rust-2018: switch hg-core and hg-cpython to rust 2018 edition

Many interesting changes have happened in Rust since the Oxidation Plan was
introduced, like the 2018 edition and procedural macros:

    - Opting in to the 2018 edition is a clear benefit in terms of future
      proofing, new (nice to have) syntactical sugar notwithstanding. It
      also has a new non-lexical, non-AST based borrow checker that has
      fewer bugs(!) and allows us to write correct code that in some cases
      would have been rejected by the old one.
    - Procedural macros allow us to use the PyO3 crate which maintainers have
      expressed the clear goal of compiling on stable, which would help in
      code maintainability compared to rust-cpython.

In this patch are the following changes:
    - Removing most `extern crate` uses
    - Updating `use` clauses (`crate` keyword, nested `use`)
    - Removing `mod.rs` in favor of an aptly named module file

Like discussed in the mailing list (
https://www.mercurial-scm.org/pipermail/mercurial-devel/2019-July/132316.html
), until Rust integration in Mercurial is considered to be out of the
experimental phase, the maximum version of Rust allowed is whatever the latest
version Debian packages.

Differential Revision: https://phab.mercurial-scm.org/D6597

rust/hg-core/src/dirstate.rs

@@ -0,0 +1,36 b''
+pub mod dirs_multiset;
+pub mod parsers;
+
+#[derive(Debug, PartialEq, Copy, Clone)]
+pub struct DirstateParents<'a> {
+    pub p1: &'a [u8],
+    pub p2: &'a [u8],
+}
+
+/// The C implementation uses all signed types. This will be an issue
+/// either when 4GB+ source files are commonplace or in 2038, whichever
+/// comes first.
+#[derive(Debug, PartialEq)]
+pub struct DirstateEntry {
+    pub state: i8,
+    pub mode: i32,
+    pub mtime: i32,
+    pub size: i32,
+}
+
+pub type DirstateVec = Vec<(Vec<u8>, DirstateEntry)>;
+
+#[derive(Debug, PartialEq)]
+pub struct CopyVecEntry<'a> {
+    pub path: &'a [u8],
+    pub copy_path: &'a [u8],
+}
+
+pub type CopyVec<'a> = Vec<CopyVecEntry<'a>>;
+
+/// The Python implementation passes either a mapping (dirstate) or a flat
+/// iterable (manifest)
+pub enum DirsIterable {
+    Dirstate(DirstateVec),
+    Manifest(Vec<Vec<u8>>),
+}

rust/hg-core/src/utils.rs

@@ -0,0 +1,45 b''
+pub mod files;
+
+pub fn replace_slice<T>(buf: &mut [T], from: &[T], to: &[T])
+where
+    T: Clone + PartialEq,
+{
+    if buf.len() < from.len() || from.len() != to.len() {
+        return;
+    }
+    for i in 0..=buf.len() - from.len() {
+        if buf[i..].starts_with(from) {
+            buf[i..(i + from.len())].clone_from_slice(to);
+        }
+    }
+}
+
+pub trait SliceExt {
+    fn trim(&self) -> &Self;
+    fn trim_end(&self) -> &Self;
+}
+
+fn is_not_whitespace(c: &u8) -> bool {
+    !(*c as char).is_whitespace()
+}
+
+impl SliceExt for [u8] {
+    fn trim(&self) -> &[u8] {
+        if let Some(first) = self.iter().position(is_not_whitespace) {
+            if let Some(last) = self.iter().rposition(is_not_whitespace) {
+                &self[first..last + 1]
+            } else {
+                unreachable!();
+            }
+        } else {
+            &[]
+        }
+    }
+    fn trim_end(&self) -> &[u8] {
+        if let Some(last) = self.iter().rposition(is_not_whitespace) {
+            &self[..last + 1]
+        } else {
+            &[]
+        }
+    }
+}

rust/hg-core/Cargo.toml

@@ -3,6 +3,7 b' 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"
 
 [lib]
 name = "hg"

rust/hg-core/src/dirstate/dirs_multiset.rs

@@ -8,10 +8,9 b''
 //! A multiset of directory names.
 //!
 //! Used to counts the references to directories in a manifest or dirstate.
+use crate::{utils::files, DirsIterable, DirstateEntry, DirstateMapError};
 use std::collections::hash_map::{Entry, Iter};
 use std::collections::HashMap;
-use {DirsIterable, DirstateEntry, DirstateMapError};
-use utils::files;
 
 #[derive(PartialEq, Debug)]
 pub struct DirsMultiset {

rust/hg-core/src/dirstate/parsers.rs

@@ -3,13 +3,13 b''
 // This software may be used and distributed according to the terms of the
 // GNU General Public License version 2 or any later version.
 
+use crate::{
+    CopyVec, CopyVecEntry, DirstateEntry, DirstatePackError, DirstateParents,
+    DirstateParseError, DirstateVec,
+};
 use byteorder::{BigEndian, ReadBytesExt, WriteBytesExt};
 use std::collections::HashMap;
 use std::io::Cursor;
-use {
-    CopyVec, CopyVecEntry, DirstateEntry, DirstatePackError, DirstateParents,
-    DirstateParseError, DirstateVec,
-};
 
 /// Parents are stored in the dirstate as byte hashes.
 const PARENT_SIZE: usize = 20;

rust/hg-core/src/filepatterns.rs

@@ -1,11 +1,13 b''
-use crate::{LineNumber, PatternError, PatternFileError};
+use crate::{
+    utils::{files::get_path_from_bytes, replace_slice, SliceExt},
+    LineNumber, PatternError, PatternFileError,
+};
+use lazy_static::lazy_static;
 use regex::bytes::Regex;
 use std::collections::HashMap;
 use std::fs::File;
 use std::io::Read;
 use std::vec::Vec;
-use utils::files::get_path_from_bytes;
-use utils::{replace_slice, SliceExt};
 
 lazy_static! {
     static ref RE_ESCAPE: Vec<Vec<u8>> = {

rust/hg-core/src/lib.rs

@@ -2,12 +2,6 b''
 //
 // This software may be used and distributed according to the terms of the
 // GNU General Public License version 2 or any later version.
-extern crate byteorder;
-extern crate memchr;
-#[macro_use]
-extern crate lazy_static;
-extern crate regex;
-
 mod ancestors;
 pub mod dagops;
 pub use ancestors::{AncestorsIterator, LazyAncestors, MissingAncestors};
@@ -50,7 +44,7 b' pub trait Graph {'
     /// Return the two parents of the given `Revision`.
     ///
     /// Each of the parents can be independently `NULL_REVISION`
-    fn parents(&self, Revision) -> Result<[Revision; 2], GraphError>;
+    fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError>;
 }
 
 pub type LineNumber = usize;

rust/hg-core/tests/test_missing_ancestors.rs

@@ -1,7 +1,3 b''
-extern crate hg;
-extern crate rand;
-extern crate rand_pcg;
-
 use hg::testing::VecGraph;
 use hg::Revision;
 use hg::*;

rust/hg-cpython/Cargo.toml

@@ -2,6 +2,7 b''
 name = "hg-cpython"
 version = "0.1.0"
 authors = ["Georges Racinet <[e-mail]>"]
+edition = "2018"
 
 [lib]
 name='rusthg'

rust/hg-cpython/src/ancestors.rs

@@ -34,13 +34,15 b''
 //! [`LazyAncestors`]: struct.LazyAncestors.html
 //! [`MissingAncestors`]: struct.MissingAncestors.html
 //! [`AncestorsIterator`]: struct.AncestorsIterator.html
-use crate::conversion::{py_set, rev_pyiter_collect};
-use cindex::Index;
+use crate::{
+    cindex::Index,
+    conversion::{py_set, rev_pyiter_collect},
+    exceptions::GraphError,
+};
 use cpython::{
     ObjectProtocol, PyClone, PyDict, PyList, PyModule, PyObject, PyResult,
     Python, PythonObject, ToPyObject,
 };
-use exceptions::GraphError;
 use hg::Revision;
 use hg::{
     AncestorsIterator as CoreIterator, LazyAncestors as CoreLazy,

rust/hg-cpython/src/cindex.rs

@@ -10,14 +10,14 b''
 //! Ideally, we should use an Index entirely implemented in Rust,
 //! but this will take some time to get there.
 #[cfg(feature = "python27")]
-extern crate python27_sys as python_sys;
+use python27_sys as python_sys;
 #[cfg(feature = "python3")]
-extern crate python3_sys as python_sys;
+use python3_sys as python_sys;
 
-use self::python_sys::PyCapsule_Import;
 use cpython::{PyClone, PyErr, PyObject, PyResult, Python};
 use hg::{Graph, GraphError, Revision, WORKING_DIRECTORY_REVISION};
 use libc::c_int;
+use python_sys::PyCapsule_Import;
 use std::ffi::CStr;
 use std::mem::transmute;
 

rust/hg-cpython/src/dagops.rs

@@ -9,10 +9,12 b''
 //! `hg-core` package.
 //!
 //! From Python, this will be seen as `mercurial.rustext.dagop`
-use crate::conversion::{py_set, rev_pyiter_collect};
-use cindex::Index;
+use crate::{
+    cindex::Index,
+    conversion::{py_set, rev_pyiter_collect},
+    exceptions::GraphError,
+};
 use cpython::{PyDict, PyModule, PyObject, PyResult, Python};
-use exceptions::GraphError;
 use hg::dagops;
 use hg::Revision;
 use std::collections::HashSet;

rust/hg-cpython/src/dirstate.rs

@@ -19,17 +19,14 b' use hg::{'
     DirstateEntry, DirstateMapError, DirstatePackError, DirstateParents,
     DirstateParseError, DirstateVec,
 };
+use libc::{c_char, c_int};
+#[cfg(feature = "python27")]
+use python27_sys::PyCapsule_Import;
+#[cfg(feature = "python3")]
+use python3_sys::PyCapsule_Import;
+use std::cell::RefCell;
 use std::collections::HashMap;
 use std::ffi::CStr;
-
-#[cfg(feature = "python27")]
-extern crate python27_sys as python_sys;
-#[cfg(feature = "python3")]
-extern crate python3_sys as python_sys;
-
-use self::python_sys::PyCapsule_Import;
-use libc::{c_char, c_int};
-use std::cell::RefCell;
 use std::mem::transmute;
 
 /// C code uses a custom `dirstate_tuple` type, checks in multiple instances

rust/hg-cpython/src/discovery.rs

@@ -12,13 +12,15 b''
 //! - [`PartialDiscover`] is the Rust implementation of
 //!   `mercurial.setdiscovery.partialdiscovery`.
 
-use crate::conversion::{py_set, rev_pyiter_collect};
-use cindex::Index;
+use crate::{
+    cindex::Index,
+    conversion::{py_set, rev_pyiter_collect},
+    exceptions::GraphError,
+};
 use cpython::{
     ObjectProtocol, PyDict, PyModule, PyObject, PyResult, Python,
     PythonObject, ToPyObject,
 };
-use exceptions::GraphError;
 use hg::discovery::PartialDiscovery as CorePartialDiscovery;
 use hg::Revision;
 

rust/hg-cpython/src/exceptions.rs

@@ -12,8 +12,10 b''
 //! existing Python exceptions if appropriate.
 //!
 //! [`GraphError`]: struct.GraphError.html
-use cpython::exc::{RuntimeError, ValueError};
-use cpython::{exc, PyErr, Python};
+use cpython::{
+    exc::{IOError, RuntimeError, ValueError},
+    py_exception, PyErr, Python,
+};
 use hg;
 
 py_exception!(rustext, GraphError, ValueError);
@@ -55,7 +57,7 b' impl PatternFileError {'
         match inner {
             hg::PatternFileError::IO(e) => {
                 let value = (e.raw_os_error().unwrap_or(2), e.to_string());
-                PyErr::new::<exc::IOError, _>(py, value)
+                PyErr::new::<IOError, _>(py, value)
             }
             hg::PatternFileError::Pattern(e, l) => match e {
                 hg::PatternError::UnsupportedSyntax(m) => {

rust/hg-cpython/src/filepatterns.rs

@@ -10,10 +10,10 b''
 //! `hg-core` crate. From Python, this will be seen as `rustext.filepatterns`
 //! and can be used as replacement for the the pure `filepatterns` Python module.
 //!
+use crate::exceptions::{PatternError, PatternFileError};
 use cpython::{
     PyBytes, PyDict, PyModule, PyObject, PyResult, PyTuple, Python, ToPyObject,
 };
-use exceptions::{PatternError, PatternFileError};
 use hg::{build_single_regex, read_pattern_file, LineNumber, PatternTuple};
 
 /// Rust does not like functions with different return signatures.

rust/hg-cpython/src/lib.rs

@@ -19,10 +19,10 b''
 //! 'Generic DAG ancestor algorithms - Rust implementation'
 //! ```
 
+/// This crate uses nested private macros, `extern crate` is still needed in
+/// 2018 edition.
 #[macro_use]
 extern crate cpython;
-extern crate hg;
-extern crate libc;
 
 pub mod ancestors;
 mod cindex;