chore(rust): bump rand 0.8 -> 0.10, rand_xoshiro 0.6 -> 0.8

CHANGELOG.md

@@ -5,6 +5,11 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+- **Rust dependency upgrades**: bumped `rand` 0.8 → 0.10 and `rand_xoshiro` 0.6 → 0.8 in the Rust backend (the two crates are coupled through `rand_core` and must move together). MSRV bumped from Rust 1.84 → 1.85 to satisfy the new dependency requirements. Three call sites in `rust/src/bootstrap.rs` updated for the `rand 0.9` API rename: `gen::<bool>()` → `random::<bool>()`, `gen::<f64>()` → `random::<f64>()`, `gen_range(0..6)` → `random_range(0..6)`. **Webb wild bootstrap byte stream shifted** as a side effect: `rand 0.9` reworked the internal algorithm for `random_range` (improved rejection sampling), so `Xoshiro256PlusPlus::seed_from_u64(seed)` followed by `random_range(0..6)` consumes RNG bytes differently than the old `gen_range(0..6)` did. Distributional properties of Webb weights are unchanged (still uniform over the 6-point support); aggregate inference (SE, p-values, CI) converges to the same values for any reasonable `n_bootstrap`. Rademacher and Mammen byte streams are bit-identical to the prior release. Anyone with a saved Rust+Webb baseline pinning specific seeded results will see different numbers; the regression test suite uses within-build seed-reproducibility (not cross-version baselines) so all internal tests pass unchanged. New regression guard `TestRustBackend::test_bootstrap_weights_bit_identity_snapshot` pins fixed-seed weights for all three weight types, so any future RNG drift fails loudly with a localized error message.
+
 ## [3.3.1] - 2026-04-25
 
 ### Changed

rust/Cargo.toml

@@ -2,7 +2,7 @@
 name = "diff_diff_rust"
 version = "3.3.1"
 edition = "2021"
-rust-version = "1.84"
+rust-version = "1.85"
 description = "Rust backend for diff-diff DiD library"
 license = "MIT"
 
@@ -25,8 +25,8 @@ openblas = ["ndarray/blas"]
 pyo3 = "0.28"
 numpy = "0.28"
 ndarray = { version = "0.17", features = ["rayon"] }
-rand = "0.8"
-rand_xoshiro = "0.6"
+rand = "0.10"
+rand_xoshiro = "0.8"
 rayon = "1.8"
 
 # Pure Rust linear algebra for SVD/matrix inversion (no external deps).

rust/src/bootstrap.rs

@@ -67,7 +67,7 @@ fn generate_rademacher_batch(n_bootstrap: usize, n_units: usize, seed: u64) -> A
         .for_each(|(i, mut row)| {
             let mut rng = Xoshiro256PlusPlus::seed_from_u64(seed.wrapping_add(i as u64));
             for elem in row.iter_mut() {
-                *elem = if rng.gen::<bool>() { 1.0 } else { -1.0 };
+                *elem = if rng.random::<bool>() { 1.0 } else { -1.0 };
             }
         });
 
@@ -102,7 +102,7 @@ fn generate_mammen_batch(n_bootstrap: usize, n_units: usize, seed: u64) -> Array
         .for_each(|(i, mut row)| {
             let mut rng = Xoshiro256PlusPlus::seed_from_u64(seed.wrapping_add(i as u64));
             for elem in row.iter_mut() {
-                *elem = if rng.gen::<f64>() < prob_neg {
+                *elem = if rng.random::<f64>() < prob_neg {
                     val_neg
                 } else {
                     val_pos
@@ -142,7 +142,7 @@ fn generate_webb_batch(n_bootstrap: usize, n_units: usize, seed: u64) -> Array2<
             let mut rng = Xoshiro256PlusPlus::seed_from_u64(seed.wrapping_add(i as u64));
             for elem in row.iter_mut() {
                 // Uniform selection: generate integer 0-5, index into weights_table
-                let bucket = rng.gen_range(0..6);
+                let bucket = rng.random_range(0..6);
                 *elem = weights_table[bucket];
             }
         });

tests/test_rust_backend.py

@@ -100,6 +100,57 @@ def test_bootstrap_different_seeds(self):
         weights2 = generate_bootstrap_weights_batch(100, 50, "rademacher", 43)
         assert not np.array_equal(weights1, weights2)
 
+    def test_bootstrap_weights_bit_identity_snapshot(self):
+        """Pin fixed-seed bootstrap weight output byte-for-byte.
+
+        Regression guard against silent RNG output drift across
+        `rand` / `rand_xoshiro` crate upgrades. Distributional moment
+        tests would not catch a byte shift that preserves the
+        distribution (e.g. `rand 0.9`'s `random_range` algorithm
+        change relative to `rand 0.8`'s `gen_range`).
+
+        If this test fails after a Rust dependency bump, the byte stream
+        has shifted. Decide deliberately whether to accept the new
+        baseline (regenerate these values) or pin to a compatible
+        crate version.
+        """
+        from diff_diff._rust_backend import generate_bootstrap_weights_batch
+
+        # Captured under rand 0.10 + rand_xoshiro 0.8 with seed=42.
+        # Rademacher and Mammen bytes match rand 0.8 + rand_xoshiro 0.6;
+        # Webb bytes shifted in the rand 0.9 random_range algorithm change.
+        expected = {
+            "rademacher": np.array(
+                [
+                    [1.0, -1.0, 1.0, 1.0],
+                    [-1.0, 1.0, 1.0, 1.0],
+                ]
+            ),
+            "mammen": np.array(
+                [
+                    [1.618033988749895, -0.6180339887498949, 1.618033988749895, -0.6180339887498949],
+                    [-0.6180339887498949, -0.6180339887498949, 1.618033988749895, 1.618033988749895],
+                ]
+            ),
+            "webb": np.array(
+                [
+                    [1.0, -1.0, 1.224744871391589, 1.0],
+                    [-1.0, 0.7071067811865476, 1.224744871391589, 1.224744871391589],
+                ]
+            ),
+        }
+        for weight_type, expected_arr in expected.items():
+            actual = generate_bootstrap_weights_batch(2, 4, weight_type, 42)
+            # Strict bit-identity: the snapshot values are either exact
+            # (Rademacher = +/-1.0) or computed once via correctly-rounded
+            # IEEE 754 sqrt in Rust (Mammen, Webb), so cross-platform
+            # bit-equality holds on conformant hardware.
+            np.testing.assert_array_equal(
+                actual,
+                expected_arr,
+                err_msg=f"{weight_type} bootstrap weights drifted from pinned baseline",
+            )
+
     # =========================================================================
     # Synthetic Weight Tests
     # =========================================================================