[SE-0467] MutableSpan

Runtimes/Core/core/CMakeLists.txt

@@ -152,6 +152,8 @@ add_library(swiftCore
   Sort.swift
   Span/Span.swift
   Span/RawSpan.swift
+  Span/MutableSpan.swift
+  Span/MutableRawSpan.swift
   StaticString.swift
   StaticPrint.swift
   Stride.swift

stdlib/public/core/Array.swift

@@ -1428,25 +1428,6 @@ extension Array: RangeReplaceableCollection {
     }
   }
 
-  @available(SwiftStdlib 6.2, *)
-  public var span: Span<Element> {
-    @lifetime(borrow self)
-    @_alwaysEmitIntoClient
-    borrowing get {
-#if _runtime(_ObjC)
-      if _slowPath(!_buffer._isNative) {
-        let buffer = _buffer.getOrAllocateAssociatedObjectBuffer()
-        let (pointer, count) = unsafe (buffer.firstElementAddress, buffer.count)
-        let span = unsafe Span(_unsafeStart: pointer, count: count)
-        return unsafe _overrideLifetime(span, borrowing: self)
-      }
-#endif
-      let (pointer, count) = unsafe (_buffer.firstElementAddress, _buffer.count)
-      let span = unsafe Span(_unsafeStart: pointer, count: count)
-      return unsafe _overrideLifetime(span, borrowing: self)
-    }
-  }
-
   @inlinable
   public __consuming func _copyToContiguousArray() -> ContiguousArray<Element> {
     if let n = _buffer.requestNativeBuffer() {
@@ -1630,6 +1611,27 @@ extension Array {
     return try unsafe _buffer.withUnsafeBufferPointer(body)
   }
 
+  @available(SwiftStdlib 6.2, *)
+  public var span: Span<Element> {
+    @lifetime(borrow self)
+    @_alwaysEmitIntoClient
+    borrowing get {
+#if _runtime(_ObjC)
+      if _slowPath(!_buffer._isNative) {
+        let buffer = _buffer.getOrAllocateAssociatedObjectBuffer()
+        let pointer = unsafe buffer.firstElementAddress
+        let count = buffer.immutableCount
+        let span = unsafe Span(_unsafeStart: pointer, count: count)
+        return unsafe _overrideLifetime(span, borrowing: self)
+      }
+#endif
+      let pointer = unsafe _buffer.firstElementAddress
+      let count = _buffer.immutableCount
+      let span = unsafe Span(_unsafeStart: pointer, count: count)
+      return unsafe _overrideLifetime(span, borrowing: self)
+    }
+  }
+
   // Superseded by the typed-throws version of this function, but retained
   // for ABI reasons.
   @_semantics("array.withUnsafeMutableBufferPointer")
@@ -1728,6 +1730,22 @@ extension Array {
     return try unsafe body(&inoutBufferPointer)
   }
 
+  @available(SwiftStdlib 6.2, *)
+  public var mutableSpan: MutableSpan<Element> {
+    @lifetime(/*inout*/borrow self)
+    @_alwaysEmitIntoClient
+    mutating get {
+      _makeMutableAndUnique()
+      // NOTE: We don't have the ability to schedule a call to
+      //       ContiguousArrayBuffer.endCOWMutation().
+      //       rdar://146785284 (lifetime analysis for end of mutation)
+      let pointer = unsafe _buffer.firstElementAddress
+      let count = _buffer.mutableCount
+      let span = unsafe MutableSpan(_unsafeStart: pointer, count: count)
+      return unsafe _overrideLifetime(span, mutating: &self)
+    }
+  }
+
   @inlinable
   public __consuming func _copyContents(
     initializing buffer: UnsafeMutableBufferPointer<Element>

stdlib/public/core/ArraySlice.swift

@@ -1116,17 +1116,6 @@ extension ArraySlice: RangeReplaceableCollection {
     }
   }
 
-  @available(SwiftStdlib 6.2, *)
-  public var span: Span<Element> {
-    @lifetime(borrow self)
-    @_alwaysEmitIntoClient
-    borrowing get {
-      let (pointer, count) = (_buffer.firstElementAddress, _buffer.count)
-      let span = unsafe Span(_unsafeStart: pointer, count: count)
-      return unsafe _overrideLifetime(span, borrowing: self)
-    }
-  }
-
   @inlinable
   public __consuming func _copyToContiguousArray() -> ContiguousArray<Element> {
     if let n = _buffer.requestNativeBuffer() {
@@ -1221,6 +1210,17 @@ extension ArraySlice {
     return try _buffer.withUnsafeBufferPointer(body)
   }
 
+  @available(SwiftStdlib 6.2, *)
+  public var span: Span<Element> {
+    @lifetime(borrow self)
+    @_alwaysEmitIntoClient
+    borrowing get {
+      let (pointer, count) = unsafe (_buffer.firstElementAddress, _buffer.count)
+      let span = unsafe Span(_unsafeStart: pointer, count: count)
+      return unsafe _overrideLifetime(span, borrowing: self)
+    }
+  }
+
   // Superseded by the typed-throws version of this function, but retained
   // for ABI reasons.
   @_semantics("array.withUnsafeMutableBufferPointer")
@@ -1300,6 +1300,21 @@ extension ArraySlice {
     return try unsafe body(&inoutBufferPointer)
   }
 
+  @available(SwiftStdlib 6.2, *)
+  public var mutableSpan: MutableSpan<Element> {
+    @lifetime(/*inout*/borrow self)
+    @_alwaysEmitIntoClient
+    mutating get {
+      _makeMutableAndUnique()
+      // NOTE: We don't have the ability to schedule a call to
+      //       ContiguousArrayBuffer.endCOWMutation().
+      //       rdar://146785284 (lifetime analysis for end of mutation)
+      let (pointer, count) = unsafe (_buffer.firstElementAddress, _buffer.count)
+      let span = unsafe MutableSpan(_unsafeStart: pointer, count: count)
+      return unsafe _overrideLifetime(span, mutating: &self)
+    }
+  }
+
   @inlinable
   public __consuming func _copyContents(
     initializing buffer: UnsafeMutableBufferPointer<Element>

stdlib/public/core/CMakeLists.txt

@@ -157,6 +157,8 @@ split_embedded_sources(
   EMBEDDED Slice.swift
   EMBEDDED SmallString.swift
   EMBEDDED Sort.swift
+  EMBEDDED Span/MutableRawSpan.swift
+  EMBEDDED Span/MutableSpan.swift
   EMBEDDED Span/RawSpan.swift
   EMBEDDED Span/Span.swift
   EMBEDDED StaticString.swift

stdlib/public/core/ContiguousArray.swift

@@ -1021,17 +1021,6 @@ extension ContiguousArray: RangeReplaceableCollection {
     }
   }
 
-  @available(SwiftStdlib 6.2, *)
-  public var span: Span<Element> {
-    @lifetime(borrow self)
-    @_alwaysEmitIntoClient
-    borrowing get {
-      let (pointer, count) = unsafe (_buffer.firstElementAddress, _buffer.count)
-      let span = unsafe Span(_unsafeStart: pointer, count: count)
-      return unsafe _overrideLifetime(span, borrowing: self)
-    }
-  }
-
   @inlinable
   public __consuming func _copyToContiguousArray() -> ContiguousArray<Element> {
     if let n = _buffer.requestNativeBuffer() {
@@ -1163,6 +1152,18 @@ extension ContiguousArray {
     return try unsafe _buffer.withUnsafeBufferPointer(body)
   }
 
+  @available(SwiftStdlib 6.2, *)
+  public var span: Span<Element> {
+    @lifetime(borrow self)
+    @_alwaysEmitIntoClient
+    borrowing get {
+      let pointer = unsafe _buffer.firstElementAddress
+      let count = _buffer.immutableCount
+      let span = unsafe Span(_unsafeStart: pointer, count: count)
+      return unsafe _overrideLifetime(span, borrowing: self)
+    }
+  }
+
   // Superseded by the typed-throws version of this function, but retained
   // for ABI reasons.
   @_semantics("array.withUnsafeMutableBufferPointer")
@@ -1241,6 +1242,22 @@ extension ContiguousArray {
     return try unsafe body(&inoutBufferPointer)
   }
 
+  @available(SwiftStdlib 6.2, *)
+  public var mutableSpan: MutableSpan<Element> {
+    @lifetime(/*inout*/borrow self)
+    @_alwaysEmitIntoClient
+    mutating get {
+      _makeMutableAndUnique()
+      // NOTE: We don't have the ability to schedule a call to
+      //       ContiguousArrayBuffer.endCOWMutation().
+      //       rdar://146785284 (lifetime analysis for end of mutation)
+      let pointer = unsafe _buffer.firstElementAddress
+      let count = _buffer.mutableCount
+      let span = unsafe MutableSpan(_unsafeStart: pointer, count: count)
+      return unsafe _overrideLifetime(span, mutating: &self)
+    }
+  }
+
   @inlinable
   public __consuming func _copyContents(
     initializing buffer: UnsafeMutableBufferPointer<Element>

stdlib/public/core/GroupInfo.json

@@ -200,6 +200,8 @@
     "UnsafeRawBufferPointer.swift"
   ],
   "Span": [
+    "MutableRawSpan.swift",
+    "MutableSpan.swift",
     "RawSpan.swift",
     "Span.swift"
   ],

stdlib/public/core/LifetimeManager.swift

@@ -297,3 +297,22 @@ internal func _overrideLifetime<
   // should be expressed by a builtin that is hidden within the function body.
   dependent
 }
+
+/// Unsafely discard any lifetime dependency on the `dependent` argument.
+/// Return a value identical to `dependent` with a lifetime dependency
+/// on the caller's exclusive borrow scope of the `source` argument.
+@unsafe
+@_unsafeNonescapableResult
+@_alwaysEmitIntoClient
+@_transparent
+@lifetime(borrow source)
+internal func _overrideLifetime<
+  T: ~Copyable & ~Escapable, U: ~Copyable & ~Escapable
+>(
+  _ dependent: consuming T,
+  mutating source: inout U
+) -> T {
+  // TODO: Remove @_unsafeNonescapableResult. Instead, the unsafe dependence
+  // should be expressed by a builtin that is hidden within the function body.
+  dependent
+}