Generate KnownTags from a tag-conventions registry (phase 2)

[dougqh]

Code-generates the KnownTags registry from a language-agnostic tag-conventions.yaml (+ a Java
overlay), replacing the hand-maintained version. Based on dougqh/tag-id-api (the dense-store
branch). Draft — the generator works end to end (main compiles, tests pass); the committed-output
wiring is the remaining piece.

From Claude:

Pipeline (buildSrc task dd-trace-java.tag-registry-generator): parse → resolve per-type tag sets
(extends/include/applies) → assign ids → assign slots by deterministic graph coloring over
per-type layers + an explicit trace_level layer → emit KnownTags.java.

• Ids encode serial | slot | intercepted (no name hash — known ids are dense-store addressed;
  the name hash is the custom/bucket path). Emitted as literals (javac constant-folds them) with a
  // tagId(...) derivation comment for auditability.
• slot is a fast-path bitmask bit, not positional storage — co-occurrence is tolerated (the scan
  is authoritative). Coloring gives co-occurring tags distinct bits (fewer scans); colorability
  derives from required. The whole mask fits one long.
• Trace-level is its own tier (trace_level section → its own TagMap layer); the per-span base
  type holds parent_id/_dd.integration/_dd.svc_src (core-set but per-span).
• Virtual keys (service/resource.name/error/sampling.priority/…) get reserved ids; the
  generated id → handler dispatch table is the on-ramp to retiring the TagInterceptor.

Verified: internal-api main compiles; KnownTagsTest (property-based resolver round-trip over ~55
tags) passes; OptimizedTagMapDenseForkedTest passes; spotless clean. Note: literal ids fold, so a
constant reference no longer triggers <clinit> — registration is via KnownTags.init().

Remaining (why draft): the generated KnownTags.java is a manual copy in src/main right now;
wire the task to emit to a committed src/generated/java + srcDir + a verifyGenerated freshness
check + format-on-generate, and route the layout reports (folded-types/tag-assignment) there as
committed artifacts.

🤖 Generated with Claude Code

[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	14.12 s	14.02 s	[-0.3%; +1.7%] (no difference)
startup:insecure-bank:tracing:Agent	12.92 s	12.99 s	[-1.3%; +0.2%] (no difference)
startup:petclinic:appsec:Agent	16.52 s	16.39 s	[-5.8%; +7.3%] (unstable)
startup:petclinic:iast:Agent	16.88 s	16.88 s	[-1.0%; +1.0%] (no difference)
startup:petclinic:profiling:Agent	16.71 s	16.81 s	[-1.9%; +0.7%] (no difference)
startup:petclinic:sca:Agent	16.93 s	16.78 s	[-0.1%; +1.8%] (no difference)
startup:petclinic:tracing:Agent	16.10 s	15.99 s	[-0.3%; +1.7%] (no difference)

Commit:369a591d · CI Pipeline · Benchmarking Platform UI

---

Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

[datadog-prod-us1-3]

🎯 Code Coverage (details)
• Patch Coverage: 97.40%
• Overall Coverage: 57.31% (-0.01%)

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 369a591 | Docs | Datadog PR Page | Give us feedback!}

[datadog-prod-us1-3]

View session in Datadog

Bits Code status: ✅ Done

Comment @DataDog to request changes

[dougqh]

Superseded by #12047 — the tag-registry code generator, rebuilt on top of the clean dense #12045 / two-tier bloom #12046 layers. Closing in favor of #12047.