test(rust): enable passing ot.th/ot.rv tracestate sampling scenarios [rust@milan.garnier/otel-tracestate-ot-th]

[MilanGarnier]

Motivation

Stacked on #7372 (the ot.th/ot.rv conformance scaffolding). Enables the Rust entries against dd-trace-rs's wire implementation (branch milan.garnier/otel-tracestate-ot-th), verified locally against a rust@0.5.1-dev+c36937d build (axum weblog) across every scenario (DEFAULT + all five sample-rate scenarios).

What does this PR do?

Flips all tests/test_otel_tracestate_sampling.py Rust entries from missing_feature to >=0.5.0-dev in manifests/rust.yml, and backfills 3 previously-unlisted classes (Test_ForwardInboundOtUnchangedWhenDropped, Test_ThOnlyDoesNotFabricateRv, Test_ThOnlyDoesNotFabricateRvWhenDropped) as missing_feature across the other 8 language manifests to preserve the "disabled for every tracer until it ships" invariant. OTLP entries (test_tracing_otlp.py, APMAPI-2172) are untouched per scope.

Local verification results (ai generated draft not reviewed)

• DEFAULT scenario: 6/9 selected tests pass. The 3 Test_ForceKeepClearsTh (A4) sub-tests fail, but not because of an ot.th gap: the local weblog used for verification (a not-yet-merged Rust Axum weblog) has no AppSec/WAF integration, so the Arachni-user-agent-triggered force-keep this test relies on never fires. The underlying "clear th, forward inherited rv" wire logic it exercises is already unit-tested and passing (tracecontext.rs::force_keep_clears_th_forwards_rv).
• Rate scenarios: only SAMPLING (rate 0.5) passes outright. OTEL_SAMPLING_RATE_0_01/0_1/0_2/0_99 all fail on a th mismatch of a few ULPs against TH_BY_RATE — two independent rounding bugs, not one:
  • TH_BY_RATE[0.1] in the test fixture itself is stale (e6666666666668); the exact-fraction value is e6666666666666, which matches both what Rust emits and dd-trace-rs's own corrected example.
  • For rate 0.01, Rust emits one ULP above the exact-fraction floor (fd70a3d70a3d71 vs fd70a3d70a3d70) — a rounding discrepancy in the unreleased libdd-sampling::OtelConsistentSampling threshold computation dd-trace-rs depends on, not in dd-trace-rs itself.

Both issues need a fix (one in this repo's fixture, one upstream in libdatadog) before these entries are actually green. Opening as draft now since the manifest/scope work itself is done and the base branch is expected to move; will flip out of draft once the rounding fixes land and a clean local rerun confirms all scenarios pass.

Base

Targets ben.db/feat-otel-tracestate-sampling-scaffolding (stacked). Retarget to main once #7372 merges.

[github-actions]

CODEOWNERS have been resolved as:

manifests/rust.yml                                                      @DataDog/apm-rust

[datadog-official]

 

⚠️ Warnings

🚦 5 Pipeline jobs failed

Testing the test | System Tests (rust, prod) / End-to-end #1 / axum 1     

🔧 Fix in code. This looks caused by changes in this PR.

Test run failed due to missing 'ot' tracestate member on probability decisions and unexpected 'th' values.

🧪 7 Tests failed · 🎯 related to the job error above

🎯 tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_01.test_emit_ot_on_probability_decision[axum] from system_tests_suite  

AssertionError: trace_id=1: no ot= tracestate member emitted on a probability decision
assert 'ot' in Tracestate(dd=s:-1;p:8133ffb164d19032;t.dm:-3)

self = <tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_01 object at 0x7ff56566c560>

    def test_emit_ot_on_probability_decision(self):
        for req, trace_id, expected_rv, expected_th, expected_sampled in self.requests:
            assert req.status_code == 200, f"trace_id={trace_id}: /make_distant_call failed"
    
            tracestate = _outbound_tracestate(req)
...

🎯 tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_1.test_emit_ot_on_probability_decision[axum] from system_tests_suite  

AssertionError: trace_id=1: no ot= tracestate member emitted on a probability decision
assert 'ot' in Tracestate(dd=s:2;p:3f64fd37061f33d5;t.dm:-3)

self = <tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_1 object at 0x7fc774d71a30>

    def test_emit_ot_on_probability_decision(self):
        for req, trace_id, expected_rv, expected_th, expected_sampled in self.requests:
            assert req.status_code == 200, f"trace_id={trace_id}: /make_distant_call failed"
    
            tracestate = _outbound_tracestate(req)
...

🎯 tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_2.test_emit_ot_on_probability_decision[axum] from system_tests_suite  

AssertionError: trace_id=1: no ot= tracestate member emitted on a probability decision
assert 'ot' in Tracestate(dd=s:2;p:d9fd7ef6edde749f;t.dm:-3)

self = <tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_2 object at 0x7f514c86d9d0>

    def test_emit_ot_on_probability_decision(self):
        for req, trace_id, expected_rv, expected_th, expected_sampled in self.requests:
            assert req.status_code == 200, f"trace_id={trace_id}: /make_distant_call failed"
    
            tracestate = _outbound_tracestate(req)
...

View all failed tests

Testing the test | System Tests (rust, prod) / End-to-end #2 / axum 2     

🔧 Fix in code. This looks caused by changes in this PR.

Test run failed due to assertion errors related to sampling priority mismatches and missing trace state members.

🧪 5 Tests failed

tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_5.test_emit_ot_on_probability_decision[axum] from system_tests_suite  

AssertionError: trace_id=1: no ot= tracestate member emitted on a probability decision
assert 'ot' in Tracestate(dd=s:2;p:7959353d0c28d299;t.dm:-3)

self = <tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_5 object at 0x7fdfc4081d00>

    def test_emit_ot_on_probability_decision(self):
        for req, trace_id, expected_rv, expected_th, expected_sampled in self.requests:
            assert req.status_code == 200, f"trace_id={trace_id}: /make_distant_call failed"
    
            tracestate = _outbound_tracestate(req)
...

tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_99.test_emit_ot_on_probability_decision[axum] from system_tests_suite  

AssertionError: trace_id=1: no ot= tracestate member emitted on a probability decision
assert 'ot' in Tracestate(dd=s:2;p:077ce93d1d290336;t.dm:-3)

self = <tests.test_otel_tracestate_sampling.Test_EmitOtOnProbabilityDecision_Rate0_99 object at 0x7f5268a6a120>

    def test_emit_ot_on_probability_decision(self):
        for req, trace_id, expected_rv, expected_th, expected_sampled in self.requests:
            assert req.status_code == 200, f"trace_id={trace_id}: /make_distant_call failed"
    
            tracestate = _outbound_tracestate(req)
...

tests.test_otel_tracestate_sampling.Test_ForceKeepClearsTh.test_force_keep_forwards_inherited_rv[axum] from system_tests_suite  

assert 0.0 == <SamplingPriority.USER_KEEP: 2>
 +  where 0.0 = <bound method DataDogLibrarySpanLegacy.get_sampling_priority of <utils.dd_types._datadog_library_trace.DataDogLibrarySpanLegacy object at 0x7f39486f7f80>>()
 +    where <bound method DataDogLibrarySpanLegacy.get_sampling_priority of <utils.dd_types._datadog_library_trace.DataDogLibrarySpanLegacy object at 0x7f39486f7f80>> = <utils.dd_types._datadog_library_trace.DataDogLibrarySpanLegacy object at 0x7f39486f7f80>.get_sampling_priority
 +  and   <SamplingPriority.USER_KEEP: 2> = SamplingPriority.USER_KEEP

self = <tests.test_otel_tracestate_sampling.Test_ForceKeepClearsTh object at 0x7f396661b740>

    def test_force_keep_forwards_inherited_rv(self):
        """An inherited rv (no th, so no upstream probability decision) is still forwarded on a local force-keep."""
        assert self.rv_only_request.status_code == 200
...

View all failed tests

Testing the test | Fail if target branch is specified     

See error

Job failed because the PR title specifies a target branch which is not allowed.

View all 5 failed jobs.

📋 Copy prompt for your agent

CI on my pull request is failing. Help me find and fix the root cause of each failing job below — they were flagged as caused by changes in this PR, so focus on the diff. For each job, explain the failure and propose a fix.

Branch: milan.garnier/feat-rs-ot.th

Testing the test | System Tests (rust, prod) / End-to-end #1 / axum 1
Commit: 6eae59bee2c250bfbc2abf8a52f196fea70bf772
Error (code / test):
4 failed tests due to missing 'ot' tracestate member on probability decisions and unexpected 'th' values.
CI job: https://github.com/DataDog/system-tests/actions/runs/30643052656/job/91198729430

Testing the test | System Tests (rust, prod) / End-to-end #2 / axum 2
Commit: 6eae59bee2c250bfbc2abf8a52f196fea70bf772
Error (code / test):
3 failed tests due to assertion errors related to sampling priority mismatches and missing trace state members.
CI job: https://github.com/DataDog/system-tests/actions/runs/30643052656/job/91198729415

ℹ️ Info

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❄️ No new flaky tests detected

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