[cxx-interop] Avoid generating ambiguous wrapper functions

lib/Macros/Sources/SwiftMacros/SwiftifyImportMacro.swift

@@ -289,8 +289,10 @@ func transformType(_ prev: TypeSyntax, _ generateSpan: Bool, _ isSizedBy: Bool)
 protocol BoundsCheckedThunkBuilder {
   func buildFunctionCall(_ pointerArgs: [Int: ExprSyntax]) throws -> ExprSyntax
   func buildBoundsChecks() throws -> [CodeBlockItemSyntax.Item]
+  // The second component of the return value is true when only the return type of the
+  // function signature was changed.
   func buildFunctionSignature(_ argTypes: [Int: TypeSyntax?], _ returnType: TypeSyntax?) throws
-    -> FunctionSignatureSyntax
+    -> (FunctionSignatureSyntax, Bool)
 }
 
 func getParam(_ signature: FunctionSignatureSyntax, _ paramIndex: Int) -> FunctionParameterSyntax {
@@ -308,6 +310,7 @@ func getParam(_ funcDecl: FunctionDeclSyntax, _ paramIndex: Int) -> FunctionPara
 
 struct FunctionCallBuilder: BoundsCheckedThunkBuilder {
   let base: FunctionDeclSyntax
+
   init(_ function: FunctionDeclSyntax) {
     base = function
   }
@@ -317,7 +320,7 @@ struct FunctionCallBuilder: BoundsCheckedThunkBuilder {
   }
 
   func buildFunctionSignature(_ argTypes: [Int: TypeSyntax?], _ returnType: TypeSyntax?) throws
-    -> FunctionSignatureSyntax {
+    -> (FunctionSignatureSyntax, Bool) {
     var newParams = base.signature.parameterClause.parameters.enumerated().filter {
       let type = argTypes[$0.offset]
       // filter out deleted parameters, i.e. ones where argTypes[i] _contains_ nil
@@ -333,7 +336,7 @@ struct FunctionCallBuilder: BoundsCheckedThunkBuilder {
     if returnType != nil {
       sig = sig.with(\.returnClause!.type, returnType!)
     }
-    return sig
+    return (sig, (argTypes.count == 0 && returnType != nil))
   }
 
   func buildFunctionCall(_ pointerArgs: [Int: ExprSyntax]) throws -> ExprSyntax {
@@ -381,7 +384,7 @@ struct CxxSpanThunkBuilder: ParamPointerBoundsThunkBuilder {
   }
 
   func buildFunctionSignature(_ argTypes: [Int: TypeSyntax?], _ returnType: TypeSyntax?) throws
-    -> FunctionSignatureSyntax {
+    -> (FunctionSignatureSyntax, Bool) {
     var types = argTypes
     let typeName = try getTypeName(oldType).text
     guard let desugaredType = typeMappings[typeName] else {
@@ -417,7 +420,7 @@ struct CxxSpanReturnThunkBuilder: BoundsCheckedThunkBuilder {
   }
 
   func buildFunctionSignature(_ argTypes: [Int: TypeSyntax?], _ returnType: TypeSyntax?) throws
-    -> FunctionSignatureSyntax {
+    -> (FunctionSignatureSyntax, Bool) {
     assert(returnType == nil)
     let typeName = try getTypeName(signature.returnClause!.type).text
     guard let desugaredType = typeMappings[typeName] else {
@@ -490,7 +493,7 @@ struct CountedOrSizedReturnPointerThunkBuilder: PointerBoundsThunkBuilder {
   }
 
   func buildFunctionSignature(_ argTypes: [Int: TypeSyntax?], _ returnType: TypeSyntax?) throws
-    -> FunctionSignatureSyntax {
+    -> (FunctionSignatureSyntax, Bool) {
     assert(returnType == nil)
     return try base.buildFunctionSignature(argTypes, newType)
   }
@@ -518,7 +521,7 @@ struct CountedOrSizedPointerThunkBuilder: ParamPointerBoundsThunkBuilder {
   public let skipTrivialCount: Bool
 
   func buildFunctionSignature(_ argTypes: [Int: TypeSyntax?], _ returnType: TypeSyntax?) throws
-    -> FunctionSignatureSyntax {
+    -> (FunctionSignatureSyntax, Bool) {
     var types = argTypes
     types[index] = try newType
     if skipTrivialCount {
@@ -1104,7 +1107,7 @@ public struct SwiftifyImportMacro: PeerMacro {
         { (prev, parsedArg) in
           parsedArg.getBoundsCheckedThunkBuilder(prev, funcDecl, skipTrivialCount)
         })
-      let newSignature = try builder.buildFunctionSignature([:], nil)
+      let (newSignature, onlyReturnTypeChanged) = try builder.buildFunctionSignature([:], nil)
       let checks =
         skipTrivialCount
         ? [] as [CodeBlockItemSyntax]
@@ -1118,6 +1121,12 @@ public struct SwiftifyImportMacro: PeerMacro {
             expression: try builder.buildFunctionCall([:]))))
       let body = CodeBlockSyntax(statements: CodeBlockItemListSyntax(checks + [call]))
       let lifetimeAttrs = lifetimeAttributes(funcDecl, lifetimeDependencies)
+      let disfavoredOverload : [AttributeListSyntax.Element] = (onlyReturnTypeChanged ? [
+        .attribute(
+          AttributeSyntax(
+            atSign: .atSignToken(),
+            attributeName: IdentifierTypeSyntax(name: "_disfavoredOverload")))
+      ] : [])
       let newFunc =
         funcDecl
         .with(\.signature, newSignature)
@@ -1138,7 +1147,8 @@ public struct SwiftifyImportMacro: PeerMacro {
                 atSign: .atSignToken(),
                 attributeName: IdentifierTypeSyntax(name: "_alwaysEmitIntoClient")))
           ]
-          + lifetimeAttrs)
+          + lifetimeAttrs
+          + disfavoredOverload)
       return [DeclSyntax(newFunc)]
     } catch let error as DiagnosticError {
       context.diagnose(

test/Interop/C/swiftify-import/counted-by-noescape.swift

@@ -14,7 +14,7 @@ import CountedByNoEscapeClang
 // CHECK:      @_alwaysEmitIntoClient public func complexExpr(_ len: Int{{.*}}, _ offset: Int{{.*}}, _ p: MutableSpan<Int{{.*}}>)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nonnull(_  p: MutableSpan<Int{{.*}}>)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nullUnspecified(_  p: MutableSpan<Int{{.*}}>)
-// CHECK-NEXT: @_alwaysEmitIntoClient public func returnPointer(_  len: Int{{.*}}) -> UnsafeMutableBufferPointer<Int{{.*}}>
+// CHECK-NEXT: @_alwaysEmitIntoClient @_disfavoredOverload public func returnPointer(_  len: Int{{.*}}) -> UnsafeMutableBufferPointer<Int{{.*}}>
 // CHECK-NEXT: @_alwaysEmitIntoClient public func shared(_ len: Int{{.*}}, _ p1: MutableSpan<Int{{.*}}>, _ p2: MutableSpan<Int{{.*}}>)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func simple(_  p: MutableSpan<Int{{.*}}>)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func swiftAttr(_  p: MutableSpan<Int{{.*}}>)

test/Interop/C/swiftify-import/counted-by.swift

@@ -14,7 +14,7 @@ import CountedByClang
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nonnull(_  p: UnsafeMutableBufferPointer<Int{{.*}}>)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nullUnspecified(_  p: UnsafeMutableBufferPointer<Int{{.*}}>)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nullable(_  p: UnsafeMutableBufferPointer<Int{{.*}}>?)
-// CHECK-NEXT: @_alwaysEmitIntoClient public func returnPointer(_  len: Int{{.*}}) -> UnsafeMutableBufferPointer<Int{{.*}}>
+// CHECK-NEXT: @_alwaysEmitIntoClient @_disfavoredOverload public func returnPointer(_  len: Int{{.*}}) -> UnsafeMutableBufferPointer<Int{{.*}}>
 // CHECK-NEXT: @_alwaysEmitIntoClient public func shared(_ len: Int{{.*}}, _ p1: UnsafeMutableBufferPointer<Int{{.*}}>, _ p2: UnsafeMutableBufferPointer<Int{{.*}}>)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func simple(_  p: UnsafeMutableBufferPointer<Int{{.*}}>)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func swiftAttr(_  p: UnsafeMutableBufferPointer<Int{{.*}}>)

test/Interop/C/swiftify-import/sized-by-noescape.swift

@@ -14,7 +14,7 @@ import SizedByNoEscapeClang
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nonnull(_ p: RawSpan)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nullUnspecified(_  p: RawSpan)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func opaque(_  p: RawSpan)
-// CHECK-NEXT: @_alwaysEmitIntoClient public func returnPointer(_ len: Int{{.*}}) -> UnsafeRawBufferPointer
+// CHECK-NEXT: @_alwaysEmitIntoClient @_disfavoredOverload public func returnPointer(_ len: Int{{.*}}) -> UnsafeRawBufferPointer
 // CHECK-NEXT: @_alwaysEmitIntoClient public func shared(_ len: Int{{.*}}, _ p1: RawSpan, _ p2: RawSpan)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func simple(_  p: RawSpan)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func swiftAttr(_  p: RawSpan)

test/Interop/C/swiftify-import/sized-by.swift

@@ -14,7 +14,7 @@ import SizedByClang
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nullUnspecified(_  p: UnsafeMutableRawBufferPointer)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func nullable(_  p: UnsafeMutableRawBufferPointer?)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func opaque(_  p: UnsafeRawBufferPointer)
-// CHECK-NEXT: @_alwaysEmitIntoClient public func returnPointer(_ len: Int{{.*}}) -> UnsafeMutableRawBufferPointer
+// CHECK-NEXT: @_alwaysEmitIntoClient @_disfavoredOverload public func returnPointer(_ len: Int{{.*}}) -> UnsafeMutableRawBufferPointer
 // CHECK-NEXT: @_alwaysEmitIntoClient public func shared(_ len: Int{{.*}}, _ p1: UnsafeMutableRawBufferPointer, _ p2: UnsafeMutableRawBufferPointer)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func simple(_  p: UnsafeMutableRawBufferPointer)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func swiftAttr(_  p: UnsafeMutableRawBufferPointer)

test/Interop/Cxx/stdlib/std-span-interface.swift

@@ -16,7 +16,7 @@ import CxxStdlib
 
 // CHECK:     struct DependsOnSelf {
 // CHECK:       @lifetime(borrow self)
-// CHECK-NEXT:  @_alwaysEmitIntoClient public mutating func get() -> Span<CInt>
+// CHECK-NEXT:  @_alwaysEmitIntoClient @_disfavoredOverload public mutating func get() -> Span<CInt>
 // CHECK-NEXT:  mutating func get() -> ConstSpanOfInt
 
 // CHECK:      func funcWithSafeWrapper(_ s: ConstSpanOfInt)
@@ -31,4 +31,4 @@ import CxxStdlib
 // CHECK-NEXT: @lifetime(s)
 // CHECK-NEXT: @_alwaysEmitIntoClient public func funcWithSafeWrapper2(_ s: borrowing Span<CInt>) -> Span<CInt>
 // CHECK-NEXT: @lifetime(borrow v)
-// CHECK-NEXT: @_alwaysEmitIntoClient public func funcWithSafeWrapper3(_ v: borrowing VecOfInt) -> Span<CInt>
+// CHECK-NEXT: @_alwaysEmitIntoClient @_disfavoredOverload public func funcWithSafeWrapper3(_ v: borrowing VecOfInt) -> Span<CInt>

test/Macros/SwiftifyImport/CountedBy/PointerReturn.swift

@@ -10,12 +10,12 @@ func myFunc(_ len: CInt) -> UnsafeMutablePointer<CInt> {
 func nonEscaping(_ len: CInt) -> UnsafePointer<CInt> {
 }
 
-// CHECK:      @_alwaysEmitIntoClient
+// CHECK:      @_alwaysEmitIntoClient @_disfavoredOverload
 // CHECK-NEXT: func myFunc(_ len: CInt) -> UnsafeMutableBufferPointer<CInt> {
 // CHECK-NEXT:     return UnsafeMutableBufferPointer<CInt> (start: myFunc(len), count: Int(len))
 // CHECK-NEXT: }
 
-// CHECK:      @_alwaysEmitIntoClient
+// CHECK:      @_alwaysEmitIntoClient @_disfavoredOverload
 // CHECK-NEXT: func nonEscaping(_ len: CInt) -> UnsafeBufferPointer<CInt> {
 // CHECK-NEXT:     return UnsafeBufferPointer<CInt> (start: nonEscaping(len), count: Int(len))
 // CHECK-NEXT: }

test/Macros/SwiftifyImport/CxxSpan/LifetimeboundSpan.swift

@@ -39,7 +39,7 @@ struct X {
 // CHECK-NEXT:     return Span(_unsafeCxxSpan: myFunc(SpanOfInt(span)))
 // CHECK-NEXT: }
 
-// CHECK:      @_alwaysEmitIntoClient @lifetime(borrow vec)
+// CHECK:      @_alwaysEmitIntoClient @lifetime(borrow vec) @_disfavoredOverload
 // CHECK-NEXT: func myFunc2(_ vec: borrowing VecOfInt) -> Span<CInt> {
 // CHECK-NEXT:     return Span(_unsafeCxxSpan: myFunc2(vec))
 // CHECK-NEXT: }
@@ -54,7 +54,7 @@ struct X {
 // CHECK-NEXT:     return Span(_unsafeCxxSpan: myFunc4(vec, SpanOfInt(span)))
 // CHECK-NEXT: }
 
-// CHECK:      @_alwaysEmitIntoClient @lifetime(borrow self)
+// CHECK:      @_alwaysEmitIntoClient @lifetime(borrow self) @_disfavoredOverload
 // CHECK-NEXT: func myFunc5() -> Span<CInt> {
 // CHECK-NEXT:     return Span(_unsafeCxxSpan: myFunc5())
 // CHECK-NEXT: }