Case 226: Header-Only Template Default Unchanged

Field	Value
Verdict	✅ NO_CHANGE
Category	No Change
Classification	Rule
Platforms	Linux, macOS, Windows
Flags	—
Detected ChangeKinds	—
Source files	catalog/cases/case226_header_only_template_default_unchanged/
Rule family	header-only-template-default-unchanged
Subject	Template and generic-programming issues

Category: Template ABI | Verdict: 🟢 NO_CHANGE (both backends)

Verdict and consumer impact

Both sides declare template <typename T, typename U = int> struct Box;. v2 only rewords a comment. No default changes, so nothing is reported. This is the negative control for case223 to case225 and case227.

Old/new diff

Comment-only change. The default is int on both sides.

abicheck command

cat > .abicheck.yml <<'EOF'
compile:
  frontend: castxml
  lang: c++
EOF
abicheck dump -H v1.h --config .abicheck.yml --depth headers -o old.json
abicheck dump -H v2.h --config .abicheck.yml --depth headers -o new.json
abicheck compare old.json new.json

Expected abicheck finding

Verdict: NO_CHANGE on castxml and clang. No template-default finding. castxml still reports the template-default gap, because it cannot record the default. A clean-looking NO_CHANGE does not mean the defaults were checked there.

Minimum evidence

min_evidence: L2.

Why abicheck catches it

The detector emits nothing for a pair whose recorded defaults match. The test for this case asserts that template_param_default_changed is absent.

Runtime failure demonstration

None.

Safe redesign

Not applicable.

---

Source files

• CMakeLists.txt
• app.cpp
• v1.cpp
• v1.h
• v2.cpp
• v2.h

See also: Compatibility Catalog · All NO_CHANGE cases · Category: No Change · Rule: Header-only template default unchanged · Subject: Template and generic-programming issues.