[PATCH v2 04/15] rust: add a ObjectID struct

["brian m. carlson" <sandals@crustytoothpaste.net>]

We'd like to be able to write some Rust code that can work with object
IDs.  Add a structure here that's identical to struct object_id in C,
for easy use in sharing across the FFI boundary.  We will use this
structure in several places in hot paths, such as index-pack or
pack-objects when converting between algorithms, so prioritize efficient
interchange over a more idiomatic Rust approach.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
---
 Makefile        |  1 +
 src/hash.rs     | 21 +++++++++++++++++++++
 src/lib.rs      |  1 +
 src/meson.build |  1 +
 4 files changed, 24 insertions(+)
 create mode 100644 src/hash.rs

diff --git a/Makefile b/Makefile
index 7e0f77e298..e1d0ae3691 100644
--- a/Makefile
+++ b/Makefile
@@ -1534,6 +1534,7 @@ CLAR_TEST_OBJS += $(UNIT_TEST_DIR)/unit-test.o
 
 UNIT_TEST_OBJS += $(UNIT_TEST_DIR)/test-lib.o
 
+RUST_SOURCES += src/hash.rs
 RUST_SOURCES += src/lib.rs
 RUST_SOURCES += src/varint.rs
 
diff --git a/src/hash.rs b/src/hash.rs
new file mode 100644
index 0000000000..0219391820
--- /dev/null
+++ b/src/hash.rs
@@ -0,0 +1,21 @@
+// This program is free software; you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation: version 2 of the License, dated June 1991.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License along
+// with this program; if not, see <https://www.gnu.org/licenses/>.
+
+pub const GIT_MAX_RAWSZ: usize = 32;
+
+/// A binary object ID.
+#[repr(C)]
+#[derive(Debug, Clone, Ord, PartialOrd, Eq, PartialEq)]
+pub struct ObjectID {
+    pub hash: [u8; GIT_MAX_RAWSZ],
+    pub algo: u32,
+}
diff --git a/src/lib.rs b/src/lib.rs
index 9da70d8b57..cf7c962509 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1 +1,2 @@
+pub mod hash;
 pub mod varint;
diff --git a/src/meson.build b/src/meson.build
index 25b9ad5a14..c77041a3fa 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -1,4 +1,5 @@
 libgit_rs_sources = [
+  'hash.rs',
   'lib.rs',
   'varint.rs',
 ]