Add support for custom git extensions (rust-lang#791)

* Add support for custom git extensions

This would allow one to use git worktrees together with sparse-checkout.

Reference: libgit2/libgit2#6031

* Mark extension methods unsafe

* Replace custom spin-lock in tests with serial-test crate

* Rewrite tests as integration tests

Author: knutwalker

libgit2-sys/lib.rs

@@ -1870,6 +1870,10 @@ git_enum! {
         GIT_OPT_ENABLE_HTTP_EXPECT_CONTINUE,
         GIT_OPT_GET_MWINDOW_FILE_LIMIT,
         GIT_OPT_SET_MWINDOW_FILE_LIMIT,
+        GIT_OPT_SET_ODB_PACKED_PRIORITY,
+        GIT_OPT_SET_ODB_LOOSE_PRIORITY,
+        GIT_OPT_GET_EXTENSIONS,
+        GIT_OPT_SET_EXTENSIONS,
     }
 }
 

src/opts.rs

@@ -1,7 +1,9 @@
 //! Bindings to libgit2's git_libgit2_opts function.
 
 use std::ffi::CString;
+use std::ptr;
 
+use crate::string_array::StringArray;
 use crate::util::Binding;
 use crate::{raw, Buf, ConfigLevel, Error, IntoCString};
 
@@ -119,6 +121,63 @@ pub fn strict_hash_verification(enabled: bool) {
     debug_assert!(error >= 0);
 }
 
+/// Returns the list of git extensions that are supported. This is the list of
+/// built-in extensions supported by libgit2 and custom extensions that have
+/// been added with [`set_extensions`]. Extensions that have been negated will
+/// not be returned.
+///
+/// # Safety
+///
+/// libgit2 stores user extensions in a static variable.
+/// This function is effectively reading a `static mut` and should be treated as such
+pub unsafe fn get_extensions() -> Result<StringArray, Error> {
+    crate::init();
+
+    let mut extensions = raw::git_strarray {
+        strings: ptr::null_mut(),
+        count: 0,
+    };
+
+    try_call!(raw::git_libgit2_opts(
+        raw::GIT_OPT_GET_EXTENSIONS as libc::c_int,
+        &mut extensions
+    ));
+
+    Ok(StringArray::from_raw(extensions))
+}
+
+/// Set that the given git extensions are supported by the caller. Extensions
+/// supported by libgit2 may be negated by prefixing them with a `!`.
+/// For example: setting extensions to `[ "!noop", "newext" ]` indicates that
+/// the caller does not want to support repositories with the `noop` extension
+/// but does want to support repositories with the `newext` extension.
+///
+/// # Safety
+///
+/// libgit2 stores user extensions in a static variable.
+/// This function is effectively modifying a `static mut` and should be treated as such
+pub unsafe fn set_extensions<E>(extensions: &[E]) -> Result<(), Error>
+where
+    for<'x> &'x E: IntoCString,
+{
+    crate::init();
+
+    let extensions = extensions
+        .iter()
+        .map(|e| e.into_c_string())
+        .collect::<Result<Vec<_>, _>>()?;
+
+    let extension_ptrs = extensions.iter().map(|e| e.as_ptr()).collect::<Vec<_>>();
+
+    try_call!(raw::git_libgit2_opts(
+        raw::GIT_OPT_SET_EXTENSIONS as libc::c_int,
+        extension_ptrs.as_ptr(),
+        extension_ptrs.len() as libc::size_t
+    ));
+
+    Ok(())
+}
+
 #[cfg(test)]
 mod test {
     use super::*;

tests/add_extensions.rs

@@ -0,0 +1,19 @@
+//! Test for `set_extensions`, which writes a global state maintained by libgit2
+
+use git2::opts::{get_extensions, set_extensions};
+use git2::Error;
+
+#[test]
+fn test_add_extensions() -> Result<(), Error> {
+    unsafe {
+        set_extensions(&["custom"])?;
+    }
+
+    let extensions = unsafe { get_extensions() }?;
+
+    assert_eq!(extensions.len(), 2);
+    assert_eq!(extensions.get(0), Some("noop"));
+    assert_eq!(extensions.get(1), Some("custom"));
+
+    Ok(())
+}

tests/get_extensions.rs

@@ -0,0 +1,14 @@
+//! Test for `get_extensions`, which reads a global state maintained by libgit2
+
+use git2::opts::get_extensions;
+use git2::Error;
+
+#[test]
+fn test_get_extensions() -> Result<(), Error> {
+    let extensions = unsafe { get_extensions() }?;
+
+    assert_eq!(extensions.len(), 1);
+    assert_eq!(extensions.get(0), Some("noop"));
+
+    Ok(())
+}

tests/remove_extensions.rs

@@ -0,0 +1,19 @@
+//! Test for `set_extensions`, which writes a global state maintained by libgit2
+
+use git2::opts::{get_extensions, set_extensions};
+use git2::Error;
+
+#[test]
+fn test_remove_extensions() -> Result<(), Error> {
+    unsafe {
+        set_extensions(&["custom", "!ignore", "!noop", "other"])?;
+    }
+
+    let extensions = unsafe { get_extensions() }?;
+
+    assert_eq!(extensions.len(), 2);
+    assert_eq!(extensions.get(0), Some("custom"));
+    assert_eq!(extensions.get(1), Some("other"));
+
+    Ok(())
+}