[swift2objc] Support properties that throw

[AmrAhmed119]

Closes #1765

• Adding support for throwing properties in swift by converting them into ordinary methods.

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pkgs/jni/lib/src/third_party/generated_bindings.dart
pkgs/objective_c/lib/src/ns_input_stream.dart

[coveralls]

coverage: 87.109% (-1.2%) from 88.352%
when pulling f5d1118 on AmrAhmed119:throwing-properties
into 7a72868 on dart-lang:main.

[liamappelbe]

You can delete this whole if statement and just return throws.

[liamappelbe]

So if I understand correctly, you've added a isCallingProperty field to the method and function declarations, which changes the originalCallStatementGenerator param passed to _transformFunction to not pass args. That transformation happens in transformMethod, which is called immediately after you set this flag. In other words, you've added a flag to the AST node, that is only set here, and then is immediately consumed. The flag is only necessary because you're merging these methods with originalCompound.methods before passing them to transformMethod.

It would be cleaner to remove isCallingProperty, and remove _convertPropertiesToMethods, and do all that transformation logic in transformProperty. transformProperty would check the throws flag and decide whether to return a PropertyDeclaration or a MethodDeclaration (the declared return type would be AstNode). Then you would merge any MethodDeclarations it returned with the other methods after they've been transformed:

// transformedProperties is a List<AstNode?>
final transformedProperties = originalCompound.properties
    .map((property) => transformProperty(
          property,
          wrappedCompoundInstance,
          parentNamer,
          transformationMap,
        )).nonNulls.toList();

final transformedMethods = originalCompound.methods
    .map((method) => transformMethod(
          method,
          wrappedCompoundInstance,
          parentNamer,
          transformationMap,
        )).nonNulls.toList();

transformedCompound.properties =
  transformedProperties.whereType<PropertyDeclaration>()
  ..sort((Declaration a, Declaration b) => a.id.compareTo(b.id));

transformedCompound.methods = (transformedMethods +
  transformedProperties.whereType<MethodDeclaration>())
  ..sort((Declaration a, Declaration b) => a.id.compareTo(b.id));

The same goes for GlobalFunctionDeclaration.