ddtrace/tracer: dereference pointers to supported types in span.SetTag

[darccio]

What does this PR do?

Adds support for pointer values on setting tags, dereferencing them iff it's a pointer to a supported value in span.SetTag.

Dereferencing more than one level of indirection is out of scope, as there is no way to do it without reflect and/or in an efficient way.

It also adds some of the existing benchmarks for SetTag to make sure the modification doesn't introduce any unnecessary allocation or overhead. They were also fixed as they had an unrelated allocation captured by the benchmark tooling.

Motivation

Protobuf generated code for nullable fields uses pointers. It's easy to forget to dereference the variable to pass the value to SetTag, leading to tags containing strings representing memory addresses instead of the desired value the pointer points to.

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

Unsure? Have a question? Request a review!

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-08-05 09:34:08

Comparing candidate commit 8c808b6 in PR branch dario.castane/apmlp-87/handle-ptrs-settag with baseline commit 277ea00 in branch main.

Some scenarios are present only in baseline or only in candidate runs. If you didn't create or remove some scenarios in your branch, this maybe a sign of crashed benchmarks 💥💥💥
Check Gitlab CI job log to find if any benchmark has crashed.

Scenarios present only in candidate:

• BenchmarkSetTagStringPtr-24

Found 9 performance improvements and 0 performance regressions! Performance is the same for 46 metrics, 1 unstable metrics.

scenario:BenchmarkSetTagMetric-24

• 🟩 allocated_mem [-4 bytes; -4 bytes] or [-100.000%; -100.000%]
• 🟩 allocations [-1; -1] or [-100.000%; -100.000%]
• 🟩 execution_time [-14.868ns; -12.372ns] or [-10.843%; -9.022%]

scenario:BenchmarkSetTagString-24

• 🟩 allocated_mem [-4 bytes; -4 bytes] or [-100.000%; -100.000%]
• 🟩 allocations [-1; -1] or [-100.000%; -100.000%]
• 🟩 execution_time [-18.732ns; -17.088ns] or [-13.932%; -12.708%]

scenario:BenchmarkSetTagStringer-24

• 🟩 allocated_mem [-4 bytes; -4 bytes] or [-100.000%; -100.000%]
• 🟩 allocations [-1; -1] or [-100.000%; -100.000%]
• 🟩 execution_time [-17.776ns; -14.624ns] or [-11.220%; -9.230%]

[darccio]

Some scenarios are present only in baseline or only in candidate runs. If you didn't create or remove some scenarios in your branch, this maybe a sign of crashed benchmarks 💥💥💥

The reported benchmark BenchmarkSetTagStringPtr-24 is new and only present in the candidate branch.

[eliottness]

Reviewing for dd-trace-go-guild (.gitlab-ci.yml)