[CODE HEALTH] Remove unused alias declarations

[thc1006]

Summary

Eliminates 29 misc-unused-alias-decls warnings flagged by clang-tidy v22, spread across 27 files in examples, exporters, sdk source, and tests. The dominant pattern was a file-scope declaration like:

namespace nostd = opentelemetry::nostd;

that was never referenced via the file-scope alias path. Uses of nostd:: inside the surrounding OPENTELEMETRY_BEGIN_NAMESPACE block resolved through namespace nesting (finding opentelemetry::nostd via parent-namespace lookup) before ever reaching the file-scope alias. Other variants flagged: common, context, metric_sdk, metric_api, metric_exporter, http_client, trace, trace_api, trace_sdk_2.

No behavior change. Every removed declaration was genuinely unreferenced per clang-tidy. Verified against three representative samples (production code with namespace nesting, test code with using namespace, examples with zero references).

Where removing a declaration left adjacent aligned lines (e.g. using M = std::map<...>; next to a removed namespace nostd = ...;), clang-format auto-collapsed the now-unnecessary alignment whitespace.

Excluded from this PR

The 30th misc-unused-alias-decls site at exporters/otlp/src/otlp_populate_attribute_utils.cc:30 is intentionally not touched, to avoid a file-level conflict with the in-flight #4090. It can be cleaned up in a trivial follow-up after #4090 lands.

Ratchet

• all-options-abiv1-preview warning_limit lowered from 418 to 389
• all-options-abiv2-preview warning_limit lowered from 424 to 395

(If #4090 lands first, this PR will need a trivial ratchet rebase from 414→385 and 420→391 — the relative drop of 29 is unchanged.)

Verification

Counts measured against artifacts of the most recent successful CI run on main (workflow clang-tidy.yaml, run 26018587378):

Preset	Before (count / limit)	After (predicted)
abiv1-preview	418 / 418	389 / 389
abiv2-preview	424 / 424	395 / 395

Sample verification of the "unused" claim was performed on three representative files (exporters/elasticsearch/src/es_log_record_exporter.cc, sdk/test/metrics/sync_metric_storage_counter_test.cc, examples/simple/main.cc) — all three confirmed the alias is genuinely dead.

Local format verification: ran clang-format --dry-run --Werror via the project's clang-format-compatible toolchain against all 27 modified source files; clean.

Test plan

• CI clang-tidy job passes both abiv1-preview and abiv2-preview at the new limits
• CI Format job passes
• CI build and test matrices pass — declarations being removed were not in any active use path

Part of #2053

[Copilot]

Pull request overview

This PR is a code-health cleanup to reduce clang-tidy misc-unused-alias-decls warnings by removing unused file-scope namespace alias declarations across examples, exporters, SDK source, and tests, and by ratcheting the clang-tidy warning limits accordingly.

Changes:

• Remove unused namespace alias declarations (e.g., namespace nostd = opentelemetry::nostd;) across multiple components.
• Update the clang-tidy GitHub Actions workflow warning limits to reflect the reduced warning count.
• Add an Unreleased changelog entry for this code-health change.

Reviewed changes

Copilot reviewed 29 out of 29 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
sdk/test/metrics/sync_metric_storage_up_down_counter_test.cc	Removes unused namespace alias; formatting cleanup in local aliases.
sdk/test/metrics/sync_metric_storage_histogram_test.cc	Removes unused namespace alias; formatting cleanup in local aliases.
sdk/test/metrics/sync_metric_storage_gauge_test.cc	Removes unused namespace alias.
sdk/test/metrics/sync_metric_storage_counter_test.cc	Removes unused namespace alias; formatting cleanup in local aliases.
sdk/test/metrics/async_metric_storage_test.cc	Removes unused namespace alias.
sdk/src/logs/logger.cc	Removes unused namespace alias inside sdk::logs.
exporters/zipkin/src/zipkin_exporter_factory.cc	Removes unused HTTP client namespace alias.
exporters/prometheus/test/collector_test.cc	Removes unused metric-related namespace aliases in tests.
exporters/prometheus/src/collector.cc	Removes unused metrics SDK namespace alias.
exporters/otlp/test/otlp_recordable_test.cc	Removes redundant unused trace namespace alias.
exporters/otlp/src/otlp_recordable.cc	Removes unused nostd namespace alias.
exporters/ostream/test/ostream_metric_test.cc	Removes unused nostd namespace alias.
exporters/elasticsearch/src/es_log_record_exporter.cc	Removes unused nostd namespace alias.
examples/zipkin/main.cc	Removes unused trace namespace alias.
examples/simple/main.cc	Removes unused trace API namespace alias.
examples/prometheus/main.cc	Removes unused common namespace alias.
examples/otlp/http_metric_main.cc	Removes unused common namespace alias.
examples/otlp/http_main.cc	Removes unused trace namespace alias.
examples/otlp/http_log_main.cc	Removes unused trace namespace alias.
examples/otlp/grpc_metric_main.cc	Removes unused common namespace alias.
examples/otlp/grpc_main.cc	Removes unused trace namespace alias.
examples/otlp/grpc_log_main.cc	Removes unused trace namespace alias.
examples/otlp/file_metric_main.cc	Removes unused common namespace alias.
examples/otlp/file_main.cc	Removes unused trace namespace alias.
examples/otlp/file_log_main.cc	Removes unused trace namespace alias.
examples/metrics_simple/metrics_ostream.cc	Removes unused common namespace alias.
CHANGELOG.md	Adds an Unreleased changelog entry for the cleanup.
api/test/trace/tracer_test.cc	Removes unused context namespace alias.
.github/workflows/clang-tidy.yaml	Lowers clang-tidy warning limits to match the reduced warnings.

[thc1006]

Good catch. The 4 using M = std::map<std::string, std::string>; lines in the storage tests (counter, histogram, up_down_counter, async) were indeed unused. clang-tidy did not flag them because misc-unused-alias-decls targets namespace aliases only, not type aliases — but the same dead-code spirit applies and the files were already in this PR.

Removed all 4 in the next force-push. Adjusted the PR title and CHANGELOG entry from "namespace alias declarations" to the broader "alias declarations" to cover both kinds.

(For symmetry: sync_metric_storage_gauge_test.cc does not declare M at all, so nothing to remove there.)

[thc1006]

The CHANGELOG entry already uses the actual PR number #4091 (visible in the diff_hunk this review comment quotes). There is no #XXXX placeholder in the current file; the body of this review comment appears to misread its own quoted diff. Same false-positive pattern reported on PR #3989, #3997, #4013, and #4090.

[marcalff]

LGTM, thanks for the cleanup.

[marcalff]

Now that some aliases are removed, extra includes can be removed as well, see IWYU failures:

/home/runner/work/opentelemetry-cpp/opentelemetry-cpp/exporters/zipkin/src/zipkin_exporter_factory.cc should remove these lines:
- #include "opentelemetry/ext/http/client/http_client.h"  // lines 7-7

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.01%. Comparing base (75e4ecc) to head (2a00ad2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #4091   +/-   ##
=======================================
  Coverage   82.01%   82.01%           
=======================================
  Files         385      385           
  Lines       16023    16023           
=======================================
  Hits        13139    13139           
  Misses       2884     2884           

Files with missing lines	Coverage Δ
...orters/elasticsearch/src/es_log_record_exporter.cc	0.00% <ø> (ø)
exporters/otlp/src/otlp_recordable.cc	90.27% <ø> (ø)
exporters/prometheus/src/collector.cc	91.67% <ø> (ø)
sdk/src/logs/logger.cc	89.42% <ø> (ø)

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