fix(core): Align beforeBreadcrumb and tracesSampler error fallbacks with spec by antonis · Pull Request #6675 · getsentry/sentry-react-native

antonis · 2026-09-04T09:10:44Z

📢 Type of change

Bugfix
New feature
Enhancement
Refactoring

📜 Description

Aligns two callback error fallbacks with the Callback Error Isolation spec:

beforeBreadcrumb throw → drop the breadcrumb. safeFactory used to return the unmodified input on error, so a throwing beforeBreadcrumb kept the original breadcrumb. It now returns null for the breadcrumb case (via a new optional onError handler), so the breadcrumb is dropped.
tracesSampler throw → fall back to tracesSampleRate. safeTracesSampler used to return a hardcoded 0 on error, silently forcing 0% sampling. It now falls back to the configured tracesSampleRate. When no rate is configured it returns undefined, which lets the core sampling pipeline discard the transaction — never substituting 0/1 as the spec forbids.

RN already met the error-log / no-rethrow / no-self-capture requirements; only these two recovery values deviated.

Out of scope (correctly untouched): beforeSend*, beforeSendSpan, beforeSendLog, and event processors are handled by the @sentry/core pipeline; profilesSampler/error_sampler don't exist in RN; and the extra RN-side isolation for initialScope/integrations is left as-is.

safeFactory/safeTracesSampler are internal utilities (not part of the public API), so there is no public API or ABI change.

💡 Motivation and Context

Fixes #6668. Silently dropping all transactions on a sampler bug, or keeping an unmodified breadcrumb when the user callback throws, are exactly the fallbacks the spec forbids.

💚 How did you test it?

Unit tests in test/utils/safe.test.ts and test/sdk.test.ts:

beforeBreadcrumb throw → result is null (dropped).
tracesSampler throw → falls back to the configured tracesSampleRate; returns undefined when no rate is configured.
Existing "does not throw" isolation tests retained.

yarn build:sdk, yarn lint:lerna, and the core Jest suite all pass.

📝 Checklist

I added tests to verify changes.
No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
I updated the docs if needed.
I updated the wizard if needed.
All tests passing.
Public API changes reviewed by another Mobile SDK team member or implemented according to the develop docs spec.
No breaking changes.

🔮 Next steps

…ith spec Per the Callback Error Isolation spec: - A throwing `beforeBreadcrumb` now drops the breadcrumb (returns null) instead of keeping the unmodified one. - A throwing `tracesSampler` now falls back to the configured `tracesSampleRate` instead of substituting a hardcoded 0. Fixes #6668 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

github-actions · 2026-09-04T09:11:05Z

Semver Impact of This PR

⚪ None (no version bump detected)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

fix(core): Align beforeBreadcrumb and tracesSampler error fallbacks with spec by antonis in #6675

ref(ios): Remove deprecated private SDK API usage by philprime in #6647
chore(deps): update Cocoa SDK to v9.27.0 by github-actions in #6670
chore(deps): update Sentry Android Gradle Plugin to v6.21.0 by github-actions in #6671
chore(deps): Bump fast-uri to ^3.1.6 to resolve security alerts by antonis in #6662
chore(deps): Bump qs to ^6.16.0 to resolve security alerts by antonis in #6663
chore(deps): Bump @xmldom/xmldom pins to patched versions to resolve security alerts by antonis in #6664
docs: Revamp root and nested AGENTS.md by antonis in #6666

_{🤖 This preview updates automatically when you update the PR.}

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

antonis · 2026-09-04T09:23:17Z

@cursor review

antonis · 2026-09-04T09:23:23Z

@sentry review

cursor

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit f52b6c8. Configure here.}

sentry · 2026-09-04T09:29:50Z

📲 Install Builds

Android

🔗 App Name	App ID	Version	Configuration
Sentry RN	io.sentry.reactnative.sample	8.25.0 (105)	Release

⚙️ sentry-react-native Build Distribution Settings

github-actions · 2026-09-04T09:37:42Z

Android (legacy) Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	415.45 ms	435.48 ms	20.03 ms
Size	50.56 MiB	56.46 MiB	5.90 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
`68672fc`+dirty	425.02 ms	487.56 ms	62.54 ms
`71abba0`+dirty	496.54 ms	525.16 ms	28.63 ms
`7ff4d0f`+dirty	413.81 ms	450.64 ms	36.83 ms
`9ad4522`+dirty	420.73 ms	444.18 ms	23.45 ms
`0a147b2`+dirty	464.71 ms	538.81 ms	74.09 ms
`d2eadf8`+dirty	414.64 ms	454.56 ms	39.92 ms
`57e0069`+dirty	413.82 ms	453.47 ms	39.65 ms
`26843eb`+dirty	532.15 ms	624.13 ms	91.98 ms
`9210ae6`+dirty	475.41 ms	525.24 ms	49.84 ms
`1e5d96d`+dirty	519.43 ms	543.62 ms	24.19 ms

App size

Revision	Plain	With Sentry	Diff
`68672fc`+dirty	48.30 MiB	53.61 MiB	5.31 MiB
`71abba0`+dirty	48.30 MiB	53.49 MiB	5.19 MiB
`7ff4d0f`+dirty	48.30 MiB	53.60 MiB	5.30 MiB
`9ad4522`+dirty	49.74 MiB	55.38 MiB	5.63 MiB
`0a147b2`+dirty	49.74 MiB	55.08 MiB	5.34 MiB
`d2eadf8`+dirty	48.30 MiB	53.48 MiB	5.18 MiB
`57e0069`+dirty	49.74 MiB	54.85 MiB	5.11 MiB
`26843eb`+dirty	49.74 MiB	55.26 MiB	5.52 MiB
`9210ae6`+dirty	48.30 MiB	53.54 MiB	5.23 MiB
`1e5d96d`+dirty	49.74 MiB	54.81 MiB	5.07 MiB

Previous results on branch: fix/callback-error-isolation-fallbacks

Startup times

Revision	Plain	With Sentry	Diff
`ae855c2`+dirty	420.33 ms	448.70 ms	28.37 ms

App size

Revision	Plain	With Sentry	Diff
`ae855c2`+dirty	50.56 MiB	56.46 MiB	5.90 MiB

github-actions · 2026-09-04T09:37:58Z

iOS (legacy) Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	3861.24 ms	1234.80 ms	-2626.45 ms
Size	5.15 MiB	6.88 MiB	1.73 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
`ecf47a2`+dirty	3835.20 ms	1222.43 ms	-2612.77 ms
`3817909`+dirty	1183.90 ms	1187.50 ms	3.60 ms
`5ee78d6`+dirty	3847.52 ms	1224.27 ms	-2623.25 ms
`890d145`+dirty	1223.59 ms	1231.37 ms	7.78 ms
`e763471`+dirty	3841.16 ms	1218.06 ms	-2623.09 ms
`3d31fcf`+dirty	3838.09 ms	1223.46 ms	-2614.63 ms
`9210ae6`+dirty	3815.93 ms	1214.14 ms	-2601.79 ms
`26843eb`+dirty	3861.60 ms	1238.77 ms	-2622.82 ms
`7a89652`+dirty	3861.46 ms	1229.61 ms	-2631.85 ms
`9ad4522`+dirty	3850.40 ms	1222.40 ms	-2628.00 ms

App size

Revision	Plain	With Sentry	Diff
`ecf47a2`+dirty	4.98 MiB	6.46 MiB	1.49 MiB
`3817909`+dirty	3.38 MiB	4.73 MiB	1.35 MiB
`5ee78d6`+dirty	5.15 MiB	6.69 MiB	1.53 MiB
`890d145`+dirty	3.38 MiB	4.77 MiB	1.38 MiB
`e763471`+dirty	4.98 MiB	6.51 MiB	1.53 MiB
`3d31fcf`+dirty	4.98 MiB	6.56 MiB	1.58 MiB
`9210ae6`+dirty	5.15 MiB	6.68 MiB	1.53 MiB
`26843eb`+dirty	4.98 MiB	6.53 MiB	1.55 MiB
`7a89652`+dirty	5.15 MiB	6.70 MiB	1.55 MiB
`9ad4522`+dirty	4.98 MiB	6.56 MiB	1.58 MiB

Previous results on branch: fix/callback-error-isolation-fallbacks

Startup times

Revision	Plain	With Sentry	Diff
`ae855c2`+dirty	3864.24 ms	1226.41 ms	-2637.83 ms

App size

Revision	Plain	With Sentry	Diff
`ae855c2`+dirty	5.15 MiB	6.88 MiB	1.73 MiB

github-actions · 2026-09-04T09:48:28Z

Android (new) Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	480.34 ms	517.98 ms	37.64 ms
Size	50.56 MiB	56.46 MiB	5.90 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
`5a010b7`+dirty	475.15 ms	519.02 ms	43.88 ms
`f9c1ed4`+dirty	520.57 ms	594.84 ms	74.27 ms
`c2e182c`+dirty	468.50 ms	545.44 ms	76.94 ms
`2c735cc`+dirty	435.20 ms	459.48 ms	24.28 ms
`af33f3b`+dirty	417.68 ms	448.04 ms	30.37 ms
`7d8c8bd`+dirty	406.06 ms	460.88 ms	54.81 ms
`890d145`+dirty	486.42 ms	514.85 ms	28.43 ms
`ef27341`+dirty	519.02 ms	553.42 ms	34.40 ms
`bf168a4`+dirty	430.60 ms	459.31 ms	28.71 ms
`41d6254`+dirty	406.20 ms	445.52 ms	39.32 ms

App size

Revision	Plain	With Sentry	Diff
`5a010b7`+dirty	48.30 MiB	53.58 MiB	5.28 MiB
`f9c1ed4`+dirty	49.74 MiB	54.86 MiB	5.12 MiB
`c2e182c`+dirty	49.74 MiB	54.85 MiB	5.11 MiB
`2c735cc`+dirty	43.94 MiB	48.94 MiB	5.00 MiB
`af33f3b`+dirty	49.74 MiB	55.09 MiB	5.35 MiB
`7d8c8bd`+dirty	48.30 MiB	53.54 MiB	5.23 MiB
`890d145`+dirty	43.94 MiB	49.00 MiB	5.06 MiB
`ef27341`+dirty	48.30 MiB	53.54 MiB	5.24 MiB
`bf168a4`+dirty	49.74 MiB	55.09 MiB	5.35 MiB
`41d6254`+dirty	48.30 MiB	53.60 MiB	5.30 MiB

Previous results on branch: fix/callback-error-isolation-fallbacks

Startup times

Revision	Plain	With Sentry	Diff
`ae855c2`+dirty	499.09 ms	532.80 ms	33.71 ms

App size

Revision	Plain	With Sentry	Diff
`ae855c2`+dirty	50.56 MiB	56.46 MiB	5.90 MiB

github-actions · 2026-09-04T09:50:04Z

iOS (new) Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	3859.77 ms	1246.67 ms	-2613.10 ms
Size	5.15 MiB	6.88 MiB	1.73 MiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
`71abba0`+dirty	3852.70 ms	1224.53 ms	-2628.16 ms
`bc0d8cf`+dirty	3834.64 ms	1223.91 ms	-2610.73 ms
`68ae91b`+dirty	3836.36 ms	1222.04 ms	-2614.32 ms
`267d3ed`+dirty	3860.14 ms	1223.39 ms	-2636.76 ms
`f170ec3`+dirty	3844.74 ms	1222.67 ms	-2622.07 ms
`b9bebee`+dirty	3858.02 ms	1231.92 ms	-2626.11 ms
`d038a14`+dirty	3831.11 ms	1216.30 ms	-2614.81 ms
`853723c`+dirty	3849.33 ms	1221.07 ms	-2628.26 ms
`e763471`+dirty	3826.10 ms	1221.52 ms	-2604.58 ms
`3d31fcf`+dirty	3857.46 ms	1237.17 ms	-2620.29 ms

App size

Revision	Plain	With Sentry	Diff
`71abba0`+dirty	5.15 MiB	6.67 MiB	1.52 MiB
`bc0d8cf`+dirty	5.15 MiB	6.67 MiB	1.51 MiB
`68ae91b`+dirty	4.98 MiB	6.46 MiB	1.48 MiB
`267d3ed`+dirty	5.15 MiB	6.69 MiB	1.54 MiB
`f170ec3`+dirty	5.15 MiB	6.69 MiB	1.53 MiB
`b9bebee`+dirty	5.15 MiB	6.68 MiB	1.53 MiB
`d038a14`+dirty	5.15 MiB	6.67 MiB	1.51 MiB
`853723c`+dirty	5.15 MiB	6.69 MiB	1.53 MiB
`e763471`+dirty	4.98 MiB	6.51 MiB	1.53 MiB
`3d31fcf`+dirty	4.98 MiB	6.56 MiB	1.58 MiB

Previous results on branch: fix/callback-error-isolation-fallbacks

Startup times

Revision	Plain	With Sentry	Diff
`ae855c2`+dirty	3856.82 ms	1223.13 ms	-2633.69 ms

App size

Revision	Plain	With Sentry	Diff
`ae855c2`+dirty	5.15 MiB	6.88 MiB	1.73 MiB

antonis and others added 2 commits September 4, 2026 11:09

docs: Reference PR in changelog entry

728ce2f

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs: Simplify changelog entry wording

f52b6c8

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

antonis added the ready-to-merge Triggers the full CI test suite label Sep 4, 2026

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antonis marked this pull request as ready for review September 4, 2026 10:27

antonis requested review from alwx and lucas-zimerman as code owners September 4, 2026 10:27

antonis force-pushed the fix/callback-error-isolation-fallbacks branch from 137631b to f52b6c8 Compare September 4, 2026 10:49

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