Annotate event adders as @discardableResult (#382)

tristanlabelle · Nov 1, 2024 · 00872a0 · 00872a0
1 parent 9a764d6
commit 00872a0
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Showing 4 changed files with 13 additions and 1 deletion.
diff --git a/Generator/Sources/CodeWriters/Swift/SwiftAttribute.swift b/Generator/Sources/CodeWriters/Swift/SwiftAttribute.swift
@@ -1,4 +1,7 @@
-public struct SwiftAttribute {
+public struct SwiftAttribute: ExpressibleByStringLiteral {
     public var literal: String
     public init(_ literal: String) { self.literal = literal }
+    public init(stringLiteral literal: String) { self.literal = literal }
+
+    public static var discardableResult: SwiftAttribute { "discardableResult" }
 }
diff --git a/Generator/Sources/SwiftWinRT/Writing/InterfaceDefinition.swift b/Generator/Sources/SwiftWinRT/Writing/InterfaceDefinition.swift
@@ -90,6 +90,7 @@ fileprivate func writeProtocol(_ interfaceDefinition: InterfaceDefinition, proje
             if let addAccessor = try event.addAccessor {
                 try writer.writeFunc(
                     documentation: projection.getDocumentationComment(event),
+                    attributes: [ .discardableResult ],
                     name: Projection.toMemberName(event),
                     params: addAccessor.params.map { try projection.toParameter(label: "adding", $0) },
                     throws: true,

diff --git a/Generator/Sources/SwiftWinRT/Writing/MemberDefinition.swift b/Generator/Sources/SwiftWinRT/Writing/MemberDefinition.swift
@@ -100,12 +100,14 @@ fileprivate func writeEventDefinition(
         projection: Projection, to writer: SwiftTypeDefinitionWriter) throws {
     let name = Projection.toMemberName(event)
 
+    // @discardableResult
     // public [static] func myEvent(adding handler: @escaping MyEventHandler) throws -> EventRegistration { ... }
     if let addAccessor = try event.addAccessor, let handlerParameter = try addAccessor.params.first {
         let handlerParamBinding = try projection.getParamBinding(handlerParameter, genericTypeArgs: typeGenericArgs)
         let eventRegistrationType = SupportModules.WinRT.eventRegistration
         try writer.writeFunc(
                 documentation: documentation ? projection.getDocumentationComment(event, classDefinition: classDefinition) : nil,
+                attributes: [ .discardableResult ],
                 visibility: overridable ? .open : .public, static: `static`,
                 name: name,
                 params: [ handlerParamBinding.toSwiftParam(label: "adding") ], throws: true,

diff --git a/InteropTests/Tests/EventTests.swift b/InteropTests/Tests/EventTests.swift
@@ -31,6 +31,7 @@ class EventTests: WinRTTestCase {
         class EventSource: WinRTPrimaryExport<IEventSourceBinding>, IEventSourceProtocol {
             private var invocationList: EventInvocationList<MinimalDelegate> = .init()
 
+            @discardableResult
             func event(adding handler: MinimalDelegate?) throws -> EventRegistration {
                 try invocationList.add(handler)
             }
@@ -44,4 +45,9 @@ class EventTests: WinRTTestCase {
             }
         }
     }
+
+    func testDiscardableResult() throws {
+        let eventSource = try XCTUnwrap(Events.createSource())
+        try eventSource.event { } // Should not produce a warning/error
+    }
 }