fix(format): keep maxshape == shape datasets contiguous

Any maxshape forced chunked storage, even one equal to the shape, which cannot grow. h5py and the library store such a dataset contiguously; we now do too unless chunks (or a filter) are requested. Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
2026-09-25 21:15:55 -05:00
parent 1dba7b465a
commit f5505fb03d
2 changed files with 50 additions and 1 deletions
@@ -547,3 +547,47 @@ fn btree_v2_index_past_one_leaf_is_refused() {
    let dir = tempfile::tempdir().unwrap();
    assert!(b.write(dir.path().join("too_many.h5")).is_err());
 }
+
+/// A maxshape equal to the shape cannot grow, so it needs no chunks: the
+/// dataset stays contiguous (as h5py makes it) unless chunks are requested.
+#[test]
+fn maxshape_equal_to_shape_stays_contiguous() {
+    let dir = tempfile::tempdir().unwrap();
+    let path = dir.path().join("ms_eq.h5");
+    let data: Vec<i32> = (0..40).collect();
+    let mut b = FileBuilder::new();
+    b.create_dataset("plain")
+        .with_i32_data(&data)
+        .with_shape(&[40])
+        .with_maxshape(&[40]);
+    b.create_dataset("chunked")
+        .with_i32_data(&data)
+        .with_shape(&[40])
+        .with_maxshape(&[40])
+        .with_chunks(&[8]);
+    b.write(&path).unwrap();
+
+    let file = File::open(&path).unwrap();
+    let plain = file.dataset("plain").unwrap();
+    assert_eq!(plain.read_i32().unwrap(), data);
+    assert_eq!(plain.max_dimensions().unwrap(), Some(vec![40]));
+    assert!(
+        plain.read_raw_ref().unwrap().is_some(),
+        "maxshape == shape should be contiguous"
+    );
+    let chunked = file.dataset("chunked").unwrap();
+    assert_eq!(chunked.read_i32().unwrap(), data);
+    assert!(chunked.read_raw_ref().unwrap().is_none());
+
+    skip_if_no_python!();
+    let out = run_python(&format!(
+        "import h5py, numpy as np\n\
+         f = h5py.File(r'{}', 'r')\n\
+         for n in ('plain', 'chunked'):\n\
+         \x20   d = f[n]\n\
+         \x20   assert np.array_equal(d[()], np.arange(40, dtype='i4')), n\n\
+         \x20   print(n, d.chunks, d.maxshape)\n",
+        path.display()
+    ));
+    assert_eq!(out, "plain None (40,)\nchunked (8,) (40,)");
+}