Description

swiftc -sil-verify-all crashes with an assertion failure in getFunctionArgOwnership ("Illegal convention for non-address types") at OperandOwnership.cpp:531 when SIL-generating a struct method whose parameter is annotated with a @propertyWrapper that exposes a projectedValue. The SIL verifier detects an illegal ownership convention in the synthesized setter for the projected value parameter ($x), indicating that SILGen emits an incorrect calling convention for the non-address projected value type.

Reproducer

@propertyWrapper
public struct Wrapper<T> {
    public var wrappedValue: T
    public init(wrappedValue: T) { self.wrappedValue = wrappedValue }
}

@propertyWrapper
public struct ProjectedValueWrapper<T> {
    public var wrappedValue: T
    public init(wrappedValue: T) { self.wrappedValue = wrappedValue }
    public init(projectedValue: Wrapper<T>) { self.wrappedValue = projectedValue.wrappedValue }
    public var projectedValue: Wrapper<T> {
        get { Wrapper(wrappedValue: wrappedValue) }
        set { wrappedValue = newValue.wrappedValue }
    }
}

public struct S {
    public func hasParameterWithAPIWrapper(@ProjectedValueWrapper x: Int) { }
}

Command

swiftc -sil-verify-all reproduce.swift

Expected behavior

The compiler should successfully lower the AST to SIL and verify ownership without assertion failures. A @propertyWrapper with a projectedValue used as a function parameter should generate correct SIL ownership conventions.

Actual behavior

Assertion failed: (false && "Illegal convention for non-address types"),
function getFunctionArgOwnership at OperandOwnership.cpp:531.

While evaluating request ASTLoweringRequest(Lowering AST to SIL for module main)
While silgen emitFunction for 'hasParameterWithAPIWrapper(x:)'
While silgen emitFunction for setter for $x
While verifying SIL function for setter for $x

Call chain

ASTLoweringRequest::evaluate
  → SILGenModule::emitSourceFile
    → SILGenModule::visitNominalTypeDecl
      → SILGenType::emitType
        → SILGenModule::emitFunction         (hasParameterWithAPIWrapper)
          → SILGenFunction::emitFunction
            → SILGenFunction::visitVarDecl   ($x projected value var)
              → SILGenModule::emitFunction   (setter for $x)
                → SILGenModule::postEmitFunction
                  → SILFunction::verify
                    → SILVerifier::checkValueBaseOwnership
                      → SILValue::verifyOwnership
                        → SILValueOwnershipChecker::check
                          → gatherNonGuaranteedUsers
                            → Operand::getOperandOwnership
                              → visitFullApply
                                → getFunctionArgOwnership  ← assertion

Root cause

When SILGen lowers a function parameter annotated with @ProjectedValueWrapper (a @propertyWrapper that exposes a projectedValue), it synthesizes a local setter for the projected value binding $x. The synthesized setter incorrectly assigns an address-only calling convention to the Wrapper<T> projected value argument, which is not an address type. The SIL verifier catches this as an illegal ownership convention. The fix should ensure that SILGen uses the correct non-address ownership convention (@owned or @guaranteed) when emitting the setter for projected value parameters of non-address wrapper types.

Environment

• Compiler: Swift 6.3 (swift-6.3-RELEASE)
• Platform: x86_64 Linux (Ubuntu 24.04.4 LTS)
• Command: swiftc -sil-verify-all reproduce.swift
• Crash site: swift/lib/SIL/Verifier/OperandOwnership.cpp:531 (getFunctionArgOwnership)
• Affected pass: SILGen (swift/lib/SILGen/)