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docs: add roadmap page outlining future plans#223
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@d-v-b d-v-b commented Jul 15, 2026

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🤖 AI text below 🤖

Adds a Roadmap page to the documentation outlining future plans and intended changes to the library.

What's in the page

  • Where we are — the 3.0 redesign goals and the resolved 2.x → 3.x transition.
  • Goals — the "v4" body of work, sloganized as "support a Zarr-based Python ecosystem for chunked arrays".
  • The Zarr stack — the seven-level model (conventions → metadata) and the package-per-level direction.
  • What we intend to change — one summary per theme: functional core, hierarchy layer, codecs, stores, performance, lazy indexing, data types, device-agnostic IO, observability, configuration, consolidated metadata, coordinated writes, missing APIs.
  • How the work will be released — three parallel streams: additive 3.x minors, deprecation accumulation, and one minimal removals-only 4.0.0; plus backwards-compatibility commitments, the lazy default-flip decision point, and out-of-scope items.
  • How to get involved.

Notes

  • The page deliberately contains no links to live content in the planning repository — only a single italicized provenance note at the top tracing the roadmap's history to d-v-b/zarr-python-planning.
  • Added to the mkdocs nav between Release Notes and Contributing, plus a towncrier doc changelog entry.
  • Verified with hatch --env docs run build: builds clean, no warnings for the new page.

🤖 Generated with Claude Code

ilan-gold and others added 18 commits July 14, 2026 15:13
Adds a Roadmap page to the documentation describing the goals for the
next major cycle of work ("v4"), the intended changes per theme, and
the three-stream release model (additive minors, deprecations, one
minimal removals-only major).

Assisted-by: ClaudeCode:claude-fable-5
* chore(deps): bump the actions group across 1 directory with 8 updates (#176)

Bumps the actions group with 8 updates in the / directory:

| Package | From | To |
| --- | --- | --- |
| [prefix-dev/setup-pixi](https://github.com/prefix-dev/setup-pixi) | `0.9.5` | `0.9.6` |
| [codecov/codecov-action](https://github.com/codecov/codecov-action) | `6.0.0` | `6.0.1` |
| [github/issue-metrics](https://github.com/github/issue-metrics) | `4.2.2` | `4.2.7` |
| [j178/prek-action](https://github.com/j178/prek-action) | `2.0.3` | `2.0.4` |
| [actions/upload-artifact](https://github.com/actions/upload-artifact) | `7.0.0` | `7.0.1` |
| [actions/download-artifact](https://github.com/actions/download-artifact) | `7.0.0` | `8.0.1` |
| [pypa/gh-action-pypi-publish](https://github.com/pypa/gh-action-pypi-publish) | `1.13.0` | `1.14.0` |
| [zizmorcore/zizmor-action](https://github.com/zizmorcore/zizmor-action) | `0.5.3` | `0.5.6` |



Updates `prefix-dev/setup-pixi` from 0.9.5 to 0.9.6
- [Release notes](https://github.com/prefix-dev/setup-pixi/releases)
- [Commits](prefix-dev/setup-pixi@1b2de7f...5185adf)

Updates `codecov/codecov-action` from 6.0.0 to 6.0.1
- [Release notes](https://github.com/codecov/codecov-action/releases)
- [Changelog](https://github.com/codecov/codecov-action/blob/main/CHANGELOG.md)
- [Commits](codecov/codecov-action@57e3a13...e79a696)

Updates `github/issue-metrics` from 4.2.2 to 4.2.7
- [Release notes](https://github.com/github/issue-metrics/releases)
- [Commits](github-community-projects/issue-metrics@c9e9838...1e38d5e)

Updates `j178/prek-action` from 2.0.3 to 2.0.4
- [Release notes](https://github.com/j178/prek-action/releases)
- [Commits](j178/prek-action@6ad8027...bdca6f1)

Updates `actions/upload-artifact` from 7.0.0 to 7.0.1
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](actions/upload-artifact@v7...043fb46)

Updates `actions/download-artifact` from 7.0.0 to 8.0.1
- [Release notes](https://github.com/actions/download-artifact/releases)
- [Commits](actions/download-artifact@v7...3e5f45b)

Updates `pypa/gh-action-pypi-publish` from 1.13.0 to 1.14.0
- [Release notes](https://github.com/pypa/gh-action-pypi-publish/releases)
- [Commits](pypa/gh-action-pypi-publish@v1.13.0...cef2210)

Updates `zizmorcore/zizmor-action` from 0.5.3 to 0.5.6
- [Release notes](https://github.com/zizmorcore/zizmor-action/releases)
- [Commits](zizmorcore/zizmor-action@b1d7e1f...5f14fd0)

---
updated-dependencies:
- dependency-name: prefix-dev/setup-pixi
  dependency-version: 0.9.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: actions
- dependency-name: codecov/codecov-action
  dependency-version: 6.0.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: actions
- dependency-name: github/issue-metrics
  dependency-version: 4.2.7
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: actions
- dependency-name: j178/prek-action
  dependency-version: 2.0.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: actions
- dependency-name: actions/upload-artifact
  dependency-version: 7.0.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: actions
- dependency-name: actions/download-artifact
  dependency-version: 8.0.1
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: actions
- dependency-name: pypa/gh-action-pypi-publish
  dependency-version: 1.14.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: actions
- dependency-name: zizmorcore/zizmor-action
  dependency-version: 0.5.6
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: actions
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

* fix: byte-order handling for structured dtypes in the bytes codec (#220)

* fix: byte-order handling for structured dtypes in the bytes codec

The bytes codec neither byte-swapped structured-dtype fields to its
configured endian on encode (numpy reports byteorder '|' for void
dtypes, so the top-level byteorder comparison never detected a
mismatch) nor honored its endian when decoding, silently corrupting
any structured data whose field byte order differed from the stored
one (e.g. virtual references to external big-endian data).

Encode now detects byte-order mismatches by comparing full dtypes via
newbyteorder, and decode reinterprets raw bytes in the stored byte
order before converting to the data type's declared byte order, so the
stored layout (codec state) and the in-memory layout (array data type)
are independent.

Closes zarr-developers#4141

Assisted-by: ClaudeCode:claude-fable-5

* test: fold structured byte-order cases into existing bytes codec tests

Extend test_endian's parametrization with structured dtypes and
test_bytes_codec_sync_roundtrip with endian/dtype parametrization plus
stored-layout and decoded-dtype assertions, instead of adding parallel
test functions for the same properties.

Assisted-by: ClaudeCode:claude-fable-5

* refactor: rename stored_dtype to view_dtype in BytesCodec decode

The variable is the dtype used to view the raw chunk bytes (byte order
from the codec's endian configuration), not a property of the stored
data or of the returned buffer, which always carries the array's
declared dtype.

Assisted-by: ClaudeCode:claude-fable-5

* docs: note that the decode-side byte-order conversion copies the chunk

Assisted-by: ClaudeCode:claude-fable-5

* docs: 3.3.0 release notes

Add missing changelog fragments for zarr-developers#3955 (datetime64/timedelta64 V3
metadata types), zarr-developers#3966 (writes to 0-dimensional sharded arrays), and the
public alias renames that accompanied the zarr-developers#3963/zarr-developers#3968 enum deprecations,
then build the 3.3.0 release notes with towncrier, consuming all
fragments accumulated since v3.2.1.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
* chore: CI worfklows for missing docs and RST docstrings

* Add linter for docs

* Add link checking workflow

* fix links

* fix: apply suggestions from code review

* refactor: readability improvements

* chore: switch lychee action to opening issue on failure

---------

Co-authored-by: Davis Bennett <davis.v.bennett@gmail.com>
…4153)

* chore: cleanup indentation and guidance for release

* Make explanation a comment
…zarr-developers#4152)

Bumps the actions group with 6 updates in the / directory:

| Package | From | To |
| --- | --- | --- |
| [actions/checkout](https://github.com/actions/checkout) | `6.0.3` | `7.0.0` |
| [astral-sh/setup-uv](https://github.com/astral-sh/setup-uv) | `8.2.0` | `8.3.2` |
| [CodSpeedHQ/action](https://github.com/codspeedhq/action) | `4.18.1` | `4.18.5` |
| [github-community-projects/issue-metrics](https://github.com/github-community-projects/issue-metrics) | `4.2.8` | `5.0.0` |
| [lycheeverse/lychee-action](https://github.com/lycheeverse/lychee-action) | `2.8.0` | `2.9.0` |
| [actions/labeler](https://github.com/actions/labeler) | `6.1.0` | `6.2.0` |



Updates `actions/checkout` from 6.0.3 to 7.0.0
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v6.0.3...9c091bb)

Updates `astral-sh/setup-uv` from 8.2.0 to 8.3.2
- [Release notes](https://github.com/astral-sh/setup-uv/releases)
- [Commits](astral-sh/setup-uv@fac544c...11f9893)

Updates `CodSpeedHQ/action` from 4.18.1 to 4.18.5
- [Release notes](https://github.com/codspeedhq/action/releases)
- [Changelog](https://github.com/CodSpeedHQ/action/blob/main/CHANGELOG.md)
- [Commits](CodSpeedHQ/action@a4a36bb...f99becd)

Updates `github-community-projects/issue-metrics` from 4.2.8 to 5.0.0
- [Release notes](https://github.com/github-community-projects/issue-metrics/releases)
- [Commits](github-community-projects/issue-metrics@44173f9...df8c49d)

Updates `lycheeverse/lychee-action` from 2.8.0 to 2.9.0
- [Release notes](https://github.com/lycheeverse/lychee-action/releases)
- [Commits](lycheeverse/lychee-action@8646ba3...e747777)

Updates `actions/labeler` from 6.1.0 to 6.2.0
- [Release notes](https://github.com/actions/labeler/releases)
- [Commits](actions/labeler@f27b608...b8dd2d9)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: 7.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: actions
- dependency-name: actions/labeler
  dependency-version: 6.2.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: actions
- dependency-name: astral-sh/setup-uv
  dependency-version: 8.3.2
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: actions
- dependency-name: CodSpeedHQ/action
  dependency-version: 4.18.5
  dependency-type: direct:production
  update-type: version-update:semver-patch
  dependency-group: actions
- dependency-name: github-community-projects/issue-metrics
  dependency-version: 5.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
  dependency-group: actions
- dependency-name: lycheeverse/lychee-action
  dependency-version: 2.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: actions
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
* fix: byte-order handling for structured dtypes in the bytes codec (#220)

* fix: byte-order handling for structured dtypes in the bytes codec

The bytes codec neither byte-swapped structured-dtype fields to its
configured endian on encode (numpy reports byteorder '|' for void
dtypes, so the top-level byteorder comparison never detected a
mismatch) nor honored its endian when decoding, silently corrupting
any structured data whose field byte order differed from the stored
one (e.g. virtual references to external big-endian data).

Encode now detects byte-order mismatches by comparing full dtypes via
newbyteorder, and decode reinterprets raw bytes in the stored byte
order before converting to the data type's declared byte order, so the
stored layout (codec state) and the in-memory layout (array data type)
are independent.

Closes zarr-developers#4141

Assisted-by: ClaudeCode:claude-fable-5

* test: fold structured byte-order cases into existing bytes codec tests

Extend test_endian's parametrization with structured dtypes and
test_bytes_codec_sync_roundtrip with endian/dtype parametrization plus
stored-layout and decoded-dtype assertions, instead of adding parallel
test functions for the same properties.

Assisted-by: ClaudeCode:claude-fable-5

* refactor: rename stored_dtype to view_dtype in BytesCodec decode

The variable is the dtype used to view the raw chunk bytes (byte order
from the codec's endian configuration), not a property of the stored
data or of the returned buffer, which always carries the array's
declared dtype.

Assisted-by: ClaudeCode:claude-fable-5

* docs: note that the decode-side byte-order conversion copies the chunk

Assisted-by: ClaudeCode:claude-fable-5

* fix(store): copy buffers on write in MemoryStore

Encoding an uncompressed chunk hands the store a zero-copy view of the
caller's array, and MemoryStore keeps whatever it is given alive in a
dict rather than serializing it. Mutating the source array after a write
therefore rewrote chunks already committed to the store, silently.

Stores that serialize on write (LocalStore, ZipStore, remote stores) are
unaffected, so they keep the full benefit of zarr-developers#3885. Only MemoryStore pays
the copy, and only where it was aliasing to begin with: an uncompressed
34 MB write goes from ~23 ms to ~39 ms, while compressed writes are
unchanged.

Copying at the store boundary rather than narrowing the fast path in
_merge_chunk_array also fixes the single-chunk case, which aliased in
v3.2.1 too.

Assisted-by: ClaudeCode:claude-opus-4.8

* docs: add changelog entry for MemoryStore buffer copy

Assisted-by: ClaudeCode:claude-opus-4.8

* docs: correct changelog
Co-authored-by: Max Jones <14077947+maxrjones@users.noreply.github.com>
Co-authored-by: Max Jones <14077947+maxrjones@users.noreply.github.com>
Co-authored-by: Max Jones <14077947+maxrjones@users.noreply.github.com>
…arr-developers#4165)

* fix: byte-order handling for structured dtypes in the bytes codec (#220)

* fix: byte-order handling for structured dtypes in the bytes codec

The bytes codec neither byte-swapped structured-dtype fields to its
configured endian on encode (numpy reports byteorder '|' for void
dtypes, so the top-level byteorder comparison never detected a
mismatch) nor honored its endian when decoding, silently corrupting
any structured data whose field byte order differed from the stored
one (e.g. virtual references to external big-endian data).

Encode now detects byte-order mismatches by comparing full dtypes via
newbyteorder, and decode reinterprets raw bytes in the stored byte
order before converting to the data type's declared byte order, so the
stored layout (codec state) and the in-memory layout (array data type)
are independent.

Closes zarr-developers#4141

Assisted-by: ClaudeCode:claude-fable-5

* test: fold structured byte-order cases into existing bytes codec tests

Extend test_endian's parametrization with structured dtypes and
test_bytes_codec_sync_roundtrip with endian/dtype parametrization plus
stored-layout and decoded-dtype assertions, instead of adding parallel
test functions for the same properties.

Assisted-by: ClaudeCode:claude-fable-5

* refactor: rename stored_dtype to view_dtype in BytesCodec decode

The variable is the dtype used to view the raw chunk bytes (byte order
from the codec's endian configuration), not a property of the stored
data or of the returned buffer, which always carries the array's
declared dtype.

Assisted-by: ClaudeCode:claude-fable-5

* docs: note that the decode-side byte-order conversion copies the chunk

Assisted-by: ClaudeCode:claude-fable-5

* fix(store): FsspecStore.close() no longer closes the filesystem

FsspecStore.close() closed the underlying filesystem's session, on the
premise that a store built by from_url "owns" the filesystem it created.
That premise does not hold: fsspec caches and shares filesystem
instances across callers (its instance cache keys on storage options,
not path), and users can hand one filesystem to many stores directly.
Closing one store therefore killed the session that sibling stores were
still using, and left the dead filesystem in fsspec's cache for later
callers.

Determining whether a filesystem is actually shared requires reaching
into fsspec's private instance cache (_cache, _fs_token, cachable) and
walking wrapper chains for caching/proxy filesystems — an implementation
detail that leaks upward and that we would have to keep in sync with
fsspec forever, getting it subtly wrong in between. The wrapper case
alone (simplecache::/dir://) already slipped through a cache-membership
check.

The filesystem's lifecycle is simply not the store's to manage. This
removes the ownership model added in the unreleased zarr-developersgh-4003: no _owns_fs,
no _close_fs, no ownership transfer in with_read_only, and close() just
marks the store not-open. The only thing given up is suppressing an
"Unclosed client session" ResourceWarning, which was true anyway — the
session belongs to a cached filesystem that outlives the store.

Since zarr-developersgh-4003 never shipped (latest release is v3.2.1), its changelog
fragment is removed rather than superseded.

Assisted-by: ClaudeCode:claude-opus-4.8

* test: skip with_read_only fs test when AsyncFileSystemWrapper is absent

test_with_read_only_shares_filesystem replaced an ownership test that
carried a guard for fsspec < 2024.12.0, and the guard was dropped in the
rewrite. The test still opens a file:// URL, which needs
AsyncFileSystemWrapper, so it failed the min_deps job.

Assisted-by: ClaudeCode:claude-opus-4.8

* docs: correct changelog claim about zarr-developersgh-4003 release status

The fragment said zarr-developersgh-4003 was unreleased with no net change for
released versions. Its text is already in the staged 3.3.0 release
notes, so the revert is a real behavior change for anyone relying on
close() releasing the session.

Assisted-by: ClaudeCode:claude-opus-4.8

* docs: remove changelog entry for unreleased versions
Co-authored-by: Max Jones <14077947+maxrjones@users.noreply.github.com>
The mkdocs-redirects plugin was generating a redirect stub for
roadmap.md pointing at the old v3.0.8 docs, which clobbered the new
roadmap page added in this PR. The developers/roadmap.html redirect is
kept so old links to the historical v3 design roadmap still resolve.

Assisted-by: ClaudeCode:claude-fable-5
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3 participants