[ravindra-RKB]

Description

Fixes #23777

TDataMember::GetOffsetCint() previously returned early if fOffset >= 0. However, when TDataMember::GetOffset() is invoked first on a data member (such as an enum constant or members where fOffset is computed as 0), it caches fOffset = 0. Consequently, subsequent calls to GetOffsetCint() would return the cached 0 instead of querying the Cling interpreter for the actual offset/address.

This change updates GetOffsetCint() to prefer gCling->DataMemberInfo_Offset(dm->fInfo) whenever fInfo is available and valid, and only fall back to fOffset when fInfo is not available. A regression unit test covering #23777 has also been added to roottest/root/meta/unit/datamem.cxx.

Checklist

• Changes are minimal and focused
• Added regression unit test verifying the fix
• Follows ROOT coding conventions

[pcanal]

I am not sure this is the right solution. A priori the value can be as well cached for these call as for the previous call. It is not clear whether there is really a need for both functions to be distinct. However this need a deep analysis of the usage pattern in ROOT and in user codes.

[ravindra-RKB]

Thanks @pcanal. Should we cache this into a dedicated fOffsetCint member instead, or do you prefer consolidating both functions? Happy to adapt based on what fits best.

[pcanal]

The firsts step is to do an analysis of whether it makes sense or not to merge the 2 or to protect them from being called in the wrong context.

[ravindra-RKB]

Looking through the codebase usages:

• GetOffset() is used for instance byte offsets (TStreamerInfo, RFieldMeta, TTree). For non-static data members, both functions yield the same offset.
• For static variables and enum constants, GetOffset() returns 0 because BuildRealData() does not track them, whereas GetOffsetCint() queries Cling, which returns the address/value.
• If called on an enum or static member, GetOffset() is technically the "wrong context" (no instance offset exists) and erroneously caches 0 into fOffset.

Would it make sense to protect GetOffset() so it returns -1 (or avoids setting fOffset = 0) when Property() & (kIsStatic | kIsEnum), or should GetOffset() delegate to Cling for static/enum members as well?

[github-actions]

Test Results

    23 files      23 suites   3d 17h 15m 4s ⏱️
 3 896 tests  3 896 ✅ 0 💤 0 ❌
79 903 runs  79 903 ✅ 0 💤 0 ❌

Results for commit 5538730.