refactor: consolidate platform-specific code

[overbalance]

Which problem is this PR solving?

Platform directories contain duplicate code with fallback chains for legacy environments that are no longer needed. Since the minimum supported versions are Node 18+ and modern browsers, globalThis and performance are universally available.

Short description of the changes

@opentelemetry/api

• Deleted entire src/platform/ directory
• Use globalThis directly instead of _globalThis
• Removed browser field mappings from package.json

@opentelemetry/api-logs

• Deleted entire src/platform/ directory
• Use globalThis directly instead of _globalThis
• Removed browser field mappings from package.json

@opentelemetry/core

• globalThis: Moved to common/globalThis.ts as deprecated re-export of globalThis
• performance: Removed wrapper files, otperformance is now a deprecated alias for performance
• Deleted platform-specific globalThis.ts and performance.ts files

@opentelemetry/resources

• Hoisted defaultServiceName to src/ with runtime check (process.argv0 in Node, fallback to unknown_service)
• Deleted entire src/platform/ directory
• Removed 4 browser field mappings from package.json
• Added unit tests for defaultServiceName

@opentelemetry/instrumentation-fetch

• Use globalThis directly instead of importing _globalThis from core

Documentation

• Updated CONTRIBUTING.md to remove outdated platform-specific code examples
• Added CHANGELOG entry

Type of change

• Refactor (non-breaking change which improves code quality)

How Has This Been Tested?

• npm test passes for all affected packages
• Browser/webworker tests pass
• Added tests for defaultServiceName (Node + browser environments)

Checklist:

• Followed the style guidelines of this project
• Unit tests have been added
• Documentation has been updated

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.39%. Comparing base (b2025ca) to head (61d0bbb).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...pentelemetry-resources/src/default-service-name.ts	83.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6208      +/-   ##
==========================================
- Coverage   95.40%   95.39%   -0.02%     
==========================================
  Files         317      314       -3     
  Lines        9514     9513       -1     
  Branches     2192     2194       +2     
==========================================
- Hits         9077     9075       -2     
- Misses        437      438       +1     

Files with missing lines	Coverage Δ
api/src/internal/global-utils.ts	100.00% <100.00%> (ø)
...tal/packages/api-logs/src/internal/global-utils.ts	100.00% <100.00%> (ø)
...ckages/opentelemetry-core/src/common/globalThis.ts	100.00% <100.00%> (ø)
...ckages/opentelemetry-resources/src/ResourceImpl.ts	98.90% <100.00%> (ø)
...pentelemetry-resources/src/default-service-name.ts	85.71% <83.33%> (ø)

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[cjihrig]

~1.8x slower than Node Buffer (acceptable: 126ns vs 70ns per call)

Even though it's nice to have shared code, I'm not sure we should make this method slower. I (and others) am already seeing drastic slowdowns in HTTP servers when OTel is enabled, and generatedId() was showing up in flame graphs (albeit only ~3% of captured stacks).

[overbalance]

@cjihrig Cool. Reverted.

[david-luna]

I like the idea of consolidating code whenever possible without affecting perf. In fact I think sdk-info.ts from core package could be consolidated as well. LGTM but let's wait for other reviews :)

[pichlermarc]

opentelemetry-core

• globalThis: Moved to common - browser's fallback chain (globalThis → self → window → global → {}) works in all environments

We should be able to deprecate this and subsequently remove it in @opentelmetry/core@3.0.0, actually. It's only used in @opentelemetry/instrumentation-fetch

suggestion: let's copy the browser's fallback chain to where it's used in @opentelemetry/instrumentation-fetch and deprecate the one in @opentelemetry/core.

[overbalance]

@pichlermarc I updated api and api-logs as well since they had the same pattern and the docs in core said to keep api in sync.

[chargome]

@overbalance
This breaks on vercel edge environments

[andreiborza]

Hi @overbalance, as @chargome mentioned, this unfortunately breaks our vercel-edge environment due to process.argv0 being a node api.

We ended up having to bundle in @opentelemetry/resources and any code that uses it. It's not ideal.

Any way we can figure out a workaround here?

[overbalance]

@chargome @andreiborza check out this other PR I've had out for review. Do you think it would solve your issue: #6257

[andreiborza]

hey, that might work! Thanks for tackling this 🙏

[trentm]

@andreiborza You said this "breaks"? What is the break? Inferring from @overbalance's PR there is warning from vercel-edge static analysis of some sort? Can you show an example?

For example, I don't recall here about warnings/breakages from this old change that was feature-testing for Node.js' process object: https://github.com/open-telemetry/opentelemetry-js/pull/4604/files#diff-7775cbc8f9eed30ff77488613bcbabec57446d86f655166fbdb5f7db4579a0b6R29

In that case it was checking global.process?.<something>.
If the code here in this PR used global.process instead of process, would that make the static analysis warnings go away?

[andreiborza]

Here's an example run of a nextjs app using our vercel-edge SDK: https://github.com/getsentry/sentry-javascript/actions/runs/20844816035/job/59886209607?pr=18734#step:16:157

We end up getting

 'A Node.js API is used (process.argv0 at line: 19) which is not supported in the Edge Runtime.\n' +

issues when building the app.

[overbalance]

Thanks @andreiborza I was able to replicate and solve the issue: #6257