add OpenHarmony (OHOS) target support

On OpenHarmony the user/process model is sandbox-based. libgit2's
owner validation (GIT_OPT_SET_OWNER_VALIDATION) compares file UID
with process EUID, which is not applicable and causes spurious
"not owned by current user" errors (code=Owner -36).

This disables owner validation on all OHOS targets
(cfg(target_env = "ohos"): aarch64/armv7/x86_64) via a
std::sync::Once in the repository opening entry points.

Also adds cross-compilation instructions to CONTRIBUTING.md.

CONTRIBUTING.md

@@ -22,5 +22,34 @@ good first issue, you can take a look at [issues labelled with
 too much context so that people not familiar with the codebase yet can still
 make a contribution.
 
+## Cross-compiling for OpenHarmony
+
+GitUI can be built for OpenHarmony (target `aarch64-unknown-linux-ohos`). This requires the [OpenHarmony SDK](https://www.openharmony.cn/) native toolchain.
+
+First, install the `aarch64-unknown-linux-ohos` Rust target:
+
+```sh
+rustup target add aarch64-unknown-linux-ohos
+```
+
+Set the following environment variables (adjust paths to your OHOS SDK location):
+
+```sh
+export OHOS_SDK=/path/to/ohos-sdk
+export CC_aarch64_unknown_linux_ohos="$OHOS_SDK/native/llvm/bin/clang"
+export CXX_aarch64_unknown_linux_ohos="$OHOS_SDK/native/llvm/bin/clang++"
+export CARGO_TARGET_AARCH64_UNKNOWN_LINUX_OHOS_LINKER="$OHOS_SDK/native/llvm/bin/clang"
+export CARGO_TARGET_AARCH64_UNKNOWN_LINUX_OHOS_AR="$OHOS_SDK/native/llvm/bin/llvm-ar"
+export CARGO_TARGET_AARCH64_UNKNOWN_LINUX_OHOS_RUSTFLAGS="-C link-arg=--sysroot=$OHOS_SDK/native/sysroot -C link-arg=-L$OHOS_SDK/native/sysroot/usr/lib/aarch64-linux-ohos -C link-arg=-Wl,--allow-multiple-definition -C link-arg=-Wl,--undefined-version -C link-arg=-Wl,--defsym=__xpg_strerror_r=0"
+```
+
+Then build:
+
+```sh
+cargo build --target aarch64-unknown-linux-ohos --release
+```
+
+> **Note:** On OpenHarmony the user/process model is sandbox-based. GitUI automatically disables libgit2's owner validation on OHOS targets to avoid spurious "not owned by current user" errors.
+
 [discord-server]: https://discord.gg/rZv4uxSQx3
 [good-first-issues]: https://github.com/gitui-org/gitui/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22

asyncgit/src/sync/repository.rs

@@ -7,6 +7,22 @@ use git2::{Repository, RepositoryOpenFlags};
 
 use crate::error::Result;
 
+#[cfg(target_env = "ohos")]
+use std::sync::Once;
+
+#[cfg(target_env = "ohos")]
+static INIT_OHOS: Once = Once::new();
+
+#[cfg(target_env = "ohos")]
+pub(crate) fn init_ohos_owner_validation() {
+	INIT_OHOS.call_once(|| {
+		#[allow(unsafe_code)]
+		unsafe {
+			git2::opts::set_verify_owner_validation(false).ok();
+		}
+	});
+}
+
 ///
 pub type RepoPathRef = RefCell<RepoPath>;
 
@@ -55,6 +71,9 @@ impl From<&str> for RepoPath {
 }
 
 pub fn repo(repo_path: &RepoPath) -> Result<Repository> {
+	#[cfg(target_env = "ohos")]
+	init_ohos_owner_validation();
+
 	let repo = Repository::open_ext(
 		repo_path.gitpath(),
 		RepositoryOpenFlags::FROM_ENV,

asyncgit/src/sync/utils.rs

@@ -26,6 +26,9 @@ pub struct Head {
 
 ///
 pub fn repo_open_error(repo_path: &RepoPath) -> Option<String> {
+	#[cfg(target_env = "ohos")]
+	super::repository::init_ohos_owner_validation();
+
 	if let Err(e) = Repository::open_ext(
 		repo_path.gitpath(),
 		RepositoryOpenFlags::FROM_ENV,