fix(build): gate CLI dictionary builder by feature

Keep dictionary-training code out of compressor-only and decompressor-only CLI
archives, where its ZDICT symbols are intentionally absent. Add a dedicated
Rust CLI archive for zstd-dictBuilder, enable the builder feature only for the
full and dictionary-builder programs, and make reduced-feature help use the
feature-independent max-level helper.

Test Plan:
- cargo test --manifest-path rust/cli/Cargo.toml --lib -- --test-threads=1 (158 passed)
- cargo test --manifest-path rust/cli/Cargo.toml --no-default-features --features cli,compression,dict-builder --lib -- --test-threads=1 (124 passed)
- cargo clippy --manifest-path rust/cli/Cargo.toml --lib -- -D warnings
- cargo clippy --manifest-path rust/cli/Cargo.toml --no-default-features --features cli,compression,dict-builder --lib -- -D warnings
- make -C programs -j2 zstd zstd-small zstd-frugal zstd-decompress zstd-compress zstd-dictBuilder
- git diff --check

programs/Makefile

@@ -125,7 +125,7 @@ RUST_CLI_STATICLIB := $(RUST_CLI_TARGET_DIR)/release/libzstd_cli_rs.a
 RUST_CLI_STATICLIB_32 := $(RUST_CLI_TARGET_DIR)/$(RUST_TARGET_32)/release/libzstd_cli_rs.a
 RUST_CLI_CARGO_FLAGS := --manifest-path $(RUST_CLI_MANIFEST) --release \
                         --target-dir $(RUST_CLI_TARGET_DIR) \
-                        --no-default-features --features cli,compression,decompression,benchmark
+                        --no-default-features --features cli,compression,decompression,benchmark,dict-builder
 
 $(RUST_CLI_STATICLIB): $(RUST_CLI_SOURCES)
 	$(CARGO) build $(RUST_CLI_CARGO_FLAGS)
@@ -206,6 +206,16 @@ RUST_COMPRESS_CLI_CARGO_FLAGS := --manifest-path $(RUST_CLI_MANIFEST) --release
 $(RUST_COMPRESS_CLI_STATICLIB): $(RUST_CLI_SOURCES)
 	$(CARGO) build $(RUST_COMPRESS_CLI_CARGO_FLAGS)
 
+RUST_DICTBUILDER_CLI_BUILD_CONFIG := cli-c1-d0-dictbuilder-$(RUST_HUF_MODE)
+RUST_DICTBUILDER_CLI_TARGET_DIR := $(RUST_DIR)/target/$(RUST_DICTBUILDER_CLI_BUILD_CONFIG)
+RUST_DICTBUILDER_CLI_STATICLIB := $(RUST_DICTBUILDER_CLI_TARGET_DIR)/release/libzstd_cli_rs.a
+RUST_DICTBUILDER_CLI_CARGO_FLAGS := --manifest-path $(RUST_CLI_MANIFEST) --release \
+                                    --target-dir $(RUST_DICTBUILDER_CLI_TARGET_DIR) \
+                                    --no-default-features --features cli,compression,dict-builder
+
+$(RUST_DICTBUILDER_CLI_STATICLIB): $(RUST_CLI_SOURCES)
+	$(CARGO) build $(RUST_DICTBUILDER_CLI_CARGO_FLAGS)
+
 # Most program objects use a configuration-hashed directory, but the compact
 # direct-source variants below do not. Give their C outputs an independent
 # mode stamp so they cannot outlive a different Rust HUF archive selection.
@@ -479,7 +489,7 @@ zstd-compress: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) zstdcli.c util.c ti
 
 ## 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 $(RUST_DICTBUILDER_STATICLIB) $(RUST_COMPRESS_CLI_STATICLIB)
+zstd-dictBuilder: $(ZSTDLIB_COMMON_SRC) $(ZSTDLIB_COMPRESS_SRC) $(ZDICT_SRC) zstdcli.c util.c timefn.c fileio.c fileio_asyncio.c dibio.c $(RUST_DICTBUILDER_STATICLIB) $(RUST_DICTBUILDER_CLI_STATICLIB)
 	$(CC) $(FLAGS) -DZSTD_NOBENCH -DZSTD_NODECOMPRESS -DZSTD_NOTRACE $^ -o $@$(EXT)
 
 RUST_DIRECT_LINK_TARGETS := zstd32 zstd-nolegacy zstd-small zstd-frugal \

rust/cli/Cargo.toml

@@ -14,6 +14,7 @@ default = ["cli", "compression", "decompression", "benchmark"]
 cli = []
 compression = []
 decompression = []
+dict-builder = ["compression"]
 helpers = []
 # The integrated benchmark archive is optional so zstd-small and zstd-frugal
 # can omit every benchmark implementation and its timing/data-generator

rust/cli/src/lib.rs

@@ -7,7 +7,7 @@ mod benchzstd;
 #[cfg(any(feature = "benchmark", feature = "helpers"))]
 #[path = "../../src/datagen.rs"]
 mod datagen;
-#[cfg(feature = "cli")]
+#[cfg(all(feature = "cli", feature = "dict-builder"))]
 #[path = "../../src/dibio.rs"]
 mod dibio;
 #[cfg(feature = "cli")]

rust/src/zstd_cli.rs

@@ -152,6 +152,7 @@ struct ZDICT_fastCover_params_t {
 
 #[repr(C)]
 #[derive(Clone, Copy, Debug, Default, PartialEq)]
+#[cfg(all(feature = "compression", feature = "dict-builder"))]
 struct ZDICT_legacy_params_t {
     selectivityLevel: c_uint,
     zParams: ZDICT_params_t,
@@ -297,7 +298,7 @@ unsafe extern "C" {
 
     /// Narrow bridge to `programs/dibio.c`. The file loader and dictionary
     /// algorithms remain on the C/Rust library side of this boundary.
-    #[cfg(feature = "compression")]
+    #[cfg(all(feature = "compression", feature = "dict-builder"))]
     fn DiB_trainFromFiles(
         dict_file_name: *const c_char,
         max_dict_size: usize,
@@ -688,7 +689,7 @@ const fn max_c_level_for_help() -> i32 {
 }
 
 fn write_basic_usage<W: Write>(out: &mut W, program_name: &str) {
-    let max_level = DEFAULT_MAX_CLEVEL;
+    let max_level = max_c_level_for_help();
     let _ = writeln!(
         out,
         "Compress or decompress the INPUT file(s); reads from STDIN if INPUT is `-` or not provided."
@@ -2538,13 +2539,13 @@ fn run_bench(cli: &Cli) -> Result<i32, String> {
 /// file loading and output path stay in that bridge for now; the selected
 /// dictionary builder symbols are supplied by the Rust library archive.
 fn run_train(cli: &Cli) -> Result<i32, String> {
-    #[cfg(not(feature = "compression"))]
+    #[cfg(not(all(feature = "compression", feature = "dict-builder")))]
     {
         let _ = cli;
-        return Err("training mode not available".to_owned());
+        Err("training mode not available".to_owned())
     }
 
-    #[cfg(feature = "compression")]
+    #[cfg(all(feature = "compression", feature = "dict-builder"))]
     {
         let default_output = cstring(DEFAULT_DICT_NAME).expect("static dictionary name");
         let output = cli.output.as_ref().unwrap_or(&default_output);