Add missing Equatable comformances

- Collect
- Contains
- Count
- Drop
- Last

RemainingCombineInterface.swift

@@ -2100,17 +2100,6 @@ extension Just {
     public func append<S>(_ elements: S) -> Publishers.Sequence<[Output], Just<Output>.Failure> where Output == S.Element, S : Sequence
 }
 
-extension Publishers.Contains : Equatable where Upstream : Equatable {
-
-    /// Returns a Boolean value that indicates whether two publishers are equivalent.
-    ///
-    /// - Parameters:
-    ///   - lhs: A contains publisher to compare for equality.
-    ///   - rhs: Another contains publisher to compare for equality.
-    /// - Returns: `true` if the two publishers’ upstream and output properties are equal, `false` otherwise.
-    public static func == (lhs: Publishers.Contains<Upstream>, rhs: Publishers.Contains<Upstream>) -> Bool
-}
-
 extension Publishers.CombineLatest : Equatable where A : Equatable, B : Equatable {
 
     /// Returns a Boolean value that indicates whether two publishers are equivalent.
@@ -2148,19 +2137,6 @@ extension Publishers.CombineLatest4 : Equatable where A : Equatable, B : Equatab
     public static func == (lhs: Publishers.CombineLatest4<A, B, C, D>, rhs: Publishers.CombineLatest4<A, B, C, D>) -> Bool
 }
 
-extension Publishers.Collect : Equatable where Upstream : Equatable {
-
-    /// Returns a Boolean value indicating whether two values are equal.
-    ///
-    /// Equality is the inverse of inequality. For any values `a` and `b`,
-    /// `a == b` implies that `a != b` is `false`.
-    ///
-    /// - Parameters:
-    ///   - lhs: A value to compare.
-    ///   - rhs: Another value to compare.
-    public static func == (lhs: Publishers.Collect<Upstream>, rhs: Publishers.Collect<Upstream>) -> Bool
-}
-
 extension Publishers.CollectByCount : Equatable where Upstream : Equatable {
 
     /// Returns a Boolean value indicating whether two values are equal.
@@ -2264,19 +2240,6 @@ extension Publishers.MergeMany : Equatable where Upstream : Equatable {
     public static func == (lhs: Publishers.MergeMany<Upstream>, rhs: Publishers.MergeMany<Upstream>) -> Bool
 }
 
-extension Publishers.Count : Equatable where Upstream : Equatable {
-
-    /// Returns a Boolean value indicating whether two values are equal.
-    ///
-    /// Equality is the inverse of inequality. For any values `a` and `b`,
-    /// `a == b` implies that `a != b` is `false`.
-    ///
-    /// - Parameters:
-    ///   - lhs: A value to compare.
-    ///   - rhs: Another value to compare.
-    public static func == (lhs: Publishers.Count<Upstream>, rhs: Publishers.Count<Upstream>) -> Bool
-}
-
 extension Publishers.Retry : Equatable where Upstream : Equatable {
 
     /// Returns a Boolean value indicating whether two values are equal.
@@ -2325,17 +2288,6 @@ extension Publishers.Concatenate : Equatable where Prefix : Equatable, Suffix :
     public static func == (lhs: Publishers.Concatenate<Prefix, Suffix>, rhs: Publishers.Concatenate<Prefix, Suffix>) -> Bool
 }
 
-extension Publishers.Last : Equatable where Upstream : Equatable {
-
-    /// Returns a Boolean value that indicates whether two publishers are equivalent.
-    ///
-    /// - Parameters:
-    ///   - lhs: A last publisher to compare for equality.
-    ///   - rhs: Another last publisher to compare for equality.
-    /// - Returns: `true` if the two publishers have equal upstream publishers, `false` otherwise.
-    public static func == (lhs: Publishers.Last<Upstream>, rhs: Publishers.Last<Upstream>) -> Bool
-}
-
 extension Publishers.Zip : Equatable where A : Equatable, B : Equatable {
 
     /// Returns a Boolean value that indicates whether two publishers are equivalent.
@@ -2398,17 +2350,6 @@ extension Publishers.Output : Equatable where Upstream : Equatable {
     public static func == (lhs: Publishers.Output<Upstream>, rhs: Publishers.Output<Upstream>) -> Bool
 }
 
-extension Publishers.Drop : Equatable where Upstream : Equatable {
-
-    /// Returns a Boolean value that indicates whether the two publishers are equivalent.
-    ///
-    /// - Parameters:
-    ///   - lhs: A drop publisher to compare for equality..
-    ///   - rhs: Another drop publisher to compare for equality..
-    /// - Returns: `true` if the publishers have equal upstream and count properties, `false` otherwise.
-    public static func == (lhs: Publishers.Drop<Upstream>, rhs: Publishers.Drop<Upstream>) -> Bool
-}
-
 /// A type of object with a publisher that emits before the object has changed.
 ///
 /// By default an `ObservableObject` will synthesize an `objectWillChange`

Sources/OpenCombine/Publishers/Publishers.Collect.swift

@@ -50,6 +50,8 @@ extension Publishers {
     }
 }
 
+extension Publishers.Collect: Equatable where Upstream: Equatable {}
+
 extension Publishers.Collect {
     private final class Inner<Downstream: Subscriber>
         : ReduceProducer<Downstream,

Sources/OpenCombine/Publishers/Publishers.Contains.swift

@@ -172,6 +172,8 @@ extension Publishers.Contains {
     }
 }
 
+extension Publishers.Contains : Equatable where Upstream: Equatable {}
+
 extension Publishers.ContainsWhere {
     private final class Inner<Downstream: Subscriber>
         : ReduceProducer<Downstream,

Sources/OpenCombine/Publishers/Publishers.Count.swift

@@ -53,6 +53,8 @@ extension Publishers {
     }
 }
 
+extension Publishers.Count: Equatable where Upstream: Equatable {}
+
 extension Publishers.Count {
     private final class Inner<Downstream: Subscriber>
         : ReduceProducer<Downstream, Upstream.Output, Int, Failure, Void>

Sources/OpenCombine/Publishers/Publishers.Drop.swift

@@ -48,6 +48,8 @@ extension Publishers {
     }
 }
 
+extension Publishers.Drop: Equatable where Upstream: Equatable {}
+
 extension Publishers.Drop {
     private final class Inner<Downstream: Subscriber>
         : Subscription,

Sources/OpenCombine/Publishers/Publishers.Last.swift

@@ -118,6 +118,8 @@ extension Publishers {
     }
 }
 
+extension Publishers.Last: Equatable where Upstream: Equatable {}
+
 extension Publishers.Last {
     private final class Inner<Downstream: Subscriber>
         : ReduceProducer<Downstream,

Tests/OpenCombineTests/PublisherTests/ScanTests.swift

@@ -312,8 +312,10 @@ final class ScanTests: XCTestCase {
     }
 }
 
-private func shouldNotBeCalled<T, U>(file: StaticString = #file,
-                                     line: UInt = #line) -> (T, U) -> T {
+private func shouldNotBeCalled<Accumulator, Value>(
+    file: StaticString = #file,
+    line: UInt = #line
+) -> (Accumulator, Value) -> Accumulator {
     return { accumulator, _ in
         XCTFail("should not be called", file: file, line: line)
         return accumulator