[6.2] Add trailing comma support in cases missing from Swift 6.1

Sources/SwiftParser/Nominals.swift

@@ -361,6 +361,11 @@ extension Parser {
             arena: self.arena
           )
         )
+
+        // If this was a trailing comma, there are no more elements
+        if at(prefix: ">") {
+          break
+        }
       } while keepGoing != nil && self.hasProgressed(&loopProgress)
     }
     let rangle = self.expectWithoutRecovery(prefix: ">", as: .rightAngle)

Sources/SwiftParser/Types.swift

@@ -430,6 +430,11 @@ extension Parser {
             arena: self.arena
           )
         )
+
+        // If this was a trailing comma, we're done parsing the list
+        if self.at(prefix: ">") {
+          break
+        }
       } while keepGoing != nil && self.hasProgressed(&loopProgress)
     }
 
@@ -1052,7 +1057,8 @@ extension Parser.Lookahead {
           return false
         }
         // Parse the comma, if the list continues.
-      } while self.consume(if: .comma) != nil && self.hasProgressed(&loopProgress)
+        // This could be the trailing comma.
+      } while self.consume(if: .comma) != nil && !self.at(prefix: ">") && self.hasProgressed(&loopProgress)
     }
 
     guard self.consume(ifPrefix: ">", as: .rightAngle) != nil else {

Tests/SwiftParserTest/DeclarationTests.swift

@@ -3529,4 +3529,31 @@ final class DeclarationTests: ParserTestCase {
       ]
     )
   }
+
+  func testTrailingCommas() {
+    assertParse(
+      """
+      protocol Baaz<
+        Foo,
+        Bar,
+      > {
+        associatedtype Foo
+        associatedtype Bar
+      }
+      """
+    )
+
+    assertParse(
+      """
+      struct Foo<
+        T1,
+        T2,
+        T3,
+      >: Baaz<
+        T1,
+        T2,
+      > {}
+      """
+    )
+  }
 }

Tests/SwiftParserTest/ExpressionTests.swift

@@ -2125,6 +2125,26 @@ final class ExpressionTests: ParserTestCase {
         """
     )
   }
+
+  func testTrailingCommasInTypeExpressions() {
+    assertParse(
+      """
+      let _ = Foo2<Int, Bool, String,>.self
+      """
+    )
+
+    assertParse(
+      """
+      let _ = Foo2<Int, Bool, String,>()
+      """
+    )
+
+    assertParse(
+      """
+      let _ = ((Int, Bool, String,) -> Void).self
+      """
+    )
+  }
 }
 
 final class MemberExprTests: ParserTestCase {

Tests/SwiftParserTest/TypeTests.swift

@@ -734,6 +734,44 @@ final class TypeTests: ParserTestCase {
       fixedSource: "func foo(test: nonisolated(nonsendinghello) () async -> Void)"
     )
   }
+
+  func testTrailingCommas() {
+    assertParse(
+      """
+      let foo: (
+        bar: String,
+        quux: String,
+      )
+      """
+    )
+
+    assertParse(
+      """
+      let closure: (
+        String,
+        String,
+      ) -> (
+        bar: String,
+        quux: String,
+      )
+      """
+    )
+
+    assertParse(
+      """
+      struct Foo<T1, T2, T3,> {}
+
+      typealias Bar<
+        T1,
+        T2,
+      > = Foo<
+        T1,
+        T2,
+        Bool,
+      >
+      """
+    )
+  }
 }
 
 final class InlineArrayTypeTests: ParserTestCase {