runtime: fix small leak in Blob deinit

[nektro]

pulled out of #21663

[robobun]

^{Updated 7:41 PM PT - Nov 17th, 2025}

❌ @nektro, your commit 0248b7c has 3 failures in Build #31939 (All Failures):

• test/js/bun/ffi/cc.test.ts - 1 failing on 🍎 14 aarch64
• test/js/bun/ffi/cc.test.ts - 1 failing on 🍎 13 aarch64
• test/integration/next-pages/test/dev-server.test.ts - 1 failing on 🍎 14 aarch64
• test/v8/v8.test.ts - pid 9591 error: addresssanitizer on 🐧 12 x64-asan

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Actionable comments posted: 1

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📥 Commits

Reviewing files that changed from the base of the PR and between 9513c1d and 0248b7c.

📒 Files selected for processing (2)

• scripts/runner.node.mjs (1 hunks)
• src/bun.js/webcore/Blob.zig (1 hunks)

🧰 Additional context used

🧠 Learnings (8)

📓 Common learnings

Learnt from: taylordotfish
Repo: oven-sh/bun PR: 22227
File: src/memory.zig:60-76
Timestamp: 2025-09-02T17:41:07.869Z
Learning: In bun's memory utilities, when handling const pointers in deinit operations, prefer compile-time errors over silent skipping to avoid hard-to-find memory leaks. Users expect explicit failures rather than silent omissions in memory management.

📚 Learning: 2025-11-14T16:07:01.064Z

Learnt from: RiskyMH
Repo: oven-sh/bun PR: 24719
File: docs/bundler/executables.mdx:527-560
Timestamp: 2025-11-14T16:07:01.064Z
Learning: In the Bun repository, certain bundler features like compile with code splitting (--compile --splitting) are CLI-only and not supported in the Bun.build() JavaScript API. Tests for CLI-only features use backend: "cli" flag (e.g., test/bundler/bundler_compile_splitting.test.ts). The CompileBuildConfig interface correctly restricts these with splitting?: never;. When documenting CLI-only bundler features, add a note clarifying they're not available via the programmatic API.

Applied to files:

• scripts/runner.node.mjs

📚 Learning: 2025-11-03T20:43:06.996Z

Learnt from: pfgithub
Repo: oven-sh/bun PR: 24273
File: src/bun.js/test/snapshot.zig:19-19
Timestamp: 2025-11-03T20:43:06.996Z
Learning: In Bun's Zig codebase, when storing JSValue objects in collections like ArrayList, use `jsc.Strong.Optional` (not raw JSValue). When adding values, wrap them with `jsc.Strong.Optional.create(value, globalThis)`. In cleanup code, iterate the collection calling `.deinit()` on each Strong.Optional item before calling `.deinit()` on the ArrayList itself. This pattern automatically handles GC protection. See examples in src/bun.js/test/ScopeFunctions.zig and src/bun.js/node/node_cluster_binding.zig.

Applied to files:

• src/bun.js/webcore/Blob.zig

📚 Learning: 2025-10-18T20:50:47.750Z

Learnt from: theshadow27
Repo: oven-sh/bun PR: 23798
File: src/bun.js/telemetry.zig:366-373
Timestamp: 2025-10-18T20:50:47.750Z
Learning: In Bun's Zig codebase (src/bun.js/bindings/JSValue.zig), the JSValue enum uses `.null` (not `.js_null`) for JavaScript's null value. Only `js_undefined` has the `js_` prefix to avoid collision with Zig's built-in `undefined` keyword. The correct enum fields are: `js_undefined`, `null`, `true`, `false`, and `zero`.

Applied to files:

• src/bun.js/webcore/Blob.zig

📚 Learning: 2025-10-01T21:49:27.862Z

Learnt from: taylordotfish
Repo: oven-sh/bun PR: 23169
File: src/bun.js/bindings/BunIDLConvert.h:29-42
Timestamp: 2025-10-01T21:49:27.862Z
Learning: In Bun's IDL bindings (src/bun.js/bindings/BunIDLConvert.h), IDLStrictNull intentionally treats both undefined and null as null (using isUndefinedOrNull()), matching WebKit's IDLNull & IDLNullable behavior. This is the correct implementation and should not be changed to only accept null.

Applied to files:

• src/bun.js/webcore/Blob.zig

📚 Learning: 2025-10-21T20:57:01.892Z

Learnt from: taylordotfish
Repo: oven-sh/bun PR: 23889
File: src/string.zig:751-752
Timestamp: 2025-10-21T20:57:01.892Z
Learning: In Zig code handling bun.String: calling deref() on an empty bun.String (String.empty or after being set to .empty) is well-defined behavior and safely does nothing (no-op). While such calls may be redundant and could be removed for code clarity, their presence is not a correctness issue.

Applied to files:

• src/bun.js/webcore/Blob.zig

📚 Learning: 2025-09-02T17:41:07.869Z

Learnt from: taylordotfish
Repo: oven-sh/bun PR: 22227
File: src/memory.zig:60-76
Timestamp: 2025-09-02T17:41:07.869Z
Learning: In bun's memory utilities, when handling const pointers in deinit operations, prefer compile-time errors over silent skipping to avoid hard-to-find memory leaks. Users expect explicit failures rather than silent omissions in memory management.

Applied to files:

• src/bun.js/webcore/Blob.zig

📚 Learning: 2025-09-02T18:32:32.309Z

Learnt from: taylordotfish
Repo: oven-sh/bun PR: 22227
File: src/bun.zig:668-675
Timestamp: 2025-09-02T18:32:32.309Z
Learning: The `std.meta.trait` module has been removed from the Zig standard library, which will cause compilation failures in functions that use it like `std.meta.trait.isSingleItemPtr()`. This affects functions like `isHeapMemory()` in `src/bun.zig`.

Applied to files:

• src/bun.js/webcore/Blob.zig

🔇 Additional comments (1)

scripts/runner.node.mjs (1)

494-510: Buildkite annotation styling change is consistent with intent

Tying style strictly to flaky ("warning" for flaky, "error" otherwise) cleanly separates flaky from hard failures and ensures vendor failures are always annotated as errors. Annotation grouping via context is preserved and no other behavior changes.

[Jarred-Sumner]

Confirming this does fix the leak. It would be better if it had a test. It would also be better if we added a separate deinit function that calls destroy explicitly instead of incrementing the reference count in the deref function.