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Case 89: Inline accessor references renamed pimpl member

Field Value
Verdict 🔴 BREAKING
Category Breaking
Platforms Linux, macOS
Flags ABI break
Detected ChangeKinds inline_body_references_renamed_member
Source files browse on GitHub

Category: Pimpl ABI | Verdict: BREAKING

What breaks

The public class exposes inline getters that reach into the pimpl implementation by member name:

class descriptor {
public:
    inline int get_class_count() const { return impl_->class_count_; }
private:
    detail::pimpl<detail::descriptor_impl> impl_;
};

In v2, detail::descriptor_impl::class_count_ is renamed to n_classes_ during a "modernize naming" cleanup. The maintainer updates the inline accessor body in the header in lockstep, so:

  • Rebuilding the library succeeds.
  • Rebuilding new consumers against v2 headers succeeds.
  • Existing consumer binaries — compiled against v1.h with the old inline body baked in — continue to reference class_count_ at the old offset. Linked against v2's descriptor_impl layout, the inline access reads the wrong field (or garbage if the layout shifted).

There is no symbol-level evidence of the break: descriptor::get_class_count is inline and has no exported symbol. There is no public-type layout change: descriptor still holds one pimpl pointer. The break lives entirely in the gap between what the consumer's inline body assumes and what the new detail layout actually is.

Why distinct from case35 + case47

  • case35 (field_rename) covers field renames in isolation. It does not exercise the inline-consumer-baked-in-body trap.
  • case47 (inline_to_outlined) is the COMPATIBLE counter-case (moving an inline to outlined is safe).
  • case89 is the interaction: field rename in a detail:: type, accessed by an inline public method whose body is shipped into consumers.

How abicheck catches it

The new inline_body_references_renamed_member detector correlates:

  1. A field_renamed (or type_field_removed + type_field_added) on a record type that lives in an internal namespace (reuses internal_leak.py::is_internal_type).
  2. An inline public method (presence of body in DWARF, no exported symbol) on a non-internal type whose member-access expression references the old field name.

When both halves match, emit a single INLINE_BODY_REFERENCES_RENAMED_MEMBER finding describing the chain descriptor::get_class_count() (inline) → impl_->class_count_ (renamed).

Real-world reference

oneDAL's pimpl idiom plus inline header accessors creates this exact risk surface for every detail::*_impl field. The class member-rename is invisible to users at source level but propagates into every consumer binary already compiled against the previous header.

Source files

See also: Examples overview · All BREAKING cases · Category: Breaking.