Use case

I'm developing a Flutter plugin for ExecuTorch, which only provides arm64 binaries for macOS (no x86_64 support). Debug builds work correctly, but release builds fail because Flutter's build_macos.dart

Issue:

• Debug: Uses -destination platform=macOS,arch=arm64 - Works
• Release: Uses -destination generic/platform=macOS - Forces arm64+x86_64 universal binary

Current code (build_macos.dart:202):

final String destination = buildInfo.isDebug
    ? 'platform=${XcodeSdk.MacOSX.displayName},arch=$arch'
    : XcodeSdk.MacOSX.genericPlatform; // Forces universal

Attempted workarounds (all failed):

• Xcode settings: ARCHS=arm64, EXCLUDED_ARCHS=x86_64, ONLY_ACTIVE_ARCH=YES
• Build flags: --dart-define=DarwinArchs=arm64 (only affects AOT compilation, not xcodebuild destination)

Reference: ExecuTorch only supports arm64 on macOS: https://docs.pytorch.org/executorch/stable/using-executorch-ios.html

Proposal

Allow developers to control architecture targeting for macOS release builds via:

Option 1: Respect DarwinArchs define for xcodebuild destination:

final String destination = buildInfo.isDebug || shouldLimitArchitecture
    ? 'platform=${XcodeSdk.MacOSX.displayName},arch=$arch'
    : XcodeSdk.MacOSX.genericPlatform;

Option 2: Add build flag:

flutter build macos --release --arch=arm64

Option 3: Package.swift configuration support to declare supported architectures.

This would enable plugins with architecture-specific dependencies to build successfully without requiring debug builds.