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…s extends The extends merge only OR-ed emitDecoratorMetadata into the base config and never carried experimentalDecorators at all. A child config that set experimentalDecorators while it extended a base config lost the flag, and a child could not clear a flag the base config set. Store both flags as Option<bool>, unset by default, and let the more specific config win in the merge, the same way useDefineForClassFields already works.
TypeScript 5.0 accepts an array for tsconfig "extends". The parser only read a string, so an array dropped every inherited option without a diagnostic. Parse each entry and walk them in order: a later entry overrides an earlier one, and the child config overrides all of them. Fixes #43097
WalkthroughThe change adds array-valued TypeScript ChangesTypeScript configuration inheritance
Suggested reviewers: Priority: ⬇️ Low Merge Risk: 🟡 Moderate · up to Projects that disable inherited decorator behavior can still be transpiled with it enabled, and configurations with 64 direct bases fail despite staying within the recursion limit. Resolve these inheritance regressions before merging. 🚥 Pre-merge checks | ✅ 4✅ Passed checks (4 passed)
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Actionable comments posted: 3
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Inline comments:
In `@src/resolver/resolver.rs`:
- Line 445: Replace the bounded raw-pointer TSConfigExtendsChain with owning
storage, such as Vec<Box<TSConfigJSON>>, and ensure cleanup invokes
TSConfigJSON::destroy. Update collect_tsconfig_extends_chain and its caller to
use the owning entries while preserving the separate maximum recursion-depth
check of 64, preventing parent allocations from leaking when collection fails
before merging.
- Around line 1570-1581: Update the flag propagation in the
enclosing_tsconfig_json handling to apply explicit decorator options rather than
OR-ing with inherited values: when emit_decorator_metadata or
experimental_decorators is Some(v), set the corresponding flag directly to v,
while leaving the existing value unchanged when the option is absent.
In `@test/js/bun/resolve/tsconfig-extends-leak.test.ts`:
- Line 161: Update the subprocess helper run and its callers so run returns all
subprocess results without asserting exitCode internally. In each caller, assert
stdout and stderr first, then assert exitCode last, including the flow
containing the existing expect(exitCode).toBe(0) assertion.
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src/bundler/transpiler.rssrc/resolver/resolver.rssrc/resolver/tsconfig_json.rssrc/runtime/api/JSTranspiler.rstest/js/bun/resolve/tsconfig-extends-leak.test.ts
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A Vec of Box<TSConfigJSON> replaces the bounded raw pointer array. A wide extends array no longer hits the 64 slot limit, and a chain that stops early frees every config it parsed.
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Nothing blocking. The comments below are optional suggestions. There is no need to push a fix for them before merging.
Beyond the inline findings, I also checked the per-directory flag merge at src/resolver/resolver.rs:1572-1579 — it still ORs experimentalDecorators/emitDecoratorMetadata across nested directory tsconfigs exactly as on base, so the new Option<bool> clearing only takes effect within a single extends chain, not between a nested tsconfig and its enclosing one. The error-path drop of the partially built chain Vec matches the base branch's behavior on overflow, so nothing new there.
Extended reasoning...
Findings were posted inline, so this note only records what else was examined. The dir_info merge at resolver.rs:1572-1579 was not changed semantically by this PR (only adapted to == Some(true)), which means the "child config can clear the flag" behavior described in the PR applies to the extends chain merged in dir_info_uncached, not to the directory-hierarchy merge; that is consistent with the base branch and the PR's stated scope, but worth the author knowing given the issue #30477 framing. The ? early-return in collect_tsconfig_extends_chain drops the Vec<Box<TSConfigJSON>> via normal Box drop rather than TSConfigJSON::destroy, the same outcome the base's BoundedArray overflow path had, so it was not raised as a new regression.
2 verified lower-impact observations (convention, logging or cleanup points) were not posted.
Track the config paths on the recursion path. An entry that is already on it is skipped with a debug log, and the chain is capped at 64 configs in total. The walk no longer returns an error. Tests now observe emitDecoratorMetadata, a missing entry, a cycle, and the order of an entry with its own extends.
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I re-reviewed after the latest pushes and found no bugs; the earlier threads (cycle handling, total chain cap, emitDecoratorMetadata and missing-entry/cycle coverage, order-sensitive fixture) are addressed in the code, so a maintainer only needs a normal look at the merge-semantics change.
What was reviewed:
- Ownership of the new
Vec<Box<TSConfigJSON>>walk: every parent goes throughTSConfigJSON::destroy, the leaf is interned viaheap::into_raw;chain.next().expect(...)is an internal invariant (the leaf is pushed unconditionally). - Cap boundary:
visiting.len() + chain.len() >= 64bounds total parsed configs, matching the oldBoundedArray<_, 64>; the cycle check byabs_pathon the recursion path. bool -> Option<bool>for both decorator flags: all readers (transpiler.rs,JSTranspiler.rsx2, theenclosing_tsconfig_jsonmerge) compare againstSome(true);jsc_hooks.rsreads the already-coerced transpiler options.- The
emitDecoratorMetadatamerge changes from OR to last-set-wins so a child can clear it (intended, per #30477) — a deliberate semantics change worth a maintainer's eyes.
Extended reasoning...
Overview
The PR touches the resolver's tsconfig handling (src/resolver/resolver.rs, src/resolver/tsconfig_json.rs) and the two consumers of the decorator flags (src/bundler/transpiler.rs, src/runtime/api/JSTranspiler.rs), plus test/js/bun/resolve/tsconfig-extends-leak.test.ts. TSConfigJSON.extends becomes a list so the TypeScript 5.0 array form is accepted, and emit_decorator_metadata/experimental_decorators become Option<bool> so a child config can explicitly set or clear them. The extends walk is rewritten from a raw-pointer BoundedArray loop to a recursive collect_tsconfig_extends_chain producing a bases-first Vec<Box<TSConfigJSON>>, with a visiting path stack for cycles and a total cap of 64.
Security risks
None specific to this change. Inputs are local tsconfig.json files; paths are joined with the existing join_abs_string_buf helper and parsed via the existing parse_tsconfig. The cap prevents unbounded work on a fan-out extends graph, and the cycle check prevents recursion on self-referencing configs. The extends inside node_modules remains ignored as before.
Level of scrutiny
Moderate. The memory-ownership story is simpler and safer than the base (Box instead of raw pointers with SAFETY notes), and I traced each acquisition to its release. The compiler enforces the field type change across consumers. The part that merits a human decision is the semantics change in the merge loop: emitDecoratorMetadata was OR-ed and is now last-set-wins, and experimentalDecorators now crosses extends boundaries at all. Both are intentional and tested but are user-visible behavior changes to a widely used config path. Skipping a failed parent (rather than stopping the chain) is only debug-logged; I flagged that earlier as pre-existing/non-blocking and have nothing new to add.
Other factors
Since my previous review the author pushed commits that address every inline thread I opened: cycle detection by abs_path, a total chain cap instead of depth-only, an order-sensitive fixture for the nested-extends test, and new tests for emitDecoratorMetadata set/clear, a missing entry, and a cycle. The new suite runs under describe.concurrent, drains pipes concurrently, and asserts stdout before the exit code. The bug hunt exited on dry_streak with zero findings. No CODEOWNERS entry covers the changed files.
Problem
"extends": ["./base.json"]in a tsconfig.json is dropped. Bun emits the TC39 decorator runtime instead of__legacyDecorateClassTSwhenexperimentalDecoratorscomes frombase.json. No diagnostic is printed. TypeScript 5.0 accepts this array form.extends_value.as_str()insrc/resolver/tsconfig_json.rs:366. An array is not a string, soextendsstays empty.src/resolver/resolver.rs):experimentalDecoratorsnever crossed an extends boundary, andemitDecoratorMetadatawas OR-ed, so a child config could not clear it. That is the cause of Bun 1.3.10 breaks --tsconfig-override flag #30477.Fix
experimental_decoratorsandemit_decorator_metadataonTSConfigJSONareOption<bool>, unset by default. The merge lets the more specific config win, the same wayuse_define_for_class_fieldsalready works. Consumers test forSome(true).extendsis a list of entries. The resolver walks them with a post-order recursion, so the chain is built base first.["a", "b"]appliesa, thenb, then the child, as in tsc. An entry with its ownextendsis resolved before the next entry. An entry already on the recursion path (a cycle) is skipped, and the chain is capped at 64 configs.test/js/bun/resolve/tsconfig-extends-leak.test.ts(8 new tests, all fail on bun 1.4.2). Alsobundler_decorator_metadata,bundler/transpiler/*decorators*,cli/run/tsconfig-override,regression/issue/{25622,27526,27575},js/bun/resolve/*.Background
dir_info_uncachedparses the tsconfig.json of a directory once and caches the merged result. The extends chain is walked there, and every intermediate config is freed after its fields move into the base config.Vec<Box<TSConfigJSON>>holds the chain. The old code used a bounded raw pointer array, filled leaf first and popped from the end. The new code fills it base first, so an array entry and its own parents land in the right place.exportsmaps and${configDir}. That PR conflicts with main and has no review yet. It can rebase over this one. Package specifier entries andextendsinsidenode_modules(Bun does not emit decorator metadata if tsconfig inherits the configuration from another file #6326) stay unsupported here.Notes
{ "extends": ["./base.json"] },bun build ./dec.ts | head -1printsvar __create = Object.create;on 1.4.3 andvar __legacyDecorateClassTS = ...with this build.["./b.json", "./base.json"]where onlybase.jsonsetsexperimentalDecorators) is what showed that the array form needs the decorator flag merge. Without commit 1 the flag only survived when the config that set it was the first entry.extends.test/bundler/bun-build-api.test.tsandtest/bundler/bundler_edgecase.test.ts. Threebytecodeand "thousands of builds" tests time out under the debug ASAN build. They do not touch tsconfig.[human-review] gate passed · iteration 0 · 5 files touched
fails on main (without fix)
passes on PR (with fix)
diff hotspot
gate history · 2 passed · 0 rejected · iteration 0
evidence per changed file
root cause · written by the author bot
Bun's tsconfig parser only accepted
extendsas a string, so the TypeScript 5.0 array form fell throughas_str()and the entire field was dropped without warning, losing every option inherited from the base configs. The fix storesextendsas a list of entries and rewrites the resolver's walk to collect the chain recursively, processing entries in order and merging bases first so later entries override earlier ones and the child config wins over all of them, with cycle detection by path and a total cap of 64 configs. Alongside this,experimentalDecoratorsandemitDecoratorMetadatab…