#9972 keeps a JSON default object materialized once it observes a member
write (`data.foo = ...`), including through a named re-export. But the
object can also diverge from its split per-key exports by *escaping*
without a write we can see: aliasing (`const o = data`), being passed to
a function (`f(data)`), or dynamic indexing (`data[k]`). A later
`data.key` read then resolves to the stale split export.

Treat any bare-symbol reference to the default -- anything other than a
static `data.key` access, which is recorded as a `MemberExpr` -- as
non-splittable, in addition to the existing member writes. Fold the
per-reference classification into one whitelist helper
(`collect_non_splittable_json_defaults` / `json_default_made_non_splittable_by`
/ `json_default_canonical_ref`), replacing the write-only
`collect_json_default_imports_with_member_write`.

Add `json_default_mutation_bailout` covering alias, call-argument,
computed-write, named-re-export, and cross-module mutation escapes, plus
a still-splittable control. The `json_default_import` snapshot also drops
the redundant split for the whole-object-use `bailout.json` case.

#9972 keeps a JSON default object materialized once it observes a member
write (`data.foo = ...`), including through a named re-export. But the
object can also diverge from its split per-key exports by *escaping*
without a write we can see: aliasing (`const o = data`), being passed to
a function (`f(data)`), or dynamic indexing (`data[k]`). A later
`data.key` read then resolves to the stale split export.

Treat any bare-symbol reference to the default -- anything other than a
static `data.key` access, which is recorded as a `MemberExpr` -- as
non-splittable, in addition to the existing member writes. Fold the
per-reference classification into one whitelist helper
(`collect_non_splittable_json_defaults` / `json_default_made_non_splittable_by`
/ `json_default_canonical_ref`), replacing the write-only
`collect_json_default_imports_with_member_write`.

Add `json_default_mutation_bailout` covering alias, call-argument,
computed-write, named-re-export, and cross-module mutation escapes, plus
a still-splittable control. The `json_default_import` snapshot also drops
the redundant split for the whole-object-use `bailout.json` case.

…9996)

## What this solves

[#9972](#9972) keeps a JSON default object materialized (instead of splitting `data.key` reads into per-key exports) once it observes a member **write** — `data.foo = ...`, including through a named re-export. But the split optimization is equally unsound when the default object **escapes** without a write rolldown can see, and `data.key` reads then resolve to the stale split export instead of the live object:

- aliasing — `const o = data; o.foo = ...`
- call argument — `f(data)` where `f` mutates it
- dynamic index — `data[k] = ...`

Minimal reproduction (alias case) — **[live REPL](https://repl.rolldown.rs/#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)**:

```js
// data.json — { "value": "before" }
import data from './data.json';
const alias = data;            // `data` escapes
alias.value = 'after';         // mutate the shared object
data.value;                    // main: "before"  ❌   (should be "after")
```

On `main` the read is compiled to a bare `value` split const (`"before"`), divorced from the mutated object.

## The fix

Flip the JSON-default scan from a **blacklist** ("optimize unless we spot a write") to a **whitelist** ("only split when every reference to the default is a plain `data.key` read"). The enabling signal: a static `data.key` access is recorded as a `MemberExpr`, so **any bare-symbol reference** to the default binding is an escape we can't reason about — mark it non-splittable, in addition to the member writes #9972 already handles. The three ad-hoc helpers are folded into one classifier (`collect_non_splittable_json_defaults` / `json_default_made_non_splittable_by` / `json_default_canonical_ref`), replacing the write-only `collect_json_default_imports_with_member_write`.

This is free in practice: if the object escapes, the whole thing is already materialized, so no per-key tree-shaking was possible to begin with — bailing only changes *which* form is emitted, never what gets dropped.

## Alternatives explored

Continuing to extend the blacklist with more mutation patterns (the #9972 direction). Rejected — it is unsound by construction: every escape pattern not yet enumerated is a latent miscompile. The whitelist is sound by construction and strictly supersedes the write-only checks.

## Tests

`tree_shaking/json_default_escape_bailout` — an **executed** fixture (real runtime asserts) covering the two escape forms `main` still mis-optimizes: **aliasing** (`const o = data`) and **passing as a call argument** (`f(data)`). Both fail on `main` and pass here.

The other non-splittable categories are intentionally **not** duplicated — each already has dedicated coverage that passes on `main`:

- computed-write → `issues/9484_computed_write`
- named-re-export / cross-module write → `tree_shaking/json_default_import` (+ `issues/9484`)
- read-only split + tree-shake (no over-bail) → `tree_shaking/json_default_import` (`foo.json`)

The `json_default_import` snapshot also drops a now-redundant split for the whole-object-use `bailout.json` case.

Full `rolldown` suite: **1771 passed, 0 failed**; `clippy --deny warnings` clean.

## Reviewer attention

- The soundness of the *"bare `Symbol` = escape"* signal — i.e. that the scanner records static `x.key` accesses as `MemberExpr` and everything else (alias, arg, dynamic index, return) falls through to a bare `Symbol`.
- No over-bail: the read-only coverage above + full green suite confirm read-only JSON defaults still split and tree-shake unused keys.

## [1.1.4] - 2026-07-01

### 🚀 Features

- disable `experimental.lazyBarrel` by default (#10071) by @shulaoda

### 🐛 Bug Fixes

- dev: disable lazy barrel in dev mode (#10060) by @shulaoda
- generate: keep full JSON interface under preserveModules namespa… (#10056) by @IWANABETHATGUY
- check finalize_other_specifiers in its own Debug attribute (#10032) by @shulaoda
- serialize the KeepAssign unused minify option as "keep_assign" (#10031) by @shulaoda
- keep fragments after the newline fragment in MagicString::last_line (#10023) by @shulaoda
- generate: undeclared JSON named exports under preserveModules (#10020) (#10027) by @IWANABETHATGUY
- deconflict: rename CJS-wrapped locals that shadow chunk-root bindings (#9921) by @IWANABETHATGUY
- rolldown: keep entry facade when a shared chunk holds another entry's module (#9997) by @hyf0
- treeshake: also bail JSON default split when the object escapes (#9996) by @IWANABETHATGUY
- don't classify await in a strict-mode function as top-level await (#9987) by @shulaoda
- avoid spurious leading newline in addon hooks (banner/footer/intro/outro) (#9989) by @shulaoda
- handle JSON default mutation bailouts (#9972) by @TheAlexLichter
- plugin: make lazy hook metadata enumerable (#9991) by @TheAlexLichter
- dev: make init errors in lazy-compiled modules catchable (#9981) by @h-a-n-a
- treeshake: keep computed-key side effects on namespace member access (#9986) by @shulaoda
- binding: validate replace plugin delimiters length instead of panicking (#9984) by @shulaoda
- reconstruct nested rest patterns in into_expression (#9980) by @IWANABETHATGUY
- reconstruct rest patterns as spread in into_expression (#9976) by @shulaoda
- preserve export keyword on multi-declarator exports under keepNames (#9974) by @shulaoda
- deterministically keep the shortest name for deduplicated assets (#9948) by @x1024
- treeshake: apply @__NO_SIDE_EFFECTS__ to cross-chunk namespace calls (#9960) by @IWANABETHATGUY

### 🚜 Refactor

- drop redundant program scope enter/leave in finalizer (#10049) by @shulaoda
- deconflict: extract collect_chunk_scope_captured_names (#10006) by @IWANABETHATGUY
- unify pre-scan multi-declarator split into one decision site (#9982) by @IWANABETHATGUY
- common: return bool from SymbolRef::is_not_reassigned (#9962) by @IWANABETHATGUY

### 📚 Documentation

- rolldown: remove outdated comment for removing parenthesized expression (#10062) by @Dunqing
- use GitHub-flavored alert for Etiquette note in contribution guide (#10012) by @IWANABETHATGUY
- replace: explain the delimiters left and right boundaries (#9985) by @shulaoda
- ast-mutation: remove stale Address Use section after pre-scan refactor (#9983) by @IWANABETHATGUY
- remove fathom (#9968) by @mdong1909
- contribution-guide: code-format main branch references (#9966) by @IWANABETHATGUY
- contribution-guide: fix stale REPL note and tidy wording (#9957) by @hyf0
- contribution-guide: clarify when to discuss before opening a PR (#9955) by @hyf0

### ⚡ Performance

- disable preserve_parens across all parse paths (#10057) by @Dunqing
- common: inline declared_symbols with SmallVec (#9920) by @IWANABETHATGUY
- common: pack TaggedSymbolRef into 8 bytes (#9919) by @IWANABETHATGUY
- sourcemap: skip newline scan on the no-sourcemap join fast path (#9936) by @Boshen

### 🧪 Testing

- dev: error in lazy module should be catchable (#9975) by @sapphi-red
- dev: reject unknown lazy compile modules (#9969) by @sapphi-red

### ⚙️ Miscellaneous Tasks

- deps: update actions/cache action to v6 (#10001) by @renovate[bot]
- trigger vite ecosystem-ci from PR comments (#10058) by @shulaoda
- deps: update napi to v3.10.0 (#10063) by @renovate[bot]
- remove unused From impl for RolldownLabelSpan (#10055) by @shulaoda
- remove dead Diagnostic::with_kind method (#10054) by @shulaoda
- remove unused StatementExt methods (#10053) by @shulaoda
- remove unused ExpressionExt methods (#10052) by @shulaoda
- remove commented-out re_export_all_names field (#10051) by @shulaoda
- deps: update pnpm to v11.9.0 (#10047) by @renovate[bot]
- remove the unused BindingGenerateHmrPatchReturn napi type (#10034) by @shulaoda
- remove the dead inline_entry_chunk_wrapping scaffolding (#10037) by @shulaoda
- deps: bump oxc_resolver to 11.22.0 (#10045) by @Boshen
- remove never-constructed MatchImportKind::_Ignore variant (#10041) by @shulaoda
- remove the unused ScheduledBuild napi struct (#10033) by @shulaoda
- remove dead compute_hmr_update_single method (#10040) by @shulaoda
- drop the redundant visited.insert in manual code splitting (#10038) by @shulaoda
- remove the dead output_assets vector in render_chunk_to_assets (#10036) by @shulaoda
- remove the unused From<String>/Display impls for BindingLogLevel (#10035) by @shulaoda
- deps: upgrade oxc to 0.138.0 and migrate to per-type AST construction (#10018) by @shulaoda
- deps: update rust crates (#9911) by @renovate[bot]
- deps: update test262 submodule for tests (#10016) by @rolldown-guard[bot]
- deps: update github actions (#9999) by @renovate[bot]
- deps: update npm packages (#10000) by @renovate[bot]

### ◀️ Revert

- "fix(plugin): make lazy hook metadata enumerable (#9991)" (#10005) by @shulaoda

### ❤️ New Contributors

* @x1024 made their first contribution in [#9948](#9948)

Co-authored-by: shulaoda <165626830+shulaoda@users.noreply.github.com>