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annotate rust/hg-cpython/src/cindex.rs @ 42609:326fdce22fb2

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rust: 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
author Rapha?l Gom?s <rgomes@octobus.net>
date Tue, 02 Jul 2019 17:15:03 +0200
parents ab0d762d89ef
children 0246bbe1045d
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1 // cindex.rs
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2 //
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3 // Copyright 2018 Georges Racinet <gracinet@anybox.fr>
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4 //
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5 // This software may be used and distributed according to the terms of the
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6 // GNU General Public License version 2 or any later version.
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7
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8 //! Bindings to use the Index defined by the parsers C extension
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9 //!
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10 //! Ideally, we should use an Index entirely implemented in Rust,
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11 //! but this will take some time to get there.
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12 #[cfg(feature = "python27")]
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13 use python27_sys as python_sys;
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14 #[cfg(feature = "python3")]
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15 use python3_sys as python_sys;
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16
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17 use cpython::{PyClone, PyErr, PyObject, PyResult, Python};
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18 use hg::{Graph, GraphError, Revision, WORKING_DIRECTORY_REVISION};
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19 use libc::c_int;
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20 use python_sys::PyCapsule_Import;
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21 use std::ffi::CStr;
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22 use std::mem::transmute;
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23
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24 type IndexParentsFn = unsafe extern "C" fn(
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25 index: *mut python_sys::PyObject,
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26 rev: c_int,
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27 ps: *mut [c_int; 2],
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28 ) -> c_int;
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29
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30 /// A `Graph` backed up by objects and functions from revlog.c
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31 ///
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32 /// This implementation of the `Graph` trait, relies on (pointers to)
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33 /// - the C index object (`index` member)
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34 /// - the `index_get_parents()` function (`parents` member)
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35 ///
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36 /// # Safety
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37 ///
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38 /// The C index itself is mutable, and this Rust exposition is **not
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39 /// protected by the GIL**, meaning that this construct isn't safe with respect
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40 /// to Python threads.
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41 ///
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42 /// All callers of this `Index` must acquire the GIL and must not release it
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43 /// while working.
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44 ///
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45 /// # TODO find a solution to make it GIL safe again.
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46 ///
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47 /// This is non trivial, and can wait until we have a clearer picture with
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48 /// more Rust Mercurial constructs.
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49 ///
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50 /// One possibility would be to a `GILProtectedIndex` wrapper enclosing
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51 /// a `Python<'p>` marker and have it be the one implementing the
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52 /// `Graph` trait, but this would mean the `Graph` implementor would become
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53 /// likely to change between subsequent method invocations of the `hg-core`
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54 /// objects (a serious change of the `hg-core` API):
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55 /// either exposing ways to mutate the `Graph`, or making it a non persistent
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56 /// parameter in the relevant methods that need one.
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57 ///
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58 /// Another possibility would be to introduce an abstract lock handle into
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59 /// the core API, that would be tied to `GILGuard` / `Python<'p>`
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60 /// in the case of the `cpython` crate bindings yet could leave room for other
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61 /// mechanisms in other contexts.
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62 pub struct Index {
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63 index: PyObject,
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64 parents: IndexParentsFn,
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65 }
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66
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67 impl Index {
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68 pub fn new(py: Python, index: PyObject) -> PyResult<Self> {
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69 Ok(Index {
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70 index: index,
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71 parents: decapsule_parents_fn(py)?,
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72 })
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73 }
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74 }
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75
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76 impl Clone for Index {
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77 fn clone(&self) -> Self {
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78 let guard = Python::acquire_gil();
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79 Index {
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80 index: self.index.clone_ref(guard.python()),
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81 parents: self.parents.clone(),
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82 }
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83 }
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84 }
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85
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86 impl Graph for Index {
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87 /// wrap a call to the C extern parents function
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88 fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
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89 if rev == WORKING_DIRECTORY_REVISION {
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90 return Err(GraphError::WorkingDirectoryUnsupported);
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91 }
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92 let mut res: [c_int; 2] = [0; 2];
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93 let code = unsafe {
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94 (self.parents)(
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95 self.index.as_ptr(),
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96 rev as c_int,
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97 &mut res as *mut [c_int; 2],
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98 )
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99 };
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100 match code {
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101 0 => Ok(res),
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102 _ => Err(GraphError::ParentOutOfRange(rev)),
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103 }
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104 }
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105 }
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106
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107 /// Return the `index_get_parents` function of the parsers C Extension module.
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108 ///
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109 /// A pointer to the function is stored in the `parsers` module as a
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110 /// standard [Python capsule](https://docs.python.org/2/c-api/capsule.html).
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111 ///
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112 /// This function retrieves the capsule and casts the function pointer
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113 ///
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114 /// Casting function pointers is one of the rare cases of
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115 /// legitimate use cases of `mem::transmute()` (see
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116 /// https://doc.rust-lang.org/std/mem/fn.transmute.html of
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117 /// `mem::transmute()`.
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118 /// It is inappropriate for architectures where
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119 /// function and data pointer sizes differ (so-called "Harvard
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120 /// architectures"), but these are nowadays mostly DSPs
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121 /// and microcontrollers, hence out of our scope.
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122 fn decapsule_parents_fn(py: Python) -> PyResult<IndexParentsFn> {
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123 unsafe {
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124 let caps_name = CStr::from_bytes_with_nul_unchecked(
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125 b"mercurial.cext.parsers.index_get_parents_CAPI\0",
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126 );
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127 let from_caps = PyCapsule_Import(caps_name.as_ptr(), 0);
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128 if from_caps.is_null() {
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129 return Err(PyErr::fetch(py));
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130 }
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131 Ok(transmute(from_caps))
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132 }
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133 }