🐛 [RUM-13741] Fix sibling uniqueness check for elements in DocumentFragment

[thomas-lebeau]

Motivation

This fixes a recurrent error in the sdk telemetry.

The error happens because currentElement.parentElement can actually be null, for example when the parent is a document fragment (in that case the parent is a Document, not an Element.)

Instead of relying on parent.firstElementChild to iterate siblings, the fix uses direct sibling traversal:

• Check previousElementSibling (backward)
• Check nextElementSibling (forward)

This approach works regardless of parent type, including when parentElement is null.

Changes

• Replaced parent.firstElementChild iteration with direct previousElementSibling and nextElementSibling traversal
• Added tests for DocumentFragment scenarios with matching and non-matching siblings

Test instructions

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.

[datadog-datadog-prod-us1]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 71.43%
• Overall Coverage: 77.25% (-0.08%)

View detailed report

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: bcfaee6 | Docs | Datadog PR Page | Was this helpful? Give us feedback!}

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	165.78 KiB	165.84 KiB	+59 B	+0.03%	✅
Rum Profiler	4.33 KiB	4.33 KiB	0 B	0.00%	✅
Rum Recorder	24.48 KiB	24.48 KiB	0 B	0.00%	✅
Logs	56.21 KiB	56.21 KiB	0 B	0.00%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	123.05 KiB	123.11 KiB	+59 B	+0.05%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0039	0.0047	+20.51%
RUM - add action	0.0129	0.014	+8.53%
RUM - add error	0.0123	0.0154	+25.20%
RUM - add timing	0.0025	0.0031	+24.00%
RUM - start view	0.003	0.0039	+30.00%
RUM - start/stop session replay recording	0.0006	0.0008	+33.33%
Logs - log message	0.0143	0.0161	+12.59%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	27.89 KiB	26.26 KiB	-1.62 KiB
RUM - add action	50.08 KiB	49.98 KiB	-104 B
RUM - add timing	27.36 KiB	26.99 KiB	-385 B
RUM - add error	55.79 KiB	56.09 KiB	+304 B
RUM - start/stop session replay recording	24.97 KiB	25.11 KiB	+147 B
RUM - start view	427.11 KiB	426.77 KiB	-347 B
Logs - log message	45.38 KiB	98.59 KiB	+53.22 KiB

🔗 RealWorld