[SR-15049] Add sendable test cases and todo for improving diagnostic wording

Author: LucianoPAlmeida

test/Concurrency/sr15049.swift

@@ -1,20 +1,44 @@
 // RUN: %target-typecheck-verify-swift -disable-availability-checking
 // REQUIRES: concurrency
 
+func testAsyncSequenceTypedPatternSendable<Seq: AsyncSequence>(_ seq: Seq) async throws where Seq.Element == Int, Seq: Sendable {
+   async let result: Int = seq.reduce(0) { $0 + $1 } // OK
+   // expected-warning@-1{{immutable value 'result' was never used; consider replacing with '_' or removing it}}
+}
+
+func testAsyncSequenceTypedPattern1Sendable<Seq: AsyncSequence>(_ seq: Seq) async throws where Seq.Element == Int, Seq: Sendable {
+   async let _: Int = seq.reduce(0) { $0 + $1 } // OK
+}
+
+func testAsyncSequenceSendable<Seq: AsyncSequence>(_ seq: Seq) async throws where Seq.Element == Int, Seq: Sendable {
+   async let result = seq.reduce(0) { $0 + $1 } // OK
+   // expected-warning@-1{{initialization of immutable value 'result' was never used; consider replacing with assignment to '_' or removing it}}
+}
+
+func testAsyncSequence1Sendable<Seq: AsyncSequence>(_ seq: Seq) async throws where Seq.Element == Int, Seq: Sendable {
+   async let _ = seq.reduce(0) { $0 + $1 } // OK
+}
+
+// TODO(diagnostics): Add a tailored wording for implicit autoclosure captures in sendable warnings, because 
+// from user perspective there is no closure capture, so diagnostic can be confusing.
 func testAsyncSequenceTypedPattern<Seq: AsyncSequence>(_ seq: Seq) async throws where Seq.Element == Int {
    async let result: Int = seq.reduce(0) { $0 + $1 } // OK
    // expected-warning@-1{{immutable value 'result' was never used; consider replacing with '_' or removing it}}
+   // expected-warning@-2{{capture of 'seq' with non-sendable type 'Seq' in a `@Sendable` closure}}
 }
 
 func testAsyncSequenceTypedPattern1<Seq: AsyncSequence>(_ seq: Seq) async throws where Seq.Element == Int {
    async let _: Int = seq.reduce(0) { $0 + $1 } // OK
+   // expected-warning@-1{{capture of 'seq' with non-sendable type 'Seq' in a `@Sendable` closure}}
 }
 
 func testAsyncSequence<Seq: AsyncSequence>(_ seq: Seq) async throws where Seq.Element == Int {
    async let result = seq.reduce(0) { $0 + $1 } // OK
    // expected-warning@-1{{initialization of immutable value 'result' was never used; consider replacing with assignment to '_' or removing it}}
+   // expected-warning@-2{{capture of 'seq' with non-sendable type 'Seq' in a `@Sendable` closure}}
 }
 
 func testAsyncSequence1<Seq: AsyncSequence>(_ seq: Seq) async throws where Seq.Element == Int {
    async let _ = seq.reduce(0) { $0 + $1 } // OK
+   // expected-warning@-1{{capture of 'seq' with non-sendable type 'Seq' in a `@Sendable` closure}}
 }