Build Rust components and ship in optional mercurial-rust package

Original patch has been tweaked by Mads Kiilerich.

mercurial-rust-metadata.patch

@@ -0,0 +1,65 @@
+# HG changeset patch
+# Parent  5bd6bcd31dd1ebb63b8914b00064f96297267af7
+Patch cargo metadata for Fedora build
+
+Backport upstream 6.2 changes to 6.1:
+ - update memmap2 to 0.5.3 (upstream ec8d9b5a5e7c)
+ - update micro-timer to 0.4.0 (upstream 8848c3453661, ec8d9b5a5e7c)
+
+Update zstd to 0.10.0 (upstream is stuck on 0.5 because MSRV)
+ - adapt for breaking changes in zstd 0.10.0
+
+Downgrade ouroboros to 0.13.0 (Fedora packaging needs update - rhbz#2027028)
+
+diff --git a/rust/hg-core/Cargo.toml b/rust/hg-core/Cargo.toml
+--- a/rust/hg-core/Cargo.toml
++++ b/rust/hg-core/Cargo.toml
+@@ -18,7 +18,7 @@ im-rc = "15.0.*"
+ itertools = "0.9"
+ lazy_static = "1.4.0"
+ libc = "0.2"
+-ouroboros = "0.15.0"
++ouroboros = ">= 0.13.0, < 0.16.0"
+ rand = "0.8.4"
+ rand_pcg = "0.3.1"
+ rand_distr = "0.4.2"
+@@ -29,10 +29,10 @@ twox-hash = "1.5.0"
+ same-file = "1.0.6"
+ tempfile = "3.1.0"
+ crossbeam-channel = "0.4"
+-micro-timer = "0.3.0"
++micro-timer = "0.4.0"
+ log = "0.4.8"
+-memmap2 = {version = "0.4", features = ["stable_deref_trait"]}
+-zstd = "0.5.3"
++memmap2 = {version = "0.5.3", features = ["stable_deref_trait"]}
++zstd = "0.10"
+ format-bytes = "0.3.0"
+ 
+ # We don't use the `miniz-oxide` backend to not change rhg benchmarks and until
+
+diff --git a/rust/hg-core/src/revlog/revlog.rs b/rust/hg-core/src/revlog/revlog.rs
+--- a/rust/hg-core/src/revlog/revlog.rs
++++ b/rust/hg-core/src/revlog/revlog.rs
+@@ -431,7 +431,7 @@ impl<'a> RevlogEntry<'a> {
+         } else {
+             let cap = self.uncompressed_len.max(0) as usize;
+             let mut buf = vec![0; cap];
+-            let len = zstd::block::decompress_to_buffer(self.bytes, &mut buf)
++            let len = zstd::bulk::decompress_to_buffer(self.bytes, &mut buf)
+                 .map_err(|_| corrupted())?;
+             if len != self.uncompressed_len as usize {
+                 Err(corrupted())
+
+diff --git a/rust/rhg/Cargo.toml b/rust/rhg/Cargo.toml
+--- a/rust/rhg/Cargo.toml
++++ b/rust/rhg/Cargo.toml
+@@ -16,7 +16,7 @@ derive_more = "0.99"
+ home = "0.5.3"
+ lazy_static = "1.4.0"
+ log = "0.4.11"
+-micro-timer = "0.3.1"
++micro-timer = "0.4.0"
+ regex = "1.3.9"
+ env_logger = "0.7.1"
+ format-bytes = "0.3.0"

mercurial.spec

@@ -1,7 +1,14 @@
+# build Rust binary and extensions
+%ifarch %{rust_arches}
+%bcond_without rust
+%else
+%bcond_with rust
+%endif
+
 Summary: Mercurial -- a distributed SCM
 Name: mercurial
 Version: 6.1.1
-Release: 2%{?dist}
+Release: 3%{?dist}
 
 # Release: 1.rc1%%{?dist}
 
@@ -12,6 +19,8 @@ License: GPLv2+
 URL: https://mercurial-scm.org/
 Source0: https://www.mercurial-scm.org/release/%{name}-%{upstreamversion}.tar.gz
 Source1: mercurial-site-start.el
+# Patch cargo metadata for dependency versions available in Fedora
+Patch0:  mercurial-rust-metadata.patch
 BuildRequires: make
 BuildRequires: bash-completion
 BuildRequires: emacs-el
@@ -22,6 +31,9 @@ BuildRequires: pkgconfig
 BuildRequires: python3-devel
 BuildRequires: python3-setuptools
 BuildRequires: python3-docutils
+%if %{with rust}
+BuildRequires: rust-packaging
+%endif
 
 Provides: hg = %{version}-%{release}
 Requires: python3
@@ -66,9 +78,54 @@ With chg, a Mercurial command server background process is created that runs
 Mercurial. When you type chg, a C program connects to that background process
 and executes Mercurial commands.
 
+%if %{with rust}
+%package rust
+Summary:    Mercurial Rust binaries and extensions
+# Effective license for the rust binaries, computed from statically linked dependencies:
+# BSD
+# GPLv2+
+# MIT
+# MIT or ASL 2.0
+# MPLv2.0
+# Python
+# Unlicense or MIT
+# zlib or ASL 2.0 or MIT
+License:    GPLv2+
+Requires:   hg = %{version}-%{release}
+
+%description rust
+This subpackage provides following Mercurial components implemented in Rust:
+
+The `rustext` extension speeds up some functionality of Mercurial, e.g.
+ancestry computations in revision graphs, status or discovery of differences
+between repositories.
+
+The experimental `rhg` executable implements a subset of the functionality of `hg` using
+only Rust, to avoid the startup cost of a Python interpreter. This subset is
+initially small but grows over time as `rhg` is improved. When fallback to the
+Python implementation is configured, `rhg` aims to be a drop-in replacement
+for `hg` that should behave the same, except that some commands run faster.
+%endif
 
 %prep
-%setup -q -n %{name}-%{upstreamversion}
+%autosetup -p1 -n %{name}-%{upstreamversion}
+
+%if %{with rust}
+pushd rust
+%cargo_prep
+popd
+
+%generate_buildrequires
+for crate in rust/hg-core rust/hg-cpython rust/rhg; do
+  cd $crate
+  # Temporarily remove  hg-core = { path = "../hg-core"}  dependencies while generating buildrequires.
+  sed -i.br -r -e '/=\s*\{[^}]+path\s*=/d' Cargo.toml
+  %cargo_generate_buildrequires
+  mv -f Cargo.toml{.br,}
+  cd - >/dev/null
+done
+%endif
+# /with rust
 
 %build
 PYTHON=%{python3} make all
@@ -78,10 +135,27 @@ pushd contrib/chg
 make
 popd
 
+%if %{with rust}
+# Mercurial build system hardcodes too much. Instead, just build with Fedora macro.
+pushd rust
+%cargo_build
+popd
+%endif
+
 %install
 %{python3} setup.py install -O1 --root %{buildroot} --prefix %{_prefix} --record=%{name}.files
 make install-doc DESTDIR=%{buildroot} MANDIR=%{_mandir}
 
+# Overrule setup.py policy "c" for module usage: always allow rust extension (if available)
+echo 'modulepolicy = b"rust+c-allow"' > %{buildroot}%{python3_sitearch}/mercurial/__modulepolicy__.py
+
+%if %{with rust}
+# We are not using the Mercurial build system to build rust, and must thus manually install relevant parts.
+install -D -m 755 -pv rust/target/release/rhg %{buildroot}%{_bindir}
+install -D -m 755 -pv rust/target/release/librusthg.so \
+        %{buildroot}%{python3_sitearch}/mercurial/rustext%{python3_ext_suffix}
+%endif
+
 grep -v -e 'hgk.py*' \
         -e "%{python3_sitearch}/mercurial/" \
         -e "%{python3_sitearch}/hgext/" \
@@ -157,6 +231,7 @@ pathfix.py -pni "%{python3}" %{buildroot}%{_bindir}/hg-ssh
 %dir %{_sysconfdir}/mercurial/hgrc.d
 %{_datadir}/bash-completion/
 %{_datadir}/zsh/site-functions/_mercurial
+%exclude %{python3_sitearch}/mercurial/rustext%{python3_ext_suffix}
 %{python3_sitearch}/mercurial/
 %{python3_sitearch}/hgext/
 %{python3_sitearch}/hgext3rd/
@@ -176,6 +251,12 @@ pathfix.py -pni "%{python3}" %{buildroot}%{_bindir}/hg-ssh
 %{_bindir}/chg
 %doc %attr(644,root,root) %{_mandir}/man?/chg.*.gz
 
+%if %{with rust}
+%files rust
+%{_bindir}/rhg
+%{python3_sitearch}/mercurial/rustext%{python3_ext_suffix}
+%endif
+
 
 #%%check
 # This will now fail everytime. Mercurial is not ported properly for Python3
@@ -185,6 +266,9 @@ pathfix.py -pni "%{python3}" %{buildroot}%{_bindir}/hg-ssh
 
 
 %changelog
+* Thu Apr 14 2022 Aleksei Bavshin <alebastr@fedoraproject.org> - 6.1.1-3
+- Build Rust components
+
 * Wed Apr 06 2022 Mads Kiilerich <mads@kiilerich.com> - 6.1.1-2
 - Undo accicental commit