Merge pull request #14035 from moiseev/compact-message

[stdlib] Improve the flatMap deprecation message

Author: moiseev

stdlib/public/core/FlatMap.swift

@@ -60,7 +60,8 @@ extension LazySequenceProtocol {
   ///
   /// - Complexity: O(1)
   @inline(__always)
-  @available(*, deprecated, renamed: "compactMap(_:)")
+  @available(*, deprecated, renamed: "compactMap(_:)",
+    message: "Please use compactMap(_:) for the case where closure returns an optional value")
   public func flatMap<ElementOfResult>(
     _ transform: @escaping (Elements.Element) -> ElementOfResult?
   ) -> LazyMapSequence<
@@ -123,7 +124,8 @@ extension LazyCollectionProtocol {
   ///   collection as its argument and returns an optional value.
   ///
   /// - Complexity: O(1)
-  @available(*, deprecated, renamed: "compactMap(_:)")
+  @available(*, deprecated, renamed: "compactMap(_:)",
+    message: "Please use compactMap(_:) for the case where closure returns an optional value")
   @_inlineable // FIXME(sil-serialize-all)
   public func flatMap<ElementOfResult>(
     _ transform: @escaping (Elements.Element) -> ElementOfResult?

stdlib/public/core/SequenceAlgorithms.swift.gyb

@@ -783,7 +783,8 @@ extension Sequence {
   /// - Complexity: O(*m* + *n*), where *m* is the length of this sequence
   ///   and *n* is the length of the result.
   @inline(__always)
-  @available(*, deprecated, renamed: "compactMap(_:)")
+  @available(*, deprecated, renamed: "compactMap(_:)",
+    message: "Please use compactMap(_:) for the case where closure returns an optional value")
   public func flatMap<ElementOfResult>(
     _ transform: (Element) throws -> ElementOfResult?
   ) rethrows -> [ElementOfResult] {

stdlib/public/core/StringRangeReplaceableCollection.swift.gyb

@@ -581,7 +581,8 @@ extension Collection {
     return try _compactMap(transform)
   }
 
-  @available(*, deprecated, renamed: "compactMap(_:)")
+  @available(*, deprecated, renamed: "compactMap(_:)",
+    message: "Please use compactMap(_:) for the case where closure returns an optional value")
   @inline(__always)
   public func flatMap(
     _ transform: (Element) throws -> String?

test/stdlib/FlatMapDeprecation.swift

@@ -3,30 +3,30 @@
 func flatMapOnSequence<
   S : Sequence
 >(xs: S, f: (S.Element) -> S.Element?) {
-  _ = xs.flatMap(f) // expected-warning {{deprecated}} expected-note {{compactMap}}
+  _ = xs.flatMap(f) // expected-warning {{'flatMap' is deprecated: Please use compactMap(_:) for the case where closure returns an optional value}} expected-note {{compactMap}}
 }
 
 func flatMapOnLazySequence<
   S : LazySequenceProtocol
 >(xs: S, f: (S.Element) -> S.Element?) {
-  _ = xs.flatMap(f) // expected-warning {{deprecated}} expected-note {{compactMap}}
+  _ = xs.flatMap(f) // expected-warning {{'flatMap' is deprecated: Please use compactMap(_:) for the case where closure returns an optional value}} expected-note {{compactMap}}
 }
 
 func flatMapOnLazyCollection<
   C : LazyCollectionProtocol
 >(xs: C, f: (C.Element) -> C.Element?) {
-  _ = xs.flatMap(f) // expected-warning {{deprecated}} expected-note {{compactMap}}
+  _ = xs.flatMap(f) // expected-warning {{'flatMap' is deprecated: Please use compactMap(_:) for the case where closure returns an optional value}} expected-note {{compactMap}}
 }
 
 func flatMapOnLazyBidirectionalCollection<
   C : LazyCollectionProtocol & BidirectionalCollection
 >(xs: C, f: (C.Element) -> C.Element?)
 where C.Elements : BidirectionalCollection {
-  _ = xs.flatMap(f) // expected-warning {{deprecated}} expected-note {{compactMap}}
+  _ = xs.flatMap(f) // expected-warning {{'flatMap' is deprecated: Please use compactMap(_:) for the case where closure returns an optional value}} expected-note {{compactMap}}
 }
 
 func flatMapOnCollectinoOfStrings<
   C : Collection
 >(xs: C, f: (C.Element) -> String?) {
-  _ = xs.flatMap(f) // expected-warning {{deprecated}} expected-note {{compactMap}}
+  _ = xs.flatMap(f) // expected-warning {{'flatMap' is deprecated: Please use compactMap(_:) for the case where closure returns an optional value}} expected-note {{compactMap}}
 }