Add missing questionToken in emitMethod/PropertyDeclaration (#16020)

Author: ikatyang

src/compiler/emitter.ts

@@ -860,6 +860,7 @@ namespace ts {
             emitDecorators(node, node.decorators);
             emitModifiers(node, node.modifiers);
             emit(node.name);
+            writeIfPresent(node.questionToken, "?");
             emitWithPrefix(": ", node.type);
             emitExpressionWithPrefix(" = ", node.initializer);
             write(";");
@@ -881,6 +882,7 @@ namespace ts {
             emitModifiers(node, node.modifiers);
             writeIfPresent(node.asteriskToken, "*");
             emit(node.name);
+            writeIfPresent(node.questionToken, "?");
             emitSignatureAndBody(node, emitSignatureHead);
         }
 

src/harness/unittests/printer.ts

@@ -98,8 +98,40 @@ namespace ts {
                     )
                 ])
             );
+
+            // https://github.com/Microsoft/TypeScript/issues/15971
+            const classWithOptionalMethodAndProperty = createClassDeclaration(
+                undefined,
+                /* modifiers */ createNodeArray([createToken(SyntaxKind.DeclareKeyword)]),
+                /* name      */ createIdentifier("X"),
+                undefined,
+                undefined,
+                createNodeArray([
+                    createMethod(
+                        undefined,
+                        undefined,
+                        undefined,
+                        /* name          */ createIdentifier("method"),
+                        /* questionToken */ createToken(SyntaxKind.QuestionToken),
+                        undefined,
+                        undefined,
+                        /* type          */ createKeywordTypeNode(SyntaxKind.VoidKeyword),
+                        undefined
+                    ),
+                    createProperty(
+                        undefined,
+                        undefined,
+                        /* name          */ createIdentifier("property"),
+                        /* questionToken */ createToken(SyntaxKind.QuestionToken),
+                        /* type          */ createKeywordTypeNode(SyntaxKind.StringKeyword),
+                        undefined
+                    ),
+                ])
+            );
+
             // tslint:enable boolean-trivia
             printsCorrectly("class", {}, printer => printer.printNode(EmitHint.Unspecified, syntheticNode, sourceFile));
+            printsCorrectly("classWithOptionalMethodAndProperty", {}, printer => printer.printNode(EmitHint.Unspecified, classWithOptionalMethodAndProperty, sourceFile));
         });
     });
 }

tests/baselines/reference/printerApi/printsNodeCorrectly.classWithOptionalMethodAndProperty.js

@@ -0,0 +1,4 @@
+declare class X {
+    method?(): void;
+    property?: string;
+}