Invalid code when emitting function type signature.

[Vbitz]

TypeScript Version: 3.1.0-dev.20180907

Search Terms:
Error emitting function type signature.

Code

Note: This behavior is using the compiler API.

import * as ts from 'typescript';

const typeNode = ts.createVariableStatement(
    [], [ts.createVariableDeclaration(
            'a',
            ts.createFunctionTypeNode(
                [], [ts.createParameter([], [], undefined, 'hello')],
                ts.createKeywordTypeNode(ts.SyntaxKind.StringKeyword)))]);

const printer = ts.createPrinter({});

console.log(printer.printNode(
    ts.EmitHint.Unspecified, typeNode,
    ts.createSourceFile('', '', ts.ScriptTarget.ES5)));

Expected behavior:
Should output:

var a: (hello) => string;

Actual behavior:

var a: hello => string;

Playground Link:

Note: This behavior is using the compiler API.

Related Issues:
I couldn't find a related issue but I think the problem is an error in https://github.com/Microsoft/TypeScript/blob/master/src/compiler/emitter.ts#L2817

[ajafff]

I'm already working on a fix. Currently struggling with compiling master...