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bundler: let a nested binding keep its name unless it would capture a reference - #41286
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Included review availability: Your plan provides up to 10 included reviews per hour; 5 remain after this review. WalkthroughSummaryThe parser records scope-level symbol uses and visit spans. AST and bundled AST representations carry this data. The number renamer uses scope-aware collision checks for nested bindings. Symbol-use accounting uses a packed API. ChangesScope-aware symbol renaming
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Updated 5:19 PM PT - Sep 3rd, 2026
✅ @Jarred-Sumner, your commit 216da0867a7a3023772509d6103acf2277269a8e passed in 🧪 To try this PR locally: bunx bun-pr 41286That installs a local version of the PR into your bun-41286 --bun |
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… reference The number renamer numbered a binding in a nested scope whenever any enclosing scope, including the chunk's merged top level, had a binding of the same name. Since #41062 put every file's top-level names in place before nested scopes are named, `const Model = factory()` next to `() => { class Model {} }` printed `Model2`, chalk@5's default export got `.name === "chalk2"`, and `var Foo = class Foo {}` / tsc's `let User = class User {}` printed `Foo2` / `User2`. The parser now records, per file, the scope of every identifier reference (`Ast::scope_uses`, only when bundling without identifier minification). The renamer keeps a nested binding's name unless the symbol that owns that name in an enclosing scope is referenced inside the binding's scope, as the printer will write it (linked imports, CommonJS namespace objects, `ns.prop` bindings, cross-chunk imports). Reserved, unbound and eval-pinned names are still always avoided; uses the linker adds, the parser's generated helpers, `module`/`exports`, and class field initializers (which decorator lowering can move into the constructor) count conservatively. Class and function expression names are declared in their own scope rather than at top level. Minified output is unchanged.
…able NumberRenamer keeps only the chunk's top-level names (interned ids + flat slots); each file's nested scopes are named by a NestedRenamer that overlays it and runs as its own thread-pool task once top-level names are final. The parser counts per-part symbol uses in a dense side table and builds the map once per part, and the bundler's parse workers use one mimalloc heap for AST nodes, AstAlloc spills and the parser arena. Also: bytecode-portability snapshot for the changed bundle output, and the follow/follow_printed doc comments.
…ne prefilter Scope members start as an inline 8-entry table (hashes first, compared as a block; names checked only on a hash match) and become a hash table past that, so resolving an identifier up the scope chain touches one cache line per scope and small scopes allocate no table. The per-part use tracker packs its generation/index probe into one word. Property accesses consult a small bit filter before hashing the name against the dot defines.
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No-Verification-Needed: source-lint fix, same behaviour
…ser tables A file's part range stops growing once it spans max(largest_source / (2 * threads), 128 KB) of source, so a large unwrapped file prints on several threads (ranges already join like files do). The parser sizes symbols, scopes_in_order and the part list from the source up front, and scope member tables start as a 4-slot inline block, then 8, then a hash table.
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In `@src/js_parser/lower/lower_esm_exports_hmr.rs`:
- Line 474: Update the HMR namespace-use removal path around append_part and
forget_part_use to carry the owning Part through the scan, then remove the
deduplicated namespace entry from Part::symbol_uses as well as clearing
P::part_use_slot. Ensure the merged-away namespace contributes no use after its
count is reset, while preserving the existing surviving-namespace behavior.
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src/ast/scope.rssrc/ast/symbol.rssrc/bundler/Chunk.rssrc/bundler/LinkerContext.rssrc/bundler/ThreadPool.rssrc/bundler/defines.rssrc/bundler/linker_context/generateChunksInParallel.rssrc/bundler/linker_context/renameSymbolsInChunk.rssrc/bundler/options.rssrc/js_parser/lib.rssrc/js_parser/lower/lower_esm_exports_hmr.rssrc/js_parser/p.rssrc/js_parser/parse/parse_entry.rssrc/js_parser/scan/scan_symbols.rssrc/js_parser/visit/mod.rssrc/js_parser/visit/visit_expr.rssrc/js_printer/renamer.rstest/bundler/bundler_bytecode_portable.test.ts
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No-Verification-Needed: snapshot-only update
…ee fns No-Verification-Needed: refactor for the mordant generic-bloat lint, same behaviour
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In `@src/bundler/linker_context/findAllImportedPartsInJSOrder.rs`:
- Around line 150-158: Compute largest_source_len once before each_ptr,
filtering input files according to the loader contract for sources emitted into
JavaScript chunks so non-JavaScript files do not affect it. Store the resulting
scalar in the shared task context and reuse it when constructing each
FindImportedPartsVisitor, removing the repeated parse_graph input scan from
per-chunk tasks.
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src/ast/scope.rssrc/bundler/linker_context/findAllImportedPartsInJSOrder.rssrc/js_parser/p.rssrc/js_parser/parse/parse_entry.rssrc/threading/ThreadPool.rs
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The minifier's character-frequency scan read every source byte through one 256-entry table, serializing on store-to-load forwarding whenever a byte repeats within a few positions. Four tables fed round-robin from 8-byte chunks and summed once at the end give the same counts at about a third of the cycles; short texts keep the direct 64-slot path.
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In `@test/bundler/bundler_bytecode_portable.test.ts`:
- Around line 454-464: Restore the minified JavaScript output hashes in the
bytecode fixtures by identifying and reverting the output-affecting change in
the minification path, including the cases represented by “bun build --bytecode
--minify features.js” and the preceding minified fixture. Keep the existing
snapshot values unless the changed output is explicitly intended; do not accept
updated hashes without corresponding coverage and an updated objective.
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src/ast/char_freq.rssrc/js_printer/renamer.rstest/bundler/bundler_bytecode_portable.test.ts
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Each per-file renaming task allocated and zeroed a u32 for every top-level name in the chunk; with tens of thousands of small files that was gigabytes of memset for no wall-clock gain. Keep only the ids the file's nested scopes bind or renumber, in a small map.
…er link It scanned every input file's length once per chunk; do it once, and only over JavaScript-like inputs.
Each per-file task created its own bump arena for the few renamed strings it produces and the chunk kept all of them alive; with 10k small files that was 10k arenas. Use the existing per-thread bundler Worker arena instead (it outlives printing), and drop NumberRenamer::arenas.
…t start The range cap came from the thread count, so range boundaries (which reach the output and the chunk hash) could differ between machines; use 128 KB of source everywhere. And clear the per-part use tracker when a part starts, as before, so decorator-metadata type lookups made during the parse pass are not attributed to the first part.
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Still open from earlier reviews (3):
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src/js_parser/p.rs:5559—Removing symbol_uses.clear_retaining_capacity() at the top of append_part drops the reset that discarded parse-pass rec… - Also unresolved: 1 minor or pre-existing, 1 blocking on lines changed since (possibly already fixed).
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…ope that prints it (#41354) ### Problem - Since 1.4.1, `bun build` of any Elysia app emits `let Check2 = ...; var Check2 = Check2;` in one block. Loading it fails: `SyntaxError: Cannot declare a var variable that shadows a let/const/class variable: 'Check2'`. Fixes #41351. - Cause: `ScopeUses::sees` (`src/js_printer/renamer.rs:1218`, from #41286) only counts identifier references. A hoisted `var` still prints its declaration in its block, so a `let` there could take the hoisted name. - The same gap lets a `let` take a parameter's or catch binding's name. When a renamed `var` takes that name instead, the output loads but computes wrong values. 1.4.1 users should upgrade even when their bundle loads. ### Fix - `visit_binding` (`src/js_parser/visit/mod.rs:803`) records a declaration point for a `var` declared below the scope it hoists to, a parameter, and a catch binding. Other bindings live in the scope that declares them. - `ScopeUses::sees` looks at the parent scope for a function body (`FunctionArgs`) and a catch block (`CatchBinding`). Those pairs form one declaration region. - Both changes only make `sees` return true more often. The worst case is a numbered name, the 1.4.0 behavior. - Verified: `identifiers/NestedBindingRenamedAroundHoistedVarDeclaration` in `test/bundler/bundler_edgecase.test.ts` (fails on main). The Elysia 1.4.29 build from the issue serves `200 ok`. Other bundler suites pass (list in Notes). ### Background - The number renamer names top-level symbols, then each file's nested scopes in pre-order, checking each binding against enclosing names. - `Ast::scope_uses` lists `(scope index, symbol)` points per reference. Scopes are numbered in pre-order, so `sees(symbol, scope)` is a range check. - A `var` in a block is hoisted to the function scope, but the block keeps its member entry and the printer writes the `var` where the source had it. <details><summary>Notes</summary> Minimal reproduction for each SyntaxError case, all with a top-level `Check` referenced in the function so the nested `Check` is renamed to `Check2`: ```js function make(cond) { OuterCheck(0); if (cond) { let Check2 = 1; var Check = Check2; } return Check; } function param(Check) { OuterCheck(0); let Check2 = "body"; return Check2; } function caught() { try { throw 0 } catch (Check) { OuterCheck(0); let Check2 = "catch"; return Check2; } } ``` On main the output is `let Check2 = 1; var Check2 = Check2`, `function param(Check2) { let Check2 }` and `catch (Check2) { let Check2 }`. With the fix each inner `let` becomes `Check22`. Silent value cases on main, checked with the debug build: `function paramVar(Check2) { OuterCheck(0); var Check; return Check; }` prints `var Check2; return Check2` and returns the argument instead of `undefined`. `try { throw 0 } catch (Check2) { var Check = "set" } return Check` prints `catch (Check2) { var Check2 = "set" }` and returns `undefined` instead of `"set"`. With the fix they print `var Check3` and `catch (Check22)`. The test covers `if`, `for`, `for-in`, `switch`, `try` and `catch` bodies, destructuring, a class next to the hoisted `var`, parameter defaults, an Annex B block function, a parameter and a catch binding the body never mentions (these fail if the `sees` parent redirect is removed), and the two value cases above. A sibling block that declares `let Check2` without mentioning the `var` keeps its name, so the fix does not number every nested binding. Suites run with the debug build: the other `NestedBinding*` tests, all of `bundler_edgecase.test.ts`, `esbuild/default`, `esbuild/lower`, `esbuild/ts`, `bundler_cjs`, `bundler_regressions`, `bun-build-api`. `bundler_bytecode_portable.test.ts` times out at the 5 s per-test ceiling under the debug build on this machine, both with and without the change. Its assertions do not depend on names. Self-reviewed: the review asked for the two value cases and the upgrade note. Both added. An Annex B block function concern was already covered: generated hoisted symbols carry a whole-file span (`take_scope_uses`, p.rs:1839). </details> <!-- robobun:evidence:begin --> --- **[human-review]** gate passed · iteration 0 · 4 files touched <details><summary>fails on main (without fix)</summary> ```console ASAN without fix: 1 failed, 11 skipped $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/bundler/bundler_edgecase.test.ts bun test v1.4.1 (e0a2b82) test/bundler/bundler_edgecase.test.ts: (pass) bundler > edgecase/EmptyFile [523.54ms] (pass) bundler > edgecase/EmptyCommonJSModule [386.39ms] (pass) bundler > edgecase/NestedRedirectToABuiltin [497.68ms] (pass) bundler > edgecase/ImportStarFunction [384.47ms] (pass) bundler > edgecase/ImportStarSyntaxErrorBug [367.33ms] (todo) bundler > edgecase/BunPluginTreeShakeImport (pass) bundler > edgecase/TemplateStringIssue622 [145.27ms] (pass) bundler > edgecase/ImportNamedFromExportStarCJS [476.93ms] (pass) bundler > edgecase/NodeEnvDefaultUnset [210.49ms] (pass) bundler > edgecase/NodeEnvDefaultDevelopment [201.78ms] (pass) bundler > edgecase/NodeEnvDefaultProduction [209.59ms] (todo) bundler > edgecase/NodeEnvOptionalChaining (pass) bundler > edgecase/StarExternal [120.20ms] (pass) bundler > edgecase/ImportNamespaceAndDefault [361.30ms] (todo) bundler > edgecase/ExternalES6ConvertedToCommonJSSimplified (pass) bundler > edgecase/ImportTrailingSlash [345.11ms] (pass) bundler > ... (truncated) release without fix: 2 failed, 11 skipped bun test v1.4.1-canary.1 (e0a2b82) test/bundler/bundler_edgecase.test.ts: (pass) bundler > edgecase/EmptyFile [12.65ms] (pass) bundler > edgecase/EmptyCommonJSModule [10.05ms] (pass) bundler > edgecase/NestedRedirectToABuiltin [9.70ms] (pass) bundler > edgecase/ImportStarFunction [8.51ms] (pass) bundler > edgecase/ImportStarSyntaxErrorBug [9.39ms] (todo) bundler > edgecase/BunPluginTreeShakeImport (pass) bundler > edgecase/TemplateStringIssue622 [4.59ms] (pass) bundler > edgecase/ImportNamedFromExportStarCJS [9.72ms] (pass) bundler > edgecase/NodeEnvDefaultUnset [4.85ms] (pass) bundler > edgecase/NodeEnvDefaultDevelopment [4.63ms] (pass) bundler > edgecase/NodeEnvDefaultProduction [4.63ms] (todo) bundler > edgecase/NodeEnvOptionalChaining (pass) bundler > edgecase/StarExternal [3.60ms] (pass) bundler > edgecase/ImportNamespaceAndDefault [9.39ms] (todo) bundler > edgecase/ExternalES6ConvertedToCommonJSSimplified (pass) bundler > edgecase/ImportTrailingSlash [9.63ms] (pass) bundler > edgecase/ValidLoaderSeenAsInvalid [3.71ms] (pass) bundler > edgecase/InvalidLoaderSegfault [2.15ms] (todo) bundler > edgecase/ScriptTagEscape (pass) bundler > edgecase/JSONDefaultImpor ... (truncated) ``` </details> <details><summary>passes on PR (with fix)</summary> ```console ASAN with fix: 11 skipped $ BUN_DEBUG_QUIET_LOGS=1 bun scripts/build.ts --profile=debug --quiet test "--reporter=junit" "--reporter-outfile=/tmp/pr_gate.xml" test/bundler/bundler_edgecase.test.ts bun test v1.4.1 (e0a2b82) test/bundler/bundler_edgecase.test.ts: (pass) bundler > edgecase/EmptyFile [583.64ms] (pass) bundler > edgecase/EmptyCommonJSModule [426.45ms] (pass) bundler > edgecase/NestedRedirectToABuiltin [433.35ms] (pass) bundler > edgecase/ImportStarFunction [460.03ms] (pass) bundler > edgecase/ImportStarSyntaxErrorBug [367.14ms] (todo) bundler > edgecase/BunPluginTreeShakeImport (pass) bundler > edgecase/TemplateStringIssue622 [117.24ms] (pass) bundler > edgecase/ImportNamedFromExportStarCJS [387.09ms] (pass) bundler > edgecase/NodeEnvDefaultUnset [283.29ms] (pass) bundler > edgecase/NodeEnvDefaultDevelopment [203.65ms] (pass) bundler > edgecase/NodeEnvDefaultProduction [208.80ms] (todo) bundler > edgecase/NodeEnvOptionalChaining (pass) bundler > edgecase/StarExternal [134.73ms] (pass) bundler > edgecase/ImportNamespaceAndDefault [467.64ms] (todo) bundler > edgecase/ExternalES6ConvertedToCommonJSSimplified (pass) bundler > edgecase/ImportTrailingSlash [352.95ms] (pass) bundler > ... (truncated) release with fix: 11 skipped $ bun scripts/build.ts --profile=release [configured] bun-profile → bun (stripped) target linux-x64-gnu build type Release build dir ./build/release revision babb134 features baseline 23 deps, 131 codegen, 1172 objects in 637ms ninja: Entering directory `/workspace/bun/build/release' [1/1244] install /workspace/bun bun install v1.4.1-canary.1 (e0a2b82) Checked 22 installs across 61 packages (no changes) [4.00ms] [2/1244] gen ErrorCode+*.h [3/1244] install /workspace/bun/packages/bun-error bun install v1.4.1-canary.1 (e0a2b82) Checked 1 install across 2 packages (no changes) [2.00ms] [4/1244] gen bindgenv2 [5/1244] fetch zlib [zlib] up to date [6/1244] install /workspace/bun/src/node-fallbacks bun install v1.4.1-canary.1 (e0a2b82) Checked 111 installs across 104 packages (no changes) [12.00ms] [7/1244] gen .bind.ts → GeneratedBindings.cpp [8/1244] gen bake.{client,server,error}.js -> bake.client.js, bake.server.js, bake.error.js [9/1244] fetch libjpeg-turbo [libjpeg-turbo] up to date [10/1217] gen node-fallbacks/react-refresh.js Bundled 1 module in 10ms react-refresh.js 4.81 KB (entry point) [11/1217] fetch tinycc ... (truncated) ``` </details> <details><summary>diff hotspot</summary> ``` src/js_parser/p.rs | 2 +- src/js_parser/visit/mod.rs | 11 +++ src/js_printer/renamer.rs | 11 +++ test/bundler/bundler_edgecase.test.ts | 170 ++++++++++++++++++++++++++++++++++ 4 files changed, 193 insertions(+), 1 deletion(-) ``` </details> **gate history** · 1 passed · 0 rejected · iteration 0 <details><summary>evidence per changed file</summary> ``` file reads edits tests src/js_parser/p.rs 5 1 15 src/js_parser/visit/mod.rs 3 2 15 src/js_printer/renamer.rs 3 3 15 test/bundler/bundler_edgecase.test.ts 2 10 15 ``` </details> <!-- robobun:evidence:end --> --------- Co-authored-by: Jarred Sumner <jarred@jarredsumner.com> Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com>
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…__proto__ tests valid now that nested bindings keep their names With two or more data files in one bundle, every hoisted "__proto__" variable after the first is renamed, so the rebuilt default object has to keep its computed key even without --minify. Cover JSON, TOML and YAML namespaces in both modes. Since #41286 a nested binding keeps its name unless it would capture a reference, so the esbuild-ported ObjectLiteralProtoSetterEdgeCases test no longer sees "__proto__2" for its nested locals. Accept either outcome as long as the shorthand never prints as "__proto__: x", and give the edgecase matrix two colliding top-level "__proto__" bindings so the renamed-shorthand path is still exercised in every mode.
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… whole bundle (#41861) ### What does this PR do? `NumberRenamer::init` (#41286) pre-sizes its root name table — the `ids` hash map and the `slots` vec — to `root_names.len() + symbol_count / 4`, where `symbol_count` is summed over `symbols.symbols_for_source`, i.e. **every symbol in the bundle**. That is fine for a single chunk, but with `--splitting` `generateChunksInParallel` builds a renamer for every chunk up front and each one stays alive in `chunk.renamer` until its chunk has been printed. So a build with N JS chunks reserves N bundle-sized tables at once. On a large app that splits into ~800 chunks (~1M symbols), each chunk reserved a ~4.4 MB hashbrown table plus a ~3 MB `Vec<NameSlot>` and used a few hundred entries of it: | | peak RSS (Linux, 4 cores) | |---|---| | before #41286 (`858f4e7`) | 6.2 GB | | `main` | 7.7 GB | | this PR | 6.2 GB | Linux only pays for the pages that get touched (the control-byte `memset` plus scattered inserts, ~2 MB per chunk). On Windows mimalloc commits the whole block when it is allocated, so the same build carried several GB of extra commit charge and, on a machine with a small commit limit, `bun build` aborted with `memory allocation of 4456464 bytes failed` — 4,456,464 bytes being exactly this table (262,144 × 16-byte `(StoreStr, u32)` buckets + control bytes). The fix sizes the table from the symbols of the files in the chunk (`files_in_order`), which is what the chunk's renamer can actually add. A non-splitting build has one chunk containing every file, so it reserves exactly what it did before and the #41286 benchmarks are unaffected. ### How did you verify your code works? Measured the build above with release builds of `858f4e7`, `main` and this branch, pinned to 4 cores, two runs each (numbers in the table; run-to-run spread ±0.1 GB). Page-fault profiles of `main` attribute the extra faults to `renamer::intern_into` and hashbrown's control-byte `memset` under `NumberRenamer::init`; both disappear with this change. Output is byte-identical (capacity is only a hint; `intern` grows the table on demand).
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…lic-imports Conflicts, both in lower_esm_exports_hmr.rs: - The `export default` statement arm keeps main's default name for an anonymous class (#41142) and passes that ref to visit_ref_to_export, as this branch does for every other export. - visit_ref_to_export: main changed one line (#41286) in the temp symbol block that this branch removed. The block stays removed.
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What
1. Nested bindings keep their names. Non-minified bundles no longer number a binding in a nested scope just because a top-level symbol in the chunk (or another enclosing binding) has the same name. A nested binding keeps its name unless the symbol that owns that name in an enclosing scope is actually referenced inside the binding's scope — so
Function#name/constructor.namematch unbundled code, Node and Rollup.class Model+ top-levelModelModel2Model.namechalk2chalkvar Foo = class Foo {}, tsc'slet User = class User {}Foo2,User2Foo,Uservar fn = function fn() {}fn2fnimport { T as U }+class T { m() { return U } }, a localparsenext tons.parse(), a localimport_xnext to a CommonJS default import)Follow-up to #41062 (that fix stands; #41054 stays fixed).
2.
bun buildis faster, mostly on large / many-module ESM inputs. Linux x64, LTO release builds of 1.4.0,main(14ab660) and this branch, hyperfine on 8 pinned cores, non-minified unless noted:bench/bundlethree.js ×100 (index.ts)bench/bundlethree.js ×10 (index10.ts)src/tree ×100 (~70k modules)src/tree ×10--packages=external)typescript.jsas entry,--format=cjs--minify(n=30)apps/10000(10k tiny JSX files),--production --sourcemapmacOS arm64 (
bunx bun-pr 41286vs 1.4 release):bench/bundlethree.js ×100 382 → 257 ms (--minify265 → 256 ms); three.jssrc/tree ×100 999 → 845 ms (--minify801 → 807 ms).--minifybuilds see only the parser-side share (the minifier has its own renamer); CJS-wrapped dependencies print as one closure and see mostly parity; bundles of thousands of tiny modules are dominated by per-module resolve/link cost and see little change.How
Renamer:
(scope, symbol)for each identifier reference into a flat per-file list (Ast::scope_uses), with scopes numbered in visit pre-order so a subtree is a range. Only when bundling without--minify-identifiers; references to unbound globals are skipped.NumberRenamerkeeps the chunk's top-level names as interned ids with one slot each (scope, count, owner). Each file's nested scopes are named by aNestedRenameroverlaying that table (sparse, undo-logged per scope) and run as parallel per-file tasks once top-level names are final. A nested binding may take a name held further out when the holder is not referenced in its scope subtree.symbol::Usecarries an "unscoped" bit), parser-generated temporaries/helpers,module/exports, TypeScript decorator-metadata type references, and class field initializers/keys count as referenced across the whole file / class body. Class and function expression names are declared in their own scope. The TS namespace closure parameter is now visible to the renamer.Parser / linker:
symbols,scopes_in_orderand the part list are sized from the source up front; the bundler's parse workers use one mimalloc heap for AST nodes,AstAllocspills and the parser arena.max(largest_source / (2 × threads), 128 KB)of source, so a large unwrapped file prints on several threads (ranges already join the way files do).CharFreq::scan(minifier) counts into four interleaved tables.Minified output can differ from main in which equally-short name a nested slot gets (scope members now iterate in declaration order, which changes the creation order of hoisted symbols); sizes move by ±0.001%. The bytecode-portability snapshot is updated for that and for the non-minified naming change.
Tests
test/bundler/bundler_edgecase.test.ts:identifiers/NestedBindingKeepsNameWhenOuterIsNotReferencedInside(fails on main),identifiers/NestedBindingRenamedWhenOuterIsReferencedInside,identifiers/NestedBindingRenamedAroundLinkedAndHoistedNames,identifiers/NestedBindingRenamedWhenOuterIsReferencedLater(capture cases that must still rename). Two existing expectations updated (bar2→barin an expected runtime error,fn2→fnin a snapshot);bundler_bytecode_portablesnapshot updated.