Case 227: Nested-Namespace Template Default Changed¶

Field	Value
Verdict	🟠 API_BREAK
Category	API Break
Classification	Rule
Platforms	Linux, macOS, Windows
Flags	API break
Detected `ChangeKind`s	`template_param_default_changed`
Source files	`catalog/cases/case227_nested_namespace_template_default_changed/`
Rule family	`nested-namespace-template-default-changed`
Subject	Template and generic-programming issues

Category: Template ABI | Verdict: 🟢 NO_CHANGE (castxml) / 🟠 API_BREAK (clang)

Verdict and consumer impact¶

The case223 change, placed in the nested namespace mylib::detail. The default for U changes from int to long. The qualified-name pairing must match the pattern under the nested scope, otherwise a real default change under detail:: would be lost.

The castxml lane reads NO_CHANGE with the template-default gap. The clang backend reports template_param_default_changed as API_BREAK.

Old/new diff¶

v1.h	v2.h
`namespace mylib::detail { template <typename T, typename U = int> struct Box; }`	`namespace mylib::detail { template <typename T, typename U = long> struct Box; }`

abicheck command¶

Use the same commands as case223, with v1.h and v2.h from this case.

Expected abicheck finding¶

castxml (default): Verdict: NO_CHANGE, Assurance: partial with the template-default gap.

clang: Verdict: API_BREAK, template_param_default_changed, named mylib::detail::Box.

Minimum evidence¶

min_evidence: L2, the public header.

Why abicheck catches it¶

Pattern records are keyed by qualified name (mylib::detail::Box), so the pairing is the same as at the top level.

Runtime failure demonstration¶

None, as in case223.

Safe redesign¶

As in case223: add an alias rather than change the default in place.

Source files¶

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