fix(di): dynamic function discovery fallback [backport 3.10]

[github-actions]

Backport b55f08f from #13947 to 3.10.

We implement a dynamic function discovery fallback when the function-from-code resolution via the GC fails. This can happen if the target application has interacted with the GC, e.g. by freezing it at a time that will prevent the current discovery from being able to resolve the function from the referenced code object.

Testing Strategy

The original issue was reproducible with a local deployment of synapse. The investigation led to the conclusion that the issue was caused by the way the application interacts with the GC https://github.com/element-hq/synapse/blob/1dc29563c1504a2523e467aa7bef6a7ac05cc60c/synapse/app/_base.py#L623C1-L629C35. Commenting out these lines makes the issue disappear. We have tested the fix against the unmodified application to verify that the proposed fix works.

Refs: DYNIS-28

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:

releasenotes/notes/fix-di-dynamic-discovery-fallback-3a5623e18584cd79.yaml  @DataDog/apm-python
ddtrace/debugging/_function/discovery.py                                @DataDog/debugger-python

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 279 ± 7 ms.

The average import time from base is: 287 ± 4 ms.

The import time difference between this PR and base is: -8.2 ± 0.2 ms.

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 2.808 ms (1.01%)

ddtrace.bootstrap.sitecustomize 2.111 ms (0.76%)

ddtrace.bootstrap.preload 1.861 ms (0.67%)

ddtrace.internal.remoteconfig.client 0.800 ms (0.29%)

ddtrace.internal.remoteconfig.constants 0.016 ms (0.01%)

ddtrace.internal.flare.flare 0.037 ms (0.01%)

logging.handlers 0.037 ms (0.01%)

ddtrace.settings.code_origin 0.025 ms (0.01%)

ddtrace.appsec._common_module_patches 0.165 ms (0.06%)

ddtrace.appsec._asm_request_context 0.165 ms (0.06%)

ddtrace.appsec._utils 0.165 ms (0.06%)

ddtrace._trace.trace_handlers 0.085 ms (0.03%)

ddtrace._trace._inferred_proxy 0.032 ms (0.01%)

ddtrace.propagation.http 0.032 ms (0.01%)

ddtrace.internal._tagset 0.032 ms (0.01%)

ddtrace 0.697 ms (0.25%)

ddtrace.internal._unpatched 0.036 ms (0.01%)

json 0.036 ms (0.01%)

json.decoder 0.036 ms (0.01%)

re 0.036 ms (0.01%)

enum 0.036 ms (0.01%)

types 0.036 ms (0.01%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-07-15 10:08:39

Comparing candidate commit 591f623 in PR branch backport-13947-to-3.10 with baseline commit 1f8c272 in branch 3.10.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 522 metrics, 2 unstable metrics.