feat(cli): move shared decompression scheduling into Rust

Move the shared-destination branch of FIO_decompressMultipleFilenames into a Rust-owned scheduler. Preserve source order, destination propagation, cursor advancement, success counting, aggregate errors, and C-owned source/format/resource behavior including --rm and output close handling.

Test Plan:
- ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/Cargo.toml decompression_multiple_shared_destination -- --test-threads=1
- ulimit -v 41943040; make -B -C programs -j1 zstd
- ulimit -v 41943040; make -B -C tests -j1 test-cli-tests

programs/fileio.c

@@ -1179,6 +1179,35 @@ typedef char FIO_rust_compress_multiple_separate_projection_size[
 int FIO_rust_compressMultipleSeparateFilenames(
         const FIO_rust_compress_multiple_separate_projection_t* projection);
 
+typedef int (*FIO_rust_decompress_multiple_file_fn)(
+        void* opaque, const char* outFileName, const char* srcFileName);
+typedef struct {
+    void* fCtx;
+    const char** srcNamesTable;
+    const char* outFileName;
+    void* opaque;
+    FIO_rust_decompress_multiple_file_fn decompressFile;
+} FIO_rust_decompress_multiple_projection_t;
+typedef char FIO_rust_decompress_multiple_fctx_offset[
+        (offsetof(FIO_rust_decompress_multiple_projection_t, fCtx) == 0) ? 1 : -1];
+typedef char FIO_rust_decompress_multiple_input_names_offset[
+        (offsetof(FIO_rust_decompress_multiple_projection_t, srcNamesTable)
+         == sizeof(void*)) ? 1 : -1];
+typedef char FIO_rust_decompress_multiple_output_name_offset[
+        (offsetof(FIO_rust_decompress_multiple_projection_t, outFileName)
+         == 2 * sizeof(void*)) ? 1 : -1];
+typedef char FIO_rust_decompress_multiple_opaque_offset[
+        (offsetof(FIO_rust_decompress_multiple_projection_t, opaque)
+         == 3 * sizeof(void*)) ? 1 : -1];
+typedef char FIO_rust_decompress_multiple_callback_offset[
+        (offsetof(FIO_rust_decompress_multiple_projection_t, decompressFile)
+         == 4 * sizeof(void*)) ? 1 : -1];
+typedef char FIO_rust_decompress_multiple_projection_size[
+        (sizeof(FIO_rust_decompress_multiple_projection_t)
+         == 4 * sizeof(void*) + sizeof(FIO_rust_decompress_multiple_file_fn)) ? 1 : -1];
+int FIO_rust_decompressMultipleFilenames(
+        const FIO_rust_decompress_multiple_projection_t* projection);
+
 enum {
     FIO_RUST_ZSTD_OK = 0,
     FIO_RUST_ZSTD_COMPRESS_ERROR = 1,
@@ -3838,6 +3867,23 @@ static int FIO_decompressSrcFile(FIO_ctx_t* const fCtx, FIO_prefs_t* const prefs
     return result;
 }
 
+typedef struct {
+    FIO_ctx_t* fCtx;
+    FIO_prefs_t* prefs;
+    dRess_t* ress;
+} FIO_rust_decompress_multiple_context_t;
+
+/* Keep source opening, format dispatch, diagnostics, and --rm in C. */
+static int FIO_rust_decompressMultipleFileCallback(void* opaque,
+                                                    const char* outFileName,
+                                                    const char* srcFileName)
+{
+    FIO_rust_decompress_multiple_context_t* const context =
+        (FIO_rust_decompress_multiple_context_t*)opaque;
+    return FIO_decompressSrcFile(
+        context->fCtx, context->prefs, *context->ress, outFileName, srcFileName);
+}
+
 
 
 int FIO_decompressFilename(FIO_ctx_t* const fCtx, FIO_prefs_t* const prefs,
@@ -3921,10 +3967,15 @@ FIO_decompressMultipleFilenames(FIO_ctx_t* const fCtx,
             if (dstFile == 0) EXM_THROW(19, "cannot open %s", outFileName);
             AIO_WritePool_setFile(ress.writeCtx, dstFile);
         }
-        for (; fCtx->currFileIdx < fCtx->nbFilesTotal; fCtx->currFileIdx++) {
+        {
-            status = FIO_decompressSrcFile(fCtx, prefs, ress, outFileName, srcNamesTable[fCtx->currFileIdx]);
+            FIO_rust_decompress_multiple_context_t callbackContext = {
-            if (!status) fCtx->nbFilesProcessed++;
+                fCtx, prefs, &ress
-            error |= status;
+            };
+            FIO_rust_decompress_multiple_projection_t projection = {
+                fCtx, srcNamesTable, outFileName,
+                &callbackContext, FIO_rust_decompressMultipleFileCallback
+            };
+            error = FIO_rust_decompressMultipleFilenames(&projection);
         }
         if ((!prefs->testMode) && (AIO_WritePool_closeFile(ress.writeCtx)))
             EXM_THROW(72, "Write error : %s : cannot properly close output file",

rust/src/fileio_asyncio.rs

@@ -332,6 +332,42 @@ const _: () = {
     );
 };
 
+pub type FIO_rust_decompress_multiple_file_fn =
+    unsafe extern "C" fn(*mut c_void, *const c_char, *const c_char) -> c_int;
+
+/// Rust owns only the shared-destination file iteration and aggregate error
+/// handling. C retains source opening, format dispatch, diagnostics, and
+/// source removal through the per-source callback.
+#[repr(C)]
+pub struct FIO_rust_decompress_multiple_projection_t {
+    pub f_ctx: *mut c_void,
+    pub src_names_table: *const *const c_char,
+    pub out_file_name: *const c_char,
+    pub opaque: *mut c_void,
+    pub decompress_file: Option<FIO_rust_decompress_multiple_file_fn>,
+}
+const _: () = {
+    assert!(std::mem::offset_of!(FIO_rust_decompress_multiple_projection_t, f_ctx) == 0);
+    assert!(
+        std::mem::offset_of!(FIO_rust_decompress_multiple_projection_t, src_names_table)
+            == size_of::<usize>()
+    );
+    assert!(
+        std::mem::offset_of!(FIO_rust_decompress_multiple_projection_t, out_file_name)
+            == 2 * size_of::<usize>()
+    );
+    assert!(
+        std::mem::offset_of!(FIO_rust_decompress_multiple_projection_t, opaque)
+            == 3 * size_of::<usize>()
+    );
+    assert!(
+        std::mem::offset_of!(FIO_rust_decompress_multiple_projection_t, decompress_file)
+            == 4 * size_of::<usize>()
+    );
+    assert!(size_of::<FIO_rust_decompress_multiple_file_fn>() == size_of::<usize>());
+    assert!(size_of::<FIO_rust_decompress_multiple_projection_t>() == 5 * size_of::<usize>());
+};
+
 pub const FIO_RUST_ZSTD_OK: c_int = 0;
 pub const FIO_RUST_ZSTD_COMPRESS_ERROR: c_int = 1;
 pub const FIO_RUST_ZSTD_INCOMPLETE_INPUT: c_int = 2;
@@ -2272,6 +2308,42 @@ pub unsafe extern "C" fn FIO_rust_compressMultipleSeparateFilenames(
     error
 }
 
+/// Iterate files that share one already-open decompression destination. The
+/// C callback retains source opening, format dispatch, diagnostics, and
+/// `--rm`; Rust preserves the non-short-circuiting loop and counter updates.
+#[no_mangle]
+pub unsafe extern "C" fn FIO_rust_decompressMultipleFilenames(
+    projection: *const FIO_rust_decompress_multiple_projection_t,
+) -> c_int {
+    assert!(!projection.is_null());
+    let projection = unsafe { &*projection };
+    assert!(!projection.f_ctx.is_null());
+    assert!(!projection.src_names_table.is_null());
+    assert!(!projection.out_file_name.is_null());
+    let decompress_file = projection
+        .decompress_file
+        .expect("shared-destination decompression callback is required");
+
+    let f_ctx = projection.f_ctx.cast::<FIO_rust_compression_context_t>();
+    let mut error = 0;
+    while unsafe { (*f_ctx).currFileIdx < (*f_ctx).nbFilesTotal } {
+        let file_index = unsafe { (*f_ctx).currFileIdx as usize };
+        let src_file_name = unsafe { *projection.src_names_table.add(file_index) };
+        let status =
+            unsafe { decompress_file(projection.opaque, projection.out_file_name, src_file_name) };
+        if status == 0 {
+            unsafe {
+                (*f_ctx).nbFilesProcessed = (*f_ctx).nbFilesProcessed.wrapping_add(1);
+            }
+        }
+        error |= status;
+        unsafe {
+            (*f_ctx).currFileIdx = (*f_ctx).currFileIdx.wrapping_add(1);
+        }
+    }
+    error
+}
+
 #[inline]
 fn zstd_adapt_level(projection: &FIO_rust_zstd_adapt_projection_t, slower: bool) -> c_int {
     if slower {
@@ -4573,6 +4645,29 @@ mod tests {
         status
     }
 
+    #[derive(Default)]
+    struct MultipleDecompressionState {
+        sources: Vec<*const c_char>,
+        destinations: Vec<*const c_char>,
+        statuses: Vec<c_int>,
+    }
+
+    unsafe extern "C" fn record_multiple_decompression_file(
+        opaque: *mut c_void,
+        destination: *const c_char,
+        source: *const c_char,
+    ) -> c_int {
+        let state = unsafe { &mut *opaque.cast::<MultipleDecompressionState>() };
+        let status = state
+            .statuses
+            .get(state.sources.len())
+            .copied()
+            .unwrap_or(0);
+        state.sources.push(source);
+        state.destinations.push(destination);
+        status
+    }
+
     #[test]
     fn compression_multiple_separate_destinations_preserves_order_and_counters() {
         let source_names = [c"zero".as_ptr(), c"one".as_ptr(), c"two".as_ptr()];
@@ -4707,6 +4802,76 @@ mod tests {
         assert_eq!(context.nbFilesProcessed, 4);
     }
 
+    #[test]
+    fn decompression_multiple_shared_destination_preserves_order_and_counters() {
+        let source_names = [c"zero".as_ptr(), c"one".as_ptr(), c"two".as_ptr()];
+        let destination = c"archive";
+        let mut context = FIO_rust_compression_context_t {
+            nbFilesTotal: 3,
+            hasStdinInput: 0,
+            hasStdoutOutput: 0,
+            currFileIdx: 1,
+            nbFilesProcessed: 5,
+            totalBytesInput: 0,
+            totalBytesOutput: 0,
+        };
+        let mut state = MultipleDecompressionState {
+            statuses: vec![0, 0],
+            ..MultipleDecompressionState::default()
+        };
+        let projection = FIO_rust_decompress_multiple_projection_t {
+            f_ctx: (&mut context as *mut FIO_rust_compression_context_t).cast(),
+            src_names_table: source_names.as_ptr(),
+            out_file_name: destination.as_ptr(),
+            opaque: (&mut state as *mut MultipleDecompressionState).cast(),
+            decompress_file: Some(record_multiple_decompression_file),
+        };
+
+        assert_eq!(
+            unsafe { FIO_rust_decompressMultipleFilenames(&projection) },
+            0
+        );
+        assert_eq!(state.sources, vec![source_names[1], source_names[2]]);
+        assert_eq!(state.destinations, vec![destination.as_ptr(); 2]);
+        assert_eq!(context.currFileIdx, 3);
+        assert_eq!(context.nbFilesProcessed, 7);
+    }
+
+    #[test]
+    fn decompression_multiple_shared_destination_accumulates_errors_without_short_circuiting() {
+        let source_names = [c"one".as_ptr(), c"two".as_ptr(), c"three".as_ptr()];
+        let destination = c"archive";
+        let mut context = FIO_rust_compression_context_t {
+            nbFilesTotal: 3,
+            hasStdinInput: 0,
+            hasStdoutOutput: 0,
+            currFileIdx: 0,
+            nbFilesProcessed: 4,
+            totalBytesInput: 0,
+            totalBytesOutput: 0,
+        };
+        let mut state = MultipleDecompressionState {
+            statuses: vec![1, 4, 2],
+            ..MultipleDecompressionState::default()
+        };
+        let projection = FIO_rust_decompress_multiple_projection_t {
+            f_ctx: (&mut context as *mut FIO_rust_compression_context_t).cast(),
+            src_names_table: source_names.as_ptr(),
+            out_file_name: destination.as_ptr(),
+            opaque: (&mut state as *mut MultipleDecompressionState).cast(),
+            decompress_file: Some(record_multiple_decompression_file),
+        };
+
+        assert_eq!(
+            unsafe { FIO_rust_decompressMultipleFilenames(&projection) },
+            1 | 4 | 2
+        );
+        assert_eq!(state.sources, source_names);
+        assert_eq!(state.destinations, vec![destination.as_ptr(); 3]);
+        assert_eq!(context.currFileIdx, 3);
+        assert_eq!(context.nbFilesProcessed, 4);
+    }
+
     struct ZstdProjectionState {
         input: [u8; 5],
         input_pos: usize,