fix: iteration block hook injection [backport 2.21] #13801
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We fix an issue with the instrumentation of the beginning of iteration blocks (e.g. for loops) whereby instrumenting the end might cause unexpected behaviour when the modified function is invoked. This is due to the bytecode VM not liking any bytecode interposed before the instruction that ends the iteration block (e.g. `END_FOR`). This also solves the problem of double-calls of the instrumented hook when hitting the beginning of such blocks. ## Checklist - [x] 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](https://ddtrace.readthedocs.io/en/stable/releasenotes.html) - The change includes or references documentation updates if necessary - Backport labels are set (if [applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)) ## 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](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces) 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](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting) (cherry picked from commit d7b62d5)
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emmettbutler
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Jun 27, 2025
tylfin
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Jun 27, 2025
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Backport d7b62d5 from #13772 to 2.21.
We fix an issue with the instrumentation of the beginning of iteration blocks (e.g. for loops) whereby instrumenting the end might cause unexpected behaviour when the modified function is invoked. This is due to the bytecode VM not liking any bytecode interposed before the instruction that ends the iteration block (e.g.
END_FOR). This also solves the problem of double-calls of the instrumented hook when hitting the beginning of such blocks.Checklist
Reviewer Checklist