Switch _zstd backend from zstd-safe to pure-Rust libzstd-rs-sys

Replace the C-library bindings (zstd-safe/zstd-sys) with Trifecta Tech Foundation's libzstd-rs-sys (pinned git rev), a c2rust translation of upstream libzstd. The module now calls its C-API-compatible functions through small owning RAII wrappers (CCtx/DCtx/CDict/DDict) with the same drop-order invariants as before. The new backend builds zstdmt_compress in, so nb_workers bounds are (0, 256) and test_zstd_multithread_compress passes for real; drop the now-obsolete expectedFailureIf marker.
youknowone · May 23, 2026 · May 23, 2026 · May 23, 2026 · May 23, 2026 · May 23, 2026
commit 1593954961276d5712d1c98dfe741eedaa4f35cb
diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -241,6 +241,7 @@ xz-sys = "0.4.6-rc.0"
 libsqlite3-sys = "0.38"
 libz-rs-sys = "0.6"
 zlib-rs = { version = "=0.6.8", default-features = false, features = ["rust-allocator", "__internal-api"] }
+libzstd-rs-sys = { git = "https://github.com/trifectatechfoundation/libzstd-rs-sys", rev = "99fb4c096a21a9b37feebe180333a2ff8645e23b" }
 lock_api = "0.4"
 log = "0.4.30"
 lz4_flex = "0.14"
@@ -320,7 +321,6 @@ which = "8"
 x509-parser = "0.18"
 xml = "1.3"
 writeable = "0.6"
-zstd-safe = { version = "7", default-features = false, features = ["std", "zdict_builder"] }
 
 # Lints
 

diff --git a/Lib/test/test_zstd.py b/Lib/test/test_zstd.py
@@ -321,11 +321,6 @@ def test_unknown_compression_parameter(self):
         with self.assertRaisesRegex(ValueError, pattern):
             ZstdCompressor(options=option)
 
-    # TODO: RUSTPYTHON
-    @unittest.expectedFailureIf(
-        not SUPPORT_MULTITHREADING,
-        "TODO: RUSTPYTHON; libzstd built without multi-threaded compression support",
-    )
     def test_zstd_multithread_compress(self):
         size = 40*_1M
         b = THIS_FILE_BYTES * (size // len(THIS_FILE_BYTES))

diff --git a/crates/stdlib/Cargo.toml b/crates/stdlib/Cargo.toml
@@ -96,9 +96,9 @@ webpki-roots = { workspace = true, optional = true }
 
 [target.'cfg(not(any(target_os = "android", target_arch = "wasm32")))'.dependencies]
 libsqlite3-sys = { workspace = true, features = ["bundled"], optional = true }
+libzstd-rs-sys = { workspace = true }
 xz = { workspace = true }
 xz-sys = { workspace = true }
-zstd-safe = { workspace = true }
 
 [target.'cfg(windows)'.dependencies]
 paste = { workspace = true }