[Dynamic Instrumentation] Add NullByRefArgAndLocal test by dudikeleti · Pull Request #7987

[Dynamic Instrumentation] Add NullByRefArgAndLocal test by dudikeleti · Pull Request #7987 · DataDog/dd-trace-dotnet

This was referenced

Dec 20, 2025

dudikeleti changed the title ~~Add NullByRefArgAndLocal test~~ [Dynamic Instrumentation] Add NullByRefArgAndLocal test

Dec 20, 2025

dudikeleti added a commit that referenced this pull request

Jan 21, 2026

## Reason for change
In some cases, we cannot rely on the method metadata to determine
whether method arguments and locals exist, as they may still be skipped.

## Implementation details
Track open nodes and open/close them as required.

## Test coverage
#7987

## Other details
This PR is part of an effort to make the Snapshot Exploration Test run
successfully end-to-end.
#7986
#7989

dudikeleti added a commit that referenced this pull request

Jan 21, 2026

…7989)

## Summary of changes
Add defensive checks for open nodes before closing them, and delay
writing `noCaptureReason` until we are certain that the array node is
closed.

## Test coverage
#7987

## Other details
This PR is part of an effort to make the Snapshot Exploration Test run
successfully end-to-end.

Related PRs:
#7986
#7988

dudikeleti added a commit that referenced this pull request

Jan 21, 2026

…l and LogArg to detect null byrefs (#7986)

## Reason for change
Some methods can legitimately produce null managed byrefs (e.g.,
MemoryMarshal.GetReference(emptySpan)), which makes ref T point to
address 0. Attempting to capture such locals/args would dereference an
invalid reference and could crash in LogLocal/LogArg
(NullReferenceException). This change makes DI runs stable and keeps
probes installed while avoiding unsafe dereferences

## Implementation details
Before reading a ref T capture input, we check Unsafe.IsNullRef(ref
value) and return early to avoid dereferencing an invalid reference.

Current behavior is to skip capturing that member entirely (no
misleading null value for non-nullable types like byte).
Follow-up option: if we decide we want the snapshot to explicitly show
this case, we can reuse the existing snapshot notCapturedReason
mechanism (no new reason added in this PR).

## Test coverage
#7987

## Other details
This PR is part of an effort to make the Snapshot Exploration Test run
successfully end-to-end.
#7988
#7989