attribute: change INVALID Type to EMPTY and mark INVALID as deprecated

[pellared]

Fixes #7932

Noticeable comment from previous PR: #7942 (comment)

Print the empty value as empty string per https://opentelemetry.io/docs/specs/otel/common/#empty-values

[Copilot]

Pull request overview

Updates the go.opentelemetry.io/otel/attribute API to treat the zero attribute.Value{} as a first-class empty value (EMPTY) instead of an invalid value, aligning behavior with the OTel empty-value spec and deprecating the old INVALID identifier.

Changes:

• Introduces attribute.EMPTY as the zero/default Type and deprecates attribute.INVALID as an alias.
• Updates Emit()/AsInterface() and hashing logic to support EMPTY semantics (emit "", interface nil, stable hash).
• Adjusts validity rules and tests to treat empty values as valid attributes.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
log/keyvalue.go	Converts attribute.EMPTY into the log package’s empty Value{}.
attribute/value.go	Adds EMPTY, deprecates INVALID, updates AsInterface/Emit behavior.
attribute/type_string.go	Regenerated Type.String() output to include EMPTY.
attribute/kv.go	Makes KeyValue.Valid() accept empty values (key-defined only).
attribute/value_test.go	Adds EMPTY test coverage and equivalence/non-equivalence cases.
attribute/kv_test.go	Updates validity and incorrect-cast tests for EMPTY.
attribute/key_test.go	Adds Emit() test case for EMPTY emitting an empty string.
attribute/hash.go	Adds EMPTY hashing discriminator and EMPTY handling.
attribute/hash_test.go	Extends hash tests/fuzzing to include empty values.
CHANGELOG.md	Documents the change and deprecation in Unreleased notes.

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[Copilot]

Pull request overview

Copilot reviewed 27 out of 27 changed files in this pull request and generated no new comments.

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[codecov]

Codecov Report

❌ Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.5%. Comparing base (205e244) to head (5539bc4).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...dk/metric/metricdata/metricdatatest/comparisons.go	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #8038     +/-   ##
=======================================
- Coverage   81.6%   81.5%   -0.1%     
=======================================
  Files        304     304             
  Lines      23425   23438     +13     
=======================================
- Hits       19128   19124      -4     
- Misses      3909    3926     +17     
  Partials     388     388             

Files with missing lines	Coverage Δ
attribute/hash.go	91.4% <100.0%> (+2.3%)	⬆️
attribute/kv.go	100.0% <100.0%> (ø)
attribute/type_string.go	60.0% <ø> (ø)
attribute/value.go	92.8% <100.0%> (+0.2%)	⬆️
...otlp/otlplog/otlploggrpc/internal/transform/log.go	96.1% <100.0%> (-2.4%)	⬇️
...otlp/otlplog/otlploghttp/internal/transform/log.go	96.1% <100.0%> (-2.4%)	⬇️
...ric/otlpmetricgrpc/internal/transform/attribute.go	96.6% <100.0%> (-3.4%)	⬇️
...ric/otlpmetrichttp/internal/transform/attribute.go	96.6% <100.0%> (-3.4%)	⬇️
...tlp/otlptrace/internal/tracetransform/attribute.go	96.7% <100.0%> (-3.3%)	⬇️
log/keyvalue.go	97.0% <100.0%> (ø)
... and 1 more

... and 3 files with indirect coverage changes

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[pellared]

Should we update the method

opentelemetry-go/sdk/metric/metricdata/metricdatatest/comparisons.go

Line 561 in eee0fe3

default:

to include Empty? Otherwise this would panic.

Fixed 8015c7d

I tried to find similar cases, but it seemed to be the only one I missed.

[MrAlias]

Awesome work 👏