportedSyntaxInFile(String, String, usize),
     TooLong(usize),
     IO(std::io::Error),
     /// Needed a pattern that can be turned into a regex but got one that
     /// can't. This should only happen through programmer error.
     NonRegexPattern(IgnorePattern),
 }
 
 impl ToString for PatternError {
     fn to_string(&self) -> String {
         match self {
             PatternError::UnsupportedSyntax(syntax) => {
                 format!("Unsupported syntax {}", syntax)
             }
             PatternError::UnsupportedSyntaxInFile(syntax, file_path, line) => {
                 format!(
                     "{}:{}: unsupported syntax {}",
                     file_path, line, syntax
                 )
             }
             PatternError::TooLong(size) => {
                 format!("matcher pattern is too long ({} bytes)", size)
             }
             PatternError::IO(e) => e.to_string(),
             PatternError::Path(e) => e.to_string(),
             PatternError::NonRegexPattern(pattern) => {
                 format!("'{:?}' cannot be turned into a regex", pattern)
             }
         }
     }
 }
 
 impl From<DirstateMapError> for DirstateError {
     fn from(e: DirstateMapError) -> Self {
         DirstateError::Map(e)
     }
 }
 
 impl From<std::io::Error> for DirstateError {
     fn from(e: std::io::Error) -> Self {
         DirstateError::IO(e)
     }
 }
 
 impl From<std::io::Error> for PatternError {
     fn from(e: std::io::Error) -> Self {
         PatternError::IO(e)
     }
 }
 
 impl From<HgPathError> for PatternError {
     fn from(e: HgPathError) -> Self {
         PatternError::Path(e)
     }
 }

rust/hg-cpython/Cargo.toml

@@ -1,29 +1,30 b''
 [package]
 name = "hg-cpython"
 version = "0.1.0"
 authors = ["Georges Racinet <[e-mail]>"]
 edition = "2018"
 
 [lib]
 name='rusthg'
 crate-type = ["cdylib"]
 
 [features]
 default = ["python27"]
+with-re2 = ["hg-core/with-re2"]
 
 # Features to build an extension module:
 python27 = ["cpython/python27-sys", "cpython/extension-module-2-7"]
 python3 = ["cpython/python3-sys", "cpython/extension-module"]
 
 # Enable one of these features to build a test executable linked to libpython:
 # e.g. cargo test --no-default-features --features python27-bin
 python27-bin = ["cpython/python27-sys"]
 python3-bin = ["cpython/python3-sys"]
 
 [dependencies]
-hg-core = { path = "../hg-core" }
+hg-core = { path = "../hg-core"}
 libc = '*'
 
 [dependencies.cpython]
 version = "0.4"
 default-features = false

setup.py

@@ -1,1727 +1,1736 b''
 #
 # This is the mercurial setup script.
 #
 # 'python setup.py install', or
 # 'python setup.py --help' for more options
 
 import os
 
 # Mercurial will never work on Python 3 before 3.5 due to a lack
 # of % formatting on bytestrings, and can't work on 3.6.0 or 3.6.1
 # due to a bug in % formatting in bytestrings.
 # We cannot support Python 3.5.0, 3.5.1, 3.5.2 because of bug in
 # codecs.escape_encode() where it raises SystemError on empty bytestring
 # bug link: https://bugs.python.org/issue25270
 supportedpy = ','.join(
     [
         '>=2.7',
         '!=3.0.*',
         '!=3.1.*',
         '!=3.2.*',
         '!=3.3.*',
         '!=3.4.*',
         '!=3.5.0',
         '!=3.5.1',
         '!=3.5.2',
         '!=3.6.0',
         '!=3.6.1',
     ]
 )
 
 import sys, platform
 import sysconfig
 
 if sys.version_info[0] >= 3:
     printf = eval('print')
     libdir_escape = 'unicode_escape'
 
     def sysstr(s):
         return s.decode('latin-1')
 
 
 else:
     libdir_escape = 'string_escape'
 
     def printf(*args, **kwargs):
         f = kwargs.get('file', sys.stdout)
         end = kwargs.get('end', '\n')
         f.write(b' '.join(args) + end)
 
     def sysstr(s):
         return s
 
 
 # Attempt to guide users to a modern pip - this means that 2.6 users
 # should have a chance of getting a 4.2 release, and when we ratchet
 # the version requirement forward again hopefully everyone will get
 # something that works for them.
 if sys.version_info < (2, 7, 0, 'final'):
     pip_message = (
         'This may be due to an out of date pip. '
         'Make sure you have pip >= 9.0.1.'
     )
     try:
         import pip
 
         pip_version = tuple([int(x) for x in pip.__version__.split('.')[:3]])
         if pip_version < (9, 0, 1):
             pip_message = (
                 'Your pip version is out of date, please install '
                 'pip >= 9.0.1. pip {} detected.'.format(pip.__version__)
             )
         else:
             # pip is new enough - it must be something else
             pip_message = ''
     except Exception:
         pass
     error = """
 Mercurial does not support Python older than 2.7.
 Python {py} detected.
 {pip}
 """.format(
         py=sys.version_info, pip=pip_message
     )
     printf(error, file=sys.stderr)
     sys.exit(1)
 
 if sys.version_info[0] >= 3:
     DYLIB_SUFFIX = sysconfig.get_config_vars()['EXT_SUFFIX']
 else:
     # deprecated in Python 3
     DYLIB_SUFFIX = sysconfig.get_config_vars()['SO']
 
 # Solaris Python packaging brain damage
 try:
     import hashlib
 
     sha = hashlib.sha1()
 except ImportError:
     try:
         import sha
 
         sha.sha  # silence unused import warning
     except ImportError:
         raise SystemExit(
             "Couldn't import standard hashlib (incomplete Python install)."
         )
 
 try:
     import zlib
 
     zlib.compressobj  # silence unused import warning
 except ImportError:
     raise SystemExit(
         "Couldn't import standard zlib (incomplete Python install)."
     )
 
 # The base IronPython distribution (as of 2.7.1) doesn't support bz2
 isironpython = False
 try:
     isironpython = (
         platform.python_implementation().lower().find("ironpython") != -1
     )
 except AttributeError:
     pass
 
 if isironpython:
     sys.stderr.write("warning: IronPython detected (no bz2 support)\n")
 else:
     try:
         import bz2
 
         bz2.BZ2Compressor  # silence unused import warning
     except ImportError:
         raise SystemExit(
             "Couldn't import standard bz2 (incomplete Python install)."
         )
 
 ispypy = "PyPy" in sys.version
 
 hgrustext = os.environ.get('HGWITHRUSTEXT')
 # TODO record it for proper rebuild upon changes
 # (see mercurial/__modulepolicy__.py)
 if hgrustext != 'cpython' and hgrustext is not None:
     hgrustext = 'direct-ffi'
 
 import ctypes
 import errno
 import stat, subprocess, time
 import re
 import shutil
 import tempfile
 from distutils import log
 
 # We have issues with setuptools on some platforms and builders. Until
 # those are resolved, setuptools is opt-in except for platforms where
 # we don't have issues.
 issetuptools = os.name == 'nt' or 'FORCE_SETUPTOOLS' in os.environ
 if issetuptools:
     from setuptools import setup
 else:
     from distutils.core import setup
 from distutils.ccompiler import new_compiler
 from distutils.core import Command, Extension
 from distutils.dist import Distribution
 from distutils.command.build import build
 from distutils.command.build_ext import build_ext
 from distutils.command.build_py import build_py
 from distutils.command.build_scripts import build_scripts
 from distutils.command.install import install
 from distutils.command.install_lib import install_lib
 from distutils.command.install_scripts import install_scripts
 from distutils.spawn import spawn, find_executable
 from distutils import file_util
 from distutils.errors import (
     CCompilerError,
     DistutilsError,
     DistutilsExecError,
 )
 from distutils.sysconfig import get_python_inc, get_config_var
 from distutils.version import StrictVersion
 
 # Explain to distutils.StrictVersion how our release candidates are versionned
 StrictVersion.version_re = re.compile(r'^(\d+)\.(\d+)(\.(\d+))?-?(rc(\d+))?$')
 
 
 def write_if_changed(path, content):
     """Write content to a file iff the content hasn't changed."""
     if os.path.exists(path):
         with open(path, 'rb') as fh:
             current = fh.read()
     else:
         current = b''
 
     if current != content:
         with open(path, 'wb') as fh:
             fh.write(content)
 
 
 scripts = ['hg']
 if os.name == 'nt':
     # We remove hg.bat if we are able to build hg.exe.
     scripts.append('contrib/win32/hg.bat')
 
 
 def cancompile(cc, code):
     tmpdir = tempfile.mkdtemp(prefix='hg-install-')
     devnull = oldstderr = None
     try:
         fname = os.path.join(tmpdir, 'testcomp.c')
         f = open(fname, 'w')
         f.write(code)
         f.close()
         # Redirect stderr to /dev/null to hide any error messages
         # from the compiler.
         # This will have to be changed if we ever have to check
         # for a function on Windows.
         devnull = open('/dev/null', 'w')
         oldstderr = os.dup(sys.stderr.fileno())
         os.dup2(devnull.fileno(), sys.stderr.fileno())
         objects = cc.compile([fname], output_dir=tmpdir)
         cc.link_executable(objects, os.path.join(tmpdir, "a.out"))
         return True
     except Exception:
         return False
     finally:
         if oldstderr is not None:
             os.dup2(oldstderr, sys.stderr.fileno())
         if devnull is not None:
             devnull.close()
         shutil.rmtree(tmpdir)
 
 
 # simplified version of distutils.ccompiler.CCompiler.has_function
 # that actually removes its temporary files.
 def hasfunction(cc, funcname):
     code = 'int main(void) { %s(); }\n' % funcname
     return cancompile(cc, code)
 
 
 def hasheader(cc, headername):
     code = '#include <%s>\nint main(void) { return 0; }\n' % headername
     return cancompile(cc, code)
 
 
 # py2exe needs to be installed to work
 try:
     import py2exe
 
     py2exe.Distribution  # silence unused import warning
     py2exeloaded = True
     # import py2exe's patched Distribution class
     from distutils.core import Distribution
 except ImportError:
     py2exeloaded = False
 
 
 def runcmd(cmd, env, cwd=None):
     p = subprocess.Popen(
         cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE, env=env, cwd=cwd
     )
     out, err = p.communicate()
     return p.returncode, out, err
 
 
 class hgcommand(object):
     def __init__(self, cmd, env):
         self.cmd = cmd
         self.env = env
 
     def run(self, args):
         cmd = self.cmd + args
         returncode, out, err = runcmd(cmd, self.env)
         err = filterhgerr(err)
         if err or returncode != 0:
             printf("stderr from '%s':" % (' '.join(cmd)), file=sys.stderr)
             printf(err, file=sys.stderr)
             return ''
         return out
 
 
 def filterhgerr(err):
     # If root is executing setup.py, but the repository is owned by
     # another user (as in "sudo python setup.py install") we will get
     # trust warnings since the .hg/hgrc file is untrusted. That is
     # fine, we don't want to load it anyway.  Python may warn about
     # a missing __init__.py in mercurial/locale, we also ignore that.
     err = [
         e
         for e in err.splitlines()
         if (
             not e.startswith(b'not trusting file')
             and not e.startswith(b'warning: Not importing')
             and not e.startswith(b'obsolete feature not enabled')
             and not e.startswith(b'*** failed to import extension')
             and not e.startswith(b'devel-warn:')
             and not (
                 e.startswith(b'(third party extension')
                 and e.endswith(b'or newer of Mercurial; disabling)')
             )
         )
     ]
     return b'\n'.join(b'  ' + e for e in err)
 
 
 def findhg():
     """Try to figure out how we should invoke hg for examining the local
     repository contents.
 
     Returns an hgcommand object."""
     # By default, prefer the "hg" command in the user's path.  This was
     # presumably the hg command that the user used to create this repository.
     #
     # This repository may require extensions or other settings that would not
     # be enabled by running the hg script directly from this local repository.
     hgenv = os.environ.copy()
     # Use HGPLAIN to disable hgrc settings that would change output formatting,
     # and disable localization for the same reasons.
     hgenv['HGPLAIN'] = '1'
     hgenv['LANGUAGE'] = 'C'
     hgcmd = ['hg']
     # Run a simple "hg log" command just to see if using hg from the user's
     # path works and can successfully interact with this repository.  Windows
     # gives precedence to hg.exe in the current directory, so fall back to the
     # python invocation of local hg, where pythonXY.dll can always be found.
     check_cmd = ['log', '-r.', '-Ttest']
     if os.name != 'nt' or not os.path.exists("hg.exe"):
         try:
             retcode, out, err = runcmd(hgcmd + check_cmd, hgenv)
         except EnvironmentError:
             retcode = -1
         if retcode == 0 and not filterhgerr(err):
             return hgcommand(hgcmd, hgenv)
 
     # Fall back to trying the local hg installation.
     hgenv = localhgenv()
     hgcmd = [sys.executable, 'hg']
     try:
         retcode, out, err = runcmd(hgcmd + check_cmd, hgenv)
     except EnvironmentError:
         retcode = -1
     if retcode == 0 and not filterhgerr(err):
         return hgcommand(hgcmd, hgenv)
 
     raise SystemExit(
         'Unable to find a working hg binary to extract the '
         'version from the repository tags'
     )
 
 
 def localhgenv():
     """Get an environment dictionary to use for invoking or importing
     mercurial from the local repository."""
     # Execute hg out of this directory with a custom environment which takes
     # care to not use any hgrc files and do no localization.
     env = {
         'HGMODULEPOLICY': 'py',
         'HGRCPATH': '',
         'LANGUAGE': 'C',
         'PATH': '',
     }  # make pypi modules that use os.environ['PATH'] happy
     if 'LD_LIBRARY_PATH' in os.environ:
         env['LD_LIBRARY_PATH'] = os.environ['LD_LIBRARY_PATH']
     if 'SystemRoot' in os.environ:
         # SystemRoot is required by Windows to load various DLLs.  See:
         # https://bugs.python.org/issue13524#msg148850
         env['SystemRoot'] = os.environ['SystemRoot']
     return env
 
 
 version = ''
 
 if os.path.isdir('.hg'):
     hg = findhg()
     cmd = ['log', '-r', '.', '--template', '{tags}\n']
     numerictags = [t for t in sysstr(hg.run(cmd)).split() if t[0:1].isdigit()]
     hgid = sysstr(hg.run(['id', '-i'])).strip()
     if not hgid:
         # Bail out if hg is having problems interacting with this repository,
         # rather than falling through and producing a bogus version number.
         # Continuing with an invalid version number will break extensions
         # that define minimumhgversion.
         raise SystemExit('Unable to determine hg version from local repository')
     if numerictags:  # tag(s) found
         version = numerictags[-1]
         if hgid.endswith('+'):  # propagate the dirty status to the tag
             version += '+'
     else:  # no tag found
         ltagcmd = ['parents', '--template', '{latesttag}']
         ltag = sysstr(hg.run(ltagcmd))
         changessincecmd = ['log', '-T', 'x\n', '-r', "only(.,'%s')" % ltag]
         changessince = len(hg.run(changessincecmd).splitlines())
         version = '%s+%s-%s' % (ltag, changessince, hgid)
     if version.endswith('+'):
         version += time.strftime('%Y%m%d')
 elif os.path.exists('.hg_archival.txt'):
     kw = dict(
         [[t.strip() for t in l.split(':', 1)] for l in open('.hg_archival.txt')]
     )
     if 'tag' in kw:
         version = kw['tag']
     elif 'latesttag' in kw:
         if 'changessincelatesttag' in kw:
             version = '%(latesttag)s+%(changessincelatesttag)s-%(node).12s' % kw
         else:
             version = '%(latesttag)s+%(latesttagdistance)s-%(node).12s' % kw
     else:
         version = kw.get('node', '')[:12]
 
 if version:
     versionb = version
     if not isinstance(versionb, bytes):
         versionb = versionb.encode('ascii')
 
     write_if_changed(
         'mercurial/__version__.py',
         b''.join(
             [
                 b'# this file is autogenerated by setup.py\n'
                 b'version = b"%s"\n' % versionb,
             ]
         ),
     )
 
 try:
     oldpolicy = os.environ.get('HGMODULEPOLICY', None)
     os.environ['HGMODULEPOLICY'] = 'py'
     from mercurial import __version__
 
     version = __version__.version
 except ImportError:
     version = b'unknown'
 finally:
     if oldpolicy is None:
         del os.environ['HGMODULEPOLICY']
     else:
         os.environ['HGMODULEPOLICY'] = oldpolicy
 
 
 class hgbuild(build):
     # Insert hgbuildmo first so that files in mercurial/locale/ are found
     # when build_py is run next.
     sub_commands = [('build_mo', None)] + build.sub_commands
 
 
 class hgbuildmo(build):
 
     description = "build translations (.mo files)"
 
     def run(self):
         if not find_executable('msgfmt'):
             self.warn(
                 "could not find msgfmt executable, no translations "
                 "will be built"
             )
             return
 
         podir = 'i18n'
         if not os.path.isdir(podir):
             self.warn("could not find %s/ directory" % podir)
             return
 
         join = os.path.join
         for po in os.listdir(podir):
             if not po.endswith('.po'):
                 continue
             pofile = join(podir, po)
             modir = join('locale', po[:-3], 'LC_MESSAGES')
             mofile = join(modir, 'hg.mo')
             mobuildfile = join('mercurial', mofile)
             cmd = ['msgfmt', '-v', '-o', mobuildfile, pofile]
             if sys.platform != 'sunos5':
                 # msgfmt on Solaris does not know about -c
                 cmd.append('-c')
             self.mkpath(join('mercurial', modir))
             self.make_file([pofile], mobuildfile, spawn, (cmd,))
 
 
 class hgdist(Distribution):
     pure = False
     rust = hgrustext is not None
     cffi = ispypy
 
     global_options = Distribution.global_options + [
         ('pure', None, "use pure (slow) Python code instead of C extensions"),
         ('rust', None, "use Rust extensions additionally to C extensions"),
     ]
 
     def has_ext_modules(self):
         # self.ext_modules is emptied in hgbuildpy.finalize_options which is
         # too late for some cases
         return not self.pure and Distribution.has_ext_modules(self)
 
 
 # This is ugly as a one-liner. So use a variable.
 buildextnegops = dict(getattr(build_ext, 'negative_options', {}))
 buildextnegops['no-zstd'] = 'zstd'
 buildextnegops['no-rust'] = 'rust'
 
 
 class hgbuildext(build_ext):
     user_options = build_ext.user_options + [
         ('zstd', None, 'compile zstd bindings [default]'),
         ('no-zstd', None, 'do not compile zstd bindings'),
         (
             'rust',
             None,
             'compile Rust extensions if they are in use '
             '(requires Cargo) [default]',
         ),
         ('no-rust', None, 'do not compile Rust extensions'),
     ]
 
     boolean_options = build_ext.boolean_options + ['zstd', 'rust']
     negative_opt = buildextnegops
 
     def initialize_options(self):
         self.zstd = True
         self.rust = True
 
         return build_ext.initialize_options(self)
 
     def finalize_options(self):
         # Unless overridden by the end user, build extensions in parallel.
         # Only influences behavior on Python 3.5+.
         if getattr(self, 'parallel', None) is None:
             self.parallel = True
 
         return build_ext.finalize_options(self)
 
     def build_extensions(self):
         ruststandalones = [
             e for e in self.extensions if isinstance(e, RustStandaloneExtension)
         ]
         self.extensions = [
             e for e in self.extensions if e not in ruststandalones
         ]
         # Filter out zstd if disabled via argument.
         if not self.zstd:
             self.extensions = [
                 e for e in self.extensions if e.name != 'mercurial.zstd'
             ]
 
         # Build Rust standalon extensions if it'll be used
         # and its build is not explictely disabled (for external build
         # as Linux distributions would do)
         if self.distribution.rust and self.rust and hgrustext != 'direct-ffi':
             for rustext in ruststandalones:
                 rustext.build('' if self.inplace else self.build_lib)
 
         return build_ext.build_extensions(self)
 
     def build_extension(self, ext):
         if (
             self.distribution.rust
             and self.rust
             and isinstance(ext, RustExtension)
         ):
             ext.rustbuild()
         try:
             build_ext.build_extension(self, ext)
         except CCompilerError:
             if not getattr(ext, 'optional', False):
                 raise
             log.warn(
                 "Failed to build optional extension '%s' (skipping)", ext.name
             )
 
 
 class hgbuildscripts(build_scripts):
     def run(self):
         if os.name != 'nt' or self.distribution.pure:
             return build_scripts.run(self)
 
         exebuilt = False
         try:
             self.run_command('build_hgexe')
             exebuilt = True
         except (DistutilsError, CCompilerError):
             log.warn('failed to build optional hg.exe')
 
         if exebuilt:
             # Copying hg.exe to the scripts build directory ensures it is
             # installed by the install_scripts command.
             hgexecommand = self.get_finalized_command('build_hgexe')
             dest = os.path.join(self.build_dir, 'hg.exe')
             self.mkpath(self.build_dir)
             self.copy_file(hgexecommand.hgexepath, dest)
 
             # Remove hg.bat because it is redundant with hg.exe.
             self.scripts.remove('contrib/win32/hg.bat')
 
         return build_scripts.run(self)
 
 
 class hgbuildpy(build_py):
     def finalize_options(self):
         build_py.finalize_options(self)
 
         if self.distribution.pure:
             self.distribution.ext_modules = []
         elif self.distribution.cffi:
             from mercurial.cffi import (
                 bdiffbuild,
                 mpatchbuild,
             )
 
             exts = [
                 mpatchbuild.ffi.distutils_extension(),
                 bdiffbuild.ffi.distutils_extension(),
             ]
             # cffi modules go here
             if sys.platform == 'darwin':
                 from mercurial.cffi import osutilbuild
 
                 exts.append(osutilbuild.ffi.distutils_extension())
             self.distribution.ext_modules = exts
         else:
             h = os.path.join(get_python_inc(), 'Python.h')
             if not os.path.exists(h):
                 raise SystemExit(
                     'Python headers are required to build '
                     'Mercurial but weren\'t found in %s' % h
                 )
 
     def run(self):
         basepath = os.path.join(self.build_lib, 'mercurial')
         self.mkpath(basepath)
 
         rust = self.distribution.rust
         if self.distribution.pure:
             modulepolicy = 'py'
         elif self.build_lib == '.':
             # in-place build should run without rebuilding and Rust extensions
             modulepolicy = 'rust+c-allow' if rust else 'allow'
         else:
             modulepolicy = 'rust+c' if rust else 'c'
 
         content = b''.join(
             [
                 b'# this file is autogenerated by setup.py\n',
                 b'modulepolicy = b"%s"\n' % modulepolicy.encode('ascii'),
             ]
         )
         write_if_changed(os.path.join(basepath, '__modulepolicy__.py'), content)
 
         build_py.run(self)
 
 
 class buildhgextindex(Command):
     description = 'generate prebuilt index of hgext (for frozen package)'
     user_options = []
     _indexfilename = 'hgext/__index__.py'
 
     def initialize_options(self):
         pass
 
     def finalize_options(self):
         pass
 
     def run(self):
         if os.path.exists(self._indexfilename):
             with open(self._indexfilename, 'w') as f:
                 f.write('# empty\n')
 
         # here no extension enabled, disabled() lists up everything
         code = (
             'import pprint; from mercurial import extensions; '
             'pprint.pprint(extensions.disabled())'
         )
         returncode, out, err = runcmd(
             [sys.executable, '-c', code], localhgenv()
         )
         if err or returncode != 0:
             raise DistutilsExecError(err)
 
         with open(self._indexfilename, 'wb') as f:
             f.write(b'# this file is autogenerated by setup.py\n')
             f.write(b'docs = ')
             f.write(out)
 
 
 class buildhgexe(build_ext):
     description = 'compile hg.exe from mercurial/exewrapper.c'
     user_options = build_ext.user_options + [
         (
             'long-paths-support',
             None,
             'enable support for long paths on '
             'Windows (off by default and '
             'experimental)',
         ),
     ]
 
     LONG_PATHS_MANIFEST = """
     <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
     <assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0">
         <application>
             <windowsSettings
             xmlns:ws2="http://schemas.microsoft.com/SMI/2016/WindowsSettings">
                 <ws2:longPathAware>true</ws2:longPathAware>
             </windowsSettings>
         </application>
     </assembly>"""
 
     def initialize_options(self):
         build_ext.initialize_options(self)
         self.long_paths_support = False
 
     def build_extensions(self):
         if os.name != 'nt':
             return
         if isinstance(self.compiler, HackedMingw32CCompiler):
             self.compiler.compiler_so = self.compiler.compiler  # no -mdll
             self.compiler.dll_libraries = []  # no -lmsrvc90
 
         pythonlib = None
 
         if getattr(sys, 'dllhandle', None):
             # Different Python installs can have different Python library
             # names. e.g. the official CPython distribution uses pythonXY.dll
             # and MinGW uses libpythonX.Y.dll.
             _kernel32 = ctypes.windll.kernel32
             _kernel32.GetModuleFileNameA.argtypes = [
                 ctypes.c_void_p,
                 ctypes.c_void_p,
                 ctypes.c_ulong,
             ]
             _kernel32.GetModuleFileNameA.restype = ctypes.c_ulong
             size = 1000
             buf = ctypes.create_string_buffer(size + 1)
             filelen = _kernel32.GetModuleFileNameA(
                 sys.dllhandle, ctypes.byref(buf), size
             )
 
             if filelen > 0 and filelen != size:
                 dllbasename = os.path.basename(buf.value)
                 if not dllbasename.lower().endswith(b'.dll'):
                     raise SystemExit(
                         'Python DLL does not end with .dll: %s' % dllbasename
                     )
                 pythonlib = dllbasename[:-4]
 
         if not pythonlib:
             log.warn(
                 'could not determine Python DLL filename; assuming pythonXY'
             )
 
             hv = sys.hexversion
             pythonlib = b'python%d%d' % (hv >> 24, (hv >> 16) & 0xFF)
 
         log.info('using %s as Python library name' % pythonlib)
         with open('mercurial/hgpythonlib.h', 'wb') as f:
             f.write(b'/* this file is autogenerated by setup.py */\n')
             f.write(b'#define HGPYTHONLIB "%s"\n' % pythonlib)
 
         macros = None
         if sys.version_info[0] >= 3:
             macros = [('_UNICODE', None), ('UNICODE', None)]
 
         objects = self.compiler.compile(
             ['mercurial/exewrapper.c'],
             output_dir=self.build_temp,
             macros=macros,
         )
         dir = os.path.dirname(self.get_ext_fullpath('dummy'))
         self.hgtarget = os.path.join(dir, 'hg')
         self.compiler.link_executable(
             objects, self.hgtarget, libraries=[], output_dir=self.build_temp
         )
         if self.long_paths_support:
             self.addlongpathsmanifest()
 
     def addlongpathsmanifest(self):
         r"""Add manifest pieces so that hg.exe understands long paths
 
         This is an EXPERIMENTAL feature, use with care.
         To enable long paths support, one needs to do two things:
         - build Mercurial with --long-paths-support option
         - change HKLM\SYSTEM\CurrentControlSet\Control\FileSystem\
                  LongPathsEnabled to have value 1.
 
         Please ignore 'warning 81010002: Unrecognized Element "longPathAware"';
         it happens because Mercurial uses mt.exe circa 2008, which is not
         yet aware of long paths support in the manifest (I think so at least).
         This does not stop mt.exe from embedding/merging the XML properly.
 
         Why resource #1 should be used for .exe manifests? I don't know and
         wasn't able to find an explanation for mortals. But it seems to work.
         """
         exefname = self.compiler.executable_filename(self.hgtarget)
         fdauto, manfname = tempfile.mkstemp(suffix='.hg.exe.manifest')
         os.close(fdauto)
         with open(manfname, 'w') as f:
             f.write(self.LONG_PATHS_MANIFEST)
         log.info("long paths manifest is written to '%s'" % manfname)
         inputresource = '-inputresource:%s;#1' % exefname
         outputresource = '-outputresource:%s;#1' % exefname
         log.info("running mt.exe to update hg.exe's manifest in-place")
         # supplying both -manifest and -inputresource to mt.exe makes
         # it merge the embedded and supplied manifests in the -outputresource
         self.spawn(
             [
                 'mt.exe',
                 '-nologo',
                 '-manifest',
                 manfname,
                 inputresource,
                 outputresource,
             ]
         )
         log.info("done updating hg.exe's manifest")
         os.remove(manfname)
 
     @property
     def hgexepath(self):
         dir = os.path.dirname(self.get_ext_fullpath('dummy'))
         return os.path.join(self.build_temp, dir, 'hg.exe')
 
 
 class hgbuilddoc(Command):
     description = 'build documentation'
     user_options = [
         ('man', None, 'generate man pages'),
         ('html', None, 'generate html pages'),
     ]
 
     def initialize_options(self):
         self.man = None
         self.html = None
 
     def finalize_options(self):
         # If --man or --html are set, only generate what we're told to.
         # Otherwise generate everything.
         have_subset = self.man is not None or self.html is not None
 
         if have_subset:
             self.man = True if self.man else False
             self.html = True if self.html else False
         else:
             self.man = True
             self.html = True
 
     def run(self):
         def normalizecrlf(p):
             with open(p, 'rb') as fh:
                 orig = fh.read()
 
             if b'\r\n' not in orig:
                 return
 
             log.info('normalizing %s to LF line endings' % p)
             with open(p, 'wb') as fh:
                 fh.write(orig.replace(b'\r\n', b'\n'))
 
         def gentxt(root):
             txt = 'doc/%s.txt' % root
             log.info('generating %s' % txt)
             res, out, err = runcmd(
                 [sys.executable, 'gendoc.py', root], os.environ, cwd='doc'
             )
             if res:
                 raise SystemExit(
                     'error running gendoc.py: %s' % '\n'.join([out, err])
                 )
 
             with open(txt, 'wb') as fh:
                 fh.write(out)
 
         def gengendoc(root):
             gendoc = 'doc/%s.gendoc.txt' % root
 
             log.info('generating %s' % gendoc)
             res, out, err = runcmd(
                 [sys.executable, 'gendoc.py', '%s.gendoc' % root],
                 os.environ,
                 cwd='doc',
             )
             if res:
                 raise SystemExit(
                     'error running gendoc: %s' % '\n'.join([out, err])
                 )
 
             with open(gendoc, 'wb') as fh:
                 fh.write(out)
 
         def genman(root):
             log.info('generating doc/%s' % root)
             res, out, err = runcmd(
                 [
                     sys.executable,
                     'runrst',
                     'hgmanpage',
                     '--halt',
                     'warning',
                     '--strip-elements-with-class',
                     'htmlonly',
                     '%s.txt' % root,
                     root,
                 ],
                 os.environ,
                 cwd='doc',
             )
             if res:
                 raise SystemExit(
                     'error running runrst: %s' % '\n'.join([out, err])
                 )
 
             normalizecrlf('doc/%s' % root)
 
         def genhtml(root):
             log.info('generating doc/%s.html' % root)
             res, out, err = runcmd(
                 [
                     sys.executable,
                     'runrst',
                     'html',
                     '--halt',
                     'warning',
                     '--link-stylesheet',
                     '--stylesheet-path',
                     'style.css',
                     '%s.txt' % root,
                     '%s.html' % root,
                 ],
                 os.environ,
                 cwd='doc',
             )
             if res:
                 raise SystemExit(
                     'error running runrst: %s' % '\n'.join([out, err])
                 )
 
             normalizecrlf('doc/%s.html' % root)
 
         # This logic is duplicated in doc/Makefile.
         sources = set(
             f
             for f in os.listdir('mercurial/helptext')
             if re.search(r'[0-9]\.txt$', f)
         )
 
         # common.txt is a one-off.
         gentxt('common')
 
         for source in sorted(sources):
             assert source[-4:] == '.txt'
             root = source[:-4]
 
             gentxt(root)
             gengendoc(root)
 
             if self.man:
                 genman(root)
             if self.html:
                 genhtml(root)
 
 
 class hginstall(install):
 
     user_options = install.user_options + [
         (
             'old-and-unmanageable',
             None,
             'noop, present for eggless setuptools compat',
         ),
         (
             'single-version-externally-managed',
             None,
             'noop, present for eggless setuptools compat',
         ),
     ]
 
     # Also helps setuptools not be sad while we refuse to create eggs.
     single_version_externally_managed = True
 
     def get_sub_commands(self):
         # Screen out egg related commands to prevent egg generation.  But allow
         # mercurial.egg-info generation, since that is part of modern
         # packaging.
         excl = set(['bdist_egg'])
         return filter(lambda x: x not in excl, install.get_sub_commands(self))
 
 
 class hginstalllib(install_lib):
     '''
     This is a specialization of install_lib that replaces the copy_file used
     there so that it supports setting the mode of files after copying them,
     instead of just preserving the mode that the files originally had.  If your
     system has a umask of something like 027, preserving the permissions when
     copying will lead to a broken install.
 
     Note that just passing keep_permissions=False to copy_file would be
     insufficient, as it might still be applying a umask.
     '''
 
     def run(self):
         realcopyfile = file_util.copy_file
 
         def copyfileandsetmode(*args, **kwargs):
             src, dst = args[0], args[1]
             dst, copied = realcopyfile(*args, **kwargs)
             if copied:
                 st = os.stat(src)
                 # Persist executable bit (apply it to group and other if user
                 # has it)
                 if st[stat.ST_MODE] & stat.S_IXUSR:
                     setmode = int('0755', 8)
                 else:
                     setmode = int('0644', 8)
                 m = stat.S_IMODE(st[stat.ST_MODE])
                 m = (m & ~int('0777', 8)) | setmode
                 os.chmod(dst, m)
 
         file_util.copy_file = copyfileandsetmode
         try:
             install_lib.run(self)
         finally:
             file_util.copy_file = realcopyfile
 
 
 class hginstallscripts(install_scripts):
     '''
     This is a specialization of install_scripts that replaces the @LIBDIR@ with
     the configured directory for modules. If possible, the path is made relative
     to the directory for scripts.
     '''
 
     def initialize_options(self):
         install_scripts.initialize_options(self)
 
         self.install_lib = None
 
     def finalize_options(self):
         install_scripts.finalize_options(self)
         self.set_undefined_options('install', ('install_lib', 'install_lib'))
 
     def run(self):
         install_scripts.run(self)
 
         # It only makes sense to replace @LIBDIR@ with the install path if
         # the install path is known. For wheels, the logic below calculates
         # the libdir to be "../..". This is because the internal layout of a
         # wheel archive looks like:
         #
         #   mercurial-3.6.1.data/scripts/hg
         #   mercurial/__init__.py
         #
         # When installing wheels, the subdirectories of the "<pkg>.data"
         # directory are translated to system local paths and files therein
         # are copied in place. The mercurial/* files are installed into the
         # site-packages directory. However, the site-packages directory
         # isn't known until wheel install time. This means we have no clue
         # at wheel generation time what the installed site-packages directory
         # will be. And, wheels don't appear to provide the ability to register
         # custom code to run during wheel installation. This all means that
         # we can't reliably set the libdir in wheels: the default behavior
         # of looking in sys.path must do.
 
         if (
             os.path.splitdrive(self.install_dir)[0]
             != os.path.splitdrive(self.install_lib)[0]
         ):
             # can't make relative paths from one drive to another, so use an
             # absolute path instead
             libdir = self.install_lib
         else:
             libdir = os.path.relpath(self.install_lib, self.install_dir)
 
         for outfile in self.outfiles:
             with open(outfile, 'rb') as fp:
                 data = fp.read()
 
             # skip binary files
             if b'\0' in data:
                 continue
 
             # During local installs, the shebang will be rewritten to the final
             # install path. During wheel packaging, the shebang has a special
             # value.
             if data.startswith(b'#!python'):
                 log.info(
                     'not rewriting @LIBDIR@ in %s because install path '
                     'not known' % outfile
                 )
                 continue
 
             data = data.replace(b'@LIBDIR@', libdir.encode(libdir_escape))
             with open(outfile, 'wb') as fp:
                 fp.write(data)
 
 
 # virtualenv installs custom distutils/__init__.py and
 # distutils/distutils.cfg files which essentially proxy back to the
 # "real" distutils in the main Python install. The presence of this
 # directory causes py2exe to pick up the "hacked" distutils package
 # from the virtualenv and "import distutils" will fail from the py2exe
 # build because the "real" distutils files can't be located.
 #
 # We work around this by monkeypatching the py2exe code finding Python
 # modules to replace the found virtualenv distutils modules with the
 # original versions via filesystem scanning. This is a bit hacky. But
 # it allows us to use virtualenvs for py2exe packaging, which is more
 # deterministic and reproducible.
 #
 # It's worth noting that the common StackOverflow suggestions for this
 # problem involve copying the original distutils files into the
 # virtualenv or into the staging directory after setup() is invoked.
 # The former is very brittle and can easily break setup(). Our hacking
 # of the found modules routine has a similar result as copying the files
 # manually. But it makes fewer assumptions about how py2exe works and
 # is less brittle.
 
 # This only catches virtualenvs made with virtualenv (as opposed to
 # venv, which is likely what Python 3 uses).
 py2exehacked = py2exeloaded and getattr(sys, 'real_prefix', None) is not None
 
 if py2exehacked:
     from distutils.command.py2exe import py2exe as buildpy2exe
     from py2exe.mf import Module as py2exemodule
 
     class hgbuildpy2exe(buildpy2exe):
         def find_needed_modules(self, mf, files, modules):
             res = buildpy2exe.find_needed_modules(self, mf, files, modules)
 
             # Replace virtualenv's distutils modules with the real ones.
             modules = {}
             for k, v in res.modules.items():
                 if k != 'distutils' and not k.startswith('distutils.'):
                     modules[k] = v
 
             res.modules = modules
 
             import opcode
 
             distutilsreal = os.path.join(
                 os.path.dirname(opcode.__file__), 'distutils'
             )
 
             for root, dirs, files in os.walk(distutilsreal):
                 for f in sorted(files):
                     if not f.endswith('.py'):
                         continue
 
                     full = os.path.join(root, f)
 
                     parents = ['distutils']
 
                     if root != distutilsreal:
                         rel = os.path.relpath(root, distutilsreal)
                         parents.extend(p for p in rel.split(os.sep))
 
                     modname = '%s.%s' % ('.'.join(parents), f[:-3])
 
                     if modname.startswith('distutils.tests.'):
                         continue
 
                     if modname.endswith('.__init__'):
                         modname = modname[: -len('.__init__')]
                         path = os.path.dirname(full)
                     else:
                         path = None
 
                     res.modules[modname] = py2exemodule(
                         modname, full, path=path
                     )
 
             if 'distutils' not in res.modules:
                 raise SystemExit('could not find distutils modules')
 
             return res
 
 
 cmdclass = {
     'build': hgbuild,
     'build_doc': hgbuilddoc,
     'build_mo': hgbuildmo,
     'build_ext': hgbuildext,
     'build_py': hgbuildpy,
     'build_scripts': hgbuildscripts,
     'build_hgextindex': buildhgextindex,
     'install': hginstall,
     'install_lib': hginstalllib,
     'install_scripts': hginstallscripts,
     'build_hgexe': buildhgexe,
 }
 
 if py2exehacked:
     cmdclass['py2exe'] = hgbuildpy2exe
 
 packages = [
     'mercurial',
     'mercurial.cext',
     'mercurial.cffi',
     'mercurial.defaultrc',
     'mercurial.helptext',
     'mercurial.helptext.internals',
     'mercurial.hgweb',
     'mercurial.interfaces',
     'mercurial.pure',
     'mercurial.thirdparty',
     'mercurial.thirdparty.attr',
     'mercurial.thirdparty.zope',
     'mercurial.thirdparty.zope.interface',
     'mercurial.utils',
     'mercurial.revlogutils',
     'mercurial.testing',
     'hgext',
     'hgext.convert',
     'hgext.fsmonitor',
     'hgext.fastannotate',
     'hgext.fsmonitor.pywatchman',
     'hgext.highlight',
     'hgext.infinitepush',
     'hgext.largefiles',
     'hgext.lfs',
     'hgext.narrow',
     'hgext.remotefilelog',
     'hgext.zeroconf',
     'hgext3rd',
     'hgdemandimport',
 ]
 if sys.version_info[0] == 2:
     packages.extend(
         [
             'mercurial.thirdparty.concurrent',
             'mercurial.thirdparty.concurrent.futures',
         ]
     )
 
 if 'HG_PY2EXE_EXTRA_INSTALL_PACKAGES' in os.environ:
     # py2exe can't cope with namespace packages very well, so we have to
     # install any hgext3rd.* extensions that we want in the final py2exe
     # image here. This is gross, but you gotta do what you gotta do.
     packages.extend(os.environ['HG_PY2EXE_EXTRA_INSTALL_PACKAGES'].split(' '))
 
 common_depends = [
     'mercurial/bitmanipulation.h',
     'mercurial/compat.h',
     'mercurial/cext/util.h',
 ]
 common_include_dirs = ['mercurial']
 
 osutil_cflags = []
 osutil_ldflags = []
 
 # platform specific macros
 for plat, func in [('bsd', 'setproctitle')]:
     if re.search(plat, sys.platform) and hasfunction(new_compiler(), func):
         osutil_cflags.append('-DHAVE_%s' % func.upper())
 
 for plat, macro, code in [
     (
         'bsd|darwin',
         'BSD_STATFS',
         '''
      #include <sys/param.h>
      #include <sys/mount.h>
      int main() { struct statfs s; return sizeof(s.f_fstypename); }
      ''',
     ),
     (
         'linux',
         'LINUX_STATFS',
         '''
      #include <linux/magic.h>
      #include <sys/vfs.h>
      int main() { struct statfs s; return sizeof(s.f_type); }
      ''',
     ),
 ]:
     if re.search(plat, sys.platform) and cancompile(new_compiler(), code):
         osutil_cflags.append('-DHAVE_%s' % macro)
 
 if sys.platform == 'darwin':
     osutil_ldflags += ['-framework', 'ApplicationServices']
 
 xdiff_srcs = [
     'mercurial/thirdparty/xdiff/xdiffi.c',
     'mercurial/thirdparty/xdiff/xprepare.c',
     'mercurial/thirdparty/xdiff/xutils.c',
 ]
 
 xdiff_headers = [
     'mercurial/thirdparty/xdiff/xdiff.h',
     'mercurial/thirdparty/xdiff/xdiffi.h',
     'mercurial/thirdparty/xdiff/xinclude.h',
     'mercurial/thirdparty/xdiff/xmacros.h',
     'mercurial/thirdparty/xdiff/xprepare.h',
     'mercurial/thirdparty/xdiff/xtypes.h',
     'mercurial/thirdparty/xdiff/xutils.h',
 ]
 
 
 class RustCompilationError(CCompilerError):
     """Exception class for Rust compilation errors."""
 
 
 class RustExtension(Extension):
     """Base classes for concrete Rust Extension classes.
     """
 
     rusttargetdir = os.path.join('rust', 'target', 'release')
 
     def __init__(
         self, mpath, sources, rustlibname, subcrate, py3_features=None, **kw
     ):
         Extension.__init__(self, mpath, sources, **kw)
         srcdir = self.rustsrcdir = os.path.join('rust', subcrate)
         self.py3_features = py3_features
 
         # adding Rust source and control files to depends so that the extension
         # gets rebuilt if they've changed
         self.depends.append(os.path.join(srcdir, 'Cargo.toml'))
         cargo_lock = os.path.join(srcdir, 'Cargo.lock')
         if os.path.exists(cargo_lock):
             self.depends.append(cargo_lock)
         for dirpath, subdir, fnames in os.walk(os.path.join(srcdir, 'src')):
             self.depends.extend(
                 os.path.join(dirpath, fname)
                 for fname in fnames
                 if os.path.splitext(fname)[1] == '.rs'
             )
 
     @staticmethod
     def rustdylibsuffix():
         """Return the suffix for shared libraries produced by rustc.
 
         See also: https://doc.rust-lang.org/reference/linkage.html
         """
         if sys.platform == 'darwin':
             return '.dylib'
         elif os.name == 'nt':
             return '.dll'
         else:
             return '.so'
 
     def rustbuild(self):
         env = os.environ.copy()
         if 'HGTEST_RESTOREENV' in env:
             # Mercurial tests change HOME to a temporary directory,
             # but, if installed with rustup, the Rust toolchain needs
             # HOME to be correct (otherwise the 'no default toolchain'
             # error message is issued and the build fails).
             # This happens currently with test-hghave.t, which does
             # invoke this build.
 
             # Unix only fix (os.path.expanduser not really reliable if
             # HOME is shadowed like this)
             import pwd
 
             env['HOME'] = pwd.getpwuid(os.getuid()).pw_dir
 
         cargocmd = ['cargo', 'rustc', '-vv', '--release']
+
+        feature_flags = []
+
         if sys.version_info[0] == 3 and self.py3_features is not None:
-            cargocmd.extend(
-                ('--features', self.py3_features, '--no-default-features')
-            )
+            feature_flags.append(self.py3_features)
+            cargocmd.append('--no-default-features')
+
+        rust_features = env.get("HG_RUST_FEATURES")
+        if rust_features:
+            feature_flags.append(rust_features)
+
+        cargocmd.extend(('--features', " ".join(feature_flags)))
+
         cargocmd.append('--')
         if sys.platform == 'darwin':
             cargocmd.extend(
                 ("-C", "link-arg=-undefined", "-C", "link-arg=dynamic_lookup")
             )
         try:
             subprocess.check_call(cargocmd, env=env, cwd=self.rustsrcdir)
         except OSError as exc:
             if exc.errno == errno.ENOENT:
                 raise RustCompilationError("Cargo not found")
             elif exc.errno == errno.EACCES:
                 raise RustCompilationError(
                     "Cargo found, but permisssion to execute it is denied"
                 )
             else:
                 raise
         except subprocess.CalledProcessError:
             raise RustCompilationError(
                 "Cargo failed. Working directory: %r, "
                 "command: %r, environment: %r"
                 % (self.rustsrcdir, cargocmd, env)
             )
 
 
 class RustEnhancedExtension(RustExtension):
     """A C Extension, conditionally enhanced with Rust code.
 
     If the HGWITHRUSTEXT environment variable is set to something else
     than 'cpython', the Rust sources get compiled and linked within
     the C target shared library object.
     """
 
     def __init__(self, mpath, sources, rustlibname, subcrate, **kw):
         RustExtension.__init__(
             self, mpath, sources, rustlibname, subcrate, **kw
         )
         if hgrustext != 'direct-ffi':
             return
         self.extra_compile_args.append('-DWITH_RUST')
         self.libraries.append(rustlibname)
         self.library_dirs.append(self.rusttargetdir)
 
     def rustbuild(self):
         if hgrustext == 'direct-ffi':
             RustExtension.rustbuild(self)
 
 
 class RustStandaloneExtension(RustExtension):
     def __init__(self, pydottedname, rustcrate, dylibname, **kw):
         RustExtension.__init__(
             self, pydottedname, [], dylibname, rustcrate, **kw
         )
         self.dylibname = dylibname
 
     def build(self, target_dir):
         self.rustbuild()
         target = [target_dir]
         target.extend(self.name.split('.'))
         target[-1] += DYLIB_SUFFIX
         shutil.copy2(
             os.path.join(
                 self.rusttargetdir, self.dylibname + self.rustdylibsuffix()
             ),
             os.path.join(*target),
         )
 
 
 extmodules = [
     Extension(
         'mercurial.cext.base85',
         ['mercurial/cext/base85.c'],
         include_dirs=common_include_dirs,
         depends=common_depends,
     ),
     Extension(
         'mercurial.cext.bdiff',
         ['mercurial/bdiff.c', 'mercurial/cext/bdiff.c'] + xdiff_srcs,
         include_dirs=common_include_dirs,
         depends=common_depends + ['mercurial/bdiff.h'] + xdiff_headers,
     ),
     Extension(
         'mercurial.cext.mpatch',
         ['mercurial/mpatch.c', 'mercurial/cext/mpatch.c'],
         include_dirs=common_include_dirs,
         depends=common_depends,
     ),
     RustEnhancedExtension(
         'mercurial.cext.parsers',
         [
             'mercurial/cext/charencode.c',
             'mercurial/cext/dirs.c',
             'mercurial/cext/manifest.c',
             'mercurial/cext/parsers.c',
             'mercurial/cext/pathencode.c',
             'mercurial/cext/revlog.c',
         ],
         'hgdirectffi',
         'hg-direct-ffi',
         include_dirs=common_include_dirs,
         depends=common_depends
         + [
             'mercurial/cext/charencode.h',
             'mercurial/cext/revlog.h',
             'rust/hg-core/src/ancestors.rs',
             'rust/hg-core/src/lib.rs',
         ],
     ),
     Extension(
         'mercurial.cext.osutil',
         ['mercurial/cext/osutil.c'],
         include_dirs=common_include_dirs,
         extra_compile_args=osutil_cflags,
         extra_link_args=osutil_ldflags,
         depends=common_depends,
     ),
     Extension(
         'mercurial.thirdparty.zope.interface._zope_interface_coptimizations',
         [
             'mercurial/thirdparty/zope/interface/_zope_interface_coptimizations.c',
         ],
     ),
     Extension(
         'mercurial.thirdparty.sha1dc',
         [
             'mercurial/thirdparty/sha1dc/cext.c',
             'mercurial/thirdparty/sha1dc/lib/sha1.c',
             'mercurial/thirdparty/sha1dc/lib/ubc_check.c',
         ],
     ),
     Extension(
         'hgext.fsmonitor.pywatchman.bser', ['hgext/fsmonitor/pywatchman/bser.c']
     ),
     RustStandaloneExtension(
         'mercurial.rustext', 'hg-cpython', 'librusthg', py3_features='python3'
     ),
 ]
 
 
 sys.path.insert(0, 'contrib/python-zstandard')
 import setup_zstd
 
 extmodules.append(
     setup_zstd.get_c_extension(
         name='mercurial.zstd', root=os.path.abspath(os.path.dirname(__file__))
     )
 )
 
 try:
     from distutils import cygwinccompiler
 
     # the -mno-cygwin option has been deprecated for years
     mingw32compilerclass = cygwinccompiler.Mingw32CCompiler
 
     class HackedMingw32CCompiler(cygwinccompiler.Mingw32CCompiler):
         def __init__(self, *args, **kwargs):
             mingw32compilerclass.__init__(self, *args, **kwargs)
             for i in 'compiler compiler_so linker_exe linker_so'.split():
                 try:
                     getattr(self, i).remove('-mno-cygwin')
                 except ValueError:
                     pass
 
     cygwinccompiler.Mingw32CCompiler = HackedMingw32CCompiler
 except ImportError:
     # the cygwinccompiler package is not available on some Python
     # distributions like the ones from the optware project for Synology
     # DiskStation boxes
     class HackedMingw32CCompiler(object):
         pass
 
 
 if os.name == 'nt':
     # Allow compiler/linker flags to be added to Visual Studio builds.  Passing
     # extra_link_args to distutils.extensions.Extension() doesn't have any
     # effect.
     from distutils import msvccompiler
 
     msvccompilerclass = msvccompiler.MSVCCompiler
 
     class HackedMSVCCompiler(msvccompiler.MSVCCompiler):
         def initialize(self):
             msvccompilerclass.initialize(self)
             # "warning LNK4197: export 'func' specified multiple times"
             self.ldflags_shared.append('/ignore:4197')
             self.ldflags_shared_debug.append('/ignore:4197')
 
     msvccompiler.MSVCCompiler = HackedMSVCCompiler
 
 packagedata = {
     'mercurial': [
         'locale/*/LC_MESSAGES/hg.mo',
         'defaultrc/*.rc',
         'dummycert.pem',
     ],
     'mercurial.helptext': ['*.txt',],
     'mercurial.helptext.internals': ['*.txt',],
 }
 
 
 def ordinarypath(p):
     return p and p[0] != '.' and p[-1] != '~'
 
 
 for root in ('templates',):
     for curdir, dirs, files in os.walk(os.path.join('mercurial', root)):
         curdir = curdir.split(os.sep, 1)[1]
         dirs[:] = filter(ordinarypath, dirs)
         for f in filter(ordinarypath, files):
             f = os.path.join(curdir, f)
             packagedata['mercurial'].append(f)
 
 datafiles = []
 
 # distutils expects version to be str/unicode. Converting it to
 # unicode on Python 2 still works because it won't contain any
 # non-ascii bytes and will be implicitly converted back to bytes
 # when operated on.
 assert isinstance(version, bytes)
 setupversion = version.decode('ascii')
 
 extra = {}
 
 py2exepackages = [
     'hgdemandimport',
     'hgext3rd',
     'hgext',
     'email',
     # implicitly imported per module policy
     # (cffi wouldn't be used as a frozen exe)
     'mercurial.cext',
     #'mercurial.cffi',
     'mercurial.pure',
 ]
 
 py2exeexcludes = []
 py2exedllexcludes = ['crypt32.dll']
 
 if issetuptools:
     extra['python_requires'] = supportedpy
 
 if py2exeloaded:
     extra['console'] = [
         {
             'script': 'hg',
             'copyright': 'Copyright (C) 2005-2020 Matt Mackall and others',
             'product_version': version,
         }
     ]
     # Sub command of 'build' because 'py2exe' does not handle sub_commands.
     # Need to override hgbuild because it has a private copy of
     # build.sub_commands.
     hgbuild.sub_commands.insert(0, ('build_hgextindex', None))
     # put dlls in sub directory so that they won't pollute PATH
     extra['zipfile'] = 'lib/library.zip'
 
     # We allow some configuration to be supplemented via environment
     # variables. This is better than setup.cfg files because it allows
     # supplementing configs instead of replacing them.
     extrapackages = os.environ.get('HG_PY2EXE_EXTRA_PACKAGES')
     if extrapackages:
         py2exepackages.extend(extrapackages.split(' '))
 
     excludes = os.environ.get('HG_PY2EXE_EXTRA_EXCLUDES')
     if excludes:
         py2exeexcludes.extend(excludes.split(' '))
 
     dllexcludes = os.environ.get('HG_PY2EXE_EXTRA_DLL_EXCLUDES')
     if dllexcludes:
         py2exedllexcludes.extend(dllexcludes.split(' '))
 
 if os.name == 'nt':
     # Windows binary file versions for exe/dll files must have the
     # form W.X.Y.Z, where W,X,Y,Z are numbers in the range 0..65535
     setupversion = setupversion.split(r'+', 1)[0]
 
 if sys.platform == 'darwin' and os.path.exists('/usr/bin/xcodebuild'):
     version = runcmd(['/usr/bin/xcodebuild', '-version'], {})[1].splitlines()
     if version:
         version = version[0]
         if sys.version_info[0] == 3:
             version = version.decode('utf-8')
         xcode4 = version.startswith('Xcode') and StrictVersion(
             version.split()[1]
         ) >= StrictVersion('4.0')
         xcode51 = re.match(r'^Xcode\s+5\.1', version) is not None
     else:
         # xcodebuild returns empty on OS X Lion with XCode 4.3 not
         # installed, but instead with only command-line tools. Assume
         # that only happens on >= Lion, thus no PPC support.
         xcode4 = True
         xcode51 = False
 
     # XCode 4.0 dropped support for ppc architecture, which is hardcoded in
     # distutils.sysconfig
     if xcode4:
         os.environ['ARCHFLAGS'] = ''
 
     # XCode 5.1 changes clang such that it now fails to compile if the
     # -mno-fused-madd flag is passed, but the version of Python shipped with
     # OS X 10.9 Mavericks includes this flag. This causes problems in all
     # C extension modules, and a bug has been filed upstream at
     # http://bugs.python.org/issue21244. We also need to patch this here
     # so Mercurial can continue to compile in the meantime.
     if xcode51:
         cflags = get_config_var('CFLAGS')
         if cflags and re.search(r'-mno-fused-madd\b', cflags) is not None:
             os.environ['CFLAGS'] = (
                 os.environ.get('CFLAGS', '') + ' -Qunused-arguments'
             )
 
 setup(
     name='mercurial',
     version=setupversion,
     author='Matt Mackall and many others',
     author_email='[e-mail]',
     url='https://mercurial-scm.org/',
     download_url='https://mercurial-scm.org/release/',
     description=(
         'Fast scalable distributed SCM (revision control, version '
         'control) system'
     ),
     long_description=(
         'Mercurial is a distributed SCM tool written in Python.'
         ' It is used by a number of large projects that require'
         ' fast, reliable distributed revision control, such as '
         'Mozilla.'
     ),
     license='GNU GPLv2 or any later version',
     classifiers=[
         'Development Status :: 6 - Mature',
         'Environment :: Console',
         'Intended Audience :: Developers',
         'Intended Audience :: System Administrators',
         'License :: OSI Approved :: GNU General Public License (GPL)',
         'Natural Language :: Danish',
         'Natural Language :: English',
         'Natural Language :: German',
         'Natural Language :: Italian',
         'Natural Language :: Japanese',
         'Natural Language :: Portuguese (Brazilian)',
         'Operating System :: Microsoft :: Windows',
         'Operating System :: OS Independent',
         'Operating System :: POSIX',
         'Programming Language :: C',
         'Programming Language :: Python',
         'Topic :: Software Development :: Version Control',
     ],
     scripts=scripts,
     packages=packages,
     ext_modules=extmodules,
     data_files=datafiles,
     package_data=packagedata,
     cmdclass=cmdclass,
     distclass=hgdist,
     options={
         'py2exe': {
             'bundle_files': 3,
             'dll_excludes': py2exedllexcludes,
             'excludes': py2exeexcludes,
             'packages': py2exepackages,
         },
         'bdist_mpkg': {
             'zipdist': False,
             'license': 'COPYING',
             'readme': 'contrib/packaging/macosx/Readme.html',
             'welcome': 'contrib/packaging/macosx/Welcome.html',
         },
     },
     **extra
 )