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# Releases
## svelte@5.56.0

### Minor Changes

- feat: allow declarations in the template
([#18282](#18282))

### Patch Changes

- perf: use `createElement` instead of `createElementNS` for HTML
elements ([#18262](#18262))

- perf: store `current_sources` as a `Set` for O(1) membership checks
([#18278](#18278))

- perf: deduplicate identical hoisted templates within a component
([#18320](#18320))

- perf: hoist `rest_props` exclude list as a module-scope `Set`
([#18252](#18252))

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Add support for Svelte 5 declaration tags — `{const x = expr}` and
`{let x = expr}` used directly in markup (no `@` prefix), introduced in
Svelte 5.56 (sveltejs/svelte#18282).

- AST: new `DeclarationTag` node + `DeclarationKind { Const, Let }`,
  mirroring the existing `ConstTag`.
- Parser: disambiguate `{const ...}`/`{let ...}` from ordinary
  expressions in `parse_expression_tag` via `peek_declaration_kind`
  (no lexer change — `const` already fires standalone via logos
  max-munch; `let` is matched by Ident text). Supports identifier,
  object `{a, b}`, and array `[a, b]`/`[head, ...tail]` targets
  (the latter via a `Text`-token-starting-with-`[` peek, since the
  lexer has no dedicated `LBracket`). Semicolons inside the tag are
  reported as errors. `{@const}` and `{constFoo}`/`{x}`/`{let}` are
  unaffected.
- Transformer: emit `const x = y;` / `let x = y;` in place, with a
  source mapping anchored to the post-keyword declaration text,
  matching the language-tools svelte2tsx reference.
- Diagnostics: declaration tags stay in the no-op group so runes in
  initializers (e.g. `{let s = $state(0)}`) are not falsely flagged.

Tests: 13 parser unit tests (both kinds, whitespace, object/array
destructuring, disambiguation, `{@const}` regression, semicolon ban,
in-`#each`), 4 parser + 6 transformer snapshots (incl. samples adapted
from language-tools ts-declaration-tag.v5 / declaration-tag-async.v5),
and corpus fixtures covering if/each/await/snippet/element/shadowing,
TS annotations + `$state`, and a must-not-panic invalid fixture.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>