Support trailing commas in types within expressions

Author: calda

Sources/SwiftParser/Types.swift

@@ -1057,7 +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/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 {