attribute: add SLICE type support

[pellared]

Fixes #7934

$ go test -run=^$ -bench=BenchmarkSlice
goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/attribute
cpu: 13th Gen Intel(R) Core(TM) i7-13800H
BenchmarkSlice/Len3/Value-20                    25297926                52.56 ns/op          144 B/op          1 allocs/op
BenchmarkSlice/Len3/KeyValue-20                 21315132                55.97 ns/op          144 B/op          1 allocs/op
BenchmarkSlice/Len3/AsSlice-20                  24214248                50.03 ns/op          144 B/op          1 allocs/op
BenchmarkSlice/Len3/String-20                   14148270                86.48 ns/op           48 B/op          1 allocs/op
BenchmarkSlice/Len3/Emit-20                     13605388                85.18 ns/op           48 B/op          1 allocs/op
BenchmarkSlice/Len5Nested/Value-20              16086171                71.30 ns/op          240 B/op          1 allocs/op
BenchmarkSlice/Len5Nested/KeyValue-20           15547844                75.81 ns/op          240 B/op          1 allocs/op
BenchmarkSlice/Len5Nested/AsSlice-20            17806996                66.16 ns/op          240 B/op          1 allocs/op
BenchmarkSlice/Len5Nested/String-20              7409064               165.2 ns/op            64 B/op          1 allocs/op
BenchmarkSlice/Len5Nested/Emit-20                7666302               161.0 ns/op            64 B/op          1 allocs/op
PASS
ok      go.opentelemetry.io/otel/attribute      12.980s

$ go test -run=^$ -bench=BenchmarkHashKVs
goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/attribute
cpu: 13th Gen Intel(R) Core(TM) i7-13800H
BenchmarkHashKVs-20      1268742               940.5 ns/op             0 B/op          0 allocs/op
PASS
ok      go.opentelemetry.io/otel/attribute      1.198s

[codecov]

Codecov Report

❌ Patch coverage is 95.96774% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.5%. Comparing base (bb6804e) to head (d6906e5).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
trace/auto.go	0.0%	6 Missing ⚠️
attribute/value.go	98.7%	3 Missing and 1 partial ⚠️
...dk/metric/metricdata/metricdatatest/comparisons.go	0.0%	3 Missing ⚠️
attribute/hash.go	94.4%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #8166     +/-   ##
=======================================
+ Coverage   82.3%   82.5%   +0.1%     
=======================================
  Files        310     310             
  Lines      24267   24555    +288     
=======================================
+ Hits       19990   20261    +271     
- Misses      3901    3916     +15     
- Partials     376     378      +2     

Files with missing lines	Coverage Δ
attribute/key.go	100.0% <100.0%> (ø)
attribute/kv.go	100.0% <100.0%> (ø)
attribute/type_string.go	60.0% <ø> (ø)
log/keyvalue.go	97.1% <100.0%> (+<0.1%)	⬆️
attribute/hash.go	94.5% <94.4%> (+2.5%)	⬆️
...dk/metric/metricdata/metricdatatest/comparisons.go	96.9% <0.0%> (-0.6%)	⬇️
attribute/value.go	97.6% <98.7%> (+0.4%)	⬆️
trace/auto.go	95.6% <0.0%> (-1.7%)	⬇️

... and 3 files with indirect coverage changes

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[MrAlias]

Overall, looks good.

I assume we're going to address the attribute limits and exporter support in a follow-up, right?

[pellared]

I assume we're going to address the attribute limits and exporter support in a follow-up, right?

Correct:

• exporters: Handle SLICE type #8162
• sdk: Apply attribute value limit for SLICE #7955

[pellared]

I am going to create a separate PR for improving the speed execution of TestHashKVsEquality which even on my machine runs for almost 10s.

EDIT: My idea is to change the test so that it only checks if hashKVs generates unique hashes. I do not think we should also check the equality operators (this is a separate concern). I have an idea how to change the test from O(n^2) to O(n). Going to submit a PR tomorrow.
EDIT 2: PR #8204

[Copilot]

Pull request overview

Adds first-class support for heterogeneous SLICE attribute values (arrays of attribute.Value) across the attribute package and downstream conversions, aligning with the OTel AnyValue array concept.

Changes:

• Introduce attribute.SLICE plus Slice/SliceValue constructors and Value.AsSlice()/string formatting support.
• Propagate SLICE handling into trace auto-conversion, log attribute conversion, hashing, and metric test comparisons.
• Add/extend unit tests, fuzz/bench coverage, and update changelog.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
trace/auto.go	Convert attribute.SLICE into telemetry nested slice values.
sdk/metric/metricdata/metricdatatest/comparisons.go	Extend attribute equality helper to handle SLICE.
log/keyvalue.go	Convert attribute.SLICE into log SliceValue recursively.
log/keyvalue_test.go	Add test coverage for SLICE conversion to log values.
log/keyvalue_bench_test.go	Add benchmark case for SLICE conversion.
attribute/value.go	Add SLICE type, constructors/accessors, formatting, and base64 writer helper.
attribute/value_test.go	Add tests for SLICE value behavior, AsSlice, and string formatting.
attribute/type_string.go	Regenerate Type.String() backing tables to include SLICE.
attribute/kv.go	Add attribute.Slice convenience constructor.
attribute/key.go	Add Key.Slice constructor.
attribute/kv_test.go	Add constructor/validity/incorrect-cast tests for SLICE.
attribute/key_test.go	Add Emit/String tests for SLICE formatting behavior.
attribute/hash.go	Add hashing support for SLICE values (including nested).
attribute/hash_test.go	Extend hash test generators + add SLICE fuzz/bench coverage.
attribute/benchmark_test.go	Add slice benchmarks for construction/access/string/emit.
CHANGELOG.md	Document new SLICE attribute type API additions.

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