Format copy expressions.

Author: allevato

Sources/SwiftFormat/PrettyPrint/TokenStreamCreator.swift

@@ -2511,6 +2511,13 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
     return .visitChildren
   }
 
+  override func visit(_ node: CopyExprSyntax) -> SyntaxVisitorContinueKind {
+    // The `copy` keyword cannot be separated from the following token or it will be parsed as an
+    // identifier.
+    after(node.copyKeyword, tokens: .space)
+    return .visitChildren
+  }
+
   override func visit(_ node: DiscardStmtSyntax) -> SyntaxVisitorContinueKind {
     // The `discard` keyword cannot be separated from the following token or it will be parsed as
     // an identifier.

Tests/SwiftFormatTests/PrettyPrint/CopyExprSyntax.swift

@@ -0,0 +1,14 @@
+final class CopyExprTests: PrettyPrintTestCase {
+  func testCopy() {
+    assertPrettyPrintEqual(
+      input: """
+        let x = copy y
+        """,
+      expected: """
+        let x =
+          copy y
+
+        """,
+      linelength: 13)
+  }
+}