refactor(compress): move CCtx construction policy to Rust

Move reset, parameter copy, and default policy resolution from
ZSTD_makeCCtxParamsFromCParams into Rust through a pointer-based ABI function.
Keep the private LDM adjustment and its invariants in C while Rust owns the
stable parameter-object policy and focused reset/resolution coverage.

Test Plan:
- worker git diff and capped format checks
- parent capped root clippy and native build
- parent capped upstream make -j1 -C tests test
- parent capped CLI clippy and tests

All parent verification is serial under a 40 GiB virtual-memory cap. Standalone
root Rust unit linking remains unavailable because the crate imports C-owned
bridge symbols.

lib/compress/zstd_compress.c

@@ -2015,6 +2015,9 @@ int ZSTD_rust_cctx_params_job_size_min(void);
 int ZSTD_rust_cctx_params_job_size_max(void);
 ZSTD_CCtx_params* ZSTD_rust_createCCtxParams(ZSTD_customMem customMem);
 size_t ZSTD_rust_freeCCtxParams(ZSTD_CCtx_params* params);
+void ZSTD_rust_makeCCtxParamsFromCParams(
+        ZSTD_CCtx_params* cctxParams,
+        const ZSTD_compressionParameters* cParams);
 void ZSTD_rust_CCtxParams_init_internal(
         ZSTD_CCtx_params* cctxParams, const ZSTD_parameters* params,
         int compressionLevel);
@@ -3615,23 +3618,14 @@ static ZSTD_CCtx_params ZSTD_makeCCtxParamsFromCParams(
         ZSTD_compressionParameters cParams)
 {
     ZSTD_CCtx_params cctxParams;
-    /* should not matter, as all cParams are presumed properly defined */
+    /* Rust owns reset, copy, and default policy.  Keep the C LDM adapter and
-    ZSTD_CCtxParams_init(&cctxParams, ZSTD_CLEVEL_DEFAULT);
+     * assertions here because they depend on the private C parameter type. */
-    cctxParams.cParams = cParams;
+    ZSTD_rust_makeCCtxParamsFromCParams(&cctxParams, &cParams);
-
-    /* Adjust advanced params according to cParams */
-    cctxParams.ldmParams.enableLdm = ZSTD_resolveEnableLdm(cctxParams.ldmParams.enableLdm, &cParams);
     if (cctxParams.ldmParams.enableLdm == ZSTD_ps_enable) {
         ZSTD_ldm_adjustParameters(&cctxParams.ldmParams, &cParams);
         assert(cctxParams.ldmParams.hashLog >= cctxParams.ldmParams.bucketSizeLog);
         assert(cctxParams.ldmParams.hashRateLog < 32);
     }
-    cctxParams.postBlockSplitter = ZSTD_resolveBlockSplitterMode(cctxParams.postBlockSplitter, &cParams);
-    cctxParams.useRowMatchFinder = ZSTD_resolveRowMatchFinderMode(cctxParams.useRowMatchFinder, &cParams);
-    cctxParams.validateSequences = ZSTD_resolveExternalSequenceValidation(cctxParams.validateSequences);
-    cctxParams.maxBlockSize = ZSTD_resolveMaxBlockSize(cctxParams.maxBlockSize);
-    cctxParams.searchForExternalRepcodes = ZSTD_resolveExternalRepcodeSearch(cctxParams.searchForExternalRepcodes,
-                                                                             cctxParams.compressionLevel);
     assert(!ZSTD_checkCParams(cParams));
     return cctxParams;
 }

rust/src/zstd_compress_params_api.rs

@@ -17,7 +17,8 @@ use crate::zstd_compress_params::{
     ZSTD_rust_params_checkCParams, ZSTD_rust_params_dedicatedDictSearchIsSupported,
     ZSTD_rust_params_dedicatedDictSearch_getCParams, ZSTD_rust_params_getBounds,
     ZSTD_rust_params_getCParamsFromCCtxParams, ZSTD_rust_params_getCParamsInternal,
-    ZSTD_rust_params_overrideCParams, ZSTD_rust_params_resolveExternalRepcodeSearch,
+    ZSTD_rust_params_overrideCParams, ZSTD_rust_params_resolveBlockSplitterMode,
+    ZSTD_rust_params_resolveEnableLdm, ZSTD_rust_params_resolveExternalRepcodeSearch,
     ZSTD_rust_params_resolveExternalSequenceValidation, ZSTD_rust_params_resolveMaxBlockSize,
     ZSTD_rust_params_resolveRowMatchFinderMode, ZSTD_CONTENTSIZE_UNKNOWN,
     ZSTD_RUST_CPM_CREATE_CDICT, ZSTD_RUST_PS_AUTO, ZSTD_RUST_PS_DISABLE, ZSTD_RUST_PS_ENABLE,
@@ -462,6 +463,43 @@ pub unsafe extern "C" fn ZSTD_rust_CCtxParams_init_internal(
     unsafe { init_internal_impl(cctx_params, zstd_params, compression_level) }
 }
 
+unsafe fn make_cctx_params_from_cparams_impl(
+    cctx_params: *mut ZSTD_CCtx_params,
+    cparams: *const ZSTD_compressionParameters,
+) {
+    unsafe {
+        let _ = init_impl(cctx_params, DEFAULT_CLEVEL);
+        (*cctx_params).cParams = *cparams;
+        (*cctx_params).ldmParams.enableLdm =
+            ZSTD_rust_params_resolveEnableLdm(ZSTD_RUST_PS_AUTO, *cparams);
+        (*cctx_params).postBlockSplitter =
+            ZSTD_rust_params_resolveBlockSplitterMode(ZSTD_RUST_PS_AUTO, *cparams);
+        (*cctx_params).useRowMatchFinder =
+            ZSTD_rust_params_resolveRowMatchFinderMode(ZSTD_RUST_PS_AUTO, *cparams);
+        (*cctx_params).validateSequences =
+            ZSTD_rust_params_resolveExternalSequenceValidation((*cctx_params).validateSequences);
+        (*cctx_params).maxBlockSize =
+            ZSTD_rust_params_resolveMaxBlockSize((*cctx_params).maxBlockSize);
+        (*cctx_params).searchForExternalRepcodes = ZSTD_rust_params_resolveExternalRepcodeSearch(
+            (*cctx_params).searchForExternalRepcodes,
+            (*cctx_params).compressionLevel,
+        );
+    }
+}
+
+/// Builds the context parameters used by the C size-estimation adapters.
+///
+/// The output is written through a pointer so the private `repr(C)` object is
+/// never returned by value across the language boundary.  C retains LDM
+/// parameter adjustment and validation assertions around this policy leaf.
+#[no_mangle]
+pub unsafe extern "C" fn ZSTD_rust_makeCCtxParamsFromCParams(
+    cctx_params: *mut ZSTD_CCtx_params,
+    cparams: *const ZSTD_compressionParameters,
+) {
+    unsafe { make_cctx_params_from_cparams_impl(cctx_params, cparams) }
+}
+
 #[inline]
 fn resolve_row_match_finder(cparams: ZSTD_compressionParameters) -> c_int {
     if (STRATEGY_GREEDY..=STRATEGY_LAZY2).contains(&cparams.strategy) && cparams.windowLog > 14 {
@@ -1564,6 +1602,44 @@ mod tests {
         }
     }
 
+    #[test]
+    fn make_cctx_params_from_cparams_resets_and_resolves_defaults() {
+        let cparams = ZSTD_compressionParameters {
+            windowLog: 27,
+            chainLog: 27,
+            hashLog: 25,
+            searchLog: 9,
+            minMatch: 4,
+            targetLength: 32,
+            strategy: STRATEGY_BTOPT,
+        };
+        let mut storage = MaybeUninit::<ZSTD_CCtx_params>::zeroed();
+        let params = storage.as_mut_ptr();
+
+        unsafe {
+            (*params).format = 1;
+            (*params).customMem.opaque = ptr::dangling_mut::<c_void>();
+            (*params).ldmParams.hashLog = 99;
+
+            ZSTD_rust_makeCCtxParamsFromCParams(params, &cparams);
+
+            assert_eq!((*params).cParams, cparams);
+            assert_eq!((*params).compressionLevel, DEFAULT_CLEVEL);
+            assert_eq!((*params).fParams.contentSizeFlag, 1);
+            assert_eq!((*params).fParams.checksumFlag, 0);
+            assert_eq!((*params).fParams.noDictIDFlag, 0);
+            assert_eq!((*params).ldmParams.enableLdm, ZSTD_RUST_PS_ENABLE);
+            assert_eq!((*params).ldmParams.hashLog, 0);
+            assert_eq!((*params).postBlockSplitter, ZSTD_RUST_PS_ENABLE);
+            assert_eq!((*params).useRowMatchFinder, ZSTD_RUST_PS_DISABLE);
+            assert_eq!((*params).validateSequences, 0);
+            assert_eq!((*params).maxBlockSize, BLOCKSIZE_MAX);
+            assert_eq!((*params).searchForExternalRepcodes, ZSTD_RUST_PS_DISABLE);
+            assert_eq!((*params).format, 0);
+            assert!((*params).customMem.opaque.is_null());
+        }
+    }
+
     #[test]
     fn advanced_init_resolves_policy_and_resets_internal_fields() {
         let cases = [