fix: Support trailing comma in function type parameters (#2608)

Author: dcodeIO

src/parser.ts

@@ -797,6 +797,7 @@ export class Parser extends DiagnosticEmitter {
           }
         } else {
           if (isSignature) {
+            if (tn.peek() == Token.CloseParen) break; // allow trailing comma
             this.error(
               DiagnosticCode.Identifier_expected,
               tn.range()

tests/parser/function-type.ts

@@ -3,3 +3,4 @@ var b: (a: i32, b: i32) => void;
 var c: (a: i32, b: i32) => (a: i32, b: i32) => void;
 var d: (a: i32, a: i32) => void; // NOTE: duplicates in type signatures doesn't in TypeScript
 var e: (a) => void; // TS1110
+var f: (a: i32, b: i32,) => (a: i32, b: i32,) => void;

tests/parser/function-type.ts.fixture.ts

@@ -3,4 +3,5 @@ var b: (a: i32, b: i32) => void;
 var c: (a: i32, b: i32) => (a: i32, b: i32) => void;
 var d: (a: i32, a: i32) => void;
 var e: (a) => void;
+var f: (a: i32, b: i32) => (a: i32, b: i32) => void;
 // ERROR 1110: "Type expected." in function-type.ts(5,10+0)