xdiff: introduce rust

Upcoming patches will accelerate and simplify xdiff, while also
porting parts of it to Rust. In preparation, add some stubs and setup
the Rust build. For now, it is easier to let cargo build rust and
have make or meson merely link against the static library that cargo
builds. In line with ongoing libification efforts, use multiple
crates to allow more modularity on the Rust side. xdiff is the crate
that this series will focus on, but we also introduce the interop
crate for future patch series.

In order to facilitate interoperability between C and Rust, introduce
C definitions for Rust primitive types in git-compat-util.h.

Signed-off-by: Ezekiel Newren <ezekielnewren@gmail.com>

Author: ezekielnewren

Makefile

@@ -919,6 +919,11 @@ TEST_SHELL_PATH = $(SHELL_PATH)
 
 LIB_FILE = libgit.a
 XDIFF_LIB = xdiff/lib.a
+ifeq ($(DEBUG), 1)
+RUST_LIB = rust/target/debug/libxdiff.a
+else
+RUST_LIB = rust/target/release/libxdiff.a
+endif
 REFTABLE_LIB = reftable/libreftable.a
 
 GENERATED_H += command-list.h
@@ -1392,6 +1397,8 @@ UNIT_TEST_OBJS += $(UNIT_TEST_DIR)/lib-reftable.o
 GITLIBS = common-main.o $(LIB_FILE) $(XDIFF_LIB) $(REFTABLE_LIB) $(LIB_FILE)
 EXTLIBS =
 
+GITLIBS += $(RUST_LIB)
+
 GIT_USER_AGENT = git/$(GIT_VERSION)
 
 ifeq ($(wildcard sha1collisiondetection/lib/sha1.h),sha1collisiondetection/lib/sha1.h)
@@ -2925,6 +2932,14 @@ $(LIB_FILE): $(LIB_OBJS)
 $(XDIFF_LIB): $(XDIFF_OBJS)
 	$(QUIET_AR)$(RM) $@ && $(AR) $(ARFLAGS) $@ $^
 
+.PHONY: $(RUST_LIB)
+$(RUST_LIB):
+ifeq ($(DEBUG), 1)
+	cd rust && RUSTFLAGS="-Aunused_imports -Adead_code" cargo build --verbose
+else
+	cd rust && RUSTFLAGS="-Aunused_imports -Adead_code" cargo build --verbose --release
+endif
+
 $(REFTABLE_LIB): $(REFTABLE_OBJS)
 	$(QUIET_AR)$(RM) $@ && $(AR) $(ARFLAGS) $@ $^
 
@@ -3756,7 +3771,10 @@ cocciclean:
 	$(RM) -r .build/contrib/coccinelle
 	$(RM) contrib/coccinelle/*.cocci.patch
 
-clean: profile-clean coverage-clean cocciclean
+rustclean:
+	cd rust && cargo clean
+
+clean: profile-clean coverage-clean cocciclean rustclean
 	$(RM) -r .build $(UNIT_TEST_BIN)
 	$(RM) GIT-TEST-SUITES
 	$(RM) po/git.pot po/git-core.pot

git-compat-util.h

@@ -196,6 +196,23 @@ static inline int is_xplatform_dir_sep(int c)
 #include "compat/msvc.h"
 #endif
 
+/* rust types */
+typedef uint8_t   u8;
+typedef uint16_t  u16;
+typedef uint32_t  u32;
+typedef uint64_t  u64;
+
+typedef int8_t    i8;
+typedef int16_t   i16;
+typedef int32_t   i32;
+typedef int64_t   i64;
+
+typedef float     f32;
+typedef double    f64;
+
+typedef size_t    usize;
+typedef ptrdiff_t isize;
+
 /* used on Mac OS X */
 #ifdef PRECOMPOSE_UNICODE
 #include "compat/precompose_utf8.h"

meson.build

@@ -267,6 +267,36 @@ version_gen_environment.set('GIT_DATE', get_option('build_date'))
 version_gen_environment.set('GIT_USER_AGENT', get_option('user_agent'))
 version_gen_environment.set('GIT_VERSION', get_option('version'))
 
+if get_option('optimization') in ['2', '3', 's', 'z']
+  rust_target = 'release'
+  rust_args = ['--release']
+  rustflags = '-Aunused_imports -Adead_code'
+else
+  rust_target = 'debug'
+  rust_args = []
+  rustflags = '-Aunused_imports -Adead_code -C debuginfo=2 -C opt-level=1 -C force-frame-pointers=yes'
+endif
+
+
+rust_leaf = custom_target('rust_leaf',
+  output: 'libxdiff.a',
+  build_by_default: true,
+  build_always_stale: true,
+  command: ['cargo', 'build',
+            '--manifest-path', meson.project_source_root() / 'rust/Cargo.toml'
+  ] + rust_args,
+  env: {
+    'RUSTFLAGS': rustflags,
+  },
+  install: false,
+)
+
+rust_xdiff_dep = declare_dependency(
+  link_args: ['-L' + meson.project_source_root() / 'rust/target' / rust_target, '-lxdiff'],
+#  include_directories: include_directories('xdiff/include'),  # Adjust if you expose headers
+)
+
+
 compiler = meson.get_compiler('c')
 
 libgit_sources = [
@@ -1677,6 +1707,8 @@ version_def_h = custom_target(
 )
 libgit_sources += version_def_h
 
+libgit_dependencies += rust_xdiff_dep
+
 libgit = declare_dependency(
   link_with: static_library('git',
     sources: libgit_sources,

rust/Cargo.lock

@@ -0,0 +1,6 @@
+[workspace]
+members = [
+    "xdiff",
+    "interop",
+]
+resolver = "2"

rust/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "interop"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+name = "interop"
+path = "src/lib.rs"
+## staticlib to generate xdiff.a for use by gcc
+## cdylib (optional) to generate xdiff.so for use by gcc
+## rlib is required by the rust unit tests
+crate-type = ["staticlib", "rlib"]
+
+[dependencies]

rust/interop/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "xdiff"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+name = "xdiff"
+path = "src/lib.rs"
+## staticlib to generate xdiff.a for use by gcc
+## cdylib (optional) to generate xdiff.so for use by gcc
+## rlib is required by the rust unit tests
+crate-type = ["staticlib", "rlib"]
+
+[dependencies]
+interop = { path = "../interop" }