chore: implement rudimentary CMake incremental build

[P403n1x87]

We speed-up the build process for local development when CMake sources are not changed in between build runs. This reduces the build time from ~3 minutes to ~20 seconds. The feature is behind the DD_CMAKE_INCREMENTAL_BUILD flag. When running tests locally with riot, one would have to make sure that the variable is set in the environment, e.g.

DD_CMAKE_INCREMENTAL_BUILD=1 riot -v run ...

Note

This is just a temporary workaround. Long-term we would want to migrate away from CMake as much as possible to reduce the complexity inside setup.py.

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

setup.py                                                                @DataDog/python-guild

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 274 ± 2 ms.

The average import time from base is: 276 ± 2 ms.

The import time difference between this PR and base is: -1.4 ± 0.1 ms.

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 1.956 ms (0.71%)

ddtrace.bootstrap.sitecustomize 1.276 ms (0.46%)

ddtrace.bootstrap.preload 1.276 ms (0.46%)

ddtrace.internal.remoteconfig.client 0.622 ms (0.23%)

ddtrace 0.680 ms (0.25%)

ddtrace.internal._unpatched 0.031 ms (0.01%)

json 0.031 ms (0.01%)

json.decoder 0.031 ms (0.01%)

re 0.031 ms (0.01%)

enum 0.031 ms (0.01%)

types 0.031 ms (0.01%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-06-12 14:32:05

Comparing candidate commit e74ebb6 in PR branch chore/cmake-incremental-builds with baseline commit fd2bcdf in branch main.

Found 0 performance improvements and 2 performance regressions! Performance is the same for 563 metrics, 5 unstable metrics.

scenario:iastaspects-upper_aspect

• 🟥 execution_time [+185.178ns; +222.014ns] or [+8.207%; +9.839%]

scenario:telemetryaddmetric-1-gauge-metric-1-times

• 🟥 execution_time [+246.144ns; +298.676ns] or [+11.600%; +14.075%]

[P403n1x87]

Total time: 16.69s
Environment:
	CARGO_BUILD_JOBS: unset
	CMAKE_BUILD_PARALLEL_LEVEL: unset
	DD_COMPILE_MODE: Release
	DD_USE_SCCACHE: False
	DD_FAST_BUILD: False
Extension build times:
	Total: 10.22s (61.24%)
	ddtrace.internal._encoding: 2.22s (13.28%)
	ddtrace.profiling.collector.stack: 1.80s (10.79%)
	ddtrace.profiling.collector._task: 0.80s (4.82%)
	ddtrace.internal.telemetry.metrics_namespaces: 0.76s (4.52%)
	ddtrace.profiling._threading: 0.63s (3.79%)
	ddtrace.internal._tagset: 0.61s (3.66%)
	ddtrace.profiling.collector._traceback: 0.56s (3.35%)
	ddtrace.vendor.psutil._psutil_posix: 0.53s (3.17%)
	ddtrace.vendor.psutil._psutil_osx: 0.52s (3.13%)
	ddtrace.profiling.collector._memalloc: 0.51s (3.06%)
	ddtrace.internal._threads: 0.40s (2.38%)
	ddtrace.internal._rand: 0.35s (2.08%)
	ddtrace.internal.native._native: 0.23s (1.36%)
	ddtrace.appsec._iast._ast.iastpatch: 0.16s (0.96%)
	ddtrace.appsec._iast._stacktrace: 0.14s (0.82%)
	ddtrace.appsec._iast._taint_tracking._native: 0.01s (0.04%)
	ddtrace.internal.datadog.profiling.stack_v2._stack_v2: 0.00s (0.01%)
	ddtrace.internal.datadog.profiling.ddup._ddup: 0.00s (0.01%)
	ddtrace.internal.datadog.profiling.crashtracker._crashtracker: 0.00s (0.00%)