## Summary

Optimize the nested scope symbol renaming pass by only processing
symbols whose names match a top-level canonical name in the same module.

- Collect canonical names of top-level symbols into a HashSet
- Only call `register_nested_scope_symbols` for nested symbols whose
names match a canonical name (or for CJS wrapped modules)
- Nested symbols that don't match any canonical name can safely shadow
cross-module top-level symbols via JavaScript's natural scoping rules

This is a follow-up optimization to #7867.

Also partially fixes
#6586 (comment)

## Test plan

- [x] Added new test case `nested_scope_same_module_conflict` to verify
the optimization behavior
- [x] Updated `nested_scope_rename_counter` test with improved comments
- [x] All existing tests pass

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Signed-off-by: Dunqing <[email protected]>
Co-authored-by: Claude Opus 4.5 <[email protected]>
Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
Co-authored-by: Copilot <[email protected]>
Co-authored-by: Yunfei He <[email protected]>
Co-authored-by: dalaoshu <[email protected]>

Note: waiting for oxc-project/oxc#18053 to merge
to unblock this (Edit: merged, and already released)

## Summary

Fixes: #6586


This PR refines the symbol renaming (deconflict) logic to correctly
handle both **top-level symbol conflicts** and **nested scope
shadowing**. The key insight is that these are two distinct problems
requiring different solutions.

Related fixes:

- #7859
- #7867 
- #7899 

This PR essentially reverts all the logic implemented in the previous
fixes while preserving the performance improvements introduced in #7867
(4%).

---

## 1. Top-Level Symbol Renaming

When bundling multiple modules into a single chunk, symbols with the
same name need unique identifiers.

**Example:**
```js
// lib.js
export const value = 1;

// other.js
export const value = 2;

// main.js
import { value } from './lib.js';
import { value as otherValue } from './other.js';
console.log(value, otherValue);
```

**Output:**
```js
const value = 1;      // lib.js - keeps original name (entry module priority)
const value$1 = 2;    // other.js - renamed to avoid conflict
console.log(value, value$1);
```

**Rules:**
- Entry module symbols get naming priority
- Subsequent conflicting symbols get suffixed: `$1`, `$2`, etc.
- Reserved names (keywords, globals like `Object`, `Promise`) are always
avoided

---

## 2. Nested Scope Symbol Renaming

This handles cases where a nested binding (function parameter, catch
clause, block-scoped variable) interacts with top-level symbols.

### Case A: NO renaming needed - Intentional shadowing

When a nested binding shadows an import that **kept its original name**,
no renaming is needed because JavaScript's scoping rules handle it
correctly.

**Example (`preserve_shadowing_param_name`):**

```js
// lib.js
export const Client = [];

// main.js
import { Client } from './lib.js';

// This param shadows the imported `Client`, but should NOT be renamed
// since shadowing is intentional and doesn't cause conflicts at runtime.
const Config = (Client) => {
  console.log(Client);   // → refers to parameter
};
console.log(Client);     // → refers to import
```

**Output:**
```js
const Client = [];
const Config = (Client) => {  // Parameter keeps its name ✓
  console.log(Client);
};
console.log(Client);
```

---

### Case B: Star import member references - Renaming needed

When a namespace import member (like `ns.foo`) is referenced inside a
function, and a nested binding would capture that reference, the nested
binding must be renamed.

**Example (`argument-treeshaking-parameter-conflict`):**

```js
// dep.js
export let value = 0;
export const mutate = () => value++;

// main.js
import * as dep from './dep';

function test(mutate) {       // Parameter named 'mutate'
  dep.mutate('hello');        // Reference to dep.mutate (top-level)
}

test();
assert.strictEqual(dep.value, 1);
```

**Output:**
```js
let value = 0;
const mutate = () => value++;

function test(mutate$1) {     // Parameter renamed to mutate$1
  mutate("hello");            // Correctly calls top-level mutate
}
test();
assert.strictEqual(value, 1);
```

**Why renaming is needed:**
1. The namespace import `dep.mutate` resolves to the top-level `mutate`
function
2. Inside `test`, the parameter `mutate` would shadow the top-level
`mutate`
3. The reference `dep.mutate('hello')` becomes just `mutate("hello")`
after bundling
4. Without renaming the parameter, this call would incorrectly invoke
the parameter instead of the top-level function
5. Solution: Rename the parameter to `mutate$1` so the reference
correctly resolves to the top-level `mutate`

---

### Case C: Named imports - Renaming needed

When a named import is renamed due to a top-level conflict, and a nested
binding has the same name as the **renamed** import, that nested binding
must be renamed to avoid capturing references.

**Example (`basic_scoped`):**

```js
// a.js
const a = 'a.js';
export { a };

// main.js
import { a as aJs } from './a';
const a = 'main.js';              // Local 'a' takes priority (entry module)

function foo(a$1) {               // Parameter named 'a$1'
  return [a$1, a, aJs];           // References: param, local, import
}

assert.deepEqual(foo('foo'), ['foo', 'main.js', 'a.js']);
```

**Output:**
```js
const a$1 = "a.js";               // Import renamed (conflicts with local 'a')
const a = "main.js";              // Local keeps name (entry module priority)

function foo(a$1$1) {             // Parameter renamed to a$1$1
  return [a$1$1, a, a$1];         // Correctly resolves all three references
}

assert.deepEqual(foo("foo"), ["foo", "main.js", "a.js"]);
```

**Why renaming is needed:**
1. `a` from `a.js` is renamed to `a$1` (conflicts with local `a` in
entry module)
2. The alias `aJs` resolves to the renamed `a$1`
3. Inside `foo`, the parameter `a$1` would capture the reference to
`aJs`
4. Solution: Rename the parameter to `a$1$1` so `aJs` correctly resolves
to the top-level `a$1`

---

> **Technical Note:** Cases B and C use the same underlying mechanism to
detect shadowing:
> 
> 1. Get the `reference_id` from the reference site (where the symbol is
used)
> 2. Use `scoping.scope_ancestors(reference.scope_id())` to walk up the
scope chain
> 3. Check if any ancestor scope has a binding with the same name as the
renamed symbol
> 4. If found, rename that nested binding to avoid capture
>
> This detection relies on oxc-project/oxc#18053
which added `scope_id` to `Reference`, enabling us to locate the exact
scope where the reference occurs.

---

### Case D: CJS wrapper parameters - Renaming needed

For CommonJS wrapped modules, nested scopes must avoid shadowing the
synthetic `exports` and `module` parameters injected by the CJS wrapper.

**Example:**
```js
// cjs-module.js (detected as CommonJS)
function helper() {
  const exports = {};  // Would shadow CJS wrapper's exports parameter
  return exports;
}
module.exports = helper;
```

**Output:**
```js
var require_cjs_module = __commonJS((exports, module) => {
  function helper() {
    const exports$1 = {};  // Renamed to avoid shadowing
    return exports$1;
  }
  module.exports = helper;
});
```

---

## Implementation Details

The renaming happens in two phases:

1. **`add_symbol_in_root_scope`** - Assigns canonical names to top-level
symbols, checking:
   - Is the name already used by another top-level symbol?
- For facade symbols (external module namespaces): would it conflict
with nested scopes in the entry module?

2. **`NestedScopeRenamer`** - Renames nested bindings that would capture
references:
- **`rename_bindings_shadowing_star_imports`** (Case B): Star import
member references (`ns.foo`)
- **`rename_bindings_shadowing_named_imports`** (Case C): Named imports
that were renamed
- **`rename_bindings_shadowing_cjs_params`** (Case D): CJS wrapper
parameter shadowing (`exports`, `module`)

---

## Test Cases

| Test | Case | Description |
|------|------|-------------|
| `preserve_shadowing_param_name` | A | Parameter shadows import, keeps
its name (intentional) |
| `argument-treeshaking-parameter-conflict` | B | Namespace member ref,
parameter renamed |
| `basic_scoped` | C | Named import renamed, nested binding renamed |
| `cjs` | D | CJS wrapper parameter shadowing |
| Rollup: `preserves-catch-argument` | A | Catch parameter shadows
import, keeps its name |
| Rollup: `class-name-conflict-2` | A | Class in block scope, keeps its
name |

> Note for reviewer: Code comments and PR description are almost
generated by Claude Code, but with careful self-review.

…r `SemanticBuilder` (#7995)

No usage after #7867

## [1.0.0-rc.1] - 2026-01-22

### 🚀 Features

- debug_info: add facade chunk elimination reason (#7980) by @IWANABETHATGUY
- support lazy barrel optimization (#7933) by @shulaoda
- add `experimental.lazyBarrel` option (#7908) by @shulaoda
- skip unused external modules from IIFE parameter list (#7978) by @sapphi-red
- add custom panic hook for better crash reporting (#7752) by @shulaoda
- treeshake: add `invalidImportSideEffects` option (#7958) by @shulaoda
- merge allow-extension emitted chunks (#7940) by @IWANABETHATGUY
- nativeMagicString generateMap (#7944) by @IWANABETHATGUY
- Include meta.magicString in RenderChunkMeta (#7943) by @IWANABETHATGUY
- debug_info: add debug info for eliminated facade chunks (#7946) by @IWANABETHATGUY
- stablize `strictExecutionOrder` and move to `output.strictExecutionOrder` from `experimental.strictExecutionOrder` (#7901) by @sapphi-red
- add documentation link to require() error message (#7898) by @Copilot
- add `codeSplitting: boolean` and deprecate `inlineDynamicImports` (#7870) by @hyf0
- dev: change lazy module URL to `/@vite/lazy` from `/lazy` (#7884) by @sapphi-red

### 🐛 Bug Fixes

- transform JS files containing `</script>` to escape template literals (#7987) by @IWANABETHATGUY
- apply avoid-breaking-exported-api = false to clippy.toml and fix clippy errors (#7982) by @Boshen
- pass `kind` from `this.resolve` (#7981) by @sapphi-red
- rolldown_plugin_vite_resolve: ignore yarn resolution errors and fallback to other resolvers (#7968) by @sapphi-red
- renamer: prevent renaming symbols when there no conflicts (#7936) by @Dunqing
- correct minifyInterExports when emitted chunk got merged (#7941) by @IWANABETHATGUY
- deduplicate entry points when module is both emitted and dynamically imported (#7885) by @IWANABETHATGUY
- dev: add `@vite-ignore` to lazy compilation proxy module import (#7883) by @sapphi-red

### 🚜 Refactor

- rust: enable clippy nursery lint group (#8002) by @Boshen
- rust: fix inconsistent_struct_constructor clippy lint (#7999) by @Boshen
- rust: fix needless_pass_by_ref_mut clippy lint (#7994) by @Boshen
- rust: fix unnecessary_wraps clippy lint (#7993) by @Boshen
- rust: fix enum_variant_names clippy lint (#7992) by @Boshen
- fix single_match clippy lint (#7997) by @Boshen
- rust: fix redundant_clone clippy lint (#7996) by @Boshen
- rust: rename CJS to Cjs to follow upper_case_acronyms lint (#7991) by @Boshen
- rust: remove unnecessary Box wrapper around Vec in MemberExprRef (#7990) by @Boshen
- import_record: make resolved_module optional (#7907) by @shulaoda
- remove unnecessary `.parse` (#7966) by @sapphi-red
- remove unused `ImportRecordMeta::IsPlainImport` (#7948) by @shulaoda
- proper set chunk meta (#7939) by @IWANABETHATGUY
- module_loader: remove `try_spawn_with_cache` (#7920) by @shulaoda
- link_stage: simplify `ImportStatus::NoMatch` to unit variant (#7909) by @shulaoda
- improve global scope symbol reservation in chunk deconfliction (#7906) by @IWANABETHATGUY
- simplify ast unwrapping in generate stage (#7900) by @IWANABETHATGUY
- generate_stage: optimize cross-chunk imports computation (#7889) by @shulaoda
- link_stage: move runtime require logic into match branch (#7892) by @shulaoda
- link_stage: simplify runtime require reference conditions (#7891) by @shulaoda
- link_stage: inline and simplify external dynamic import check (#7890) by @shulaoda
- generate_stage: simplify external module import collection logic (#7887) by @shulaoda
- avoid redundant module lookup in TLA computation (#7886) by @shulaoda
- dev: `devEngine.compileEntry` does not return null (#7882) by @sapphi-red
- dev: fix type errors for test HMR runtime (#7881) by @sapphi-red
- dev: move `clientId` property to `DevRuntime` base class (#7880) by @sapphi-red
- dev: generate client id in browser (#7878) by @hyf0

### 📚 Documentation

- apis: organize hook filters documentation and add composable filters section (#8003) by @sapphi-red
- update `vitepress-plugin-group-icons` (#7947) by @yuyinws
- add in-depth documentation for lazy barrel optimization (#7969) by @shulaoda
- bump theme & update activeMatch for reference (#7963) by @mdong1909
- mark `build()` API as experimental (#7954) by @sapphi-red
- enhance search functionality with improved scoring and filtering logic (#7935) by @hyf0
- add minor comments to multiple types (#7930) by @sapphi-red
- refactor advanedChunks related content to adapt manual code splitting concept (#7925) by @hyf0
- apis: add content to Bundler API page (#7926) by @sapphi-red
- apis: restructure plugin API related docs (#7924) by @sapphi-red
- add plugin API docs (#7923) by @sapphi-red
- apis: add docs to important APIs (#7913) by @sapphi-red
- move the important APIs to the top of the sidebar (#7912) by @sapphi-red
- apis: add more content to CLI documentation (#7911) by @sapphi-red
- apis: generate CLI docs from --help output (#7910) by @sapphi-red
- add fathom analytics (#7896) by @mdong1909

### ⚡ Performance

- use u32 for string indices in string_wizard and rolldown to reduce memory usage (#7989) by @IWANABETHATGUY
- rust: remove all usages of `with_scope_tree_child_ids(true)` for `SemanticBuilder` (#7995) by @Dunqing
- renamer: skip unnecessary nested scope symbol processing (#7899) by @Dunqing
- module_loader: use ArcStr for importer_id to avoid string copy (#7922) by @shulaoda
- module_loader: defer `ModuleTaskOwner` construction until needed (#7921) by @shulaoda
- renamer: optimize symbol renaming by eliminating `rename_non_root_symbol` pass (#7867) by @Dunqing

### 🧪 Testing

- add lazy barrel optimization test cases (#7967) by @shulaoda

### ⚙️ Miscellaneous Tasks

- remove lazy barrel option (#8010) by @shulaoda
- mark watch API as experimental (#8004) by @sapphi-red
- deps: update dependency lodash-es to v4.17.23 [security] (#8001) by @renovate[bot]
- git ignore zed local config (#7988) by @IWANABETHATGUY
- setup publint for published packages (#7972) by @Copilot
- enable `tagged_template_transform ` uncondionally (#7975) by @IWANABETHATGUY
- deps: update oxc to v0.110.0 (#7964) by @renovate[bot]
- deps: update oxc apps (#7962) by @renovate[bot]
- ai: add upgrade-oxc Claude skill (#7957) by @Boshen
- deps: update rollup submodule for tests to v4.55.2 (#7959) by @sapphi-red
- deps: update test262 submodule for tests (#7960) by @sapphi-red
- deps: update crate-ci/typos action to v1.42.1 (#7961) by @renovate[bot]
- deps: update rust crates (#7951) by @renovate[bot]
- deps: update npm packages (#7953) by @renovate[bot]
- deps: update github-actions (#7952) by @renovate[bot]
- deps: update npm packages (#7950) by @renovate[bot]
- format magic-string test before write to disk (#7945) by @IWANABETHATGUY
- deps: update dependency rolldown-plugin-dts to ^0.21.0 (#7915) by @renovate[bot]
- deps: update dependency oxlint-tsgolint to v0.11.1 (#7914) by @renovate[bot]
- deps: update dependency diff to v8.0.3 [security] (#7904) by @renovate[bot]
- remove outdated TODO comment in `collect_depended_symbols` (#7888) by @shulaoda
- deps: update oxc resolver to v11.16.3 (#7876) by @renovate[bot]