fix: make CIBW_ARCHS parsing case-insensitive and platform-aware

[henryiii]

🤖 AI text below 🤖

Problem

CIBW_ARCHS architecture parsing was case-sensitive and platform-ambiguous. In cibuildwheel/architecture.py, Architecture.parse_config used a case-sensitive StrEnum lookup (cls(arch_str)). The enum carries both a lowercase arm64 member (value "arm64", used by macOS/Android) and an uppercase ARM64 member (value "ARM64", used by Windows), plus AMD64/x86_64, etc.

This caused surprising behavior:

• Architecture.parse_config("arm64", platform="windows") returned {Architecture.arm64} (the macOS member!) with no error, then failed later in allowed_architectures_check with a confusing Invalid archs option message.
• Architecture.parse_config("ARM64", platform="windows") worked.
• "amd64" (lowercase) failed to parse entirely, while "AMD64" worked.

So Windows-on-ARM users had to use exact-case ARM64/AMD64.

Fix

The name lookup is now case-insensitive and resolves to the member valid for the target platform. A new helper Architecture._parse_arch_name first matches case-insensitively against Architecture.all_archs(platform), then falls back to a case-insensitive match across all members so the existing clear ConfigurationError still fires for genuinely invalid names. The special tokens (auto, native, all, auto64, auto32) are untouched.

After the fix:

• parse_config("arm64", "windows") == {Architecture.ARM64}
• parse_config("ARM64", "macos") == {Architecture.arm64}
• lowercase amd64 / x86 work on Windows
• an actually-invalid name still raises ConfigurationError

Tests

Added parametrized unit tests in unit_test/architecture_test.py covering the cases above.

Closes #2373

[joerick]

Nice, yeah I imagine this has been a little paper cut for a some people.

[agriyakhetarpal]

Thanks! Makes sense to me. Personally, this never hit me because we documented AMD64/ARM64 in capital letters in the docs well, and I used them as such, never questioning why – but I recognise that others have been hitting it.