build(rust): link migrated code into native libraries

Build feature-matched Rust archives for the native Make library path. Flatten
their members into libzstd.a so static consumers resolve C-to-Rust and
Rust-to-C references in one archive, and whole-archive link shared outputs so
every migrated public ABI export remains available.

Rust compression and decompression features now mirror the C partial-library
switches. This prevents compression-only artifacts from retaining DDict
references to decompression-only C helpers.

Add a C archive smoke test that round-trips data and exercises the DDict
lifecycle through lib/libzstd.a, rather than direct test-object links.

Test Plan:
- cargo fmt, strict Clippy, cargo test --all-targets, release build
- Rust checks with compression-only, decompression-only, and no features
- full, partial, forced-HUF, and 32-bit static/shared Make library probes
- test-rust-lib-smoke, fuzzer, zstreamtest, and invalidDictionaries

Refs: rust/README.md

lib/Makefile

@@ -48,6 +48,82 @@ ifneq ($(ZSTD_LIB_DICTBUILDER), 0)
   ZSTD_FILES += $(ZSTD_DICTBUILDER_FILES)
 endif
 
+# The migrated implementation is built as a Rust static archive.  The archive
+# is feature-specific so a build forced to use a particular HUF decoder never
+# reuses the default decoder implementation.  RUST_TARGET can be set for a
+# cross build; -m32 selects the supported 32-bit Linux target automatically.
+CARGO ?= cargo
+RUST_DIR ?= ../rust
+RUST_MANIFEST := $(RUST_DIR)/Cargo.toml
+RUST_SOURCES := $(RUST_MANIFEST) $(RUST_DIR)/Cargo.lock \
+                $(shell find $(RUST_DIR)/src -type f -name '*.rs' -print)
+
+RUST_HUF_FORCE_X1 := $(HUF_FORCE_DECOMPRESS_X1)
+RUST_HUF_FORCE_X2 := $(HUF_FORCE_DECOMPRESS_X2)
+ifneq ($(filter -DHUF_FORCE_DECOMPRESS_X1 -DHUF_FORCE_DECOMPRESS_X1=%,$(CPPFLAGS) $(CFLAGS) $(MOREFLAGS)),)
+RUST_HUF_FORCE_X1 := 1
+endif
+ifneq ($(filter -DHUF_FORCE_DECOMPRESS_X2 -DHUF_FORCE_DECOMPRESS_X2=%,$(CPPFLAGS) $(CFLAGS) $(MOREFLAGS)),)
+RUST_HUF_FORCE_X2 := 1
+endif
+
+ifneq ($(RUST_HUF_FORCE_X1),0)
+ifneq ($(RUST_HUF_FORCE_X2),0)
+$(error HUF_FORCE_DECOMPRESS_X1 and HUF_FORCE_DECOMPRESS_X2 are mutually exclusive)
+endif
+endif
+
+empty :=
+space := $(empty) $(empty)
+comma := ,
+
+RUST_CARGO_FEATURES :=
+ifneq ($(ZSTD_LIB_COMPRESSION),0)
+RUST_CARGO_FEATURES += compression
+endif
+ifneq ($(ZSTD_LIB_DECOMPRESSION),0)
+RUST_CARGO_FEATURES += decompression
+endif
+
+RUST_HUF_FEATURE :=
+RUST_BUILD_CONFIG := c$(ZSTD_LIB_COMPRESSION)-d$(ZSTD_LIB_DECOMPRESSION)-default
+ifneq ($(RUST_HUF_FORCE_X1),0)
+RUST_HUF_FEATURE := huf-force-decompress-x1
+RUST_BUILD_CONFIG := c$(ZSTD_LIB_COMPRESSION)-d$(ZSTD_LIB_DECOMPRESSION)-huf-force-decompress-x1
+endif
+ifneq ($(RUST_HUF_FORCE_X2),0)
+RUST_HUF_FEATURE := huf-force-decompress-x2
+RUST_BUILD_CONFIG := c$(ZSTD_LIB_COMPRESSION)-d$(ZSTD_LIB_DECOMPRESSION)-huf-force-decompress-x2
+endif
+ifneq ($(RUST_HUF_FEATURE),)
+ifneq ($(ZSTD_LIB_DECOMPRESSION),0)
+RUST_CARGO_FEATURES += $(RUST_HUF_FEATURE)
+endif
+endif
+RUST_CARGO_FEATURES := $(subst $(space),$(comma),$(strip $(RUST_CARGO_FEATURES)))
+
+RUST_TARGET ?=
+ifeq ($(strip $(RUST_TARGET)),)
+ifneq ($(filter -m32,$(CC) $(CPPFLAGS) $(CFLAGS) $(MOREFLAGS)),)
+RUST_TARGET := i686-unknown-linux-gnu
+endif
+endif
+
+RUST_TARGET_DIR := $(RUST_DIR)/target/$(RUST_BUILD_CONFIG)
+RUST_CARGO_FLAGS := --manifest-path $(RUST_MANIFEST) --release \
+                    --target-dir $(RUST_TARGET_DIR) --no-default-features
+ifneq ($(RUST_CARGO_FEATURES),)
+RUST_CARGO_FLAGS += --features $(RUST_CARGO_FEATURES)
+endif
+ifneq ($(strip $(RUST_TARGET)),)
+RUST_CARGO_FLAGS += --target $(RUST_TARGET)
+RUST_TARGET_COMPONENT := /$(RUST_TARGET)
+endif
+RUST_STATICLIB := $(RUST_TARGET_DIR)$(RUST_TARGET_COMPONENT)/release/libzstd_rs.a
+
+$(RUST_STATICLIB): $(RUST_SOURCES)
+	$(CARGO) build $(RUST_CARGO_FLAGS)
+
 ZSTD_LOCAL_SRC := $(notdir $(ZSTD_FILES))
 ZSTD_LOCAL_OBJ0 := $(ZSTD_LOCAL_SRC:.c=.o)
 ZSTD_LOCAL_OBJ := $(ZSTD_LOCAL_OBJ0:.S=.o)
@@ -91,6 +167,15 @@ else
   SHARED_EXT_VER = $(SHARED_EXT).$(LIBVER)
 endif
 
+# A dynamic library must retain every migrated public Rust export, including
+# functions no C object calls directly. GNU-like linkers need an explicit
+# whole-archive region for that; Darwin spells the same operation force_load.
+ifeq ($(UNAME_TARGET_SYSTEM), Darwin)
+RUST_DYNLIB_LINK = -Wl,-force_load,$(abspath $(RUST_STATICLIB))
+else
+RUST_DYNLIB_LINK = -Wl,--whole-archive $(RUST_STATICLIB) -Wl,--no-whole-archive
+endif
+
 
 .PHONY: all
 all: lib
@@ -118,14 +203,20 @@ else
 ZSTD_STATICLIB_DIR := $(BUILD_DIR)/static
 ZSTD_STATICLIB := $(ZSTD_STATICLIB_DIR)/libzstd.a
 ZSTD_STATICLIB_OBJ := $(addprefix $(ZSTD_STATICLIB_DIR)/,$(ZSTD_LOCAL_OBJ))
+ZSTD_STATICLIB_RUST_DIR := $(ZSTD_STATICLIB_DIR)/rust
 $(ZSTD_STATICLIB): ARFLAGS = rcs
 $(ZSTD_STATICLIB): | $(ZSTD_STATICLIB_DIR)
-$(ZSTD_STATICLIB): $(ZSTD_STATICLIB_OBJ)
+$(ZSTD_STATICLIB): $(ZSTD_STATICLIB_OBJ) $(RUST_STATICLIB)
   # Check for multithread flag at target execution time
 	$(if $(filter -DZSTD_MULTITHREAD,$(CPPFLAGS)),\
     @echo compiling multi-threaded static library $(LIBVER),\
     @echo compiling single-threaded static library $(LIBVER))
-	$(AR) $(ARFLAGS) $@ $^
+	$(RM) -rf $(ZSTD_STATICLIB_RUST_DIR)
+	$(MKDIR) $(ZSTD_STATICLIB_RUST_DIR)
+	(cd $(ZSTD_STATICLIB_RUST_DIR) && $(AR) x $(abspath $(RUST_STATICLIB)))
+	$(RM) -f $@
+	$(AR) $(ARFLAGS) $@ $(ZSTD_STATICLIB_OBJ) $(ZSTD_STATICLIB_RUST_DIR)/*.o
+	$(RM) -rf $(ZSTD_STATICLIB_RUST_DIR)
 
 libzstd.a: $(ZSTD_STATICLIB)
 	cp -f $< $@
@@ -135,9 +226,9 @@ endif
 ifneq (,$(filter Windows%,$(TARGET_SYSTEM)))
 
 LIBZSTD = dll/libzstd.dll
-$(LIBZSTD): $(ZSTD_FILES)
+$(LIBZSTD): $(ZSTD_FILES) $(RUST_STATICLIB)
 	@echo compiling dynamic library $(LIBVER)
-	$(CC) $(FLAGS) -DZSTD_DLL_EXPORT=1 -Wl,--out-implib,dll/libzstd.dll.a -shared $^ -o $@
+	$(CC) $(FLAGS) -DZSTD_DLL_EXPORT=1 -Wl,--out-implib,dll/libzstd.dll.a -shared $(ZSTD_FILES) $(RUST_DYNLIB_LINK) -o $@
 
 else  # not Windows
 
@@ -161,12 +252,12 @@ ZSTD_DYNLIB := $(ZSTD_DYNLIB_DIR)/$(LIBZSTD)
 ZSTD_DYNLIB_OBJ := $(addprefix $(ZSTD_DYNLIB_DIR)/,$(ZSTD_LOCAL_OBJ))
 
 $(ZSTD_DYNLIB): | $(ZSTD_DYNLIB_DIR)
-$(ZSTD_DYNLIB): $(ZSTD_DYNLIB_OBJ)
+$(ZSTD_DYNLIB): $(ZSTD_DYNLIB_OBJ) $(RUST_STATICLIB)
 # Check for multithread flag at target execution time
 	$(if $(filter -DZSTD_MULTITHREAD,$(CPPFLAGS)),\
     @echo compiling multi-threaded dynamic library $(LIBVER),\
     @echo compiling single-threaded dynamic library $(LIBVER))
-	$(CC) $(FLAGS) $^ $(LDFLAGS) $(SONAME_FLAGS) -o $@
+	$(CC) $(FLAGS) $(ZSTD_DYNLIB_OBJ) $(RUST_DYNLIB_LINK) $(LDFLAGS) $(SONAME_FLAGS) -o $@
 	@echo creating versioned links
 	ln -sf $@ libzstd.$(SHARED_EXT_MAJOR)
 	ln -sf $@ libzstd.$(SHARED_EXT)
@@ -248,14 +339,14 @@ ZSTDMT_FILES = zstdmt_compress.c
 ZSTD_NOMT_FILES = $(filter-out $(ZSTDMT_FILES),$(notdir $(ZSTD_FILES)))
 libzstd-nomt: CFLAGS += -fPIC -fvisibility=hidden
 libzstd-nomt: LDFLAGS += -shared
-libzstd-nomt: $(ZSTD_NOMT_FILES)
+libzstd-nomt: $(ZSTD_NOMT_FILES) $(RUST_STATICLIB)
 	@echo compiling single-thread dynamic library $(LIBVER)
 	@echo files : $(ZSTD_NOMT_FILES)
 	@if echo "$(ZSTD_NOMT_FILES)" | tr ' ' '\n' | $(GREP) -q zstdmt; then \
         echo "Error: Found zstdmt in list."; \
         exit 1; \
     fi
-	$(CC) $(FLAGS) $^ $(LDFLAGS) $(SONAME_FLAGS) -o $@
+	$(CC) $(FLAGS) $(ZSTD_NOMT_FILES) $(RUST_DYNLIB_LINK) $(LDFLAGS) $(SONAME_FLAGS) -o $@
 
 .PHONY: clean
 clean: