Add function and comments in build.bzl

Signed-off-by: Quanyi Ma <eli@patch.sh>

Author: genedna

third-party/rust/crates/zstd-sys/2.0.14+zstd.1.5.7/BUCK

@@ -8,14 +8,13 @@ load("//third-party/rust/crates/zstd-sys/2.0.14+zstd.1.5.7:build.bzl", "get_rust
 cxx_library(
     name = "zstd_c",
     srcs = glob([
-        "zstd/lib/common/**/*.c",
-        "zstd/lib/compress/**/*.c",
-        "zstd/lib/decompress/**/*.c",
-        "zstd/lib/dictBuilder/**/*.c",
-        "zstd/lib/legacy/**/*.c",
-        "zstd/contrib/seekable_format/**/*.c",
-        "zstd/lib/decompress/huf_decompress_amd64.S",
-    ]),
+        "zstd/lib/common/*.c",
+        "zstd/lib/compress/*.c",
+        "zstd/lib/decompress/*.c",
+    ]) + select({
+        "DEFAULT": ["zstd/lib/decompress/huf_decompress_amd64.S"],
+        "ovr_config//os:windows": [],
+    }),
     headers = glob([
         "zstd/lib/**/*.h",
         "wasm-shim/**/*.h",

third-party/rust/crates/zstd-sys/2.0.14+zstd.1.5.7/build.bzl

@@ -1,6 +1,71 @@
+"""Build configuration module for zstd-sys crate.
+
+This module provides functionality for configuring Rust features and standard library
+support for the zstd-sys crate build process. It handles feature flag management and
+platform-specific configurations.
+"""
+
 def get_rust_features():
     features_config = read_config("rust", "features", "")
 
     if features_config == "":
         return ["legacy", "zdict_builder"]  # Default features
-    return [f.strip() for f in features_config.split(",") if f.strip()]
+    return [f.strip() for f in features_config.split(",") if f.strip()]
+
+
+def get_std_feature():
+    """Determines whether the std feature should be enabled based on target platform.
+    
+    Checks the target architecture and OS to decide if the standard library feature
+    should be enabled. Currently enables std for wasm32 architecture or hermit OS.
+    
+    ```rust
+    let target_arch =
+        std::env::var("CARGO_CFG_TARGET_ARCH").unwrap_or_default();
+    let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
+
+    if target_arch == "wasm32" || target_os == "hermit" {
+        cargo_print(&"rustc-cfg=feature=\"std\"");
+    }
+    ```
+
+    Returns:
+        A list containing "std" if the feature should be enabled, empty list otherwise.
+    """
+    arch = read_config("target", "arch", "")
+    os = read_config("target", "os", "")
+    
+    # Enable std feature for wasm32 or hermit OS targets
+    if arch == "wasm32" or os == "hermit":
+        return ["std"]
+    return []
+
+def zstd_features(features: list[str]) -> list[str]:
+    """Generates zstd compilation flags based on enabled features.
+    
+    Takes a list of enabled features and returns corresponding zstd compilation flags.
+    Handles features like multithreading, legacy support, thin mode, and assembly
+    optimizations.
+
+    Args:
+        features: List of enabled feature strings to configure zstd compilation
+
+    Returns:
+        List of C compilation flags needed for the requested features
+    """
+    flags = []
+    if "zstdmt" in features:
+        flags.append("-DZSTD_MULTITHREAD")
+    if "legacy" in features:
+        flags += ["-DZSTD_LEGACY_SUPPORT=1", "-Izstd/lib/legacy"]
+    if "thin" in features:
+        flags += [
+            "-DHUF_FORCE_DECOMPRESS_X1",
+            "-DZSTD_FORCE_DECOMPRESS_SEQUENCES_SHORT",
+            "-DZSTD_NO_INLINE",
+            "-DZSTD_STRIP_ERROR_STRINGS",
+            "-DDYNAMIC_BMI2=0",
+        ]
+    if "no_asm" in features:
+        flags.append("-DZSTD_DISABLE_ASM")
+    return flags