Write a C++ constant of an allocating type as const, not constexpr [patch]

[matt-edmondson]

Fixes #101

What was wrong

CppGenerator wrote constexpr on every constant field, whatever its type. That happened in two places: SpellStorage for FieldDeclaration, and GenerateField for a constant VariableDeclaration class member.

string maps to std::string, so the output was static constexpr std::string / inline constexpr std::string. That compiles only while the value fits libstdc++'s small-string buffer. A longer value fails in g++ 13 with "not a constant expression because it refers to a result of 'operator new'", and under C++17 it is never valid.

Change

• A new IsLiteralType check covers the standard-library types the generator emits that allocate: std::string, std::vector, std::map and std::any.
• A constant of one of these types is now written as:
  • inline const at namespace scope
  • inline static const inside a type
• These keep constexpr as before:
  • literal types
  • pointers and references
  • caller-defined types, such as the reflection-table exemplar's holo::reflect::FieldInfo

Tests

• CppGeneratedSourceCompilesTests.ALongConstantStringCompilesWhereverAConstantMayStand compiles a constant longer than the small-string buffer with the real C++ compiler, with -std=c++20 -pedantic. It covers three positions: namespace scope, a static field in a struct, and a class-member VariableDeclaration.
• CppGeneratorTests.ConstantField_OfANonLiteralType_IsConstRatherThanConstexpr pins the spellings, and checks that int keeps constexpr.
• With the generator change reverted, both tests fail. g++ reports the exact error from the issue.
• Full suite: 989 passed, 0 failed.

🤖 Generated with Claude Code

https://claude.ai/code/session_01HsaGezbczZSL9fXfQafs7x

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Generated by Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
88.9% Coverage on New Code
0.0% Duplication on New Code

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