build(rust): rebuild the archive for C test and CLI links

Make Rust sources normal prerequisites of native C test executables and CLI
builds. A changed Rust module now rebuilds libzstd_rs.a and relinks the target,
instead of relying on a manually prepared archive that can silently be stale.

The archive is linked after C objects, allowing migrated C shims to resolve
their Rust ABI symbols while remaining compatible with the existing makefile
flows. The migration guide now documents this behavior.

Test Plan:
- make -B -C tests fuzzer
- ./tests/fuzzer -i1 --no-big-tests
- make -B -C programs zstd
- ./programs/zstd --version

Refs: rust/README.md

programs/Makefile

@@ -21,6 +21,19 @@ zstd-release:
 LIBZSTD_MK_DIR = ../lib
 include $(LIBZSTD_MK_DIR)/libzstd.mk
 
+# Link the in-progress Rust implementation after C objects whenever a program
+# uses a migrated C shim. Source inputs are prerequisites so a changed Rust
+# module rebuilds the archive and relinks the executable automatically.
+CARGO ?= cargo
+RUST_DIR := ../rust
+RUST_MANIFEST := $(RUST_DIR)/Cargo.toml
+RUST_STATICLIB := $(RUST_DIR)/target/release/libzstd_rs.a
+RUST_SOURCES := $(RUST_MANIFEST) $(RUST_DIR)/Cargo.lock \
+                $(shell find $(RUST_DIR)/src -type f -name '*.rs' -print)
+
+$(RUST_STATICLIB): $(RUST_SOURCES)
+	$(CARGO) build --manifest-path $(RUST_MANIFEST) --release
+
 ifeq ($(shell $(CC) -v 2>&1 | $(GREP) -c "gcc version "), 1)
   ALIGN_LOOP = -falign-loops=32
 else
@@ -152,7 +165,7 @@ else
 # BUILD_DIR is defined
 
 ZSTD_OBJ := $(addprefix $(BUILD_DIR)/, $(ZSTD_ALL_OBJ))
-$(BUILD_DIR)/zstd : $(ZSTD_OBJ)
+$(BUILD_DIR)/zstd : $(ZSTD_OBJ) $(RUST_STATICLIB)
 	@echo "$(THREAD_MSG)"
 	@echo "$(ZLIB_MSG)"
 	@echo "$(LZMA_MSG)"
@@ -199,7 +212,7 @@ zstd32 : $(ZSTDLIB_FULL_SRC) $(ZSTD_CLI_SRC)
 CLEAN += zstd-nolegacy
 zstd-nolegacy : LDFLAGS += $(THREAD_LD) $(ZLIBLD) $(LZMALD) $(LZ4LD) $(DEBUGFLAGS_LD)
 zstd-nolegacy : CPPFLAGS += -UZSTD_LEGACY_SUPPORT -DZSTD_LEGACY_SUPPORT=0
-zstd-nolegacy : $(ZSTDLIB_CORE_SRC) $(ZDICT_SRC) $(ZSTD_CLI_OBJ)
+zstd-nolegacy : $(ZSTDLIB_CORE_SRC) $(ZDICT_SRC) $(ZSTD_CLI_OBJ) $(RUST_STATICLIB)
 	$(CC) $(FLAGS) $^ -o $@$(EXT) $(LDFLAGS)
 
 .PHONY: zstd-nomt
@@ -253,20 +266,20 @@ endif
 ## zstd-small: minimal target, supporting only zstd compression and decompression. no bench. no legacy. no other format.
 CLEAN += zstd-small zstd-frugal
 zstd-small: CFLAGS = -Os -Wl,-s
-zstd-frugal zstd-small: $(ZSTDLIB_CORE_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c
+zstd-frugal zstd-small: $(ZSTDLIB_CORE_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c $(RUST_STATICLIB)
 	$(CC) $(FLAGS) -DZSTD_NOBENCH -DZSTD_NODICT -DZSTD_NOTRACE -UZSTD_LEGACY_SUPPORT -DZSTD_LEGACY_SUPPORT=0 $^ -o $@$(EXT)
 
 CLEAN += zstd-decompress
-zstd-decompress: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_DECOMPRESS_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c
+zstd-decompress: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_DECOMPRESS_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c $(RUST_STATICLIB)
 	$(CC) $(FLAGS) -DZSTD_NOBENCH -DZSTD_NODICT -DZSTD_NOCOMPRESS -DZSTD_NOTRACE -UZSTD_LEGACY_SUPPORT -DZSTD_LEGACY_SUPPORT=0 $^ -o $@$(EXT)
 
 CLEAN += zstd-compress
-zstd-compress: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c
+zstd-compress: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c $(RUST_STATICLIB)
 	$(CC) $(FLAGS) -DZSTD_NOBENCH -DZSTD_NODICT -DZSTD_NODECOMPRESS -DZSTD_NOTRACE -UZSTD_LEGACY_SUPPORT -DZSTD_LEGACY_SUPPORT=0 $^ -o $@$(EXT)
 
 ## zstd-dictBuilder: executable supporting dictionary creation and compression (only)
 CLEAN += zstd-dictBuilder
-zstd-dictBuilder: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) $(ZDICT_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c dibio.c
+zstd-dictBuilder: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) $(ZDICT_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c dibio.c $(RUST_STATICLIB)
 	$(CC) $(FLAGS) -DZSTD_NOBENCH -DZSTD_NODECOMPRESS -DZSTD_NOTRACE $^ -o $@$(EXT)
 
 CLEAN += zstdmt

rust/README.md

@@ -39,9 +39,10 @@ source file whose implementation has moved to Rust remains in the original
 makefile source list as a small shim so header configuration and platform
 preprocessor behavior stay available during the transition.
 
-The original test makefile links `target/release/libzstd_rs.a` with whole-archive
-semantics. Rebuild the Rust archive before running C tests so the executable
-does not use a stale implementation.
+The test and program makefiles make `target/release/libzstd_rs.a` a normal
+link prerequisite. They rebuild the Rust archive and relink the executable
+when a Rust source changes, so original C tests do not accidentally use a stale
+implementation.
 
 ## Validation
 

tests/Makefile

@@ -36,6 +36,18 @@ PRGDIR  = ../programs
 PYTHON ?= python3
 TESTARTEFACT := versionsTest
 
+# The Rust implementation is linked into C compatibility tests. Keep the
+# archive a real prerequisite so a changed Rust source always relinks a test.
+CARGO ?= cargo
+RUST_DIR := ../rust
+RUST_MANIFEST := $(RUST_DIR)/Cargo.toml
+RUST_STATICLIB := $(RUST_DIR)/target/release/libzstd_rs.a
+RUST_SOURCES := $(RUST_MANIFEST) $(RUST_DIR)/Cargo.lock \
+                $(shell find $(RUST_DIR)/src -type f -name '*.rs' -print)
+
+$(RUST_STATICLIB): $(RUST_SOURCES)
+	$(CARGO) build --manifest-path $(RUST_MANIFEST) --release
+
 DEBUGFLAGS += -g -Wno-c++-compat
 CPPFLAGS   += -I$(LIB_SRCDIR) -I$(LIB_SRCDIR)/common -I$(LIB_SRCDIR)/compress -I$(LIB_SRCDIR)/legacy \
               -I$(LIB_SRCDIR)/dictBuilder -I$(LIB_SRCDIR)/deprecated -I$(PRGDIR) \
@@ -74,7 +86,6 @@ MULTITHREAD_CPP = -DZSTD_MULTITHREAD
 MULTITHREAD_LD  = -pthread
 endif
 MULTITHREAD = $(MULTITHREAD_CPP) $(MULTITHREAD_LD)
-LDFLAGS += -Wl,--whole-archive ../rust/target/release/libzstd_rs.a -Wl,--no-whole-archive
 
 VOID = /dev/null
 ZSTREAM_TESTTIME ?= -T90s
@@ -245,6 +256,15 @@ CLEAN += poolTests
 poolTests : $(PRGDIR)/util.c $(PRGDIR)/timefn.c poolTests.c $(LIB_SRCDIR)/common/pool.c $(LIB_SRCDIR)/common/threading.c $(LIB_SRCDIR)/common/zstd_common.c $(LIB_SRCDIR)/common/error_private.c
 	$(LINK.c) $(MULTITHREAD) $^ -o $@$(EXT)
 
+# These static C test executables exercise Rust replacements. The normal
+# prerequisite is also an archive input, placed after C sources by `$^`, and
+# rebuilding Rust therefore relinks rather than leaving a stale implementation.
+RUST_LINK_TARGETS := $(FULLBENCHS) fuzzer fuzzer32 zstreamtest zstreamtest32 \
+                     zstreamtest_asan zstreamtest_tsan zstreamtest_ubsan \
+                     paramgrill roundTripCrash longmatch largeDictionary \
+                     invalidDictionaries legacy decodecorpus poolTests
+$(RUST_LINK_TARGETS): $(RUST_STATICLIB)
+
 .PHONY: versionsTest
 versionsTest: clean
 	$(PYTHON) test-zstd-versions.py