Include Default Parameter Values in Signature Help

From https://github.com/Microsoft/vscode/issues/28925

TypeScript Version: 2.4.0

Feature Request
signatureHelp current shows when a parameter is optional but does not include any information about that parameter's default value:

function foo(x = 10) { }
foo(|)

Result of TSServer signatureHelp on foo

[Trace  - 5:42:22 PM] Response received: signatureHelp (378). Request took 20 ms. Success: true 
Result: {
    "items": [
        {
            "isVariadic": false,
            "prefixDisplayParts": [
                {
                    "text": "foo",
                    "kind": "functionName"
                },
                {
                    "text": "(",
                    "kind": "punctuation"
                }
            ],
            "suffixDisplayParts": [
                {
                    "text": ")",
                    "kind": "punctuation"
                },
                {
                    "text": ":",
                    "kind": "punctuation"
                },
                {
                    "text": " ",
                    "kind": "space"
                },
                {
                    "text": "void",
                    "kind": "keyword"
                }
            ],
            "separatorDisplayParts": [
                {
                    "text": ",",
                    "kind": "punctuation"
                },
                {
                    "text": " ",
                    "kind": "space"
                }
            ],
            "parameters": [
                {
                    "name": "x",
                    "documentation": [],
                    "displayParts": [
                        {
                            "text": "x",
                            "kind": "parameterName"
                        },
                        {
                            "text": "?",
                            "kind": "punctuation"
                        },
                        {
                            "text": ":",
                            "kind": "punctuation"
                        },
                        {
                            "text": " ",
                            "kind": "space"
                        },
                        {
                            "text": "number",
                            "kind": "keyword"
                        }
                    ],
                    "isOptional": true
                }
            ],
            "documentation": [],
            "tags": []
        }
    ],
    "applicableSpan": {
        "start": {
            "line": 3,
            "offset": 5
        },
        "end": {
            "line": 3,
            "offset": 5
        }
    },
    "selectedItemIndex": 0,
    "argumentIndex": 0,
    "argumentCount": 0
}

When the default value is a simple literal type, it would be helpful to display this default value in the signature help. This information could be included in the displayParts response

Inizia dalla risposta TSServer signatureHelp mostrata nell’issue e segui l’implementazione della guida alla firma nel servizio linguistico TypeScript. Verifica come vengono assemblati i displayParts dei parametri, quindi fai comparire in quella risposta il semplice caso di un valore predefinito e verifica la guida alla firma risultante con l’esempio foo.