Format discard statements.

Author: allevato

Sources/SwiftFormat/PrettyPrint/TokenStreamCreator.swift

@@ -2511,6 +2511,13 @@ fileprivate final class TokenStreamCreator: SyntaxVisitor {
     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.
+    after(node.discardKeyword, tokens: .space)
+    return .visitChildren
+  }
+
   override func visit(_ node: InheritanceClauseSyntax) -> SyntaxVisitorContinueKind {
     // Normally, the open-break is placed before the open token. In this case, it's intentionally
     // ordered differently so that the inheritance list can start on the current line and only

Tests/SwiftFormatTests/PrettyPrint/DiscardStmtTests.swift

@@ -0,0 +1,13 @@
+final class DiscardStmtTests: PrettyPrintTestCase {
+  func testDiscard() {
+    assertPrettyPrintEqual(
+      input: """
+        discard self
+        """,
+      expected: """
+        discard self
+
+        """,
+      linelength: 9)
+  }
+}